From d83061b1df195caeb5eb515ff9028d37068c5350 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Thu, 8 Feb 2018 15:50:38 -0800
Subject: [PATCH 01/34] Added a unit test to repro the issue

---
 .../Legacy/TagHelperParseTreeRewriter.cs      |  2 +-
 .../Legacy/TagHelperParseTreeRewriterTest.cs  | 49 ++++++++++++++++---
 2 files changed, 44 insertions(+), 7 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index 2059522263..79b013f32d 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -488,7 +488,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            if (HasAllowedChildren())
+            if (child.Kind == SpanKindInternal.Comment || HasAllowedChildren())
             {
                 var content = child.Content;
                 if (!string.IsNullOrWhiteSpace(content))
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index 2feccbe1a4..04892592dd 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -254,7 +254,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             var descriptors = new TagHelperDescriptor[]
             {
                 TagHelperDescriptorBuilder.Create("InputTagHelper", "SomeAssembly")
-                    .TagMatchingRuleDescriptor(rule => 
+                    .TagMatchingRuleDescriptor(rule =>
                         rule
                         .RequireTagName("input")
                         .RequireTagStructure(TagStructure.WithoutEndTag))
@@ -371,7 +371,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     .TagMatchingRuleDescriptor(rule => rule.RequireTagName("strong"))
                     .Build(),
             };
-            
+
             // Act & Assert
             EvaluateData(
                 descriptors,
@@ -793,7 +793,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             var descriptors = new TagHelperDescriptor[]
             {
                 TagHelperDescriptorBuilder.Create("StrongTagHelper", "SomeAssembly")
-                    .TagMatchingRuleDescriptor(rule => 
+                    .TagMatchingRuleDescriptor(rule =>
                         rule
                         .RequireTagName("strong")
                         .RequireAttributeDescriptor(attribute => attribute.Name("required")))
@@ -830,7 +830,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     .TagMatchingRuleDescriptor(rule => rule.RequireTagName("strong"))
                     .Build(),
                 TagHelperDescriptorBuilder.Create("BRTagHelper", "SomeAssembly")
-                    .TagMatchingRuleDescriptor(rule => 
+                    .TagMatchingRuleDescriptor(rule =>
                         rule
                         .RequireTagName("br")
                         .RequireTagStructure(TagStructure.WithoutEndTag))
@@ -1108,6 +1108,43 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             EvaluateData(descriptors, documentContent, (MarkupBlock)expectedOutput, (RazorDiagnostic[])expectedErrors);
         }
 
+        [Fact]
+        public void Rewrite_AllowsCommentsAsChildren()
+        {
+            // Arrangestring documentContent,
+            IEnumerable<string> allowedChildren = new List<string> { "b" };
+            string literalPrefix = "";
+            string commentOutput = $"<!--Hello World-->";
+            string expectedOutput = $"<p>{literalPrefix}{commentOutput}<b>asdf</b></p>";
+
+            var pTagHelperBuilder = TagHelperDescriptorBuilder
+                .Create("PTagHelper", "SomeAssembly")
+                .TagMatchingRuleDescriptor(rule => rule.RequireTagName("p"));
+            foreach (var childTag in allowedChildren)
+            {
+                pTagHelperBuilder.AllowChildTag(childTag);
+            }
+
+            var descriptors = new TagHelperDescriptor[]
+            {
+                    pTagHelperBuilder.Build()
+            };
+
+            var factory = new SpanFactory();
+            var blockFactory = new BlockFactory(factory);
+
+            var expectedMarkup = new MarkupBlock(
+                new MarkupTagHelperBlock("p",
+                    factory.Markup($"{literalPrefix}{commentOutput}")));
+
+            // Act & Assert
+            EvaluateData(
+                descriptors,
+                expectedOutput,
+                expectedMarkup,
+                Array.Empty<RazorDiagnostic>());
+        }
+
         [Fact]
         public void Rewrite_UnderstandsNullTagNameWithAllowedChildrenForCatchAll()
         {
@@ -1173,7 +1210,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             var descriptors = new TagHelperDescriptor[]
             {
                 TagHelperDescriptorBuilder.Create("InputTagHelper", "SomeAssembly")
-                    .TagMatchingRuleDescriptor(rule => 
+                    .TagMatchingRuleDescriptor(rule =>
                         rule
                         .RequireTagName("input")
                         .RequireTagStructure(TagStructure.WithoutEndTag))
@@ -1646,7 +1683,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             var descriptors = new TagHelperDescriptor[]
             {
                 TagHelperDescriptorBuilder.Create("pTagHelper", "SomeAssembly")
-                    .TagMatchingRuleDescriptor(rule => 
+                    .TagMatchingRuleDescriptor(rule =>
                         rule
                         .RequireTagName("p")
                         .RequireAttributeDescriptor(attribute => attribute.Name("class")))

From e7076a291ddabd30aa80b98041fb6f00b4f29f4c Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Mon, 12 Feb 2018 22:03:53 -0800
Subject: [PATCH 02/34] Ignoring markup comments during validation

---
 .../Legacy/TagHelperParseTreeRewriter.cs              |  7 ++++++-
 .../Legacy/TagHelperParseTreeRewriterTest.cs          | 11 +++++++----
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index 79b013f32d..73b545dd33 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -116,7 +116,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         continue;
                     }
                 }
-                else
+                else if (!IsCommentTag((Span)child))
                 {
                     ValidateParentAllowsContent((Span)child, errorSink);
                 }
@@ -817,6 +817,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return relevantSymbol.Type == HtmlSymbolType.ForwardSlash;
         }
 
+        private static bool IsCommentTag(Span span)
+        {
+            return span.Content.StartsWith("<!--");
+        }
+
         private static void EnsureTagBlock(Block tagBlock)
         {
             Debug.Assert(tagBlock.Type == BlockKindInternal.Tag);
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index 04892592dd..bf0ae602db 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -1113,9 +1113,9 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
             // Arrangestring documentContent,
             IEnumerable<string> allowedChildren = new List<string> { "b" };
-            string literalPrefix = "";
+            string literal = "asdf";
             string commentOutput = $"<!--Hello World-->";
-            string expectedOutput = $"<p>{literalPrefix}{commentOutput}<b>asdf</b></p>";
+            string expectedOutput = $"<p><b>{literal}</b>{commentOutput}</p>";
 
             var pTagHelperBuilder = TagHelperDescriptorBuilder
                 .Create("PTagHelper", "SomeAssembly")
@@ -1127,7 +1127,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
             var descriptors = new TagHelperDescriptor[]
             {
-                    pTagHelperBuilder.Build()
+                pTagHelperBuilder.Build()
             };
 
             var factory = new SpanFactory();
@@ -1135,7 +1135,10 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
             var expectedMarkup = new MarkupBlock(
                 new MarkupTagHelperBlock("p",
-                    factory.Markup($"{literalPrefix}{commentOutput}")));
+                    blockFactory.MarkupTagBlock("<b>"),
+                    factory.Markup(literal),
+                    blockFactory.MarkupTagBlock("</b>"),
+                    factory.Markup(commentOutput)));
 
             // Act & Assert
             EvaluateData(

From 900c927d72e29f7f92ff3f0f1d4f6cbd06e904ee Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Mon, 12 Feb 2018 22:14:01 -0800
Subject: [PATCH 03/34] Revert unnecessary change

---
 .../Legacy/TagHelperParseTreeRewriter.cs                        | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index 73b545dd33..f046a8eea4 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -488,7 +488,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            if (child.Kind == SpanKindInternal.Comment || HasAllowedChildren())
+            if (HasAllowedChildren())
             {
                 var content = child.Content;
                 if (!string.IsNullOrWhiteSpace(content))

From 7d8d56cc9b2148197ac8e470d70a5972a65c8790 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Tue, 13 Feb 2018 13:34:16 -0800
Subject: [PATCH 04/34] Ignoring razor comments during validation

---
 .../Legacy/TagHelperParseTreeRewriter.cs      |  9 ++--
 .../Legacy/TagHelperParseTreeRewriterTest.cs  | 47 ++++++++++++++++++-
 2 files changed, 52 insertions(+), 4 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index f046a8eea4..01361a9893 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -116,7 +116,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         continue;
                     }
                 }
-                else if (!IsCommentTag((Span)child))
+                else if (!IsComment((Span)child))
                 {
                     ValidateParentAllowsContent((Span)child, errorSink);
                 }
@@ -817,9 +817,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return relevantSymbol.Type == HtmlSymbolType.ForwardSlash;
         }
 
-        private static bool IsCommentTag(Span span)
+        private static bool IsComment(Span span)
         {
-            return span.Content.StartsWith("<!--");
+            bool isHtmlComment = span.Content?.StartsWith("<!--") == true;
+            bool isRazorComment = span.Parent?.Type == BlockKindInternal.Comment;
+
+            return isHtmlComment || isRazorComment;
         }
 
         private static void EnsureTagBlock(Block tagBlock)
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index bf0ae602db..4a640b1990 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -1109,7 +1109,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         }
 
         [Fact]
-        public void Rewrite_AllowsCommentsAsChildren()
+        public void Rewrite_AllowsHtmlCommentsAsChildren()
         {
             // Arrangestring documentContent,
             IEnumerable<string> allowedChildren = new List<string> { "b" };
@@ -1148,6 +1148,51 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 Array.Empty<RazorDiagnostic>());
         }
 
+        [Fact]
+        public void Rewrite_AllowsRazorCommentsAsChildren()
+        {
+            // Arrangestring documentContent,
+            IEnumerable<string> allowedChildren = new List<string> { "b" };
+            string literal = "asdf";
+            string commentOutput = $"@*{literal}*@";
+            string expectedOutput = $"<p><b>{literal}</b>{commentOutput}</p>";
+
+            var pTagHelperBuilder = TagHelperDescriptorBuilder
+                .Create("PTagHelper", "SomeAssembly")
+                .TagMatchingRuleDescriptor(rule => rule.RequireTagName("p"));
+            foreach (var childTag in allowedChildren)
+            {
+                pTagHelperBuilder.AllowChildTag(childTag);
+            }
+
+            var descriptors = new TagHelperDescriptor[]
+            {
+                pTagHelperBuilder.Build()
+            };
+
+            var factory = new SpanFactory();
+            var blockFactory = new BlockFactory(factory);
+
+            var expectedMarkup = new MarkupBlock(
+                new MarkupTagHelperBlock("p",
+                    blockFactory.MarkupTagBlock("<b>"),
+                    factory.Markup(literal),
+                    blockFactory.MarkupTagBlock("</b>"),
+                    new CommentBlock(
+                        Factory.MarkupTransition(HtmlSymbolType.RazorCommentTransition).Accepts(AcceptedCharactersInternal.None),
+                        Factory.MetaMarkup("*", HtmlSymbolType.RazorCommentStar).Accepts(AcceptedCharactersInternal.None),
+                        Factory.Span(SpanKindInternal.Comment, new HtmlSymbol(literal, HtmlSymbolType.RazorComment)).Accepts(AcceptedCharactersInternal.Any),
+                        Factory.MetaMarkup("*", HtmlSymbolType.RazorCommentStar).Accepts(AcceptedCharactersInternal.None),
+                        Factory.MarkupTransition(HtmlSymbolType.RazorCommentTransition).Accepts(AcceptedCharactersInternal.None))));
+
+            // Act & Assert
+            EvaluateData(
+                descriptors,
+                expectedOutput,
+                expectedMarkup,
+                Array.Empty<RazorDiagnostic>());
+        }
+
         [Fact]
         public void Rewrite_UnderstandsNullTagNameWithAllowedChildrenForCatchAll()
         {

From b2ae175d39d3ae03f8cfb157406b7e8ee6db1097 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Tue, 13 Feb 2018 15:58:12 -0800
Subject: [PATCH 05/34] Moved the comment check into the
 "ValidateParentAllowsContent" method

---
 .../Legacy/TagHelperParseTreeRewriter.cs                      | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index 01361a9893..930b928949 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -116,7 +116,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         continue;
                     }
                 }
-                else if (!IsComment((Span)child))
+                else
                 {
                     ValidateParentAllowsContent((Span)child, errorSink);
                 }
@@ -488,7 +488,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            if (HasAllowedChildren())
+            if (HasAllowedChildren() && !IsComment(child))
             {
                 var content = child.Content;
                 if (!string.IsNullOrWhiteSpace(content))

From 696a65c7805a1713121a72079d0899d258c613a7 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Thu, 15 Feb 2018 18:15:34 -0800
Subject: [PATCH 06/34] Added new BlockType - HtmlComment Updated the
 HtmlMarkupParser to understand the HtmlCOmments, and treat those as blocks.

---
 .../Legacy/BlockKindInternal.cs               |   4 +-
 .../Legacy/HtmlMarkupParser.cs                |  45 ++++---
 .../Legacy/TagHelperParseTreeRewriter.cs      |  14 +-
 .../BlockKind.cs                              |   4 +-
 .../Legacy/TagHelperParseTreeRewriterTest.cs  | 122 ++++++++++++++++--
 .../Language/Legacy/BlockTypes.cs             |  10 ++
 6 files changed, 165 insertions(+), 34 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/BlockKindInternal.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/BlockKindInternal.cs
index c515770ca7..9f9886164c 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/BlockKindInternal.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/BlockKindInternal.cs
@@ -18,6 +18,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         // Special
         Comment = 8,
-        Tag = 9
+        Tag = 9,
+
+        HtmlComment = 10
     }
 }
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index 4fdee1322f..332023b775 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -207,6 +207,10 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             if (last != null)
             {
                 Accept(last);
+                if (At(HtmlSymbolType.OpenAngle) && last.Type == HtmlSymbolType.Text)
+                {
+                    Output(SpanKindInternal.Markup);
+                }
             }
         }
 
@@ -494,26 +498,34 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             {
                 if (CurrentSymbol.Type == HtmlSymbolType.DoubleHyphen)
                 {
-                    AcceptAndMoveNext();
-
-                    Span.EditHandler.AcceptedCharacters = AcceptedCharactersInternal.Any;
-                    while (!EndOfFile)
+                    using (Context.Builder.StartBlock(BlockKindInternal.HtmlComment))
                     {
-                        SkipToAndParseCode(HtmlSymbolType.DoubleHyphen);
-                        if (At(HtmlSymbolType.DoubleHyphen))
+                        AcceptAndMoveNext();
+
+                        Span.EditHandler.AcceptedCharacters = AcceptedCharactersInternal.Any;
+                        while (!EndOfFile)
                         {
-                            AcceptWhile(HtmlSymbolType.DoubleHyphen);
-
-                            if (At(HtmlSymbolType.Text) &&
-                                string.Equals(CurrentSymbol.Content, "-", StringComparison.Ordinal))
+                            SkipToAndParseCode(HtmlSymbolType.DoubleHyphen);
+                            if (At(HtmlSymbolType.DoubleHyphen))
                             {
-                                AcceptAndMoveNext();
-                            }
+                                AcceptWhile(HtmlSymbolType.DoubleHyphen);
 
-                            if (At(HtmlSymbolType.CloseAngle))
-                            {
-                                AcceptAndMoveNext();
-                                return true;
+                                if (At(HtmlSymbolType.Text) &&
+                                    string.Equals(CurrentSymbol.Content, "-", StringComparison.Ordinal))
+                                {
+                                    AcceptAndMoveNext();
+                                }
+
+                                if (At(HtmlSymbolType.CloseAngle))
+                                {
+                                    // This is the end of a comment block
+                                    Accept(this.CurrentSymbol);
+                                    Output(SpanKindInternal.Markup);
+
+                                    NextToken();
+                                    //AcceptAndMoveNext();
+                                    return true;
+                                }
                             }
                         }
                     }
@@ -1476,6 +1488,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     {
                         AcceptAndMoveNext(); // Accept '<'
                         BangTag();
+
                         return;
                     }
 
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index 930b928949..6cac8b46ea 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -488,7 +488,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            if (HasAllowedChildren() && !IsComment(child))
+            if (HasAllowedChildren() && !IsComment(child) && child.Kind != SpanKindInternal.Transition && child.Kind != SpanKindInternal.Code)
             {
                 var content = child.Content;
                 if (!string.IsNullOrWhiteSpace(content))
@@ -817,14 +817,18 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return relevantSymbol.Type == HtmlSymbolType.ForwardSlash;
         }
 
-        private static bool IsComment(Span span)
+        internal static bool IsComment(Span span)
         {
-            bool isHtmlComment = span.Content?.StartsWith("<!--") == true;
-            bool isRazorComment = span.Parent?.Type == BlockKindInternal.Comment;
+            Block currentBlock = span.Parent;
+            while (currentBlock != null && currentBlock.Type != BlockKindInternal.Comment && currentBlock.Type != BlockKindInternal.HtmlComment)
+            {
+                currentBlock = currentBlock.Parent;
+            }
 
-            return isHtmlComment || isRazorComment;
+            return currentBlock != null;
         }
 
+
         private static void EnsureTagBlock(Block tagBlock)
         {
             Debug.Assert(tagBlock.Type == BlockKindInternal.Tag);
diff --git a/src/Microsoft.VisualStudio.Editor.Razor/BlockKind.cs b/src/Microsoft.VisualStudio.Editor.Razor/BlockKind.cs
index 48ad2e4fb4..2559231329 100644
--- a/src/Microsoft.VisualStudio.Editor.Razor/BlockKind.cs
+++ b/src/Microsoft.VisualStudio.Editor.Razor/BlockKind.cs
@@ -19,6 +19,8 @@ namespace Microsoft.VisualStudio.Editor.Razor
 
         // Special
         Comment,
-        Tag
+        Tag,
+
+        HtmlComment
     }
 }
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index 4a640b1990..45a1ffa907 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -1109,12 +1109,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         }
 
         [Fact]
-        public void Rewrite_AllowsHtmlCommentsAsChildren()
+        public void Rewrite_AllowsSimpleHtmlCommentsAsChildren()
         {
             // Arrangestring documentContent,
             IEnumerable<string> allowedChildren = new List<string> { "b" };
             string literal = "asdf";
-            string commentOutput = $"<!--Hello World-->";
+            string commentOutput = "<!--Hello World-->";
             string expectedOutput = $"<p><b>{literal}</b>{commentOutput}</p>";
 
             var pTagHelperBuilder = TagHelperDescriptorBuilder
@@ -1138,7 +1138,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     blockFactory.MarkupTagBlock("<b>"),
                     factory.Markup(literal),
                     blockFactory.MarkupTagBlock("</b>"),
-                    factory.Markup(commentOutput)));
+                    new HtmlCommentBlock(factory.Markup(commentOutput))));
 
             // Act & Assert
             EvaluateData(
@@ -1148,6 +1148,58 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 Array.Empty<RazorDiagnostic>());
         }
 
+        [Fact]
+        public void Rewrite_FailsForContentWithCommentsAsChildren()
+        {
+            // Arrangestring documentContent,
+            Func<string, string, string, int, int, RazorDiagnostic> nestedTagError =
+                    (childName, parentName, allowed, location, length) =>
+                    RazorDiagnosticFactory.CreateTagHelper_InvalidNestedTag(
+                        new SourceSpan(absoluteIndex: location, lineIndex: 0, characterIndex: location, length: length), childName, parentName, allowed);
+            Func<string, string, int, int, RazorDiagnostic> nestedContentError =
+                (parentName, allowed, location, length) =>
+                RazorDiagnosticFactory.CreateTagHelper_CannotHaveNonTagContent(
+                    new SourceSpan(absoluteIndex: location, lineIndex: 0, characterIndex: location, length: length), parentName, allowed);
+
+            IEnumerable<string> allowedChildren = new List<string> { "b" };
+            string comment1 = "Hello";
+            string literal = "asdf";
+            string comment2 = "World";
+            string expectedOutput = $"<p><!--{comment1}-->{literal}<!--{comment2}--></p>";
+
+            var pTagHelperBuilder = TagHelperDescriptorBuilder
+                .Create("PTagHelper", "SomeAssembly")
+                .TagMatchingRuleDescriptor(rule => rule.RequireTagName("p"));
+            foreach (var childTag in allowedChildren)
+            {
+                pTagHelperBuilder.AllowChildTag(childTag);
+            }
+
+            var descriptors = new TagHelperDescriptor[]
+            {
+                pTagHelperBuilder.Build()
+            };
+
+            var factory = new SpanFactory();
+            var blockFactory = new BlockFactory(factory);
+
+            var expectedMarkup = new MarkupBlock(
+                new MarkupTagHelperBlock("p",
+                    new HtmlCommentBlock(factory.Markup($"<!--{comment1}-->")),
+                    factory.Markup(literal),
+                    new HtmlCommentBlock(factory.Markup($"<!--{comment2}-->"))));
+
+            // Act & Assert
+            EvaluateData(
+                descriptors,
+                expectedOutput,
+                expectedMarkup,
+                new[]
+                {
+                    nestedContentError("p", "b", 15, 4),
+                });
+        }
+
         [Fact]
         public void Rewrite_AllowsRazorCommentsAsChildren()
         {
@@ -1193,6 +1245,54 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 Array.Empty<RazorDiagnostic>());
         }
 
+        [Fact]
+        public void Rewrite_AllowsRazorMarkupInHtmlComment()
+        {
+            // Arrangestring documentContent,
+            IEnumerable<string> allowedChildren = new List<string> { "b" };
+            string literal = "asdf";
+            string part1 = "<!--Hello ";
+            string part2 = "World";
+            string part3 = "-->";
+            string expectedOutput = $"<p><b>{literal}</b>{part1}@{part2}{part3}</p>";
+
+            var pTagHelperBuilder = TagHelperDescriptorBuilder
+                .Create("PTagHelper", "SomeAssembly")
+                .TagMatchingRuleDescriptor(rule => rule.RequireTagName("p"));
+            foreach (var childTag in allowedChildren)
+            {
+                pTagHelperBuilder.AllowChildTag(childTag);
+            }
+
+            var descriptors = new TagHelperDescriptor[]
+            {
+                pTagHelperBuilder.Build()
+            };
+
+            var factory = new SpanFactory();
+            var blockFactory = new BlockFactory(factory);
+
+            var expectedMarkup = new MarkupBlock(
+                new MarkupTagHelperBlock("p",
+                    blockFactory.MarkupTagBlock("<b>"),
+                    factory.Markup(literal),
+                    blockFactory.MarkupTagBlock("</b>"),
+                    new HtmlCommentBlock(factory.Markup(part1),
+                     new ExpressionBlock(
+                        factory.CodeTransition(),
+                        factory.Code(part2)
+                            .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
+                            .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
+                    factory.Markup(part3))));
+
+            // Act & Assert
+            EvaluateData(
+                descriptors,
+                expectedOutput,
+                expectedMarkup,
+                Array.Empty<RazorDiagnostic>());
+        }
+
         [Fact]
         public void Rewrite_UnderstandsNullTagNameWithAllowedChildrenForCatchAll()
         {
@@ -3993,7 +4093,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     new MarkupBlock(
                         new MarkupTagBlock(
                             factory.Markup("<foo>")),
-                        factory.Markup("<!-- Hello World -->"),
+                        new HtmlCommentBlock( factory.Markup("<!-- Hello World -->")),
                         new MarkupTagBlock(
                             factory.Markup("</foo>")))
                 };
@@ -4003,13 +4103,13 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     new MarkupBlock(
                         new MarkupTagBlock(
                             factory.Markup("<foo>")),
-                        factory.Markup("<!-- "),
-                        new ExpressionBlock(
-                            factory.CodeTransition(),
-                            factory.Code("foo")
-                                   .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
-                                   .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
-                        factory.Markup(" -->"),
+                        new HtmlCommentBlock(factory.Markup("<!-- "),
+                            new ExpressionBlock(
+                                factory.CodeTransition(),
+                                factory.Code("foo")
+                                       .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
+                                       .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
+                            factory.Markup(" -->")),
                         new MarkupTagBlock(
                             factory.Markup("</foo>")))
                 };
diff --git a/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockTypes.cs b/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockTypes.cs
index c08e88d56f..56deb6b460 100644
--- a/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockTypes.cs
+++ b/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockTypes.cs
@@ -217,4 +217,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
         }
     }
+
+    internal class HtmlCommentBlock : Block
+    {
+        private const BlockKindInternal ThisBlockKind = BlockKindInternal.HtmlComment;
+
+        public HtmlCommentBlock(params SyntaxTreeNode[] children)
+            : base(ThisBlockKind, children, ParentChunkGenerator.Null)
+        {
+        }
+    }
 }

From f42754371eeefedfab9ec2ca2f2192ae3854bc32 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Tue, 20 Feb 2018 18:24:27 -0800
Subject: [PATCH 07/34] HtmlMarkupParser is now aware of HtmlComment blocks.
 Majority (if not all, will confirm soon) tests have been updated to account
 for HtmlComment blocks.

---
 .../Legacy/HtmlMarkupParser.cs                | 49 ++++++++++++++-----
 .../Legacy/CSharpSectionTest.cs               | 11 +++--
 .../Legacy/HtmlBlockTest.cs                   | 33 +++++++------
 .../Legacy/TagHelperParseTreeRewriterTest.cs  | 48 +++++++++---------
 .../TagHelperParseTreeRewriterTests.cs        | 26 ++++++++++
 ...lCommentWithQuote_Double_DesignTime.ir.txt |  3 +-
 ...HtmlCommentWithQuote_Double_Runtime.ir.txt |  3 +-
 ...lCommentWithQuote_Single_DesignTime.ir.txt |  3 +-
 ...HtmlCommentWithQuote_Single_Runtime.ir.txt |  3 +-
 .../Language/Legacy/BlockFactory.cs           | 21 ++++++++
 10 files changed, 144 insertions(+), 56 deletions(-)
 create mode 100644 test/Microsoft.AspNetCore.Razor.Language.Test/TagHelperParseTreeRewriterTests.cs

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index 332023b775..fc675b6e47 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -207,10 +207,6 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             if (last != null)
             {
                 Accept(last);
-                if (At(HtmlSymbolType.OpenAngle) && last.Type == HtmlSymbolType.Text)
-                {
-                    Output(SpanKindInternal.Markup);
-                }
             }
         }
 
@@ -501,31 +497,57 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     using (Context.Builder.StartBlock(BlockKindInternal.HtmlComment))
                     {
                         AcceptAndMoveNext();
+                        Output(SpanKindInternal.Markup, AcceptedCharactersInternal.None);
 
-                        Span.EditHandler.AcceptedCharacters = AcceptedCharactersInternal.Any;
+                        Span.EditHandler.AcceptedCharacters = AcceptedCharactersInternal.WhiteSpace;
                         while (!EndOfFile)
                         {
                             SkipToAndParseCode(HtmlSymbolType.DoubleHyphen);
                             if (At(HtmlSymbolType.DoubleHyphen))
                             {
-                                AcceptWhile(HtmlSymbolType.DoubleHyphen);
+                                var lastDoubleHyphen = CurrentSymbol;
+                                AcceptWhile(s =>
+                                {
+                                    if (NextIs(HtmlSymbolType.DoubleHyphen))
+                                    {
+                                        lastDoubleHyphen = s;
+                                        return true;
+                                    }
+
+                                    NextToken();
+                                    EnsureCurrent();
+                                    return false;
+                                });
 
                                 if (At(HtmlSymbolType.Text) &&
                                     string.Equals(CurrentSymbol.Content, "-", StringComparison.Ordinal))
                                 {
+                                    // Doing this here to maintain the order of symbols
+                                    if (!NextIs(HtmlSymbolType.CloseAngle))
+                                    {
+                                        Accept(lastDoubleHyphen);
+                                        lastDoubleHyphen = null;
+                                    }
+
                                     AcceptAndMoveNext();
                                 }
 
                                 if (At(HtmlSymbolType.CloseAngle))
                                 {
-                                    // This is the end of a comment block
-                                    Accept(this.CurrentSymbol);
-                                    Output(SpanKindInternal.Markup);
+                                    // Output the content in the comment block as a separate markup
+                                    Output(SpanKindInternal.Markup, AcceptedCharactersInternal.WhiteSpace);
+
+                                    // This is the end of a comment block
+                                    Accept(lastDoubleHyphen);
+                                    AcceptAndMoveNext();
+                                    Output(SpanKindInternal.Markup, AcceptedCharactersInternal.None);
 
-                                    NextToken();
-                                    //AcceptAndMoveNext();
                                     return true;
                                 }
+                                else if (lastDoubleHyphen != null)
+                                {
+                                    Accept(lastDoubleHyphen);
+                                }
                             }
                         }
                     }
@@ -1486,6 +1508,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     // Checking to see if we meet the conditions of a special '!' tag: <!DOCTYPE, <![CDATA[, <!--.
                     if (!IsBangEscape(lookahead: 1))
                     {
+                        if (Lookahead(2)?.Type == HtmlSymbolType.DoubleHyphen)
+                        {
+                            Output(SpanKindInternal.Markup);
+                        }
+
                         AcceptAndMoveNext(); // Accept '<'
                         BangTag();
 
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/CSharpSectionTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/CSharpSectionTest.cs
index 3ae95b1994..3e2fbac20f 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/CSharpSectionTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/CSharpSectionTest.cs
@@ -367,7 +367,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
             // Act & Assert
             ParseDocumentTest(
-                "@section foo      " 
+                "@section foo      "
                 + Environment.NewLine
                 + Environment.NewLine
                 + Environment.NewLine
@@ -606,7 +606,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         Factory.Span(SpanKindInternal.Markup, " ", CSharpSymbolType.WhiteSpace).Accepts(AcceptedCharactersInternal.AllWhiteSpace),
                         Factory.MetaCode("{").AutoCompleteWith(null, atEndOfSpan: true).Accepts(AcceptedCharactersInternal.None),
                         new MarkupBlock(
-                            Factory.Markup("<!-- -->")),
+                            BlockFactory.HtmlCommentBlock(" "),
+                            Factory.EmptyHtml()),
                         Factory.MetaCode("}").Accepts(AcceptedCharactersInternal.None)),
                     Factory.EmptyHtml()));
         }
@@ -630,7 +631,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         Factory.Span(SpanKindInternal.Markup, " ", CSharpSymbolType.WhiteSpace).Accepts(AcceptedCharactersInternal.AllWhiteSpace),
                         Factory.MetaCode("{").AutoCompleteWith(null, atEndOfSpan: true).Accepts(AcceptedCharactersInternal.None),
                         new MarkupBlock(
-                            Factory.Markup("<!-- > \" '-->")),
+                            BlockFactory.HtmlCommentBlock(" > \" '"),
+                            Factory.EmptyHtml()),
                         Factory.MetaCode("}").Accepts(AcceptedCharactersInternal.None)),
                     Factory.EmptyHtml()));
         }
@@ -655,7 +657,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                             Factory.Markup(Environment.NewLine),
                             new MarkupTagBlock(
                                 Factory.Markup("<a" + Environment.NewLine)),
-                            Factory.Markup("<!--  > \" '-->")),
+                                BlockFactory.HtmlCommentBlock("  > \" '"),
+                                Factory.EmptyHtml()),
                         Factory.MetaCode("}").Accepts(AcceptedCharactersInternal.None)),
                     Factory.EmptyHtml()));
         }
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
index f54ba50d37..f8d4b0fcd9 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
@@ -23,7 +23,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         Factory.Code(Environment.NewLine).AsStatement().AutoCompleteWith(null),
                         new MarkupBlock(
                             Factory.Markup("    "),
-                            Factory.Markup("<!-- Hello, I'm a comment that shouldn't break razor --->").Accepts(AcceptedCharactersInternal.None),
+                            BlockFactory.HtmlCommentBlock(" Hello, I'm a comment that shouldn't break razor -"),
                             Factory.Markup(Environment.NewLine).Accepts(AcceptedCharactersInternal.None)),
                         Factory.EmptyCSharp().AsStatement(),
                         Factory.MetaCode("}").Accepts(AcceptedCharactersInternal.None)),
@@ -333,7 +333,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         [Fact]
         public void ParseBlockSupportsCommentAsBlock()
         {
-            SingleSpanBlockTest("<!-- foo -->", BlockKindInternal.Markup, SpanKindInternal.Markup, acceptedCharacters: AcceptedCharactersInternal.None);
+            ParseBlockTest("<!-- foo -->", new MarkupBlock( BlockFactory.HtmlCommentBlock(" foo ")));
         }
 
         [Fact]
@@ -344,8 +344,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     new MarkupTagBlock(
                         Factory.Markup("<foo>").Accepts(AcceptedCharactersInternal.None)),
                     Factory.Markup("bar"),
-                    Factory.Markup("<!-- zoop -->").Accepts(AcceptedCharactersInternal.None),
-                    Factory.Markup("baz"),
+                    BlockFactory.HtmlCommentBlock(" zoop "),
+                    Factory.Markup("baz").Accepts(AcceptedCharactersInternal.None),
                     new MarkupTagBlock(
                         Factory.Markup("</foo>").Accepts(AcceptedCharactersInternal.None))));
         }
@@ -355,7 +355,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             get
             {
                 var factory = new SpanFactory();
-
+                var blockFactory = new BlockFactory(factory);
                 return new TheoryData<string, MarkupBlock>
                 {
                     {
@@ -363,7 +363,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         new MarkupBlock(
                             new MarkupTagBlock(
                                 factory.Markup("<div>").Accepts(AcceptedCharactersInternal.None)),
-                            factory.Markup("<!--- Hello World --->").Accepts(AcceptedCharactersInternal.None),
+                            blockFactory.HtmlCommentBlock("- Hello World -"),
                             new MarkupTagBlock(
                                 factory.Markup("</div>").Accepts(AcceptedCharactersInternal.None)))
                     },
@@ -372,7 +372,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         new MarkupBlock(
                             new MarkupTagBlock(
                                 factory.Markup("<div>").Accepts(AcceptedCharactersInternal.None)),
-                            factory.Markup("<!---- Hello World ---->").Accepts(AcceptedCharactersInternal.None),
+                            blockFactory.HtmlCommentBlock("-- Hello World --"),
                             new MarkupTagBlock(
                                 factory.Markup("</div>").Accepts(AcceptedCharactersInternal.None)))
                     },
@@ -381,7 +381,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         new MarkupBlock(
                             new MarkupTagBlock(
                                 factory.Markup("<div>").Accepts(AcceptedCharactersInternal.None)),
-                            factory.Markup("<!----- Hello World ----->").Accepts(AcceptedCharactersInternal.None),
+                            blockFactory.HtmlCommentBlock("--- Hello World ---"),
                             new MarkupTagBlock(
                                 factory.Markup("</div>").Accepts(AcceptedCharactersInternal.None)))
                     },
@@ -390,7 +390,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         new MarkupBlock(
                             new MarkupTagBlock(
                                 factory.Markup("<div>").Accepts(AcceptedCharactersInternal.None)),
-                            factory.Markup("<!----- Hello < --- > World </div> ----->").Accepts(AcceptedCharactersInternal.None),
+                           blockFactory.HtmlCommentBlock("--- Hello < --- > World </div> ---"),
                             new MarkupTagBlock(
                                 factory.Markup("</div>").Accepts(AcceptedCharactersInternal.None)))
                     },
@@ -410,19 +410,24 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         [Fact]
         public void ParseBlockProperlyBalancesCommentStartAndEndTags()
         {
-            SingleSpanBlockTest("<!--<foo></bar>-->", BlockKindInternal.Markup, SpanKindInternal.Markup, acceptedCharacters: AcceptedCharactersInternal.None);
+            ParseBlockTest("<!--<foo></bar>-->", new MarkupBlock(BlockFactory.HtmlCommentBlock("<foo></bar>")));
         }
 
         [Fact]
         public void ParseBlockTerminatesAtEOFWhenParsingComment()
         {
-            SingleSpanBlockTest("<!--<foo>", "<!--<foo>", BlockKindInternal.Markup, SpanKindInternal.Markup);
+            ParseBlockTest(
+                "<!--<foo>",
+                new MarkupBlock(
+                    new HtmlCommentBlock(Factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None)),
+                    Factory.Markup("<foo>").Accepts(AcceptedCharactersInternal.WhiteSpace),
+                    Factory.EmptyHtml()));
         }
 
         [Fact]
         public void ParseBlockOnlyTerminatesCommentOnFullEndSequence()
         {
-            SingleSpanBlockTest("<!--<foo>--</bar>-->", BlockKindInternal.Markup, SpanKindInternal.Markup, acceptedCharacters: AcceptedCharactersInternal.None);
+            ParseBlockTest("<!--<foo>--</bar>-->", new MarkupBlock(BlockFactory.HtmlCommentBlock("<foo>--</bar>")));
         }
 
         [Fact]
@@ -432,8 +437,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 new MarkupBlock(
                     new MarkupTagBlock(
                         Factory.Markup("<foo>").Accepts(AcceptedCharactersInternal.None)),
-                    Factory.Markup("<!--<foo></bar-->").Accepts(AcceptedCharactersInternal.None),
-                    Factory.Markup("-->"),
+                    BlockFactory.HtmlCommentBlock("<foo></bar"),
+                    Factory.Markup("-->").Accepts(AcceptedCharactersInternal.None),
                     new MarkupTagBlock(
                         Factory.Markup("</foo>").Accepts(AcceptedCharactersInternal.None))));
         }
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index 45a1ffa907..ceca9e86f2 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -1114,8 +1114,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             // Arrangestring documentContent,
             IEnumerable<string> allowedChildren = new List<string> { "b" };
             string literal = "asdf";
-            string commentOutput = "<!--Hello World-->";
-            string expectedOutput = $"<p><b>{literal}</b>{commentOutput}</p>";
+            string commentOutput = "Hello World";
+            string expectedOutput = $"<p><b>{literal}</b><!--{commentOutput}--></p>";
 
             var pTagHelperBuilder = TagHelperDescriptorBuilder
                 .Create("PTagHelper", "SomeAssembly")
@@ -1138,7 +1138,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     blockFactory.MarkupTagBlock("<b>"),
                     factory.Markup(literal),
                     blockFactory.MarkupTagBlock("</b>"),
-                    new HtmlCommentBlock(factory.Markup(commentOutput))));
+                    blockFactory.HtmlCommentBlock(commentOutput)));
 
             // Act & Assert
             EvaluateData(
@@ -1185,9 +1185,9 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
             var expectedMarkup = new MarkupBlock(
                 new MarkupTagHelperBlock("p",
-                    new HtmlCommentBlock(factory.Markup($"<!--{comment1}-->")),
+                    blockFactory.HtmlCommentBlock(comment1),
                     factory.Markup(literal),
-                    new HtmlCommentBlock(factory.Markup($"<!--{comment2}-->"))));
+                    blockFactory.HtmlCommentBlock(comment2)));
 
             // Act & Assert
             EvaluateData(
@@ -1251,10 +1251,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             // Arrangestring documentContent,
             IEnumerable<string> allowedChildren = new List<string> { "b" };
             string literal = "asdf";
-            string part1 = "<!--Hello ";
+            string part1 = "Hello ";
             string part2 = "World";
-            string part3 = "-->";
-            string expectedOutput = $"<p><b>{literal}</b>{part1}@{part2}{part3}</p>";
+            string commentStart = "<!--";
+            string commentEnd = "-->";
+            string expectedOutput = $"<p><b>{literal}</b>{commentStart}{part1}@{part2}{commentEnd}</p>";
 
             var pTagHelperBuilder = TagHelperDescriptorBuilder
                 .Create("PTagHelper", "SomeAssembly")
@@ -1277,13 +1278,13 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     blockFactory.MarkupTagBlock("<b>"),
                     factory.Markup(literal),
                     blockFactory.MarkupTagBlock("</b>"),
-                    new HtmlCommentBlock(factory.Markup(part1),
-                     new ExpressionBlock(
-                        factory.CodeTransition(),
-                        factory.Code(part2)
-                            .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
-                            .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
-                    factory.Markup(part3))));
+                    blockFactory.HtmlCommentBlock(
+                        factory.Markup(part1).Accepts(AcceptedCharactersInternal.WhiteSpace),
+                         new ExpressionBlock(
+                            factory.CodeTransition(),
+                            factory.Code(part2)
+                                .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
+                                .Accepts(AcceptedCharactersInternal.NonWhiteSpace)))));
 
             // Act & Assert
             EvaluateData(
@@ -4086,14 +4087,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             get
             {
                 var factory = new SpanFactory();
-
+                var blockFactory = new BlockFactory(factory);
                 yield return new object[]
                 {
                     "<foo><!-- Hello World --></foo>",
                     new MarkupBlock(
                         new MarkupTagBlock(
                             factory.Markup("<foo>")),
-                        new HtmlCommentBlock( factory.Markup("<!-- Hello World -->")),
+                        blockFactory.HtmlCommentBlock (" Hello World "),
                         new MarkupTagBlock(
                             factory.Markup("</foo>")))
                 };
@@ -4103,13 +4104,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     new MarkupBlock(
                         new MarkupTagBlock(
                             factory.Markup("<foo>")),
-                        new HtmlCommentBlock(factory.Markup("<!-- "),
+                        blockFactory.HtmlCommentBlock(
+                            factory.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace),
                             new ExpressionBlock(
                                 factory.CodeTransition(),
                                 factory.Code("foo")
-                                       .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
-                                       .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
-                            factory.Markup(" -->")),
+                                    .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
+                                    .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
+                            factory.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace)),
                         new MarkupTagBlock(
                             factory.Markup("</foo>")))
                 };
@@ -4185,8 +4187,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         new ExpressionBlock(
                             factory.CodeTransition(),
                             factory.Code("foo")
-                                   .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
-                                   .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
+                                .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
+                                .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
                         factory.Markup(" ]]>"),
                         new MarkupTagBlock(
                             factory.Markup("</foo>")))
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TagHelperParseTreeRewriterTests.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/TagHelperParseTreeRewriterTests.cs
new file mode 100644
index 0000000000..a24a9c8d4f
--- /dev/null
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TagHelperParseTreeRewriterTests.cs
@@ -0,0 +1,26 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Microsoft.AspNetCore.Razor.Language.Legacy;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Razor.Language.Test
+{
+    public class TagHelperParseTreeRewriterTests
+    {
+        public void IsComment_ReturnsTrueForSpanInHtmlCommentBlock()
+        {
+            // Arrange
+            SpanFactory spanFactory = new SpanFactory();
+            
+            Span content = spanFactory.Markup("<!-- comment -->");
+            Block commentBlock = new HtmlCommentBlock(content);
+
+            // Act
+            bool actualResult = TagHelperParseTreeRewriter.IsComment(content);
+
+            // Assert
+            Assert.True(actualResult);
+        }
+    }
+}
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt
index aa6a00864d..615f0fce97 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt
@@ -10,7 +10,8 @@ Document -
                 IntermediateToken -  - CSharp - #pragma warning restore 0414
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Double.cshtml)
-                    IntermediateToken - (0:0,0 [12] HtmlCommentWithQuote_Double.cshtml) - Html - <!-- " -->\n
+                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Double.cshtml) - Html - <!-- " -->
+                    IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Double.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Double.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Double.cshtml) - Html -  src="~/images/submit.png"
                     IntermediateToken - (42:1,30 [3] HtmlCommentWithQuote_Double.cshtml) - Html -  />
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt
index 343985c189..7adfc1650b 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt
@@ -5,7 +5,8 @@ Document -
         ClassDeclaration -  - public - TestFiles_IntegrationTests_CodeGenerationIntegrationTest_HtmlCommentWithQuote_Double_Runtime -  - 
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Double.cshtml)
-                    IntermediateToken - (0:0,0 [12] HtmlCommentWithQuote_Double.cshtml) - Html - <!-- " -->\n
+                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Double.cshtml) - Html - <!-- " -->
+                    IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Double.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Double.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Double.cshtml) - Html -  src="~/images/submit.png"
                     IntermediateToken - (42:1,30 [3] HtmlCommentWithQuote_Double.cshtml) - Html -  />
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt
index 04795676d1..0e342fcf51 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt
@@ -10,7 +10,8 @@ Document -
                 IntermediateToken -  - CSharp - #pragma warning restore 0414
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Single.cshtml)
-                    IntermediateToken - (0:0,0 [12] HtmlCommentWithQuote_Single.cshtml) - Html - <!-- ' -->\n
+                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Single.cshtml) - Html - <!-- ' -->
+                    IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Single.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Single.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Single.cshtml) - Html -  src="~/images/submit.png"
                     IntermediateToken - (42:1,30 [3] HtmlCommentWithQuote_Single.cshtml) - Html -  />
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt
index 65aafb6fe7..137c2a042c 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt
@@ -5,7 +5,8 @@ Document -
         ClassDeclaration -  - public - TestFiles_IntegrationTests_CodeGenerationIntegrationTest_HtmlCommentWithQuote_Single_Runtime -  - 
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Single.cshtml)
-                    IntermediateToken - (0:0,0 [12] HtmlCommentWithQuote_Single.cshtml) - Html - <!-- ' -->\n
+                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Single.cshtml) - Html - <!-- ' -->
+                    IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Single.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Single.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Single.cshtml) - Html -  src="~/images/submit.png"
                     IntermediateToken - (42:1,30 [3] HtmlCommentWithQuote_Single.cshtml) - Html -  />
diff --git a/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs b/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs
index 5c2ee95394..a58d3b0c87 100644
--- a/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs
+++ b/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs
@@ -55,6 +55,27 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             );
         }
 
+        public HtmlCommentBlock HtmlCommentBlock(string content)
+        {
+            return new HtmlCommentBlock(new SyntaxTreeNode[] {
+                _factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None),
+                _factory.Markup(content).Accepts(AcceptedCharactersInternal.WhiteSpace),
+                _factory.Markup("-->").Accepts(AcceptedCharactersInternal.None) });
+        }
+
+        public HtmlCommentBlock HtmlCommentBlock(params SyntaxTreeNode[] syntaxTreeNodes)
+        {
+            var nodes = new List<SyntaxTreeNode>();
+            nodes.Add(_factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None));
+            if (syntaxTreeNodes != null)
+            {
+                nodes.AddRange(syntaxTreeNodes);
+            }
+            nodes.Add(_factory.Markup("-->").Accepts(AcceptedCharactersInternal.None));
+
+            return new HtmlCommentBlock(nodes.ToArray());
+        }
+
         public Block TagHelperBlock(
             string tagName,
             TagMode tagMode,

From 2949470a4383fd22f89fb11be5b1c7beb08dab77 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Tue, 20 Feb 2018 22:20:48 -0800
Subject: [PATCH 08/34] Fixed all the tests to reflect HtmlComment block type
 support

---
 .../Legacy/HtmlDocumentTest.cs                |  8 +++++++-
 .../Legacy/HtmlTagsTest.cs                    |  2 +-
 .../Legacy/HtmlToCodeSwitchTest.cs            | 15 +++++++-------
 .../Legacy/TagHelperParseTreeRewriterTest.cs  | 20 +++++++++----------
 ...lCommentWithQuote_Double_DesignTime.ir.txt |  4 +++-
 ...HtmlCommentWithQuote_Double_Runtime.ir.txt |  4 +++-
 ...lCommentWithQuote_Single_DesignTime.ir.txt |  4 +++-
 ...HtmlCommentWithQuote_Single_Runtime.ir.txt |  4 +++-
 .../Language/Legacy/BlockFactory.cs           | 16 +++++++--------
 9 files changed, 45 insertions(+), 32 deletions(-)

diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs
index 0f06fe578a..9f0e11218b 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs
@@ -214,7 +214,13 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         [Fact]
         public void ParseDocumentReturnsOneMarkupSegmentIfNoCodeBlocksEncountered()
         {
-            SingleSpanDocumentTest("Foo Baz<!--Foo-->Bar<!--F> Qux", BlockKindInternal.Markup, SpanKindInternal.Markup);
+            ParseDocumentTest("Foo Baz<!--Foo-->Bar<!--F> Qux",
+                new MarkupBlock(
+                    Factory.Markup("Foo Baz"),
+                    BlockFactory.HtmlCommentBlock("Foo"),
+                    Factory.Markup("Bar"),
+                    new HtmlCommentBlock(Factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None)),
+                    Factory.Markup("F> Qux").Accepts(AcceptedCharactersInternal.WhiteSpace)));
         }
 
         [Fact]
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlTagsTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlTagsTest.cs
index 0a86c7a06b..5f22a1bae7 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlTagsTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlTagsTest.cs
@@ -60,7 +60,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
             ParseBlockTest("<!--Foo--> Bar",
                 new MarkupBlock(
-                    Factory.Markup("<!--Foo-->").Accepts(AcceptedCharactersInternal.None),
+                    BlockFactory.HtmlCommentBlock("Foo"),
                     Factory.Markup(" ").Accepts(AcceptedCharactersInternal.None)));
         }
 
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlToCodeSwitchTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlToCodeSwitchTest.cs
index 29c1dfb81a..928762fbc6 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlToCodeSwitchTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlToCodeSwitchTest.cs
@@ -112,13 +112,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 new MarkupBlock(
                     new MarkupTagBlock(
                         Factory.Markup("<foo>").Accepts(AcceptedCharactersInternal.None)),
-                    Factory.Markup("<!-- "),
-                    new ExpressionBlock(
-                        Factory.CodeTransition(),
-                        Factory.Code("foo")
-                               .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
-                               .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
-                    Factory.Markup(" -->").Accepts(AcceptedCharactersInternal.None),
+                    BlockFactory.HtmlCommentBlock(Factory, f => new SyntaxTreeNode[] {
+                        f.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace),
+                        new ExpressionBlock(
+                            f.CodeTransition(),
+                            f.Code("foo")
+                                   .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
+                                   .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
+                            f.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace) }),
                     new MarkupTagBlock(
                         Factory.Markup("</foo>").Accepts(AcceptedCharactersInternal.None))));
         }
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index ceca9e86f2..425b728716 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -1278,13 +1278,13 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     blockFactory.MarkupTagBlock("<b>"),
                     factory.Markup(literal),
                     blockFactory.MarkupTagBlock("</b>"),
-                    blockFactory.HtmlCommentBlock(
-                        factory.Markup(part1).Accepts(AcceptedCharactersInternal.WhiteSpace),
+                    BlockFactory.HtmlCommentBlock(factory, f => new SyntaxTreeNode[] {
+                        f.Markup(part1).Accepts(AcceptedCharactersInternal.WhiteSpace),
                          new ExpressionBlock(
-                            factory.CodeTransition(),
-                            factory.Code(part2)
+                            f.CodeTransition(),
+                            f.Code(part2)
                                 .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
-                                .Accepts(AcceptedCharactersInternal.NonWhiteSpace)))));
+                                .Accepts(AcceptedCharactersInternal.NonWhiteSpace)) })));
 
             // Act & Assert
             EvaluateData(
@@ -4104,14 +4104,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     new MarkupBlock(
                         new MarkupTagBlock(
                             factory.Markup("<foo>")),
-                        blockFactory.HtmlCommentBlock(
-                            factory.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace),
+                        BlockFactory.HtmlCommentBlock(factory, f=> new SyntaxTreeNode[]{
+                            f.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace),
                             new ExpressionBlock(
-                                factory.CodeTransition(),
-                                factory.Code("foo")
+                                f.CodeTransition(),
+                                f.Code("foo")
                                     .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
                                     .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
-                            factory.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace)),
+                            factory.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace) }),
                         new MarkupTagBlock(
                             factory.Markup("</foo>")))
                 };
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt
index 615f0fce97..4523eae7a3 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt
@@ -10,7 +10,9 @@ Document -
                 IntermediateToken -  - CSharp - #pragma warning restore 0414
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Double.cshtml)
-                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Double.cshtml) - Html - <!-- " -->
+                    IntermediateToken - (0:0,0 [4] HtmlCommentWithQuote_Double.cshtml) - Html - <!--
+                    IntermediateToken - (4:0,4 [3] HtmlCommentWithQuote_Double.cshtml) - Html -  " 
+                    IntermediateToken - (7:0,7 [3] HtmlCommentWithQuote_Double.cshtml) - Html - -->
                     IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Double.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Double.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Double.cshtml) - Html -  src="~/images/submit.png"
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt
index 7adfc1650b..046cad8407 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt
@@ -5,7 +5,9 @@ Document -
         ClassDeclaration -  - public - TestFiles_IntegrationTests_CodeGenerationIntegrationTest_HtmlCommentWithQuote_Double_Runtime -  - 
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Double.cshtml)
-                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Double.cshtml) - Html - <!-- " -->
+                    IntermediateToken - (0:0,0 [4] HtmlCommentWithQuote_Double.cshtml) - Html - <!--
+                    IntermediateToken - (4:0,4 [3] HtmlCommentWithQuote_Double.cshtml) - Html -  " 
+                    IntermediateToken - (7:0,7 [3] HtmlCommentWithQuote_Double.cshtml) - Html - -->
                     IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Double.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Double.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Double.cshtml) - Html -  src="~/images/submit.png"
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt
index 0e342fcf51..8b5f5b3ed5 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt
@@ -10,7 +10,9 @@ Document -
                 IntermediateToken -  - CSharp - #pragma warning restore 0414
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Single.cshtml)
-                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Single.cshtml) - Html - <!-- ' -->
+                    IntermediateToken - (0:0,0 [4] HtmlCommentWithQuote_Single.cshtml) - Html - <!--
+                    IntermediateToken - (4:0,4 [3] HtmlCommentWithQuote_Single.cshtml) - Html -  ' 
+                    IntermediateToken - (7:0,7 [3] HtmlCommentWithQuote_Single.cshtml) - Html - -->
                     IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Single.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Single.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Single.cshtml) - Html -  src="~/images/submit.png"
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt
index 137c2a042c..8596f51503 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt
@@ -5,7 +5,9 @@ Document -
         ClassDeclaration -  - public - TestFiles_IntegrationTests_CodeGenerationIntegrationTest_HtmlCommentWithQuote_Single_Runtime -  - 
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Single.cshtml)
-                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Single.cshtml) - Html - <!-- ' -->
+                    IntermediateToken - (0:0,0 [4] HtmlCommentWithQuote_Single.cshtml) - Html - <!--
+                    IntermediateToken - (4:0,4 [3] HtmlCommentWithQuote_Single.cshtml) - Html -  ' 
+                    IntermediateToken - (7:0,7 [3] HtmlCommentWithQuote_Single.cshtml) - Html - -->
                     IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Single.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Single.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Single.cshtml) - Html -  src="~/images/submit.png"
diff --git a/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs b/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs
index a58d3b0c87..2551fee917 100644
--- a/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs
+++ b/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs
@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
 
 namespace Microsoft.AspNetCore.Razor.Language.Legacy
@@ -57,21 +58,18 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         public HtmlCommentBlock HtmlCommentBlock(string content)
         {
-            return new HtmlCommentBlock(new SyntaxTreeNode[] {
-                _factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None),
-                _factory.Markup(content).Accepts(AcceptedCharactersInternal.WhiteSpace),
-                _factory.Markup("-->").Accepts(AcceptedCharactersInternal.None) });
+            return HtmlCommentBlock(_factory, f => new SyntaxTreeNode[] { f.Markup(content).Accepts(AcceptedCharactersInternal.WhiteSpace) });
         }
 
-        public HtmlCommentBlock HtmlCommentBlock(params SyntaxTreeNode[] syntaxTreeNodes)
+        public static HtmlCommentBlock HtmlCommentBlock(SpanFactory factory, Func<SpanFactory, IEnumerable<SyntaxTreeNode>> nodesBuilder = null)
         {
             var nodes = new List<SyntaxTreeNode>();
-            nodes.Add(_factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None));
-            if (syntaxTreeNodes != null)
+            nodes.Add(factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None));
+            if (nodesBuilder != null)
             {
-                nodes.AddRange(syntaxTreeNodes);
+                nodes.AddRange(nodesBuilder(factory));
             }
-            nodes.Add(_factory.Markup("-->").Accepts(AcceptedCharactersInternal.None));
+            nodes.Add(factory.Markup("-->").Accepts(AcceptedCharactersInternal.None));
 
             return new HtmlCommentBlock(nodes.ToArray());
         }

From 0c8dddcc40e1f0d9856ca380afd263a2d7f0308f Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Thu, 22 Feb 2018 17:05:13 -0800
Subject: [PATCH 09/34] Added the AllowHtmlCommentsInTagHelpers feature flag to
 control behavior of having comments in TagHelpers

---
 .../Legacy/TagHelperParseTreeRewriter.cs              |  8 +++++++-
 .../RazorParserFeatureFlags.cs                        | 11 +++++++++--
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index 6cac8b46ea..a4c9906b1a 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -488,7 +488,13 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            if (HasAllowedChildren() && !IsComment(child) && child.Kind != SpanKindInternal.Transition && child.Kind != SpanKindInternal.Code)
+            var isDisallowedContent = true;
+            if (_featureFlags.AllowHtmlCommentsInTagHelpers)
+            {
+                isDisallowedContent = !IsComment(child) && child.Kind != SpanKindInternal.Transition && child.Kind != SpanKindInternal.Code;
+            }
+
+            if (HasAllowedChildren() && isDisallowedContent)
             {
                 var content = child.Content;
                 if (!string.IsNullOrWhiteSpace(content))
diff --git a/src/Microsoft.AspNetCore.Razor.Language/RazorParserFeatureFlags.cs b/src/Microsoft.AspNetCore.Razor.Language/RazorParserFeatureFlags.cs
index 0629eb9af8..409718b640 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/RazorParserFeatureFlags.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/RazorParserFeatureFlags.cs
@@ -8,26 +8,33 @@ namespace Microsoft.AspNetCore.Razor.Language
         public static RazorParserFeatureFlags Create(RazorLanguageVersion version)
         {
             var allowMinimizedBooleanTagHelperAttributes = false;
+            var allowHtmlCommentsInTagHelpers = false;
 
             if (version.CompareTo(RazorLanguageVersion.Version_2_1) >= 0)
             {
                 // Added in 2.1
                 allowMinimizedBooleanTagHelperAttributes = true;
+                allowHtmlCommentsInTagHelpers = true;
             }
 
-            return new DefaultRazorParserFeatureFlags(allowMinimizedBooleanTagHelperAttributes);
+            return new DefaultRazorParserFeatureFlags(allowMinimizedBooleanTagHelperAttributes, allowHtmlCommentsInTagHelpers);
         }
 
         public abstract bool AllowMinimizedBooleanTagHelperAttributes { get; }
 
+        public abstract bool AllowHtmlCommentsInTagHelpers { get; }
+
         private class DefaultRazorParserFeatureFlags : RazorParserFeatureFlags
         {
-            public DefaultRazorParserFeatureFlags(bool allowMinimizedBooleanTagHelperAttributes)
+            public DefaultRazorParserFeatureFlags(bool allowMinimizedBooleanTagHelperAttributes, bool allowHtmlCommentsInTagHelpers)
             {
                 AllowMinimizedBooleanTagHelperAttributes = allowMinimizedBooleanTagHelperAttributes;
+                AllowHtmlCommentsInTagHelpers = allowHtmlCommentsInTagHelpers;
             }
 
             public override bool AllowMinimizedBooleanTagHelperAttributes { get; }
+
+            public override bool AllowHtmlCommentsInTagHelpers { get; }
         }
     }
 }

From 1796abcbcde83996b6b0da6ff5fa85f682b29e21 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Thu, 22 Feb 2018 17:07:52 -0800
Subject: [PATCH 10/34] Updated the test TagHelperBlockRewriteTest class

---
 .../Legacy/TagHelperBlockRewriterTest.cs            | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperBlockRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperBlockRewriterTest.cs
index 9b2adc4d07..88c774c93c 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperBlockRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperBlockRewriterTest.cs
@@ -2950,7 +2950,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                                 intType),
                             RazorDiagnosticFactory.CreateParsing_TagHelperIndexerAttributeNameMustIncludeKey(
                                 new SourceSpan(7, 0, 7, 11),
-                                "int-prefix-", 
+                                "int-prefix-",
                                 "input"),
                         }
                     },
@@ -2973,7 +2973,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                                 stringType),
                             RazorDiagnosticFactory.CreateParsing_TagHelperIndexerAttributeNameMustIncludeKey(
                                 new SourceSpan(7, 0, 7, 14),
-                                "string-prefix-", 
+                                "string-prefix-",
                                 "input"),
                         }
                     },
@@ -3638,7 +3638,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                             RazorDiagnosticFactory.CreateTagHelper_EmptyBoundAttribute(
                                 new SourceSpan(7, 0, 7, 21),
                                 "bound-required-string",
-                                "input", 
+                                "input",
                                 stringType),
                         }
                     },
@@ -3962,7 +3962,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     .Build(),
             };
 
-            var featureFlags = new TestRazorParserFeatureFlags(allowMinimizedBooleanTagHelperAttributes: false);
+            var featureFlags = new TestRazorParserFeatureFlags(allowMinimizedBooleanTagHelperAttributes: false, allowHtmlCommentsInTagHelper: false);
 
             var expectedOutput = new MarkupBlock(
                 new MarkupTagHelperBlock(
@@ -3994,12 +3994,15 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private class TestRazorParserFeatureFlags : RazorParserFeatureFlags
         {
-            public TestRazorParserFeatureFlags(bool allowMinimizedBooleanTagHelperAttributes)
+            public TestRazorParserFeatureFlags(bool allowMinimizedBooleanTagHelperAttributes, bool allowHtmlCommentsInTagHelper)
             {
                 AllowMinimizedBooleanTagHelperAttributes = allowMinimizedBooleanTagHelperAttributes;
+                AllowHtmlCommentsInTagHelpers = allowHtmlCommentsInTagHelper;
             }
 
             public override bool AllowMinimizedBooleanTagHelperAttributes { get; }
+
+            public override bool AllowHtmlCommentsInTagHelpers { get; }
         }
     }
 }

From 9c3adba40ff470c164cfccdcc895733648f8bec2 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Mon, 5 Mar 2018 17:28:23 -0800
Subject: [PATCH 11/34] Updated the Comments detection to comply with HTML 5
 specification

---
 .../Legacy/HtmlMarkupParser.cs                | 151 ++++++++++++++----
 .../Legacy/TokenizerBackedParser.cs           |  47 ++++++
 .../Legacy/HtmlBlockTest.cs                   |   4 +-
 .../Legacy/HtmlDocumentTest.cs                |   3 +-
 4 files changed, 170 insertions(+), 35 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index fc675b6e47..2fe84b5a33 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -492,7 +492,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
             if (AcceptAndMoveNext())
             {
-                if (CurrentSymbol.Type == HtmlSymbolType.DoubleHyphen)
+                if (IsHtmlCommentAhead())
                 {
                     using (Context.Builder.StartBlock(BlockKindInternal.HtmlComment))
                     {
@@ -505,32 +505,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                             SkipToAndParseCode(HtmlSymbolType.DoubleHyphen);
                             if (At(HtmlSymbolType.DoubleHyphen))
                             {
-                                var lastDoubleHyphen = CurrentSymbol;
-                                AcceptWhile(s =>
-                                {
-                                    if (NextIs(HtmlSymbolType.DoubleHyphen))
-                                    {
-                                        lastDoubleHyphen = s;
-                                        return true;
-                                    }
-
-                                    NextToken();
-                                    EnsureCurrent();
-                                    return false;
-                                });
-
-                                if (At(HtmlSymbolType.Text) &&
-                                    string.Equals(CurrentSymbol.Content, "-", StringComparison.Ordinal))
-                                {
-                                    // Doing this here to maintain the order of symbols
-                                    if (!NextIs(HtmlSymbolType.CloseAngle))
-                                    {
-                                        Accept(lastDoubleHyphen);
-                                        lastDoubleHyphen = null;
-                                    }
-
-                                    AcceptAndMoveNext();
-                                }
+                                var lastDoubleHyphen = AcceptAllButLastDoubleHypens();
 
                                 if (At(HtmlSymbolType.CloseAngle))
                                 {
@@ -541,7 +516,6 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                                     Accept(lastDoubleHyphen);
                                     AcceptAndMoveNext();
                                     Output(SpanKindInternal.Markup, AcceptedCharactersInternal.None);
-
                                     return true;
                                 }
                                 else if (lastDoubleHyphen != null)
@@ -551,8 +525,6 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                             }
                         }
                     }
-
-                    return false;
                 }
                 else if (CurrentSymbol.Type == HtmlSymbolType.LeftBracket)
                 {
@@ -571,6 +543,125 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return false;
         }
 
+        private HtmlSymbol AcceptAllButLastDoubleHypens()
+        {
+            var lastDoubleHyphen = CurrentSymbol;
+            AcceptWhile(s =>
+            {
+                if (NextIs(HtmlSymbolType.DoubleHyphen))
+                {
+                    lastDoubleHyphen = s;
+                    return true;
+                }
+
+                NextToken();
+                EnsureCurrent();
+                return false;
+            });
+
+            if (At(HtmlSymbolType.Text) && IsDashSymbol(CurrentSymbol))
+            {
+                // Doing this here to maintain the order of symbols
+                if (!NextIs(HtmlSymbolType.CloseAngle))
+                {
+                    Accept(lastDoubleHyphen);
+                    lastDoubleHyphen = null;
+                }
+
+                AcceptAndMoveNext();
+            }
+
+            return lastDoubleHyphen;
+        }
+
+        private static bool IsDashSymbol(HtmlSymbol symbol)
+        {
+            return string.Equals(symbol.Content, "-", StringComparison.Ordinal);
+        }
+
+        private bool IsHtmlCommentAhead()
+        {
+            /*
+             * From HTML5 Specification, available at http://www.w3.org/TR/html52/syntax.html#comments
+             * 
+             * Comments must have the following format:
+             * 1. The string "<!--"
+             * 2. Optionally, text, with the additional restriction that the text
+             *      2.1 must not start with the string ">" nor start with the string "->"
+             *      2.2 nor contain the strings "<!--", "-->", or "--!>"
+             *      2.3 nor end with the string "<!-".
+             * 3. The string "-->"
+             * 
+             * */
+
+            if (CurrentSymbol.Type != HtmlSymbolType.DoubleHyphen)
+            {
+                return false;
+            }
+
+            // Check condition 2.1
+            if (NextIs(HtmlSymbolType.CloseAngle) || NextIs(next => IsDashSymbol(next) && NextIs(HtmlSymbolType.CloseAngle)))
+            {
+                return false;
+            }
+
+            // Check condition 2.2
+            bool isValidComment = false;
+            LookaheadUntil((s, p) =>
+            {
+                bool breakLookahead = false;
+                if (s.Type == HtmlSymbolType.DoubleHyphen)
+                {
+                    if (NextIs(HtmlSymbolType.CloseAngle))
+                    {
+                        // We're at the end of a comment. check the condition 2.3 to make sure the text ending is allowed.
+                        isValidComment = !EndsWithSymbolsSequence(p, HtmlSymbolType.OpenAngle, HtmlSymbolType.Bang, HtmlSymbolType.DoubleHyphen);
+                        breakLookahead = true;
+                    }
+                    else if (NextIs(ns => IsDashSymbol(ns) && NextIs(HtmlSymbolType.CloseAngle)))
+                    {
+                        // This is also a valid closing comment case, as the dashes lookup is treated with DoubleHyphen symbols first.
+                        isValidComment = true;
+                        breakLookahead = true;
+                    }
+                    else if (NextIs(ns => ns.Type == HtmlSymbolType.Bang && NextIs(HtmlSymbolType.CloseAngle)))
+                    {
+                        isValidComment = false;
+                        breakLookahead = true;
+                    }
+                }
+                else if (s.Type == HtmlSymbolType.OpenAngle)
+                {
+                    if (NextIs(ns => ns.Type == HtmlSymbolType.Bang && NextIs(HtmlSymbolType.DoubleHyphen)))
+                    {
+                        isValidComment = false;
+                        breakLookahead = true;
+                    }
+                }
+
+                return breakLookahead;
+            });
+
+            return isValidComment;
+        }
+
+        private bool EndsWithSymbolsSequence(IEnumerable<HtmlSymbol> symbols, params HtmlSymbolType[] sequenceToMatchWith)
+        {
+            int index = sequenceToMatchWith.Length;
+            foreach (var previousSymbol in symbols)
+            {
+                if (index == 0)
+                {
+                    break;
+                }
+
+                if (sequenceToMatchWith[--index] != previousSymbol.Type)
+                    return false;
+            }
+
+            return index == 0;
+        }
+
         private bool CData()
         {
             if (CurrentSymbol.Type == HtmlSymbolType.Text && string.Equals(CurrentSymbol.Content, "cdata", StringComparison.OrdinalIgnoreCase))
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
index 6f564eb442..1819407076 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
@@ -109,6 +109,53 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return symbols[count];
         }
 
+        /// <summary>
+        /// Looks forward until the specified condition is met.
+        /// </summary>
+        /// <param name="condition">A predicate accepting the symbol being evaluated and the list of symbols which have been looped through.</param>
+        /// <returns>true, if the condition was met. false - if the condition wasn't met and the last symbol has already been processed.</returns>
+        /// <remarks>The list of previous symbols is passed in the reverse order. So the last processed element will be the first one in the list.</remarks>
+        protected bool LookaheadUntil(Func<TSymbol, IEnumerable<TSymbol>, bool> condition)
+        {
+            if (condition == null)
+            {
+                throw new ArgumentNullException(nameof(condition));
+            }
+
+            bool matchFound = false;
+
+            // We add 1 in order to store the current symbol.
+            var symbols = new List<TSymbol>();
+            symbols.Add(CurrentSymbol);
+
+            while (true)
+            {
+                if (!NextToken())
+                {
+                    break;
+                }
+
+                symbols.Add(CurrentSymbol);
+                if (condition(CurrentSymbol, symbols.Reverse<TSymbol>()))
+                {
+                    matchFound = true;
+                    break;
+                }
+            }
+
+            // Restore Tokenizer's location to where it was pointing before the look-ahead.
+            for (var i = symbols.Count - 1; i >= 0; i--)
+            {
+                PutBack(symbols[i]);
+            }
+
+            // The PutBacks above will set CurrentSymbol to null. EnsureCurrent will set our CurrentSymbol to the
+            // next symbol.
+            EnsureCurrent();
+
+            return matchFound;
+        }
+
         protected internal bool NextToken()
         {
             PreviousSymbol = CurrentSymbol;
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
index f8d4b0fcd9..5d3d46a831 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
@@ -419,9 +419,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             ParseBlockTest(
                 "<!--<foo>",
                 new MarkupBlock(
-                    new HtmlCommentBlock(Factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None)),
-                    Factory.Markup("<foo>").Accepts(AcceptedCharactersInternal.WhiteSpace),
-                    Factory.EmptyHtml()));
+                    Factory.Markup("<!--<foo>").Accepts(AcceptedCharactersInternal.None)));
         }
 
         [Fact]
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs
index 9f0e11218b..b7f5eeb87d 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs
@@ -219,8 +219,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     Factory.Markup("Foo Baz"),
                     BlockFactory.HtmlCommentBlock("Foo"),
                     Factory.Markup("Bar"),
-                    new HtmlCommentBlock(Factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None)),
-                    Factory.Markup("F> Qux").Accepts(AcceptedCharactersInternal.WhiteSpace)));
+                    Factory.Markup("<!--F> Qux")));
         }
 
         [Fact]

From 0f820c5f11105d269c7ee8cbab1addf2a9e1e068 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Wed, 7 Mar 2018 14:52:33 -0800
Subject: [PATCH 12/34] Added tests for the LookaheadUntil method

---
 .../Legacy/TokenizerLookaheadTest.cs          | 99 +++++++++++++++++++
 1 file changed, 99 insertions(+)

diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
index 6abd70ad3e..a9ac4be740 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
@@ -56,6 +56,83 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             Assert.Equal("pre-existing values", tokenizer.Buffer.ToString(), StringComparer.Ordinal);
         }
 
+        [Fact]
+        public void LookaheadUntil_PassesThePreviousSymbolsInReverseOrder()
+        {
+            // Arrange
+            var source = TestRazorSourceDocument.Create("asdf--fvd--<");
+            var options = RazorParserOptions.CreateDefault();
+            var context = new ParserContext(source, options);
+
+            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+
+            // Act
+            Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
+            var i = 3;
+            var symbolFound = tokenizer.LookaheadUntil((s, p) =>
+            {
+                symbols.Push(s);
+                return --i == 0;
+            });
+
+            // Assert
+            Assert.Equal(3, symbols.Count);
+            Assert.Equal(new HtmlSymbol("fvd", HtmlSymbolType.Text), symbols.Pop());
+            Assert.Equal(new HtmlSymbol("--", HtmlSymbolType.DoubleHyphen), symbols.Pop());
+            Assert.Equal(new HtmlSymbol("asdf", HtmlSymbolType.Text), symbols.Pop());
+        }
+
+        [Fact]
+        public void LookaheadUntil_ReturnsFalseAfterIteratingOverAllSymbolsIfConditionIsNotMet()
+        {
+            // Arrange
+            var source = TestRazorSourceDocument.Create("asdf--fvd");
+            var options = RazorParserOptions.CreateDefault();
+            var context = new ParserContext(source, options);
+
+            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+
+            // Act
+            Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
+            var symbolFound = tokenizer.LookaheadUntil((s, p) =>
+            {
+                symbols.Push(s);
+                return false;
+            });
+
+            // Assert
+            Assert.False(symbolFound);
+            Assert.Equal(3, symbols.Count);
+            Assert.Equal(new HtmlSymbol("fvd", HtmlSymbolType.Text), symbols.Pop());
+            Assert.Equal(new HtmlSymbol("--", HtmlSymbolType.DoubleHyphen), symbols.Pop());
+            Assert.Equal(new HtmlSymbol("asdf", HtmlSymbolType.Text), symbols.Pop());
+        }
+
+        [Fact]
+        public void LookaheadUntil_ReturnsTrueAndBreaksIteration()
+        {
+            // Arrange
+            var source = TestRazorSourceDocument.Create("asdf--fvd");
+            var options = RazorParserOptions.CreateDefault();
+            var context = new ParserContext(source, options);
+
+            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+
+            // Act
+            Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
+            var symbolFound = tokenizer.LookaheadUntil((s, p) =>
+            {
+                symbols.Push(s);
+                return s.Type == HtmlSymbolType.DoubleHyphen;
+            });
+
+            // Assert
+            Assert.True(symbolFound);
+            Assert.Equal(2, symbols.Count);
+            Assert.Equal(new HtmlSymbol("--", HtmlSymbolType.DoubleHyphen), symbols.Pop());
+            Assert.Equal(new HtmlSymbol("asdf", HtmlSymbolType.Text), symbols.Pop());
+        }
+
         private class ExposedTokenizer : Tokenizer<CSharpSymbol, CSharpSymbolType>
         {
             public ExposedTokenizer(string input)
@@ -116,5 +193,27 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 throw new NotImplementedException();
             }
         }
+
+        private class TestTokenizerBackedParser : TokenizerBackedParser<HtmlTokenizer, HtmlSymbol, HtmlSymbolType>
+        {
+            internal TestTokenizerBackedParser(LanguageCharacteristics<HtmlTokenizer, HtmlSymbol, HtmlSymbolType> language, ParserContext context) : base(language, context)
+            {
+            }
+
+            public override void ParseBlock()
+            {
+                throw new NotImplementedException();
+            }
+
+            protected override bool SymbolTypeEquals(HtmlSymbolType x, HtmlSymbolType y)
+            {
+                throw new NotImplementedException();
+            }
+
+            internal new bool LookaheadUntil(Func<HtmlSymbol, IEnumerable<HtmlSymbol>, bool> condition)
+            {
+                return base.LookaheadUntil(condition);
+            }
+        }
     }
 }

From f2b9696298141dda80c4810f2953f2bb806b7cf2 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Wed, 7 Mar 2018 16:34:12 -0800
Subject: [PATCH 13/34] Naming improvements and test code cleanup

---
 .../Legacy/HtmlMarkupParser.cs                | 12 ++++----
 .../Legacy/TokenizerLookaheadTest.cs          | 28 +++++++++----------
 2 files changed, 19 insertions(+), 21 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index 2fe84b5a33..fb5237866e 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -614,8 +614,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 {
                     if (NextIs(HtmlSymbolType.CloseAngle))
                     {
-                        // We're at the end of a comment. check the condition 2.3 to make sure the text ending is allowed.
-                        isValidComment = !EndsWithSymbolsSequence(p, HtmlSymbolType.OpenAngle, HtmlSymbolType.Bang, HtmlSymbolType.DoubleHyphen);
+                        // Check condition 2.3: We're at the end of a comment. Check to make sure the text ending is allowed.
+                        isValidComment = !SymbolSequenceEndsWithItems(p, HtmlSymbolType.OpenAngle, HtmlSymbolType.Bang, HtmlSymbolType.DoubleHyphen);
                         breakLookahead = true;
                     }
                     else if (NextIs(ns => IsDashSymbol(ns) && NextIs(HtmlSymbolType.CloseAngle)))
@@ -645,17 +645,17 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return isValidComment;
         }
 
-        private bool EndsWithSymbolsSequence(IEnumerable<HtmlSymbol> symbols, params HtmlSymbolType[] sequenceToMatchWith)
+        internal static bool SymbolSequenceEndsWithItems(IEnumerable<HtmlSymbol> sequence, params HtmlSymbolType[] items)
         {
-            int index = sequenceToMatchWith.Length;
-            foreach (var previousSymbol in symbols)
+            int index = items.Length;
+            foreach (var previousSymbol in sequence)
             {
                 if (index == 0)
                 {
                     break;
                 }
 
-                if (sequenceToMatchWith[--index] != previousSymbol.Type)
+                if (items[--index] != previousSymbol.Type)
                     return false;
             }
 
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
index a9ac4be740..74d0c075f3 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
@@ -60,11 +60,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         public void LookaheadUntil_PassesThePreviousSymbolsInReverseOrder()
         {
             // Arrange
-            var source = TestRazorSourceDocument.Create("asdf--fvd--<");
-            var options = RazorParserOptions.CreateDefault();
-            var context = new ParserContext(source, options);
-
-            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+            var tokenizer = CreateContentTokenizer("asdf--fvd--<");
 
             // Act
             Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
@@ -86,11 +82,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         public void LookaheadUntil_ReturnsFalseAfterIteratingOverAllSymbolsIfConditionIsNotMet()
         {
             // Arrange
-            var source = TestRazorSourceDocument.Create("asdf--fvd");
-            var options = RazorParserOptions.CreateDefault();
-            var context = new ParserContext(source, options);
-
-            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+            var tokenizer = CreateContentTokenizer("asdf--fvd");
 
             // Act
             Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
@@ -112,11 +104,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         public void LookaheadUntil_ReturnsTrueAndBreaksIteration()
         {
             // Arrange
-            var source = TestRazorSourceDocument.Create("asdf--fvd");
-            var options = RazorParserOptions.CreateDefault();
-            var context = new ParserContext(source, options);
-
-            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+            var tokenizer = CreateContentTokenizer("asdf--fvd");
 
             // Act
             Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
@@ -133,6 +121,16 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             Assert.Equal(new HtmlSymbol("asdf", HtmlSymbolType.Text), symbols.Pop());
         }
 
+        private static TestTokenizerBackedParser CreateContentTokenizer(string content)
+        {
+            var source = TestRazorSourceDocument.Create(content);
+            var options = RazorParserOptions.CreateDefault();
+            var context = new ParserContext(source, options);
+
+            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+            return tokenizer;
+        }
+
         private class ExposedTokenizer : Tokenizer<CSharpSymbol, CSharpSymbolType>
         {
             public ExposedTokenizer(string input)

From 42362bea975255b2eedab00f75b1a27d411b8cf9 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Thu, 8 Mar 2018 13:29:18 -0800
Subject: [PATCH 14/34] Applied PR feedback (unit testst will be added as part
 of a separate commit)

---
 .../Legacy/HtmlMarkupParser.cs                | 45 +++++++++----------
 .../Legacy/TagHelperParseTreeRewriter.cs      | 43 +++++++++---------
 .../Legacy/TokenizerBackedParser.cs           |  3 +-
 3 files changed, 45 insertions(+), 46 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index 2fe84b5a33..46599d4100 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -496,6 +496,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 {
                     using (Context.Builder.StartBlock(BlockKindInternal.HtmlComment))
                     {
+                        // Accept the double-hyphen symbol at the beginning of the comment block.
                         AcceptAndMoveNext();
                         Output(SpanKindInternal.Markup, AcceptedCharactersInternal.None);
 
@@ -503,25 +504,22 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         while (!EndOfFile)
                         {
                             SkipToAndParseCode(HtmlSymbolType.DoubleHyphen);
-                            if (At(HtmlSymbolType.DoubleHyphen))
+                            var lastDoubleHyphen = AcceptAllButLastDoubleHypens();
+
+                            if (At(HtmlSymbolType.CloseAngle))
                             {
-                                var lastDoubleHyphen = AcceptAllButLastDoubleHypens();
+                                // Output the content in the comment block as a separate markup
+                                Output(SpanKindInternal.Markup, AcceptedCharactersInternal.WhiteSpace);
 
-                                if (At(HtmlSymbolType.CloseAngle))
-                                {
-                                    // Output the content in the comment block as a separate markup
-                                    Output(SpanKindInternal.Markup, AcceptedCharactersInternal.WhiteSpace);
-
-                                    // This is the end of a comment block
-                                    Accept(lastDoubleHyphen);
-                                    AcceptAndMoveNext();
-                                    Output(SpanKindInternal.Markup, AcceptedCharactersInternal.None);
-                                    return true;
-                                }
-                                else if (lastDoubleHyphen != null)
-                                {
-                                    Accept(lastDoubleHyphen);
-                                }
+                                // This is the end of a comment block
+                                Accept(lastDoubleHyphen);
+                                AcceptAndMoveNext();
+                                Output(SpanKindInternal.Markup, AcceptedCharactersInternal.None);
+                                return true;
+                            }
+                            else if (lastDoubleHyphen != null)
+                            {
+                                Accept(lastDoubleHyphen);
                             }
                         }
                     }
@@ -606,28 +604,27 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             }
 
             // Check condition 2.2
-            bool isValidComment = false;
+            var isValidComment = false;
             LookaheadUntil((s, p) =>
             {
-                bool breakLookahead = false;
                 if (s.Type == HtmlSymbolType.DoubleHyphen)
                 {
                     if (NextIs(HtmlSymbolType.CloseAngle))
                     {
                         // We're at the end of a comment. check the condition 2.3 to make sure the text ending is allowed.
                         isValidComment = !EndsWithSymbolsSequence(p, HtmlSymbolType.OpenAngle, HtmlSymbolType.Bang, HtmlSymbolType.DoubleHyphen);
-                        breakLookahead = true;
+                        return true;
                     }
                     else if (NextIs(ns => IsDashSymbol(ns) && NextIs(HtmlSymbolType.CloseAngle)))
                     {
                         // This is also a valid closing comment case, as the dashes lookup is treated with DoubleHyphen symbols first.
                         isValidComment = true;
-                        breakLookahead = true;
+                        return true;
                     }
                     else if (NextIs(ns => ns.Type == HtmlSymbolType.Bang && NextIs(HtmlSymbolType.CloseAngle)))
                     {
                         isValidComment = false;
-                        breakLookahead = true;
+                        return true;
                     }
                 }
                 else if (s.Type == HtmlSymbolType.OpenAngle)
@@ -635,11 +632,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     if (NextIs(ns => ns.Type == HtmlSymbolType.Bang && NextIs(HtmlSymbolType.DoubleHyphen)))
                     {
                         isValidComment = false;
-                        breakLookahead = true;
+                        return true;
                     }
                 }
 
-                return breakLookahead;
+                return false;
             });
 
             return isValidComment;
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index a4c9906b1a..d5d65c2985 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -488,28 +488,31 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            var isDisallowedContent = true;
-            if (_featureFlags.AllowHtmlCommentsInTagHelpers)
+            if (HasAllowedChildren())
             {
-                isDisallowedContent = !IsComment(child) && child.Kind != SpanKindInternal.Transition && child.Kind != SpanKindInternal.Code;
-            }
-
-            if (HasAllowedChildren() && isDisallowedContent)
-            {
-                var content = child.Content;
-                if (!string.IsNullOrWhiteSpace(content))
+                var isDisallowedContent = true;
+                if (_featureFlags.AllowHtmlCommentsInTagHelpers)
                 {
-                    var trimmedStart = content.TrimStart();
-                    var whitespace = content.Substring(0, content.Length - trimmedStart.Length);
-                    var errorStart = SourceLocationTracker.Advance(child.Start, whitespace);
-                    var length = trimmedStart.TrimEnd().Length;
-                    var allowedChildren = _currentTagHelperTracker.AllowedChildren;
-                    var allowedChildrenString = string.Join(", ", allowedChildren);
-                    errorSink.OnError(
-                        RazorDiagnosticFactory.CreateTagHelper_CannotHaveNonTagContent(
-                            new SourceSpan(errorStart, length),
-                            _currentTagHelperTracker.TagName,
-                            allowedChildrenString));
+                    isDisallowedContent = !IsComment(child) && child.Kind != SpanKindInternal.Transition && child.Kind != SpanKindInternal.Code;
+                }
+
+                if (isDisallowedContent)
+                {
+                    var content = child.Content;
+                    if (!string.IsNullOrWhiteSpace(content))
+                    {
+                        var trimmedStart = content.TrimStart();
+                        var whitespace = content.Substring(0, content.Length - trimmedStart.Length);
+                        var errorStart = SourceLocationTracker.Advance(child.Start, whitespace);
+                        var length = trimmedStart.TrimEnd().Length;
+                        var allowedChildren = _currentTagHelperTracker.AllowedChildren;
+                        var allowedChildrenString = string.Join(", ", allowedChildren);
+                        errorSink.OnError(
+                            RazorDiagnosticFactory.CreateTagHelper_CannotHaveNonTagContent(
+                                new SourceSpan(errorStart, length),
+                                _currentTagHelperTracker.TagName,
+                                allowedChildrenString));
+                    }
                 }
             }
         }
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
index 1819407076..98763ad0a3 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
@@ -122,9 +122,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 throw new ArgumentNullException(nameof(condition));
             }
 
-            bool matchFound = false;
+            var matchFound = false;
 
-            // We add 1 in order to store the current symbol.
             var symbols = new List<TSymbol>();
             symbols.Add(CurrentSymbol);
 

From e6f68eb244bc4247fdabeb9ced8798dbdded3b90 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Thu, 8 Feb 2018 15:50:38 -0800
Subject: [PATCH 15/34] Added a unit test to repro the issue

---
 .../Legacy/TagHelperParseTreeRewriter.cs      |  2 +-
 .../Legacy/TagHelperParseTreeRewriterTest.cs  | 49 ++++++++++++++++---
 2 files changed, 44 insertions(+), 7 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index 2059522263..79b013f32d 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -488,7 +488,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            if (HasAllowedChildren())
+            if (child.Kind == SpanKindInternal.Comment || HasAllowedChildren())
             {
                 var content = child.Content;
                 if (!string.IsNullOrWhiteSpace(content))
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index 2feccbe1a4..04892592dd 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -254,7 +254,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             var descriptors = new TagHelperDescriptor[]
             {
                 TagHelperDescriptorBuilder.Create("InputTagHelper", "SomeAssembly")
-                    .TagMatchingRuleDescriptor(rule => 
+                    .TagMatchingRuleDescriptor(rule =>
                         rule
                         .RequireTagName("input")
                         .RequireTagStructure(TagStructure.WithoutEndTag))
@@ -371,7 +371,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     .TagMatchingRuleDescriptor(rule => rule.RequireTagName("strong"))
                     .Build(),
             };
-            
+
             // Act & Assert
             EvaluateData(
                 descriptors,
@@ -793,7 +793,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             var descriptors = new TagHelperDescriptor[]
             {
                 TagHelperDescriptorBuilder.Create("StrongTagHelper", "SomeAssembly")
-                    .TagMatchingRuleDescriptor(rule => 
+                    .TagMatchingRuleDescriptor(rule =>
                         rule
                         .RequireTagName("strong")
                         .RequireAttributeDescriptor(attribute => attribute.Name("required")))
@@ -830,7 +830,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     .TagMatchingRuleDescriptor(rule => rule.RequireTagName("strong"))
                     .Build(),
                 TagHelperDescriptorBuilder.Create("BRTagHelper", "SomeAssembly")
-                    .TagMatchingRuleDescriptor(rule => 
+                    .TagMatchingRuleDescriptor(rule =>
                         rule
                         .RequireTagName("br")
                         .RequireTagStructure(TagStructure.WithoutEndTag))
@@ -1108,6 +1108,43 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             EvaluateData(descriptors, documentContent, (MarkupBlock)expectedOutput, (RazorDiagnostic[])expectedErrors);
         }
 
+        [Fact]
+        public void Rewrite_AllowsCommentsAsChildren()
+        {
+            // Arrangestring documentContent,
+            IEnumerable<string> allowedChildren = new List<string> { "b" };
+            string literalPrefix = "";
+            string commentOutput = $"<!--Hello World-->";
+            string expectedOutput = $"<p>{literalPrefix}{commentOutput}<b>asdf</b></p>";
+
+            var pTagHelperBuilder = TagHelperDescriptorBuilder
+                .Create("PTagHelper", "SomeAssembly")
+                .TagMatchingRuleDescriptor(rule => rule.RequireTagName("p"));
+            foreach (var childTag in allowedChildren)
+            {
+                pTagHelperBuilder.AllowChildTag(childTag);
+            }
+
+            var descriptors = new TagHelperDescriptor[]
+            {
+                    pTagHelperBuilder.Build()
+            };
+
+            var factory = new SpanFactory();
+            var blockFactory = new BlockFactory(factory);
+
+            var expectedMarkup = new MarkupBlock(
+                new MarkupTagHelperBlock("p",
+                    factory.Markup($"{literalPrefix}{commentOutput}")));
+
+            // Act & Assert
+            EvaluateData(
+                descriptors,
+                expectedOutput,
+                expectedMarkup,
+                Array.Empty<RazorDiagnostic>());
+        }
+
         [Fact]
         public void Rewrite_UnderstandsNullTagNameWithAllowedChildrenForCatchAll()
         {
@@ -1173,7 +1210,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             var descriptors = new TagHelperDescriptor[]
             {
                 TagHelperDescriptorBuilder.Create("InputTagHelper", "SomeAssembly")
-                    .TagMatchingRuleDescriptor(rule => 
+                    .TagMatchingRuleDescriptor(rule =>
                         rule
                         .RequireTagName("input")
                         .RequireTagStructure(TagStructure.WithoutEndTag))
@@ -1646,7 +1683,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             var descriptors = new TagHelperDescriptor[]
             {
                 TagHelperDescriptorBuilder.Create("pTagHelper", "SomeAssembly")
-                    .TagMatchingRuleDescriptor(rule => 
+                    .TagMatchingRuleDescriptor(rule =>
                         rule
                         .RequireTagName("p")
                         .RequireAttributeDescriptor(attribute => attribute.Name("class")))

From 41b7d90ea8bf4e633c2e24542e55424a8ab80072 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Mon, 12 Feb 2018 22:03:53 -0800
Subject: [PATCH 16/34] Ignoring markup comments during validation

---
 .../Legacy/TagHelperParseTreeRewriter.cs              |  7 ++++++-
 .../Legacy/TagHelperParseTreeRewriterTest.cs          | 11 +++++++----
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index 79b013f32d..73b545dd33 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -116,7 +116,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         continue;
                     }
                 }
-                else
+                else if (!IsCommentTag((Span)child))
                 {
                     ValidateParentAllowsContent((Span)child, errorSink);
                 }
@@ -817,6 +817,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return relevantSymbol.Type == HtmlSymbolType.ForwardSlash;
         }
 
+        private static bool IsCommentTag(Span span)
+        {
+            return span.Content.StartsWith("<!--");
+        }
+
         private static void EnsureTagBlock(Block tagBlock)
         {
             Debug.Assert(tagBlock.Type == BlockKindInternal.Tag);
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index 04892592dd..bf0ae602db 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -1113,9 +1113,9 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
             // Arrangestring documentContent,
             IEnumerable<string> allowedChildren = new List<string> { "b" };
-            string literalPrefix = "";
+            string literal = "asdf";
             string commentOutput = $"<!--Hello World-->";
-            string expectedOutput = $"<p>{literalPrefix}{commentOutput}<b>asdf</b></p>";
+            string expectedOutput = $"<p><b>{literal}</b>{commentOutput}</p>";
 
             var pTagHelperBuilder = TagHelperDescriptorBuilder
                 .Create("PTagHelper", "SomeAssembly")
@@ -1127,7 +1127,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
             var descriptors = new TagHelperDescriptor[]
             {
-                    pTagHelperBuilder.Build()
+                pTagHelperBuilder.Build()
             };
 
             var factory = new SpanFactory();
@@ -1135,7 +1135,10 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
             var expectedMarkup = new MarkupBlock(
                 new MarkupTagHelperBlock("p",
-                    factory.Markup($"{literalPrefix}{commentOutput}")));
+                    blockFactory.MarkupTagBlock("<b>"),
+                    factory.Markup(literal),
+                    blockFactory.MarkupTagBlock("</b>"),
+                    factory.Markup(commentOutput)));
 
             // Act & Assert
             EvaluateData(

From 47228dd8221dda317cb83b2178a23b3ddd704813 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Mon, 12 Feb 2018 22:14:01 -0800
Subject: [PATCH 17/34] Revert unnecessary change

---
 .../Legacy/TagHelperParseTreeRewriter.cs                        | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index 73b545dd33..f046a8eea4 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -488,7 +488,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            if (child.Kind == SpanKindInternal.Comment || HasAllowedChildren())
+            if (HasAllowedChildren())
             {
                 var content = child.Content;
                 if (!string.IsNullOrWhiteSpace(content))

From 679acdc5d4aaf7591e5ca34296c553b415dc5caa Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Tue, 13 Feb 2018 13:34:16 -0800
Subject: [PATCH 18/34] Ignoring razor comments during validation

---
 .../Legacy/TagHelperParseTreeRewriter.cs      |  9 ++--
 .../Legacy/TagHelperParseTreeRewriterTest.cs  | 47 ++++++++++++++++++-
 2 files changed, 52 insertions(+), 4 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index f046a8eea4..01361a9893 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -116,7 +116,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         continue;
                     }
                 }
-                else if (!IsCommentTag((Span)child))
+                else if (!IsComment((Span)child))
                 {
                     ValidateParentAllowsContent((Span)child, errorSink);
                 }
@@ -817,9 +817,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return relevantSymbol.Type == HtmlSymbolType.ForwardSlash;
         }
 
-        private static bool IsCommentTag(Span span)
+        private static bool IsComment(Span span)
         {
-            return span.Content.StartsWith("<!--");
+            bool isHtmlComment = span.Content?.StartsWith("<!--") == true;
+            bool isRazorComment = span.Parent?.Type == BlockKindInternal.Comment;
+
+            return isHtmlComment || isRazorComment;
         }
 
         private static void EnsureTagBlock(Block tagBlock)
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index bf0ae602db..4a640b1990 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -1109,7 +1109,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         }
 
         [Fact]
-        public void Rewrite_AllowsCommentsAsChildren()
+        public void Rewrite_AllowsHtmlCommentsAsChildren()
         {
             // Arrangestring documentContent,
             IEnumerable<string> allowedChildren = new List<string> { "b" };
@@ -1148,6 +1148,51 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 Array.Empty<RazorDiagnostic>());
         }
 
+        [Fact]
+        public void Rewrite_AllowsRazorCommentsAsChildren()
+        {
+            // Arrangestring documentContent,
+            IEnumerable<string> allowedChildren = new List<string> { "b" };
+            string literal = "asdf";
+            string commentOutput = $"@*{literal}*@";
+            string expectedOutput = $"<p><b>{literal}</b>{commentOutput}</p>";
+
+            var pTagHelperBuilder = TagHelperDescriptorBuilder
+                .Create("PTagHelper", "SomeAssembly")
+                .TagMatchingRuleDescriptor(rule => rule.RequireTagName("p"));
+            foreach (var childTag in allowedChildren)
+            {
+                pTagHelperBuilder.AllowChildTag(childTag);
+            }
+
+            var descriptors = new TagHelperDescriptor[]
+            {
+                pTagHelperBuilder.Build()
+            };
+
+            var factory = new SpanFactory();
+            var blockFactory = new BlockFactory(factory);
+
+            var expectedMarkup = new MarkupBlock(
+                new MarkupTagHelperBlock("p",
+                    blockFactory.MarkupTagBlock("<b>"),
+                    factory.Markup(literal),
+                    blockFactory.MarkupTagBlock("</b>"),
+                    new CommentBlock(
+                        Factory.MarkupTransition(HtmlSymbolType.RazorCommentTransition).Accepts(AcceptedCharactersInternal.None),
+                        Factory.MetaMarkup("*", HtmlSymbolType.RazorCommentStar).Accepts(AcceptedCharactersInternal.None),
+                        Factory.Span(SpanKindInternal.Comment, new HtmlSymbol(literal, HtmlSymbolType.RazorComment)).Accepts(AcceptedCharactersInternal.Any),
+                        Factory.MetaMarkup("*", HtmlSymbolType.RazorCommentStar).Accepts(AcceptedCharactersInternal.None),
+                        Factory.MarkupTransition(HtmlSymbolType.RazorCommentTransition).Accepts(AcceptedCharactersInternal.None))));
+
+            // Act & Assert
+            EvaluateData(
+                descriptors,
+                expectedOutput,
+                expectedMarkup,
+                Array.Empty<RazorDiagnostic>());
+        }
+
         [Fact]
         public void Rewrite_UnderstandsNullTagNameWithAllowedChildrenForCatchAll()
         {

From a940a4cd919330405d0ff221c691497edc245385 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Tue, 13 Feb 2018 15:58:12 -0800
Subject: [PATCH 19/34] Moved the comment check into the
 "ValidateParentAllowsContent" method

---
 .../Legacy/TagHelperParseTreeRewriter.cs                      | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index 01361a9893..930b928949 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -116,7 +116,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         continue;
                     }
                 }
-                else if (!IsComment((Span)child))
+                else
                 {
                     ValidateParentAllowsContent((Span)child, errorSink);
                 }
@@ -488,7 +488,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            if (HasAllowedChildren())
+            if (HasAllowedChildren() && !IsComment(child))
             {
                 var content = child.Content;
                 if (!string.IsNullOrWhiteSpace(content))

From ad8485addd7b481abe0c187c29f5b7e8b5bc073e Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Thu, 15 Feb 2018 18:15:34 -0800
Subject: [PATCH 20/34] Added new BlockType - HtmlComment Updated the
 HtmlMarkupParser to understand the HtmlCOmments, and treat those as blocks.

---
 .../Legacy/BlockKindInternal.cs               |   4 +-
 .../Legacy/HtmlMarkupParser.cs                |  45 ++++---
 .../Legacy/TagHelperParseTreeRewriter.cs      |  14 +-
 .../BlockKind.cs                              |   4 +-
 .../Legacy/TagHelperParseTreeRewriterTest.cs  | 122 ++++++++++++++++--
 .../Language/Legacy/BlockTypes.cs             |  10 ++
 6 files changed, 165 insertions(+), 34 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/BlockKindInternal.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/BlockKindInternal.cs
index c515770ca7..9f9886164c 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/BlockKindInternal.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/BlockKindInternal.cs
@@ -18,6 +18,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         // Special
         Comment = 8,
-        Tag = 9
+        Tag = 9,
+
+        HtmlComment = 10
     }
 }
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index 4fdee1322f..332023b775 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -207,6 +207,10 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             if (last != null)
             {
                 Accept(last);
+                if (At(HtmlSymbolType.OpenAngle) && last.Type == HtmlSymbolType.Text)
+                {
+                    Output(SpanKindInternal.Markup);
+                }
             }
         }
 
@@ -494,26 +498,34 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             {
                 if (CurrentSymbol.Type == HtmlSymbolType.DoubleHyphen)
                 {
-                    AcceptAndMoveNext();
-
-                    Span.EditHandler.AcceptedCharacters = AcceptedCharactersInternal.Any;
-                    while (!EndOfFile)
+                    using (Context.Builder.StartBlock(BlockKindInternal.HtmlComment))
                     {
-                        SkipToAndParseCode(HtmlSymbolType.DoubleHyphen);
-                        if (At(HtmlSymbolType.DoubleHyphen))
+                        AcceptAndMoveNext();
+
+                        Span.EditHandler.AcceptedCharacters = AcceptedCharactersInternal.Any;
+                        while (!EndOfFile)
                         {
-                            AcceptWhile(HtmlSymbolType.DoubleHyphen);
-
-                            if (At(HtmlSymbolType.Text) &&
-                                string.Equals(CurrentSymbol.Content, "-", StringComparison.Ordinal))
+                            SkipToAndParseCode(HtmlSymbolType.DoubleHyphen);
+                            if (At(HtmlSymbolType.DoubleHyphen))
                             {
-                                AcceptAndMoveNext();
-                            }
+                                AcceptWhile(HtmlSymbolType.DoubleHyphen);
 
-                            if (At(HtmlSymbolType.CloseAngle))
-                            {
-                                AcceptAndMoveNext();
-                                return true;
+                                if (At(HtmlSymbolType.Text) &&
+                                    string.Equals(CurrentSymbol.Content, "-", StringComparison.Ordinal))
+                                {
+                                    AcceptAndMoveNext();
+                                }
+
+                                if (At(HtmlSymbolType.CloseAngle))
+                                {
+                                    // This is the end of a comment block
+                                    Accept(this.CurrentSymbol);
+                                    Output(SpanKindInternal.Markup);
+
+                                    NextToken();
+                                    //AcceptAndMoveNext();
+                                    return true;
+                                }
                             }
                         }
                     }
@@ -1476,6 +1488,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     {
                         AcceptAndMoveNext(); // Accept '<'
                         BangTag();
+
                         return;
                     }
 
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index 930b928949..6cac8b46ea 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -488,7 +488,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            if (HasAllowedChildren() && !IsComment(child))
+            if (HasAllowedChildren() && !IsComment(child) && child.Kind != SpanKindInternal.Transition && child.Kind != SpanKindInternal.Code)
             {
                 var content = child.Content;
                 if (!string.IsNullOrWhiteSpace(content))
@@ -817,14 +817,18 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return relevantSymbol.Type == HtmlSymbolType.ForwardSlash;
         }
 
-        private static bool IsComment(Span span)
+        internal static bool IsComment(Span span)
         {
-            bool isHtmlComment = span.Content?.StartsWith("<!--") == true;
-            bool isRazorComment = span.Parent?.Type == BlockKindInternal.Comment;
+            Block currentBlock = span.Parent;
+            while (currentBlock != null && currentBlock.Type != BlockKindInternal.Comment && currentBlock.Type != BlockKindInternal.HtmlComment)
+            {
+                currentBlock = currentBlock.Parent;
+            }
 
-            return isHtmlComment || isRazorComment;
+            return currentBlock != null;
         }
 
+
         private static void EnsureTagBlock(Block tagBlock)
         {
             Debug.Assert(tagBlock.Type == BlockKindInternal.Tag);
diff --git a/src/Microsoft.VisualStudio.Editor.Razor/BlockKind.cs b/src/Microsoft.VisualStudio.Editor.Razor/BlockKind.cs
index 48ad2e4fb4..2559231329 100644
--- a/src/Microsoft.VisualStudio.Editor.Razor/BlockKind.cs
+++ b/src/Microsoft.VisualStudio.Editor.Razor/BlockKind.cs
@@ -19,6 +19,8 @@ namespace Microsoft.VisualStudio.Editor.Razor
 
         // Special
         Comment,
-        Tag
+        Tag,
+
+        HtmlComment
     }
 }
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index 4a640b1990..45a1ffa907 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -1109,12 +1109,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         }
 
         [Fact]
-        public void Rewrite_AllowsHtmlCommentsAsChildren()
+        public void Rewrite_AllowsSimpleHtmlCommentsAsChildren()
         {
             // Arrangestring documentContent,
             IEnumerable<string> allowedChildren = new List<string> { "b" };
             string literal = "asdf";
-            string commentOutput = $"<!--Hello World-->";
+            string commentOutput = "<!--Hello World-->";
             string expectedOutput = $"<p><b>{literal}</b>{commentOutput}</p>";
 
             var pTagHelperBuilder = TagHelperDescriptorBuilder
@@ -1138,7 +1138,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     blockFactory.MarkupTagBlock("<b>"),
                     factory.Markup(literal),
                     blockFactory.MarkupTagBlock("</b>"),
-                    factory.Markup(commentOutput)));
+                    new HtmlCommentBlock(factory.Markup(commentOutput))));
 
             // Act & Assert
             EvaluateData(
@@ -1148,6 +1148,58 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 Array.Empty<RazorDiagnostic>());
         }
 
+        [Fact]
+        public void Rewrite_FailsForContentWithCommentsAsChildren()
+        {
+            // Arrangestring documentContent,
+            Func<string, string, string, int, int, RazorDiagnostic> nestedTagError =
+                    (childName, parentName, allowed, location, length) =>
+                    RazorDiagnosticFactory.CreateTagHelper_InvalidNestedTag(
+                        new SourceSpan(absoluteIndex: location, lineIndex: 0, characterIndex: location, length: length), childName, parentName, allowed);
+            Func<string, string, int, int, RazorDiagnostic> nestedContentError =
+                (parentName, allowed, location, length) =>
+                RazorDiagnosticFactory.CreateTagHelper_CannotHaveNonTagContent(
+                    new SourceSpan(absoluteIndex: location, lineIndex: 0, characterIndex: location, length: length), parentName, allowed);
+
+            IEnumerable<string> allowedChildren = new List<string> { "b" };
+            string comment1 = "Hello";
+            string literal = "asdf";
+            string comment2 = "World";
+            string expectedOutput = $"<p><!--{comment1}-->{literal}<!--{comment2}--></p>";
+
+            var pTagHelperBuilder = TagHelperDescriptorBuilder
+                .Create("PTagHelper", "SomeAssembly")
+                .TagMatchingRuleDescriptor(rule => rule.RequireTagName("p"));
+            foreach (var childTag in allowedChildren)
+            {
+                pTagHelperBuilder.AllowChildTag(childTag);
+            }
+
+            var descriptors = new TagHelperDescriptor[]
+            {
+                pTagHelperBuilder.Build()
+            };
+
+            var factory = new SpanFactory();
+            var blockFactory = new BlockFactory(factory);
+
+            var expectedMarkup = new MarkupBlock(
+                new MarkupTagHelperBlock("p",
+                    new HtmlCommentBlock(factory.Markup($"<!--{comment1}-->")),
+                    factory.Markup(literal),
+                    new HtmlCommentBlock(factory.Markup($"<!--{comment2}-->"))));
+
+            // Act & Assert
+            EvaluateData(
+                descriptors,
+                expectedOutput,
+                expectedMarkup,
+                new[]
+                {
+                    nestedContentError("p", "b", 15, 4),
+                });
+        }
+
         [Fact]
         public void Rewrite_AllowsRazorCommentsAsChildren()
         {
@@ -1193,6 +1245,54 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 Array.Empty<RazorDiagnostic>());
         }
 
+        [Fact]
+        public void Rewrite_AllowsRazorMarkupInHtmlComment()
+        {
+            // Arrangestring documentContent,
+            IEnumerable<string> allowedChildren = new List<string> { "b" };
+            string literal = "asdf";
+            string part1 = "<!--Hello ";
+            string part2 = "World";
+            string part3 = "-->";
+            string expectedOutput = $"<p><b>{literal}</b>{part1}@{part2}{part3}</p>";
+
+            var pTagHelperBuilder = TagHelperDescriptorBuilder
+                .Create("PTagHelper", "SomeAssembly")
+                .TagMatchingRuleDescriptor(rule => rule.RequireTagName("p"));
+            foreach (var childTag in allowedChildren)
+            {
+                pTagHelperBuilder.AllowChildTag(childTag);
+            }
+
+            var descriptors = new TagHelperDescriptor[]
+            {
+                pTagHelperBuilder.Build()
+            };
+
+            var factory = new SpanFactory();
+            var blockFactory = new BlockFactory(factory);
+
+            var expectedMarkup = new MarkupBlock(
+                new MarkupTagHelperBlock("p",
+                    blockFactory.MarkupTagBlock("<b>"),
+                    factory.Markup(literal),
+                    blockFactory.MarkupTagBlock("</b>"),
+                    new HtmlCommentBlock(factory.Markup(part1),
+                     new ExpressionBlock(
+                        factory.CodeTransition(),
+                        factory.Code(part2)
+                            .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
+                            .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
+                    factory.Markup(part3))));
+
+            // Act & Assert
+            EvaluateData(
+                descriptors,
+                expectedOutput,
+                expectedMarkup,
+                Array.Empty<RazorDiagnostic>());
+        }
+
         [Fact]
         public void Rewrite_UnderstandsNullTagNameWithAllowedChildrenForCatchAll()
         {
@@ -3993,7 +4093,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     new MarkupBlock(
                         new MarkupTagBlock(
                             factory.Markup("<foo>")),
-                        factory.Markup("<!-- Hello World -->"),
+                        new HtmlCommentBlock( factory.Markup("<!-- Hello World -->")),
                         new MarkupTagBlock(
                             factory.Markup("</foo>")))
                 };
@@ -4003,13 +4103,13 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     new MarkupBlock(
                         new MarkupTagBlock(
                             factory.Markup("<foo>")),
-                        factory.Markup("<!-- "),
-                        new ExpressionBlock(
-                            factory.CodeTransition(),
-                            factory.Code("foo")
-                                   .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
-                                   .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
-                        factory.Markup(" -->"),
+                        new HtmlCommentBlock(factory.Markup("<!-- "),
+                            new ExpressionBlock(
+                                factory.CodeTransition(),
+                                factory.Code("foo")
+                                       .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
+                                       .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
+                            factory.Markup(" -->")),
                         new MarkupTagBlock(
                             factory.Markup("</foo>")))
                 };
diff --git a/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockTypes.cs b/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockTypes.cs
index c08e88d56f..56deb6b460 100644
--- a/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockTypes.cs
+++ b/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockTypes.cs
@@ -217,4 +217,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
         }
     }
+
+    internal class HtmlCommentBlock : Block
+    {
+        private const BlockKindInternal ThisBlockKind = BlockKindInternal.HtmlComment;
+
+        public HtmlCommentBlock(params SyntaxTreeNode[] children)
+            : base(ThisBlockKind, children, ParentChunkGenerator.Null)
+        {
+        }
+    }
 }

From e1fbea24f119f9526c61e227b8e96e16a9b56360 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Tue, 20 Feb 2018 18:24:27 -0800
Subject: [PATCH 21/34] HtmlMarkupParser is now aware of HtmlComment blocks.
 Majority (if not all, will confirm soon) tests have been updated to account
 for HtmlComment blocks.

---
 .../Legacy/HtmlMarkupParser.cs                | 49 ++++++++++++++-----
 .../Legacy/CSharpSectionTest.cs               | 11 +++--
 .../Legacy/HtmlBlockTest.cs                   | 33 +++++++------
 .../Legacy/TagHelperParseTreeRewriterTest.cs  | 48 +++++++++---------
 .../TagHelperParseTreeRewriterTests.cs        | 26 ++++++++++
 ...lCommentWithQuote_Double_DesignTime.ir.txt |  3 +-
 ...HtmlCommentWithQuote_Double_Runtime.ir.txt |  3 +-
 ...lCommentWithQuote_Single_DesignTime.ir.txt |  3 +-
 ...HtmlCommentWithQuote_Single_Runtime.ir.txt |  3 +-
 .../Language/Legacy/BlockFactory.cs           | 21 ++++++++
 10 files changed, 144 insertions(+), 56 deletions(-)
 create mode 100644 test/Microsoft.AspNetCore.Razor.Language.Test/TagHelperParseTreeRewriterTests.cs

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index 332023b775..fc675b6e47 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -207,10 +207,6 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             if (last != null)
             {
                 Accept(last);
-                if (At(HtmlSymbolType.OpenAngle) && last.Type == HtmlSymbolType.Text)
-                {
-                    Output(SpanKindInternal.Markup);
-                }
             }
         }
 
@@ -501,31 +497,57 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     using (Context.Builder.StartBlock(BlockKindInternal.HtmlComment))
                     {
                         AcceptAndMoveNext();
+                        Output(SpanKindInternal.Markup, AcceptedCharactersInternal.None);
 
-                        Span.EditHandler.AcceptedCharacters = AcceptedCharactersInternal.Any;
+                        Span.EditHandler.AcceptedCharacters = AcceptedCharactersInternal.WhiteSpace;
                         while (!EndOfFile)
                         {
                             SkipToAndParseCode(HtmlSymbolType.DoubleHyphen);
                             if (At(HtmlSymbolType.DoubleHyphen))
                             {
-                                AcceptWhile(HtmlSymbolType.DoubleHyphen);
+                                var lastDoubleHyphen = CurrentSymbol;
+                                AcceptWhile(s =>
+                                {
+                                    if (NextIs(HtmlSymbolType.DoubleHyphen))
+                                    {
+                                        lastDoubleHyphen = s;
+                                        return true;
+                                    }
+
+                                    NextToken();
+                                    EnsureCurrent();
+                                    return false;
+                                });
 
                                 if (At(HtmlSymbolType.Text) &&
                                     string.Equals(CurrentSymbol.Content, "-", StringComparison.Ordinal))
                                 {
+                                    // Doing this here to maintain the order of symbols
+                                    if (!NextIs(HtmlSymbolType.CloseAngle))
+                                    {
+                                        Accept(lastDoubleHyphen);
+                                        lastDoubleHyphen = null;
+                                    }
+
                                     AcceptAndMoveNext();
                                 }
 
                                 if (At(HtmlSymbolType.CloseAngle))
                                 {
-                                    // This is the end of a comment block
-                                    Accept(this.CurrentSymbol);
-                                    Output(SpanKindInternal.Markup);
+                                    // Output the content in the comment block as a separate markup
+                                    Output(SpanKindInternal.Markup, AcceptedCharactersInternal.WhiteSpace);
+
+                                    // This is the end of a comment block
+                                    Accept(lastDoubleHyphen);
+                                    AcceptAndMoveNext();
+                                    Output(SpanKindInternal.Markup, AcceptedCharactersInternal.None);
 
-                                    NextToken();
-                                    //AcceptAndMoveNext();
                                     return true;
                                 }
+                                else if (lastDoubleHyphen != null)
+                                {
+                                    Accept(lastDoubleHyphen);
+                                }
                             }
                         }
                     }
@@ -1486,6 +1508,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     // Checking to see if we meet the conditions of a special '!' tag: <!DOCTYPE, <![CDATA[, <!--.
                     if (!IsBangEscape(lookahead: 1))
                     {
+                        if (Lookahead(2)?.Type == HtmlSymbolType.DoubleHyphen)
+                        {
+                            Output(SpanKindInternal.Markup);
+                        }
+
                         AcceptAndMoveNext(); // Accept '<'
                         BangTag();
 
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/CSharpSectionTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/CSharpSectionTest.cs
index 3ae95b1994..3e2fbac20f 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/CSharpSectionTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/CSharpSectionTest.cs
@@ -367,7 +367,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
             // Act & Assert
             ParseDocumentTest(
-                "@section foo      " 
+                "@section foo      "
                 + Environment.NewLine
                 + Environment.NewLine
                 + Environment.NewLine
@@ -606,7 +606,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         Factory.Span(SpanKindInternal.Markup, " ", CSharpSymbolType.WhiteSpace).Accepts(AcceptedCharactersInternal.AllWhiteSpace),
                         Factory.MetaCode("{").AutoCompleteWith(null, atEndOfSpan: true).Accepts(AcceptedCharactersInternal.None),
                         new MarkupBlock(
-                            Factory.Markup("<!-- -->")),
+                            BlockFactory.HtmlCommentBlock(" "),
+                            Factory.EmptyHtml()),
                         Factory.MetaCode("}").Accepts(AcceptedCharactersInternal.None)),
                     Factory.EmptyHtml()));
         }
@@ -630,7 +631,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         Factory.Span(SpanKindInternal.Markup, " ", CSharpSymbolType.WhiteSpace).Accepts(AcceptedCharactersInternal.AllWhiteSpace),
                         Factory.MetaCode("{").AutoCompleteWith(null, atEndOfSpan: true).Accepts(AcceptedCharactersInternal.None),
                         new MarkupBlock(
-                            Factory.Markup("<!-- > \" '-->")),
+                            BlockFactory.HtmlCommentBlock(" > \" '"),
+                            Factory.EmptyHtml()),
                         Factory.MetaCode("}").Accepts(AcceptedCharactersInternal.None)),
                     Factory.EmptyHtml()));
         }
@@ -655,7 +657,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                             Factory.Markup(Environment.NewLine),
                             new MarkupTagBlock(
                                 Factory.Markup("<a" + Environment.NewLine)),
-                            Factory.Markup("<!--  > \" '-->")),
+                                BlockFactory.HtmlCommentBlock("  > \" '"),
+                                Factory.EmptyHtml()),
                         Factory.MetaCode("}").Accepts(AcceptedCharactersInternal.None)),
                     Factory.EmptyHtml()));
         }
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
index f54ba50d37..f8d4b0fcd9 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
@@ -23,7 +23,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         Factory.Code(Environment.NewLine).AsStatement().AutoCompleteWith(null),
                         new MarkupBlock(
                             Factory.Markup("    "),
-                            Factory.Markup("<!-- Hello, I'm a comment that shouldn't break razor --->").Accepts(AcceptedCharactersInternal.None),
+                            BlockFactory.HtmlCommentBlock(" Hello, I'm a comment that shouldn't break razor -"),
                             Factory.Markup(Environment.NewLine).Accepts(AcceptedCharactersInternal.None)),
                         Factory.EmptyCSharp().AsStatement(),
                         Factory.MetaCode("}").Accepts(AcceptedCharactersInternal.None)),
@@ -333,7 +333,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         [Fact]
         public void ParseBlockSupportsCommentAsBlock()
         {
-            SingleSpanBlockTest("<!-- foo -->", BlockKindInternal.Markup, SpanKindInternal.Markup, acceptedCharacters: AcceptedCharactersInternal.None);
+            ParseBlockTest("<!-- foo -->", new MarkupBlock( BlockFactory.HtmlCommentBlock(" foo ")));
         }
 
         [Fact]
@@ -344,8 +344,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     new MarkupTagBlock(
                         Factory.Markup("<foo>").Accepts(AcceptedCharactersInternal.None)),
                     Factory.Markup("bar"),
-                    Factory.Markup("<!-- zoop -->").Accepts(AcceptedCharactersInternal.None),
-                    Factory.Markup("baz"),
+                    BlockFactory.HtmlCommentBlock(" zoop "),
+                    Factory.Markup("baz").Accepts(AcceptedCharactersInternal.None),
                     new MarkupTagBlock(
                         Factory.Markup("</foo>").Accepts(AcceptedCharactersInternal.None))));
         }
@@ -355,7 +355,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             get
             {
                 var factory = new SpanFactory();
-
+                var blockFactory = new BlockFactory(factory);
                 return new TheoryData<string, MarkupBlock>
                 {
                     {
@@ -363,7 +363,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         new MarkupBlock(
                             new MarkupTagBlock(
                                 factory.Markup("<div>").Accepts(AcceptedCharactersInternal.None)),
-                            factory.Markup("<!--- Hello World --->").Accepts(AcceptedCharactersInternal.None),
+                            blockFactory.HtmlCommentBlock("- Hello World -"),
                             new MarkupTagBlock(
                                 factory.Markup("</div>").Accepts(AcceptedCharactersInternal.None)))
                     },
@@ -372,7 +372,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         new MarkupBlock(
                             new MarkupTagBlock(
                                 factory.Markup("<div>").Accepts(AcceptedCharactersInternal.None)),
-                            factory.Markup("<!---- Hello World ---->").Accepts(AcceptedCharactersInternal.None),
+                            blockFactory.HtmlCommentBlock("-- Hello World --"),
                             new MarkupTagBlock(
                                 factory.Markup("</div>").Accepts(AcceptedCharactersInternal.None)))
                     },
@@ -381,7 +381,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         new MarkupBlock(
                             new MarkupTagBlock(
                                 factory.Markup("<div>").Accepts(AcceptedCharactersInternal.None)),
-                            factory.Markup("<!----- Hello World ----->").Accepts(AcceptedCharactersInternal.None),
+                            blockFactory.HtmlCommentBlock("--- Hello World ---"),
                             new MarkupTagBlock(
                                 factory.Markup("</div>").Accepts(AcceptedCharactersInternal.None)))
                     },
@@ -390,7 +390,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         new MarkupBlock(
                             new MarkupTagBlock(
                                 factory.Markup("<div>").Accepts(AcceptedCharactersInternal.None)),
-                            factory.Markup("<!----- Hello < --- > World </div> ----->").Accepts(AcceptedCharactersInternal.None),
+                           blockFactory.HtmlCommentBlock("--- Hello < --- > World </div> ---"),
                             new MarkupTagBlock(
                                 factory.Markup("</div>").Accepts(AcceptedCharactersInternal.None)))
                     },
@@ -410,19 +410,24 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         [Fact]
         public void ParseBlockProperlyBalancesCommentStartAndEndTags()
         {
-            SingleSpanBlockTest("<!--<foo></bar>-->", BlockKindInternal.Markup, SpanKindInternal.Markup, acceptedCharacters: AcceptedCharactersInternal.None);
+            ParseBlockTest("<!--<foo></bar>-->", new MarkupBlock(BlockFactory.HtmlCommentBlock("<foo></bar>")));
         }
 
         [Fact]
         public void ParseBlockTerminatesAtEOFWhenParsingComment()
         {
-            SingleSpanBlockTest("<!--<foo>", "<!--<foo>", BlockKindInternal.Markup, SpanKindInternal.Markup);
+            ParseBlockTest(
+                "<!--<foo>",
+                new MarkupBlock(
+                    new HtmlCommentBlock(Factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None)),
+                    Factory.Markup("<foo>").Accepts(AcceptedCharactersInternal.WhiteSpace),
+                    Factory.EmptyHtml()));
         }
 
         [Fact]
         public void ParseBlockOnlyTerminatesCommentOnFullEndSequence()
         {
-            SingleSpanBlockTest("<!--<foo>--</bar>-->", BlockKindInternal.Markup, SpanKindInternal.Markup, acceptedCharacters: AcceptedCharactersInternal.None);
+            ParseBlockTest("<!--<foo>--</bar>-->", new MarkupBlock(BlockFactory.HtmlCommentBlock("<foo>--</bar>")));
         }
 
         [Fact]
@@ -432,8 +437,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 new MarkupBlock(
                     new MarkupTagBlock(
                         Factory.Markup("<foo>").Accepts(AcceptedCharactersInternal.None)),
-                    Factory.Markup("<!--<foo></bar-->").Accepts(AcceptedCharactersInternal.None),
-                    Factory.Markup("-->"),
+                    BlockFactory.HtmlCommentBlock("<foo></bar"),
+                    Factory.Markup("-->").Accepts(AcceptedCharactersInternal.None),
                     new MarkupTagBlock(
                         Factory.Markup("</foo>").Accepts(AcceptedCharactersInternal.None))));
         }
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index 45a1ffa907..ceca9e86f2 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -1114,8 +1114,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             // Arrangestring documentContent,
             IEnumerable<string> allowedChildren = new List<string> { "b" };
             string literal = "asdf";
-            string commentOutput = "<!--Hello World-->";
-            string expectedOutput = $"<p><b>{literal}</b>{commentOutput}</p>";
+            string commentOutput = "Hello World";
+            string expectedOutput = $"<p><b>{literal}</b><!--{commentOutput}--></p>";
 
             var pTagHelperBuilder = TagHelperDescriptorBuilder
                 .Create("PTagHelper", "SomeAssembly")
@@ -1138,7 +1138,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     blockFactory.MarkupTagBlock("<b>"),
                     factory.Markup(literal),
                     blockFactory.MarkupTagBlock("</b>"),
-                    new HtmlCommentBlock(factory.Markup(commentOutput))));
+                    blockFactory.HtmlCommentBlock(commentOutput)));
 
             // Act & Assert
             EvaluateData(
@@ -1185,9 +1185,9 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
             var expectedMarkup = new MarkupBlock(
                 new MarkupTagHelperBlock("p",
-                    new HtmlCommentBlock(factory.Markup($"<!--{comment1}-->")),
+                    blockFactory.HtmlCommentBlock(comment1),
                     factory.Markup(literal),
-                    new HtmlCommentBlock(factory.Markup($"<!--{comment2}-->"))));
+                    blockFactory.HtmlCommentBlock(comment2)));
 
             // Act & Assert
             EvaluateData(
@@ -1251,10 +1251,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             // Arrangestring documentContent,
             IEnumerable<string> allowedChildren = new List<string> { "b" };
             string literal = "asdf";
-            string part1 = "<!--Hello ";
+            string part1 = "Hello ";
             string part2 = "World";
-            string part3 = "-->";
-            string expectedOutput = $"<p><b>{literal}</b>{part1}@{part2}{part3}</p>";
+            string commentStart = "<!--";
+            string commentEnd = "-->";
+            string expectedOutput = $"<p><b>{literal}</b>{commentStart}{part1}@{part2}{commentEnd}</p>";
 
             var pTagHelperBuilder = TagHelperDescriptorBuilder
                 .Create("PTagHelper", "SomeAssembly")
@@ -1277,13 +1278,13 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     blockFactory.MarkupTagBlock("<b>"),
                     factory.Markup(literal),
                     blockFactory.MarkupTagBlock("</b>"),
-                    new HtmlCommentBlock(factory.Markup(part1),
-                     new ExpressionBlock(
-                        factory.CodeTransition(),
-                        factory.Code(part2)
-                            .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
-                            .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
-                    factory.Markup(part3))));
+                    blockFactory.HtmlCommentBlock(
+                        factory.Markup(part1).Accepts(AcceptedCharactersInternal.WhiteSpace),
+                         new ExpressionBlock(
+                            factory.CodeTransition(),
+                            factory.Code(part2)
+                                .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
+                                .Accepts(AcceptedCharactersInternal.NonWhiteSpace)))));
 
             // Act & Assert
             EvaluateData(
@@ -4086,14 +4087,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             get
             {
                 var factory = new SpanFactory();
-
+                var blockFactory = new BlockFactory(factory);
                 yield return new object[]
                 {
                     "<foo><!-- Hello World --></foo>",
                     new MarkupBlock(
                         new MarkupTagBlock(
                             factory.Markup("<foo>")),
-                        new HtmlCommentBlock( factory.Markup("<!-- Hello World -->")),
+                        blockFactory.HtmlCommentBlock (" Hello World "),
                         new MarkupTagBlock(
                             factory.Markup("</foo>")))
                 };
@@ -4103,13 +4104,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     new MarkupBlock(
                         new MarkupTagBlock(
                             factory.Markup("<foo>")),
-                        new HtmlCommentBlock(factory.Markup("<!-- "),
+                        blockFactory.HtmlCommentBlock(
+                            factory.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace),
                             new ExpressionBlock(
                                 factory.CodeTransition(),
                                 factory.Code("foo")
-                                       .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
-                                       .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
-                            factory.Markup(" -->")),
+                                    .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
+                                    .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
+                            factory.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace)),
                         new MarkupTagBlock(
                             factory.Markup("</foo>")))
                 };
@@ -4185,8 +4187,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         new ExpressionBlock(
                             factory.CodeTransition(),
                             factory.Code("foo")
-                                   .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
-                                   .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
+                                .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
+                                .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
                         factory.Markup(" ]]>"),
                         new MarkupTagBlock(
                             factory.Markup("</foo>")))
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TagHelperParseTreeRewriterTests.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/TagHelperParseTreeRewriterTests.cs
new file mode 100644
index 0000000000..a24a9c8d4f
--- /dev/null
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TagHelperParseTreeRewriterTests.cs
@@ -0,0 +1,26 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Microsoft.AspNetCore.Razor.Language.Legacy;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Razor.Language.Test
+{
+    public class TagHelperParseTreeRewriterTests
+    {
+        public void IsComment_ReturnsTrueForSpanInHtmlCommentBlock()
+        {
+            // Arrange
+            SpanFactory spanFactory = new SpanFactory();
+            
+            Span content = spanFactory.Markup("<!-- comment -->");
+            Block commentBlock = new HtmlCommentBlock(content);
+
+            // Act
+            bool actualResult = TagHelperParseTreeRewriter.IsComment(content);
+
+            // Assert
+            Assert.True(actualResult);
+        }
+    }
+}
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt
index aa6a00864d..615f0fce97 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt
@@ -10,7 +10,8 @@ Document -
                 IntermediateToken -  - CSharp - #pragma warning restore 0414
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Double.cshtml)
-                    IntermediateToken - (0:0,0 [12] HtmlCommentWithQuote_Double.cshtml) - Html - <!-- " -->\n
+                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Double.cshtml) - Html - <!-- " -->
+                    IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Double.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Double.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Double.cshtml) - Html -  src="~/images/submit.png"
                     IntermediateToken - (42:1,30 [3] HtmlCommentWithQuote_Double.cshtml) - Html -  />
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt
index 343985c189..7adfc1650b 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt
@@ -5,7 +5,8 @@ Document -
         ClassDeclaration -  - public - TestFiles_IntegrationTests_CodeGenerationIntegrationTest_HtmlCommentWithQuote_Double_Runtime -  - 
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Double.cshtml)
-                    IntermediateToken - (0:0,0 [12] HtmlCommentWithQuote_Double.cshtml) - Html - <!-- " -->\n
+                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Double.cshtml) - Html - <!-- " -->
+                    IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Double.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Double.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Double.cshtml) - Html -  src="~/images/submit.png"
                     IntermediateToken - (42:1,30 [3] HtmlCommentWithQuote_Double.cshtml) - Html -  />
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt
index 04795676d1..0e342fcf51 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt
@@ -10,7 +10,8 @@ Document -
                 IntermediateToken -  - CSharp - #pragma warning restore 0414
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Single.cshtml)
-                    IntermediateToken - (0:0,0 [12] HtmlCommentWithQuote_Single.cshtml) - Html - <!-- ' -->\n
+                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Single.cshtml) - Html - <!-- ' -->
+                    IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Single.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Single.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Single.cshtml) - Html -  src="~/images/submit.png"
                     IntermediateToken - (42:1,30 [3] HtmlCommentWithQuote_Single.cshtml) - Html -  />
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt
index 65aafb6fe7..137c2a042c 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt
@@ -5,7 +5,8 @@ Document -
         ClassDeclaration -  - public - TestFiles_IntegrationTests_CodeGenerationIntegrationTest_HtmlCommentWithQuote_Single_Runtime -  - 
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Single.cshtml)
-                    IntermediateToken - (0:0,0 [12] HtmlCommentWithQuote_Single.cshtml) - Html - <!-- ' -->\n
+                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Single.cshtml) - Html - <!-- ' -->
+                    IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Single.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Single.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Single.cshtml) - Html -  src="~/images/submit.png"
                     IntermediateToken - (42:1,30 [3] HtmlCommentWithQuote_Single.cshtml) - Html -  />
diff --git a/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs b/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs
index 5c2ee95394..a58d3b0c87 100644
--- a/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs
+++ b/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs
@@ -55,6 +55,27 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             );
         }
 
+        public HtmlCommentBlock HtmlCommentBlock(string content)
+        {
+            return new HtmlCommentBlock(new SyntaxTreeNode[] {
+                _factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None),
+                _factory.Markup(content).Accepts(AcceptedCharactersInternal.WhiteSpace),
+                _factory.Markup("-->").Accepts(AcceptedCharactersInternal.None) });
+        }
+
+        public HtmlCommentBlock HtmlCommentBlock(params SyntaxTreeNode[] syntaxTreeNodes)
+        {
+            var nodes = new List<SyntaxTreeNode>();
+            nodes.Add(_factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None));
+            if (syntaxTreeNodes != null)
+            {
+                nodes.AddRange(syntaxTreeNodes);
+            }
+            nodes.Add(_factory.Markup("-->").Accepts(AcceptedCharactersInternal.None));
+
+            return new HtmlCommentBlock(nodes.ToArray());
+        }
+
         public Block TagHelperBlock(
             string tagName,
             TagMode tagMode,

From 6f515bb7637fcf70b4a692a626c92e84e5ef208c Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Tue, 20 Feb 2018 22:20:48 -0800
Subject: [PATCH 22/34] Fixed all the tests to reflect HtmlComment block type
 support

---
 .../Legacy/HtmlDocumentTest.cs                |  8 +++++++-
 .../Legacy/HtmlTagsTest.cs                    |  2 +-
 .../Legacy/HtmlToCodeSwitchTest.cs            | 15 +++++++-------
 .../Legacy/TagHelperParseTreeRewriterTest.cs  | 20 +++++++++----------
 ...lCommentWithQuote_Double_DesignTime.ir.txt |  4 +++-
 ...HtmlCommentWithQuote_Double_Runtime.ir.txt |  4 +++-
 ...lCommentWithQuote_Single_DesignTime.ir.txt |  4 +++-
 ...HtmlCommentWithQuote_Single_Runtime.ir.txt |  4 +++-
 .../Language/Legacy/BlockFactory.cs           | 16 +++++++--------
 9 files changed, 45 insertions(+), 32 deletions(-)

diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs
index 0f06fe578a..9f0e11218b 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs
@@ -214,7 +214,13 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         [Fact]
         public void ParseDocumentReturnsOneMarkupSegmentIfNoCodeBlocksEncountered()
         {
-            SingleSpanDocumentTest("Foo Baz<!--Foo-->Bar<!--F> Qux", BlockKindInternal.Markup, SpanKindInternal.Markup);
+            ParseDocumentTest("Foo Baz<!--Foo-->Bar<!--F> Qux",
+                new MarkupBlock(
+                    Factory.Markup("Foo Baz"),
+                    BlockFactory.HtmlCommentBlock("Foo"),
+                    Factory.Markup("Bar"),
+                    new HtmlCommentBlock(Factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None)),
+                    Factory.Markup("F> Qux").Accepts(AcceptedCharactersInternal.WhiteSpace)));
         }
 
         [Fact]
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlTagsTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlTagsTest.cs
index 0a86c7a06b..5f22a1bae7 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlTagsTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlTagsTest.cs
@@ -60,7 +60,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         {
             ParseBlockTest("<!--Foo--> Bar",
                 new MarkupBlock(
-                    Factory.Markup("<!--Foo-->").Accepts(AcceptedCharactersInternal.None),
+                    BlockFactory.HtmlCommentBlock("Foo"),
                     Factory.Markup(" ").Accepts(AcceptedCharactersInternal.None)));
         }
 
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlToCodeSwitchTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlToCodeSwitchTest.cs
index 29c1dfb81a..928762fbc6 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlToCodeSwitchTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlToCodeSwitchTest.cs
@@ -112,13 +112,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 new MarkupBlock(
                     new MarkupTagBlock(
                         Factory.Markup("<foo>").Accepts(AcceptedCharactersInternal.None)),
-                    Factory.Markup("<!-- "),
-                    new ExpressionBlock(
-                        Factory.CodeTransition(),
-                        Factory.Code("foo")
-                               .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
-                               .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
-                    Factory.Markup(" -->").Accepts(AcceptedCharactersInternal.None),
+                    BlockFactory.HtmlCommentBlock(Factory, f => new SyntaxTreeNode[] {
+                        f.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace),
+                        new ExpressionBlock(
+                            f.CodeTransition(),
+                            f.Code("foo")
+                                   .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
+                                   .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
+                            f.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace) }),
                     new MarkupTagBlock(
                         Factory.Markup("</foo>").Accepts(AcceptedCharactersInternal.None))));
         }
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index ceca9e86f2..425b728716 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -1278,13 +1278,13 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     blockFactory.MarkupTagBlock("<b>"),
                     factory.Markup(literal),
                     blockFactory.MarkupTagBlock("</b>"),
-                    blockFactory.HtmlCommentBlock(
-                        factory.Markup(part1).Accepts(AcceptedCharactersInternal.WhiteSpace),
+                    BlockFactory.HtmlCommentBlock(factory, f => new SyntaxTreeNode[] {
+                        f.Markup(part1).Accepts(AcceptedCharactersInternal.WhiteSpace),
                          new ExpressionBlock(
-                            factory.CodeTransition(),
-                            factory.Code(part2)
+                            f.CodeTransition(),
+                            f.Code(part2)
                                 .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
-                                .Accepts(AcceptedCharactersInternal.NonWhiteSpace)))));
+                                .Accepts(AcceptedCharactersInternal.NonWhiteSpace)) })));
 
             // Act & Assert
             EvaluateData(
@@ -4104,14 +4104,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     new MarkupBlock(
                         new MarkupTagBlock(
                             factory.Markup("<foo>")),
-                        blockFactory.HtmlCommentBlock(
-                            factory.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace),
+                        BlockFactory.HtmlCommentBlock(factory, f=> new SyntaxTreeNode[]{
+                            f.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace),
                             new ExpressionBlock(
-                                factory.CodeTransition(),
-                                factory.Code("foo")
+                                f.CodeTransition(),
+                                f.Code("foo")
                                     .AsImplicitExpression(CSharpCodeParser.DefaultKeywords)
                                     .Accepts(AcceptedCharactersInternal.NonWhiteSpace)),
-                            factory.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace)),
+                            factory.Markup(" ").Accepts(AcceptedCharactersInternal.WhiteSpace) }),
                         new MarkupTagBlock(
                             factory.Markup("</foo>")))
                 };
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt
index 615f0fce97..4523eae7a3 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_DesignTime.ir.txt
@@ -10,7 +10,9 @@ Document -
                 IntermediateToken -  - CSharp - #pragma warning restore 0414
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Double.cshtml)
-                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Double.cshtml) - Html - <!-- " -->
+                    IntermediateToken - (0:0,0 [4] HtmlCommentWithQuote_Double.cshtml) - Html - <!--
+                    IntermediateToken - (4:0,4 [3] HtmlCommentWithQuote_Double.cshtml) - Html -  " 
+                    IntermediateToken - (7:0,7 [3] HtmlCommentWithQuote_Double.cshtml) - Html - -->
                     IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Double.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Double.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Double.cshtml) - Html -  src="~/images/submit.png"
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt
index 7adfc1650b..046cad8407 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Double_Runtime.ir.txt
@@ -5,7 +5,9 @@ Document -
         ClassDeclaration -  - public - TestFiles_IntegrationTests_CodeGenerationIntegrationTest_HtmlCommentWithQuote_Double_Runtime -  - 
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Double.cshtml)
-                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Double.cshtml) - Html - <!-- " -->
+                    IntermediateToken - (0:0,0 [4] HtmlCommentWithQuote_Double.cshtml) - Html - <!--
+                    IntermediateToken - (4:0,4 [3] HtmlCommentWithQuote_Double.cshtml) - Html -  " 
+                    IntermediateToken - (7:0,7 [3] HtmlCommentWithQuote_Double.cshtml) - Html - -->
                     IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Double.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Double.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Double.cshtml) - Html -  src="~/images/submit.png"
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt
index 0e342fcf51..8b5f5b3ed5 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_DesignTime.ir.txt
@@ -10,7 +10,9 @@ Document -
                 IntermediateToken -  - CSharp - #pragma warning restore 0414
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Single.cshtml)
-                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Single.cshtml) - Html - <!-- ' -->
+                    IntermediateToken - (0:0,0 [4] HtmlCommentWithQuote_Single.cshtml) - Html - <!--
+                    IntermediateToken - (4:0,4 [3] HtmlCommentWithQuote_Single.cshtml) - Html -  ' 
+                    IntermediateToken - (7:0,7 [3] HtmlCommentWithQuote_Single.cshtml) - Html - -->
                     IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Single.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Single.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Single.cshtml) - Html -  src="~/images/submit.png"
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt
index 137c2a042c..8596f51503 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/HtmlCommentWithQuote_Single_Runtime.ir.txt
@@ -5,7 +5,9 @@ Document -
         ClassDeclaration -  - public - TestFiles_IntegrationTests_CodeGenerationIntegrationTest_HtmlCommentWithQuote_Single_Runtime -  - 
             MethodDeclaration -  - public async - System.Threading.Tasks.Task - ExecuteAsync
                 HtmlContent - (0:0,0 [45] HtmlCommentWithQuote_Single.cshtml)
-                    IntermediateToken - (0:0,0 [10] HtmlCommentWithQuote_Single.cshtml) - Html - <!-- ' -->
+                    IntermediateToken - (0:0,0 [4] HtmlCommentWithQuote_Single.cshtml) - Html - <!--
+                    IntermediateToken - (4:0,4 [3] HtmlCommentWithQuote_Single.cshtml) - Html -  ' 
+                    IntermediateToken - (7:0,7 [3] HtmlCommentWithQuote_Single.cshtml) - Html - -->
                     IntermediateToken - (10:0,10 [2] HtmlCommentWithQuote_Single.cshtml) - Html - \n
                     IntermediateToken - (12:1,0 [4] HtmlCommentWithQuote_Single.cshtml) - Html - <img
                     IntermediateToken - (16:1,4 [26] HtmlCommentWithQuote_Single.cshtml) - Html -  src="~/images/submit.png"
diff --git a/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs b/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs
index a58d3b0c87..2551fee917 100644
--- a/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs
+++ b/test/Microsoft.AspNetCore.Razor.Test.Common/Language/Legacy/BlockFactory.cs
@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
 
 namespace Microsoft.AspNetCore.Razor.Language.Legacy
@@ -57,21 +58,18 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         public HtmlCommentBlock HtmlCommentBlock(string content)
         {
-            return new HtmlCommentBlock(new SyntaxTreeNode[] {
-                _factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None),
-                _factory.Markup(content).Accepts(AcceptedCharactersInternal.WhiteSpace),
-                _factory.Markup("-->").Accepts(AcceptedCharactersInternal.None) });
+            return HtmlCommentBlock(_factory, f => new SyntaxTreeNode[] { f.Markup(content).Accepts(AcceptedCharactersInternal.WhiteSpace) });
         }
 
-        public HtmlCommentBlock HtmlCommentBlock(params SyntaxTreeNode[] syntaxTreeNodes)
+        public static HtmlCommentBlock HtmlCommentBlock(SpanFactory factory, Func<SpanFactory, IEnumerable<SyntaxTreeNode>> nodesBuilder = null)
         {
             var nodes = new List<SyntaxTreeNode>();
-            nodes.Add(_factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None));
-            if (syntaxTreeNodes != null)
+            nodes.Add(factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None));
+            if (nodesBuilder != null)
             {
-                nodes.AddRange(syntaxTreeNodes);
+                nodes.AddRange(nodesBuilder(factory));
             }
-            nodes.Add(_factory.Markup("-->").Accepts(AcceptedCharactersInternal.None));
+            nodes.Add(factory.Markup("-->").Accepts(AcceptedCharactersInternal.None));
 
             return new HtmlCommentBlock(nodes.ToArray());
         }

From 0af42204eb05400ff5c505c0fa4d81b39298eb6d Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Thu, 22 Feb 2018 17:05:13 -0800
Subject: [PATCH 23/34] Added the AllowHtmlCommentsInTagHelpers feature flag to
 control behavior of having comments in TagHelpers

---
 .../Legacy/TagHelperParseTreeRewriter.cs              |  8 +++++++-
 .../RazorParserFeatureFlags.cs                        | 11 +++++++++--
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index 6cac8b46ea..a4c9906b1a 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -488,7 +488,13 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            if (HasAllowedChildren() && !IsComment(child) && child.Kind != SpanKindInternal.Transition && child.Kind != SpanKindInternal.Code)
+            var isDisallowedContent = true;
+            if (_featureFlags.AllowHtmlCommentsInTagHelpers)
+            {
+                isDisallowedContent = !IsComment(child) && child.Kind != SpanKindInternal.Transition && child.Kind != SpanKindInternal.Code;
+            }
+
+            if (HasAllowedChildren() && isDisallowedContent)
             {
                 var content = child.Content;
                 if (!string.IsNullOrWhiteSpace(content))
diff --git a/src/Microsoft.AspNetCore.Razor.Language/RazorParserFeatureFlags.cs b/src/Microsoft.AspNetCore.Razor.Language/RazorParserFeatureFlags.cs
index 0629eb9af8..409718b640 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/RazorParserFeatureFlags.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/RazorParserFeatureFlags.cs
@@ -8,26 +8,33 @@ namespace Microsoft.AspNetCore.Razor.Language
         public static RazorParserFeatureFlags Create(RazorLanguageVersion version)
         {
             var allowMinimizedBooleanTagHelperAttributes = false;
+            var allowHtmlCommentsInTagHelpers = false;
 
             if (version.CompareTo(RazorLanguageVersion.Version_2_1) >= 0)
             {
                 // Added in 2.1
                 allowMinimizedBooleanTagHelperAttributes = true;
+                allowHtmlCommentsInTagHelpers = true;
             }
 
-            return new DefaultRazorParserFeatureFlags(allowMinimizedBooleanTagHelperAttributes);
+            return new DefaultRazorParserFeatureFlags(allowMinimizedBooleanTagHelperAttributes, allowHtmlCommentsInTagHelpers);
         }
 
         public abstract bool AllowMinimizedBooleanTagHelperAttributes { get; }
 
+        public abstract bool AllowHtmlCommentsInTagHelpers { get; }
+
         private class DefaultRazorParserFeatureFlags : RazorParserFeatureFlags
         {
-            public DefaultRazorParserFeatureFlags(bool allowMinimizedBooleanTagHelperAttributes)
+            public DefaultRazorParserFeatureFlags(bool allowMinimizedBooleanTagHelperAttributes, bool allowHtmlCommentsInTagHelpers)
             {
                 AllowMinimizedBooleanTagHelperAttributes = allowMinimizedBooleanTagHelperAttributes;
+                AllowHtmlCommentsInTagHelpers = allowHtmlCommentsInTagHelpers;
             }
 
             public override bool AllowMinimizedBooleanTagHelperAttributes { get; }
+
+            public override bool AllowHtmlCommentsInTagHelpers { get; }
         }
     }
 }

From 6885fb15d0c7c9cb8cf7224f7a6ddec2bf6df427 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Thu, 22 Feb 2018 17:07:52 -0800
Subject: [PATCH 24/34] Updated the test TagHelperBlockRewriteTest class

---
 .../Legacy/TagHelperBlockRewriterTest.cs            | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperBlockRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperBlockRewriterTest.cs
index 9b2adc4d07..88c774c93c 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperBlockRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperBlockRewriterTest.cs
@@ -2950,7 +2950,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                                 intType),
                             RazorDiagnosticFactory.CreateParsing_TagHelperIndexerAttributeNameMustIncludeKey(
                                 new SourceSpan(7, 0, 7, 11),
-                                "int-prefix-", 
+                                "int-prefix-",
                                 "input"),
                         }
                     },
@@ -2973,7 +2973,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                                 stringType),
                             RazorDiagnosticFactory.CreateParsing_TagHelperIndexerAttributeNameMustIncludeKey(
                                 new SourceSpan(7, 0, 7, 14),
-                                "string-prefix-", 
+                                "string-prefix-",
                                 "input"),
                         }
                     },
@@ -3638,7 +3638,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                             RazorDiagnosticFactory.CreateTagHelper_EmptyBoundAttribute(
                                 new SourceSpan(7, 0, 7, 21),
                                 "bound-required-string",
-                                "input", 
+                                "input",
                                 stringType),
                         }
                     },
@@ -3962,7 +3962,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     .Build(),
             };
 
-            var featureFlags = new TestRazorParserFeatureFlags(allowMinimizedBooleanTagHelperAttributes: false);
+            var featureFlags = new TestRazorParserFeatureFlags(allowMinimizedBooleanTagHelperAttributes: false, allowHtmlCommentsInTagHelper: false);
 
             var expectedOutput = new MarkupBlock(
                 new MarkupTagHelperBlock(
@@ -3994,12 +3994,15 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private class TestRazorParserFeatureFlags : RazorParserFeatureFlags
         {
-            public TestRazorParserFeatureFlags(bool allowMinimizedBooleanTagHelperAttributes)
+            public TestRazorParserFeatureFlags(bool allowMinimizedBooleanTagHelperAttributes, bool allowHtmlCommentsInTagHelper)
             {
                 AllowMinimizedBooleanTagHelperAttributes = allowMinimizedBooleanTagHelperAttributes;
+                AllowHtmlCommentsInTagHelpers = allowHtmlCommentsInTagHelper;
             }
 
             public override bool AllowMinimizedBooleanTagHelperAttributes { get; }
+
+            public override bool AllowHtmlCommentsInTagHelpers { get; }
         }
     }
 }

From 33814fb6347ba4f27c3eb8da7d23ce4e8a06a974 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Mon, 5 Mar 2018 17:28:23 -0800
Subject: [PATCH 25/34] Updated the Comments detection to comply with HTML 5
 specification

---
 .../Legacy/HtmlMarkupParser.cs                | 151 ++++++++++++++----
 .../Legacy/TokenizerBackedParser.cs           |  47 ++++++
 .../Legacy/HtmlBlockTest.cs                   |   4 +-
 .../Legacy/HtmlDocumentTest.cs                |   3 +-
 4 files changed, 170 insertions(+), 35 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index fc675b6e47..2fe84b5a33 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -492,7 +492,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
             if (AcceptAndMoveNext())
             {
-                if (CurrentSymbol.Type == HtmlSymbolType.DoubleHyphen)
+                if (IsHtmlCommentAhead())
                 {
                     using (Context.Builder.StartBlock(BlockKindInternal.HtmlComment))
                     {
@@ -505,32 +505,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                             SkipToAndParseCode(HtmlSymbolType.DoubleHyphen);
                             if (At(HtmlSymbolType.DoubleHyphen))
                             {
-                                var lastDoubleHyphen = CurrentSymbol;
-                                AcceptWhile(s =>
-                                {
-                                    if (NextIs(HtmlSymbolType.DoubleHyphen))
-                                    {
-                                        lastDoubleHyphen = s;
-                                        return true;
-                                    }
-
-                                    NextToken();
-                                    EnsureCurrent();
-                                    return false;
-                                });
-
-                                if (At(HtmlSymbolType.Text) &&
-                                    string.Equals(CurrentSymbol.Content, "-", StringComparison.Ordinal))
-                                {
-                                    // Doing this here to maintain the order of symbols
-                                    if (!NextIs(HtmlSymbolType.CloseAngle))
-                                    {
-                                        Accept(lastDoubleHyphen);
-                                        lastDoubleHyphen = null;
-                                    }
-
-                                    AcceptAndMoveNext();
-                                }
+                                var lastDoubleHyphen = AcceptAllButLastDoubleHypens();
 
                                 if (At(HtmlSymbolType.CloseAngle))
                                 {
@@ -541,7 +516,6 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                                     Accept(lastDoubleHyphen);
                                     AcceptAndMoveNext();
                                     Output(SpanKindInternal.Markup, AcceptedCharactersInternal.None);
-
                                     return true;
                                 }
                                 else if (lastDoubleHyphen != null)
@@ -551,8 +525,6 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                             }
                         }
                     }
-
-                    return false;
                 }
                 else if (CurrentSymbol.Type == HtmlSymbolType.LeftBracket)
                 {
@@ -571,6 +543,125 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return false;
         }
 
+        private HtmlSymbol AcceptAllButLastDoubleHypens()
+        {
+            var lastDoubleHyphen = CurrentSymbol;
+            AcceptWhile(s =>
+            {
+                if (NextIs(HtmlSymbolType.DoubleHyphen))
+                {
+                    lastDoubleHyphen = s;
+                    return true;
+                }
+
+                NextToken();
+                EnsureCurrent();
+                return false;
+            });
+
+            if (At(HtmlSymbolType.Text) && IsDashSymbol(CurrentSymbol))
+            {
+                // Doing this here to maintain the order of symbols
+                if (!NextIs(HtmlSymbolType.CloseAngle))
+                {
+                    Accept(lastDoubleHyphen);
+                    lastDoubleHyphen = null;
+                }
+
+                AcceptAndMoveNext();
+            }
+
+            return lastDoubleHyphen;
+        }
+
+        private static bool IsDashSymbol(HtmlSymbol symbol)
+        {
+            return string.Equals(symbol.Content, "-", StringComparison.Ordinal);
+        }
+
+        private bool IsHtmlCommentAhead()
+        {
+            /*
+             * From HTML5 Specification, available at http://www.w3.org/TR/html52/syntax.html#comments
+             * 
+             * Comments must have the following format:
+             * 1. The string "<!--"
+             * 2. Optionally, text, with the additional restriction that the text
+             *      2.1 must not start with the string ">" nor start with the string "->"
+             *      2.2 nor contain the strings "<!--", "-->", or "--!>"
+             *      2.3 nor end with the string "<!-".
+             * 3. The string "-->"
+             * 
+             * */
+
+            if (CurrentSymbol.Type != HtmlSymbolType.DoubleHyphen)
+            {
+                return false;
+            }
+
+            // Check condition 2.1
+            if (NextIs(HtmlSymbolType.CloseAngle) || NextIs(next => IsDashSymbol(next) && NextIs(HtmlSymbolType.CloseAngle)))
+            {
+                return false;
+            }
+
+            // Check condition 2.2
+            bool isValidComment = false;
+            LookaheadUntil((s, p) =>
+            {
+                bool breakLookahead = false;
+                if (s.Type == HtmlSymbolType.DoubleHyphen)
+                {
+                    if (NextIs(HtmlSymbolType.CloseAngle))
+                    {
+                        // We're at the end of a comment. check the condition 2.3 to make sure the text ending is allowed.
+                        isValidComment = !EndsWithSymbolsSequence(p, HtmlSymbolType.OpenAngle, HtmlSymbolType.Bang, HtmlSymbolType.DoubleHyphen);
+                        breakLookahead = true;
+                    }
+                    else if (NextIs(ns => IsDashSymbol(ns) && NextIs(HtmlSymbolType.CloseAngle)))
+                    {
+                        // This is also a valid closing comment case, as the dashes lookup is treated with DoubleHyphen symbols first.
+                        isValidComment = true;
+                        breakLookahead = true;
+                    }
+                    else if (NextIs(ns => ns.Type == HtmlSymbolType.Bang && NextIs(HtmlSymbolType.CloseAngle)))
+                    {
+                        isValidComment = false;
+                        breakLookahead = true;
+                    }
+                }
+                else if (s.Type == HtmlSymbolType.OpenAngle)
+                {
+                    if (NextIs(ns => ns.Type == HtmlSymbolType.Bang && NextIs(HtmlSymbolType.DoubleHyphen)))
+                    {
+                        isValidComment = false;
+                        breakLookahead = true;
+                    }
+                }
+
+                return breakLookahead;
+            });
+
+            return isValidComment;
+        }
+
+        private bool EndsWithSymbolsSequence(IEnumerable<HtmlSymbol> symbols, params HtmlSymbolType[] sequenceToMatchWith)
+        {
+            int index = sequenceToMatchWith.Length;
+            foreach (var previousSymbol in symbols)
+            {
+                if (index == 0)
+                {
+                    break;
+                }
+
+                if (sequenceToMatchWith[--index] != previousSymbol.Type)
+                    return false;
+            }
+
+            return index == 0;
+        }
+
         private bool CData()
         {
             if (CurrentSymbol.Type == HtmlSymbolType.Text && string.Equals(CurrentSymbol.Content, "cdata", StringComparison.OrdinalIgnoreCase))
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
index 6f564eb442..1819407076 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
@@ -109,6 +109,53 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return symbols[count];
         }
 
+        /// <summary>
+        /// Looks forward until the specified condition is met.
+        /// </summary>
+        /// <param name="condition">A predicate accepting the symbol being evaluated and the list of symbols which have been looped through.</param>
+        /// <returns>true, if the condition was met. false - if the condition wasn't met and the last symbol has already been processed.</returns>
+        /// <remarks>The list of previous symbols is passed in the reverse order. So the last processed element will be the first one in the list.</remarks>
+        protected bool LookaheadUntil(Func<TSymbol, IEnumerable<TSymbol>, bool> condition)
+        {
+            if (condition == null)
+            {
+                throw new ArgumentNullException(nameof(condition));
+            }
+
+            bool matchFound = false;
+
+            // We add 1 in order to store the current symbol.
+            var symbols = new List<TSymbol>();
+            symbols.Add(CurrentSymbol);
+
+            while (true)
+            {
+                if (!NextToken())
+                {
+                    break;
+                }
+
+                symbols.Add(CurrentSymbol);
+                if (condition(CurrentSymbol, symbols.Reverse<TSymbol>()))
+                {
+                    matchFound = true;
+                    break;
+                }
+            }
+
+            // Restore Tokenizer's location to where it was pointing before the look-ahead.
+            for (var i = symbols.Count - 1; i >= 0; i--)
+            {
+                PutBack(symbols[i]);
+            }
+
+            // The PutBacks above will set CurrentSymbol to null. EnsureCurrent will set our CurrentSymbol to the
+            // next symbol.
+            EnsureCurrent();
+
+            return matchFound;
+        }
+
         protected internal bool NextToken()
         {
             PreviousSymbol = CurrentSymbol;
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
index f8d4b0fcd9..5d3d46a831 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
@@ -419,9 +419,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             ParseBlockTest(
                 "<!--<foo>",
                 new MarkupBlock(
-                    new HtmlCommentBlock(Factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None)),
-                    Factory.Markup("<foo>").Accepts(AcceptedCharactersInternal.WhiteSpace),
-                    Factory.EmptyHtml()));
+                    Factory.Markup("<!--<foo>").Accepts(AcceptedCharactersInternal.None)));
         }
 
         [Fact]
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs
index 9f0e11218b..b7f5eeb87d 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlDocumentTest.cs
@@ -219,8 +219,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     Factory.Markup("Foo Baz"),
                     BlockFactory.HtmlCommentBlock("Foo"),
                     Factory.Markup("Bar"),
-                    new HtmlCommentBlock(Factory.Markup("<!--").Accepts(AcceptedCharactersInternal.None)),
-                    Factory.Markup("F> Qux").Accepts(AcceptedCharactersInternal.WhiteSpace)));
+                    Factory.Markup("<!--F> Qux")));
         }
 
         [Fact]

From 632c9dead748364837d3a27736feea0fc53c308e Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Wed, 7 Mar 2018 14:52:33 -0800
Subject: [PATCH 26/34] Added tests for the LookaheadUntil method

---
 .../Legacy/TokenizerLookaheadTest.cs          | 99 +++++++++++++++++++
 1 file changed, 99 insertions(+)

diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
index 6abd70ad3e..a9ac4be740 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
@@ -56,6 +56,83 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             Assert.Equal("pre-existing values", tokenizer.Buffer.ToString(), StringComparer.Ordinal);
         }
 
+        [Fact]
+        public void LookaheadUntil_PassesThePreviousSymbolsInReverseOrder()
+        {
+            // Arrange
+            var source = TestRazorSourceDocument.Create("asdf--fvd--<");
+            var options = RazorParserOptions.CreateDefault();
+            var context = new ParserContext(source, options);
+
+            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+
+            // Act
+            Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
+            var i = 3;
+            var symbolFound = tokenizer.LookaheadUntil((s, p) =>
+            {
+                symbols.Push(s);
+                return --i == 0;
+            });
+
+            // Assert
+            Assert.Equal(3, symbols.Count);
+            Assert.Equal(new HtmlSymbol("fvd", HtmlSymbolType.Text), symbols.Pop());
+            Assert.Equal(new HtmlSymbol("--", HtmlSymbolType.DoubleHyphen), symbols.Pop());
+            Assert.Equal(new HtmlSymbol("asdf", HtmlSymbolType.Text), symbols.Pop());
+        }
+
+        [Fact]
+        public void LookaheadUntil_ReturnsFalseAfterIteratingOverAllSymbolsIfConditionIsNotMet()
+        {
+            // Arrange
+            var source = TestRazorSourceDocument.Create("asdf--fvd");
+            var options = RazorParserOptions.CreateDefault();
+            var context = new ParserContext(source, options);
+
+            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+
+            // Act
+            Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
+            var symbolFound = tokenizer.LookaheadUntil((s, p) =>
+            {
+                symbols.Push(s);
+                return false;
+            });
+
+            // Assert
+            Assert.False(symbolFound);
+            Assert.Equal(3, symbols.Count);
+            Assert.Equal(new HtmlSymbol("fvd", HtmlSymbolType.Text), symbols.Pop());
+            Assert.Equal(new HtmlSymbol("--", HtmlSymbolType.DoubleHyphen), symbols.Pop());
+            Assert.Equal(new HtmlSymbol("asdf", HtmlSymbolType.Text), symbols.Pop());
+        }
+
+        [Fact]
+        public void LookaheadUntil_ReturnsTrueAndBreaksIteration()
+        {
+            // Arrange
+            var source = TestRazorSourceDocument.Create("asdf--fvd");
+            var options = RazorParserOptions.CreateDefault();
+            var context = new ParserContext(source, options);
+
+            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+
+            // Act
+            Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
+            var symbolFound = tokenizer.LookaheadUntil((s, p) =>
+            {
+                symbols.Push(s);
+                return s.Type == HtmlSymbolType.DoubleHyphen;
+            });
+
+            // Assert
+            Assert.True(symbolFound);
+            Assert.Equal(2, symbols.Count);
+            Assert.Equal(new HtmlSymbol("--", HtmlSymbolType.DoubleHyphen), symbols.Pop());
+            Assert.Equal(new HtmlSymbol("asdf", HtmlSymbolType.Text), symbols.Pop());
+        }
+
         private class ExposedTokenizer : Tokenizer<CSharpSymbol, CSharpSymbolType>
         {
             public ExposedTokenizer(string input)
@@ -116,5 +193,27 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 throw new NotImplementedException();
             }
         }
+
+        private class TestTokenizerBackedParser : TokenizerBackedParser<HtmlTokenizer, HtmlSymbol, HtmlSymbolType>
+        {
+            internal TestTokenizerBackedParser(LanguageCharacteristics<HtmlTokenizer, HtmlSymbol, HtmlSymbolType> language, ParserContext context) : base(language, context)
+            {
+            }
+
+            public override void ParseBlock()
+            {
+                throw new NotImplementedException();
+            }
+
+            protected override bool SymbolTypeEquals(HtmlSymbolType x, HtmlSymbolType y)
+            {
+                throw new NotImplementedException();
+            }
+
+            internal new bool LookaheadUntil(Func<HtmlSymbol, IEnumerable<HtmlSymbol>, bool> condition)
+            {
+                return base.LookaheadUntil(condition);
+            }
+        }
     }
 }

From 32e2c533c701ff432569ddd766614e95ee9b4475 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Wed, 7 Mar 2018 16:34:12 -0800
Subject: [PATCH 27/34] Naming improvements and test code cleanup

---
 .../Legacy/HtmlMarkupParser.cs                | 12 ++++----
 .../Legacy/TokenizerLookaheadTest.cs          | 28 +++++++++----------
 2 files changed, 19 insertions(+), 21 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index 2fe84b5a33..fb5237866e 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -614,8 +614,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 {
                     if (NextIs(HtmlSymbolType.CloseAngle))
                     {
-                        // We're at the end of a comment. check the condition 2.3 to make sure the text ending is allowed.
-                        isValidComment = !EndsWithSymbolsSequence(p, HtmlSymbolType.OpenAngle, HtmlSymbolType.Bang, HtmlSymbolType.DoubleHyphen);
+                        // Check condition 2.3: We're at the end of a comment. Check to make sure the text ending is allowed.
+                        isValidComment = !SymbolSequenceEndsWithItems(p, HtmlSymbolType.OpenAngle, HtmlSymbolType.Bang, HtmlSymbolType.DoubleHyphen);
                         breakLookahead = true;
                     }
                     else if (NextIs(ns => IsDashSymbol(ns) && NextIs(HtmlSymbolType.CloseAngle)))
@@ -645,17 +645,17 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return isValidComment;
         }
 
-        private bool EndsWithSymbolsSequence(IEnumerable<HtmlSymbol> symbols, params HtmlSymbolType[] sequenceToMatchWith)
+        internal static bool SymbolSequenceEndsWithItems(IEnumerable<HtmlSymbol> sequence, params HtmlSymbolType[] items)
         {
-            int index = sequenceToMatchWith.Length;
-            foreach (var previousSymbol in symbols)
+            int index = items.Length;
+            foreach (var previousSymbol in sequence)
             {
                 if (index == 0)
                 {
                     break;
                 }
 
-                if (sequenceToMatchWith[--index] != previousSymbol.Type)
+                if (items[--index] != previousSymbol.Type)
                     return false;
             }
 
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
index a9ac4be740..74d0c075f3 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
@@ -60,11 +60,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         public void LookaheadUntil_PassesThePreviousSymbolsInReverseOrder()
         {
             // Arrange
-            var source = TestRazorSourceDocument.Create("asdf--fvd--<");
-            var options = RazorParserOptions.CreateDefault();
-            var context = new ParserContext(source, options);
-
-            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+            var tokenizer = CreateContentTokenizer("asdf--fvd--<");
 
             // Act
             Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
@@ -86,11 +82,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         public void LookaheadUntil_ReturnsFalseAfterIteratingOverAllSymbolsIfConditionIsNotMet()
         {
             // Arrange
-            var source = TestRazorSourceDocument.Create("asdf--fvd");
-            var options = RazorParserOptions.CreateDefault();
-            var context = new ParserContext(source, options);
-
-            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+            var tokenizer = CreateContentTokenizer("asdf--fvd");
 
             // Act
             Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
@@ -112,11 +104,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         public void LookaheadUntil_ReturnsTrueAndBreaksIteration()
         {
             // Arrange
-            var source = TestRazorSourceDocument.Create("asdf--fvd");
-            var options = RazorParserOptions.CreateDefault();
-            var context = new ParserContext(source, options);
-
-            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+            var tokenizer = CreateContentTokenizer("asdf--fvd");
 
             // Act
             Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
@@ -133,6 +121,16 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             Assert.Equal(new HtmlSymbol("asdf", HtmlSymbolType.Text), symbols.Pop());
         }
 
+        private static TestTokenizerBackedParser CreateContentTokenizer(string content)
+        {
+            var source = TestRazorSourceDocument.Create(content);
+            var options = RazorParserOptions.CreateDefault();
+            var context = new ParserContext(source, options);
+
+            var tokenizer = new TestTokenizerBackedParser(HtmlLanguageCharacteristics.Instance, context);
+            return tokenizer;
+        }
+
         private class ExposedTokenizer : Tokenizer<CSharpSymbol, CSharpSymbolType>
         {
             public ExposedTokenizer(string input)

From 7357fa04eab7b18e72647d2368204b06feb9dc6d Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Thu, 8 Mar 2018 13:29:18 -0800
Subject: [PATCH 28/34] Applied PR feedback (unit testst will be added as part
 of a separate commit)

---
 .../Legacy/HtmlMarkupParser.cs                | 45 +++++++++----------
 .../Legacy/TagHelperParseTreeRewriter.cs      | 43 +++++++++---------
 .../Legacy/TokenizerBackedParser.cs           |  3 +-
 3 files changed, 45 insertions(+), 46 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index fb5237866e..dcd0254c29 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -496,6 +496,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 {
                     using (Context.Builder.StartBlock(BlockKindInternal.HtmlComment))
                     {
+                        // Accept the double-hyphen symbol at the beginning of the comment block.
                         AcceptAndMoveNext();
                         Output(SpanKindInternal.Markup, AcceptedCharactersInternal.None);
 
@@ -503,25 +504,22 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         while (!EndOfFile)
                         {
                             SkipToAndParseCode(HtmlSymbolType.DoubleHyphen);
-                            if (At(HtmlSymbolType.DoubleHyphen))
+                            var lastDoubleHyphen = AcceptAllButLastDoubleHypens();
+
+                            if (At(HtmlSymbolType.CloseAngle))
                             {
-                                var lastDoubleHyphen = AcceptAllButLastDoubleHypens();
+                                // Output the content in the comment block as a separate markup
+                                Output(SpanKindInternal.Markup, AcceptedCharactersInternal.WhiteSpace);
 
-                                if (At(HtmlSymbolType.CloseAngle))
-                                {
-                                    // Output the content in the comment block as a separate markup
-                                    Output(SpanKindInternal.Markup, AcceptedCharactersInternal.WhiteSpace);
-
-                                    // This is the end of a comment block
-                                    Accept(lastDoubleHyphen);
-                                    AcceptAndMoveNext();
-                                    Output(SpanKindInternal.Markup, AcceptedCharactersInternal.None);
-                                    return true;
-                                }
-                                else if (lastDoubleHyphen != null)
-                                {
-                                    Accept(lastDoubleHyphen);
-                                }
+                                // This is the end of a comment block
+                                Accept(lastDoubleHyphen);
+                                AcceptAndMoveNext();
+                                Output(SpanKindInternal.Markup, AcceptedCharactersInternal.None);
+                                return true;
+                            }
+                            else if (lastDoubleHyphen != null)
+                            {
+                                Accept(lastDoubleHyphen);
                             }
                         }
                     }
@@ -606,28 +604,27 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             }
 
             // Check condition 2.2
-            bool isValidComment = false;
+            var isValidComment = false;
             LookaheadUntil((s, p) =>
             {
-                bool breakLookahead = false;
                 if (s.Type == HtmlSymbolType.DoubleHyphen)
                 {
                     if (NextIs(HtmlSymbolType.CloseAngle))
                     {
                         // Check condition 2.3: We're at the end of a comment. Check to make sure the text ending is allowed.
                         isValidComment = !SymbolSequenceEndsWithItems(p, HtmlSymbolType.OpenAngle, HtmlSymbolType.Bang, HtmlSymbolType.DoubleHyphen);
-                        breakLookahead = true;
+                        return true;
                     }
                     else if (NextIs(ns => IsDashSymbol(ns) && NextIs(HtmlSymbolType.CloseAngle)))
                     {
                         // This is also a valid closing comment case, as the dashes lookup is treated with DoubleHyphen symbols first.
                         isValidComment = true;
-                        breakLookahead = true;
+                        return true;
                     }
                     else if (NextIs(ns => ns.Type == HtmlSymbolType.Bang && NextIs(HtmlSymbolType.CloseAngle)))
                     {
                         isValidComment = false;
-                        breakLookahead = true;
+                        return true;
                     }
                 }
                 else if (s.Type == HtmlSymbolType.OpenAngle)
@@ -635,11 +632,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     if (NextIs(ns => ns.Type == HtmlSymbolType.Bang && NextIs(HtmlSymbolType.DoubleHyphen)))
                     {
                         isValidComment = false;
-                        breakLookahead = true;
+                        return true;
                     }
                 }
 
-                return breakLookahead;
+                return false;
             });
 
             return isValidComment;
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
index a4c9906b1a..d5d65c2985 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs
@@ -488,28 +488,31 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            var isDisallowedContent = true;
-            if (_featureFlags.AllowHtmlCommentsInTagHelpers)
+            if (HasAllowedChildren())
             {
-                isDisallowedContent = !IsComment(child) && child.Kind != SpanKindInternal.Transition && child.Kind != SpanKindInternal.Code;
-            }
-
-            if (HasAllowedChildren() && isDisallowedContent)
-            {
-                var content = child.Content;
-                if (!string.IsNullOrWhiteSpace(content))
+                var isDisallowedContent = true;
+                if (_featureFlags.AllowHtmlCommentsInTagHelpers)
                 {
-                    var trimmedStart = content.TrimStart();
-                    var whitespace = content.Substring(0, content.Length - trimmedStart.Length);
-                    var errorStart = SourceLocationTracker.Advance(child.Start, whitespace);
-                    var length = trimmedStart.TrimEnd().Length;
-                    var allowedChildren = _currentTagHelperTracker.AllowedChildren;
-                    var allowedChildrenString = string.Join(", ", allowedChildren);
-                    errorSink.OnError(
-                        RazorDiagnosticFactory.CreateTagHelper_CannotHaveNonTagContent(
-                            new SourceSpan(errorStart, length),
-                            _currentTagHelperTracker.TagName,
-                            allowedChildrenString));
+                    isDisallowedContent = !IsComment(child) && child.Kind != SpanKindInternal.Transition && child.Kind != SpanKindInternal.Code;
+                }
+
+                if (isDisallowedContent)
+                {
+                    var content = child.Content;
+                    if (!string.IsNullOrWhiteSpace(content))
+                    {
+                        var trimmedStart = content.TrimStart();
+                        var whitespace = content.Substring(0, content.Length - trimmedStart.Length);
+                        var errorStart = SourceLocationTracker.Advance(child.Start, whitespace);
+                        var length = trimmedStart.TrimEnd().Length;
+                        var allowedChildren = _currentTagHelperTracker.AllowedChildren;
+                        var allowedChildrenString = string.Join(", ", allowedChildren);
+                        errorSink.OnError(
+                            RazorDiagnosticFactory.CreateTagHelper_CannotHaveNonTagContent(
+                                new SourceSpan(errorStart, length),
+                                _currentTagHelperTracker.TagName,
+                                allowedChildrenString));
+                    }
                 }
             }
         }
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
index 1819407076..98763ad0a3 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
@@ -122,9 +122,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 throw new ArgumentNullException(nameof(condition));
             }
 
-            bool matchFound = false;
+            var matchFound = false;
 
-            // We add 1 in order to store the current symbol.
             var symbols = new List<TSymbol>();
             symbols.Add(CurrentSymbol);
 

From faccd90aa54014892a09ff443bd42f978e73a8ef Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Thu, 8 Mar 2018 16:36:56 -0800
Subject: [PATCH 29/34] Added unit-tests to validate new methods

---
 .../Legacy/HtmlMarkupParser.cs                |  11 +-
 .../Legacy/TokenizerBackedParser.cs           |  16 +-
 .../Legacy/HtmlMarkupParserTests.cs           | 171 ++++++++++++++++++
 3 files changed, 187 insertions(+), 11 deletions(-)
 create mode 100644 test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index dcd0254c29..e9dcf36d5c 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -541,7 +541,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return false;
         }
 
-        private HtmlSymbol AcceptAllButLastDoubleHypens()
+        protected HtmlSymbol AcceptAllButLastDoubleHypens()
         {
             var lastDoubleHyphen = CurrentSymbol;
             AcceptWhile(s =>
@@ -552,11 +552,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     return true;
                 }
 
-                NextToken();
-                EnsureCurrent();
                 return false;
             });
 
+            NextToken();
+            EnsureCurrent();
+
             if (At(HtmlSymbolType.Text) && IsDashSymbol(CurrentSymbol))
             {
                 // Doing this here to maintain the order of symbols
@@ -572,12 +573,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return lastDoubleHyphen;
         }
 
-        private static bool IsDashSymbol(HtmlSymbol symbol)
+        internal static bool IsDashSymbol(HtmlSymbol symbol)
         {
             return string.Equals(symbol.Content, "-", StringComparison.Ordinal);
         }
 
-        private bool IsHtmlCommentAhead()
+        protected bool IsHtmlCommentAhead()
         {
             /*
              * From HTML5 Specification, available at http://www.w3.org/TR/html52/syntax.html#comments
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
index 98763ad0a3..2b6e55090a 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
@@ -300,12 +300,16 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         protected internal bool NextIs(Func<TSymbol, bool> condition)
         {
             var cur = CurrentSymbol;
-            NextToken();
-            var result = condition(CurrentSymbol);
-            PutCurrentBack();
-            PutBack(cur);
-            EnsureCurrent();
-            return result;
+            if (NextToken())
+            {
+                var result = condition(CurrentSymbol);
+                PutCurrentBack();
+                PutBack(cur);
+                EnsureCurrent();
+                return result;
+            }
+
+            return false;
         }
 
         protected internal bool Was(TSymbolType type)
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs
new file mode 100644
index 0000000000..db47d47b73
--- /dev/null
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs
@@ -0,0 +1,171 @@
+using System.Collections.Generic;
+using Microsoft.AspNetCore.Razor.Language.Legacy;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
+{
+    public class HtmlMarkupParserTests
+    {
+        private static readonly HtmlSymbol doubleHyphenSymbol = new HtmlSymbol("--", HtmlSymbolType.DoubleHyphen);
+
+        public static IEnumerable<object[]> NonDashSymbols
+        {
+            get
+            {
+                yield return new[] { new HtmlSymbol("--", HtmlSymbolType.DoubleHyphen) };
+                yield return new[] { new HtmlSymbol("asdf", HtmlSymbolType.Text) };
+                yield return new[] { new HtmlSymbol(">", HtmlSymbolType.CloseAngle) };
+                yield return new[] { new HtmlSymbol("<", HtmlSymbolType.OpenAngle) };
+                yield return new[] { new HtmlSymbol("!", HtmlSymbolType.Bang) };
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(NonDashSymbols))]
+        public void IsDashSymbol_ReturnsFalseForNonDashSymbol(object symbol)
+        {
+            // Arrange
+            HtmlSymbol convertedSymbol = (HtmlSymbol)symbol;
+
+            // Act & Assert
+            Assert.False(HtmlMarkupParser.IsDashSymbol(convertedSymbol));
+        }
+
+        [Fact]
+        public void IsDashSymbol_ReturnsTrueForADashSymbol()
+        {
+            // Arrange
+            HtmlSymbol dashSymbol = new HtmlSymbol("-", HtmlSymbolType.Text);
+
+            // Act & Assert
+            Assert.True(HtmlMarkupParser.IsDashSymbol(dashSymbol));
+        }
+
+        [Fact]
+        public void AcceptAllButLastDoubleHypens_ReturnsTheOnlyDoubleHyphenSymbol()
+        {
+            // Arrange
+            TestHtmlMarkupParser sut = CreateTestParserForContent("-->");
+
+            // Act
+            HtmlSymbol symbol = sut.AcceptAllButLastDoubleHypens();
+
+            // Assert
+            Assert.Equal(doubleHyphenSymbol, symbol);
+            Assert.True(sut.At(HtmlSymbolType.CloseAngle));
+            Assert.Equal(doubleHyphenSymbol, sut.PreviousSymbol);
+        }
+
+        [Fact]
+        public void AcceptAllButLastDoubleHypens_ReturnsTheDoubleHyphenSymbolAfterAcceptingTheDash()
+        {
+            // Arrange
+            TestHtmlMarkupParser sut = CreateTestParserForContent("--->");
+
+            // Act
+            HtmlSymbol symbol = sut.AcceptAllButLastDoubleHypens();
+
+            // Assert
+            Assert.Equal(doubleHyphenSymbol, symbol);
+            Assert.True(sut.At(HtmlSymbolType.CloseAngle));
+            Assert.True(HtmlMarkupParser.IsDashSymbol(sut.PreviousSymbol));
+        }
+
+        [Fact]
+        public void IsHtmlCommentAhead_ReturnsTrueForEmptyCommentTag()
+        {
+            // Arrange
+            TestHtmlMarkupParser sut = CreateTestParserForContent("---->");
+
+            // Act & Assert
+            Assert.True(sut.IsHtmlCommentAhead());
+        }
+
+        [Fact]
+        public void IsHtmlCommentAhead_ReturnsTrueForValidCommentTag()
+        {
+            // Arrange
+            TestHtmlMarkupParser sut = CreateTestParserForContent("-- Some comment content in here -->");
+
+            // Act & Assert
+            Assert.True(sut.IsHtmlCommentAhead());
+        }
+
+        [Fact]
+        public void IsHtmlCommentAhead_ReturnsTrueForValidCommentTagWithExtraDashesAtClosingTag()
+        {
+            // Arrange
+            TestHtmlMarkupParser sut = CreateTestParserForContent("-- Some comment content in here ----->");
+
+            // Act & Assert
+            Assert.True(sut.IsHtmlCommentAhead());
+        }
+
+        [Fact]
+        public void IsHtmlCommentAhead_ReturnsTrueForValidCommentTagWithExtraInfoAfter()
+        {
+            // Arrange
+            TestHtmlMarkupParser sut = CreateTestParserForContent("-- comment --> the first part is a valid comment without the Open angle and bang symbols");
+
+            // Act & Assert
+            Assert.True(sut.IsHtmlCommentAhead());
+        }
+
+        [Fact]
+        public void IsHtmlCommentAhead_ReturnsFalseForNotClosedComment()
+        {
+            // Arrange
+            TestHtmlMarkupParser sut = CreateTestParserForContent("-- not closed comment");
+
+            // Act & Assert
+            Assert.False(sut.IsHtmlCommentAhead());
+        }
+
+        [Fact]
+        public void IsHtmlCommentAhead_ReturnsFalseForCommentWithoutLastClosingAngle()
+        {
+            // Arrange
+            TestHtmlMarkupParser sut = CreateTestParserForContent("-- not closed comment--");
+
+            // Act & Assert
+            Assert.False(sut.IsHtmlCommentAhead());
+        }
+
+        private class TestHtmlMarkupParser : HtmlMarkupParser
+        {
+            public new HtmlSymbol PreviousSymbol
+            {
+                get => base.PreviousSymbol;
+            }
+
+            public new bool IsHtmlCommentAhead()
+            {
+                return base.IsHtmlCommentAhead();
+            }
+
+            public TestHtmlMarkupParser(ParserContext context) : base(context)
+            {
+                this.EnsureCurrent();
+            }
+
+            public new HtmlSymbol AcceptAllButLastDoubleHypens()
+            {
+                return base.AcceptAllButLastDoubleHypens();
+            }
+
+            public override void BuildSpan(SpanBuilder span, SourceLocation start, string content)
+            {
+                base.BuildSpan(span, start, content);
+            }
+        }
+
+        private static TestHtmlMarkupParser CreateTestParserForContent(string content)
+        {
+            var source = TestRazorSourceDocument.Create(content);
+            var options = RazorParserOptions.CreateDefault();
+            var context = new ParserContext(source, options);
+
+            return new TestHtmlMarkupParser(context);
+        }
+    }
+}

From 1318a835119529db22a0602bd0e603bf16f771c3 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Thu, 8 Mar 2018 17:13:34 -0800
Subject: [PATCH 30/34] Fixed the NextIs method to put back the symbol, when at
 the end of the file

---
 .../Legacy/TokenizerBackedParser.cs                          | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
index 2b6e55090a..7911380d0f 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
@@ -308,6 +308,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 EnsureCurrent();
                 return result;
             }
+            else
+            {
+                PutBack(cur);
+                EnsureCurrent();
+            }
 
             return false;
         }

From 6c8c6a777cd78b332298c31e63e8d9e34919b1a8 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Fri, 9 Mar 2018 09:16:17 -0800
Subject: [PATCH 31/34] - Clarified the code where the comment content ending
 is checked to be allowed or not. - Added more unit tests

---
 .../Legacy/HtmlMarkupParser.cs                | 25 +++++---
 .../Legacy/TokenizerBackedParser.cs           |  2 +-
 .../Legacy/HtmlMarkupParserTests.cs           | 61 +++++++++++++++----
 .../Legacy/TokenizerLookaheadTest.cs          | 24 +++++---
 4 files changed, 79 insertions(+), 33 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index e9dcf36d5c..39841d4835 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -613,7 +613,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                     if (NextIs(HtmlSymbolType.CloseAngle))
                     {
                         // Check condition 2.3: We're at the end of a comment. Check to make sure the text ending is allowed.
-                        isValidComment = !SymbolSequenceEndsWithItems(p, HtmlSymbolType.OpenAngle, HtmlSymbolType.Bang, HtmlSymbolType.DoubleHyphen);
+                        isValidComment = !IsCommentContentDisallowed(p);
                         return true;
                     }
                     else if (NextIs(ns => IsDashSymbol(ns) && NextIs(HtmlSymbolType.CloseAngle)))
@@ -643,21 +643,28 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return isValidComment;
         }
 
-        internal static bool SymbolSequenceEndsWithItems(IEnumerable<HtmlSymbol> sequence, params HtmlSymbolType[] items)
+        /// <summary>
+        /// Verifies, that the sequence doesn't end with the "&lt;!-" HtmlSymbols. Note, the first symbol is an opening bracket symbol
+        /// </summary>
+        internal static bool IsCommentContentDisallowed(IEnumerable<HtmlSymbol> sequence)
         {
-            int index = items.Length;
-            foreach (var previousSymbol in sequence)
+            var reversedSequence = sequence.Reverse();
+            var disallowEnding = new[] { new HtmlSymbol("-", HtmlSymbolType.Text), new HtmlSymbol("!", HtmlSymbolType.Bang), new HtmlSymbol("<", HtmlSymbolType.OpenAngle) };
+            var index = 0;
+            foreach (var item in reversedSequence)
             {
-                if (index == 0)
+                if (!item.Equals(disallowEnding[index++]))
                 {
-                    break;
+                    return false;
                 }
 
-                if (items[--index] != previousSymbol.Type)
-                    return false;
+                if (index == disallowEnding.Length)
+                {
+                    return true;
+                }
             }
 
-            return index == 0;
+            return false;
         }
 
         private bool CData()
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
index 7911380d0f..01fa0b11e1 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/TokenizerBackedParser.cs
@@ -135,7 +135,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 }
 
                 symbols.Add(CurrentSymbol);
-                if (condition(CurrentSymbol, symbols.Reverse<TSymbol>()))
+                if (condition(CurrentSymbol, symbols))
                 {
                     matchFound = true;
                     break;
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs
index db47d47b73..c3e0cb87e1 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs
@@ -1,4 +1,6 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
+using System.Linq;
 using Microsoft.AspNetCore.Razor.Language.Legacy;
 using Xunit;
 
@@ -25,7 +27,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
         public void IsDashSymbol_ReturnsFalseForNonDashSymbol(object symbol)
         {
             // Arrange
-            HtmlSymbol convertedSymbol = (HtmlSymbol)symbol;
+            var convertedSymbol = (HtmlSymbol)symbol;
 
             // Act & Assert
             Assert.False(HtmlMarkupParser.IsDashSymbol(convertedSymbol));
@@ -35,7 +37,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
         public void IsDashSymbol_ReturnsTrueForADashSymbol()
         {
             // Arrange
-            HtmlSymbol dashSymbol = new HtmlSymbol("-", HtmlSymbolType.Text);
+            var dashSymbol = new HtmlSymbol("-", HtmlSymbolType.Text);
 
             // Act & Assert
             Assert.True(HtmlMarkupParser.IsDashSymbol(dashSymbol));
@@ -45,10 +47,10 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
         public void AcceptAllButLastDoubleHypens_ReturnsTheOnlyDoubleHyphenSymbol()
         {
             // Arrange
-            TestHtmlMarkupParser sut = CreateTestParserForContent("-->");
+            var sut = CreateTestParserForContent("-->");
 
             // Act
-            HtmlSymbol symbol = sut.AcceptAllButLastDoubleHypens();
+            var symbol = sut.AcceptAllButLastDoubleHypens();
 
             // Assert
             Assert.Equal(doubleHyphenSymbol, symbol);
@@ -60,10 +62,10 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
         public void AcceptAllButLastDoubleHypens_ReturnsTheDoubleHyphenSymbolAfterAcceptingTheDash()
         {
             // Arrange
-            TestHtmlMarkupParser sut = CreateTestParserForContent("--->");
+            var sut = CreateTestParserForContent("--->");
 
             // Act
-            HtmlSymbol symbol = sut.AcceptAllButLastDoubleHypens();
+            var symbol = sut.AcceptAllButLastDoubleHypens();
 
             // Assert
             Assert.Equal(doubleHyphenSymbol, symbol);
@@ -75,7 +77,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
         public void IsHtmlCommentAhead_ReturnsTrueForEmptyCommentTag()
         {
             // Arrange
-            TestHtmlMarkupParser sut = CreateTestParserForContent("---->");
+            var sut = CreateTestParserForContent("---->");
 
             // Act & Assert
             Assert.True(sut.IsHtmlCommentAhead());
@@ -85,7 +87,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
         public void IsHtmlCommentAhead_ReturnsTrueForValidCommentTag()
         {
             // Arrange
-            TestHtmlMarkupParser sut = CreateTestParserForContent("-- Some comment content in here -->");
+            var sut = CreateTestParserForContent("-- Some comment content in here -->");
 
             // Act & Assert
             Assert.True(sut.IsHtmlCommentAhead());
@@ -95,7 +97,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
         public void IsHtmlCommentAhead_ReturnsTrueForValidCommentTagWithExtraDashesAtClosingTag()
         {
             // Arrange
-            TestHtmlMarkupParser sut = CreateTestParserForContent("-- Some comment content in here ----->");
+            var sut = CreateTestParserForContent("-- Some comment content in here ----->");
 
             // Act & Assert
             Assert.True(sut.IsHtmlCommentAhead());
@@ -105,7 +107,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
         public void IsHtmlCommentAhead_ReturnsTrueForValidCommentTagWithExtraInfoAfter()
         {
             // Arrange
-            TestHtmlMarkupParser sut = CreateTestParserForContent("-- comment --> the first part is a valid comment without the Open angle and bang symbols");
+            var sut = CreateTestParserForContent("-- comment --> the first part is a valid comment without the Open angle and bang symbols");
 
             // Act & Assert
             Assert.True(sut.IsHtmlCommentAhead());
@@ -115,7 +117,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
         public void IsHtmlCommentAhead_ReturnsFalseForNotClosedComment()
         {
             // Arrange
-            TestHtmlMarkupParser sut = CreateTestParserForContent("-- not closed comment");
+            var sut = CreateTestParserForContent("-- not closed comment");
 
             // Act & Assert
             Assert.False(sut.IsHtmlCommentAhead());
@@ -125,12 +127,45 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
         public void IsHtmlCommentAhead_ReturnsFalseForCommentWithoutLastClosingAngle()
         {
             // Arrange
-            TestHtmlMarkupParser sut = CreateTestParserForContent("-- not closed comment--");
+            var sut = CreateTestParserForContent("-- not closed comment--");
 
             // Act & Assert
             Assert.False(sut.IsHtmlCommentAhead());
         }
 
+        [Fact]
+        public void IsCommentContentDisallowed_ReturnsFalseForAllowedContent()
+        {
+            // Arrange
+            var expectedSymbol1 = new HtmlSymbol("a", HtmlSymbolType.Text);
+            var sequence = Enumerable.Range((int)'a', 26).Select(item => new HtmlSymbol(((char)item).ToString(), HtmlSymbolType.Text));
+
+            // Act & Assert
+            Assert.False(HtmlMarkupParser.IsCommentContentDisallowed(sequence));
+        }
+
+        [Fact]
+        public void IsCommentContentDisallowed_ReturnsTrueForDisallowedContent()
+        {
+            // Arrange
+            var expectedSymbol1 = new HtmlSymbol("a", HtmlSymbolType.Text);
+            var sequence = new[] { new HtmlSymbol("<", HtmlSymbolType.OpenAngle), new HtmlSymbol("!", HtmlSymbolType.Bang), new HtmlSymbol("-", HtmlSymbolType.Text) };
+
+            // Act & Assert
+            Assert.True(HtmlMarkupParser.IsCommentContentDisallowed(sequence));
+        }
+
+        [Fact]
+        public void IsCommentContentDisallowed_ReturnsFalseForEmptyContent()
+        {
+            // Arrange
+            var expectedSymbol1 = new HtmlSymbol("a", HtmlSymbolType.Text);
+            var sequence = Array.Empty<HtmlSymbol>();
+
+            // Act & Assert
+            Assert.False(HtmlMarkupParser.IsCommentContentDisallowed(sequence));
+        }
+
         private class TestHtmlMarkupParser : HtmlMarkupParser
         {
             public new HtmlSymbol PreviousSymbol
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
index 74d0c075f3..aa9ea560cc 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TokenizerLookaheadTest.cs
@@ -3,7 +3,7 @@
 
 using System;
 using System.Collections.Generic;
-using System.IO;
+using System.Linq;
 using System.Text;
 using Xunit;
 
@@ -57,25 +57,29 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         }
 
         [Fact]
-        public void LookaheadUntil_PassesThePreviousSymbolsInReverseOrder()
+        public void LookaheadUntil_PassesThePreviousSymbolsInTheSameOrder()
         {
             // Arrange
             var tokenizer = CreateContentTokenizer("asdf--fvd--<");
 
             // Act
-            Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
             var i = 3;
+            IEnumerable<HtmlSymbol> previousSymbols = null;
             var symbolFound = tokenizer.LookaheadUntil((s, p) =>
             {
-                symbols.Push(s);
+                previousSymbols = p;
                 return --i == 0;
             });
 
             // Assert
-            Assert.Equal(3, symbols.Count);
-            Assert.Equal(new HtmlSymbol("fvd", HtmlSymbolType.Text), symbols.Pop());
-            Assert.Equal(new HtmlSymbol("--", HtmlSymbolType.DoubleHyphen), symbols.Pop());
-            Assert.Equal(new HtmlSymbol("asdf", HtmlSymbolType.Text), symbols.Pop());
+            Assert.Equal(4, previousSymbols.Count());
+
+            // For the very first element, there will be no previous items, so null is expected
+            var orderIndex = 0;
+            Assert.Null(previousSymbols.ElementAt(orderIndex++));
+            Assert.Equal(new HtmlSymbol("asdf", HtmlSymbolType.Text), previousSymbols.ElementAt(orderIndex++));
+            Assert.Equal(new HtmlSymbol("--", HtmlSymbolType.DoubleHyphen), previousSymbols.ElementAt(orderIndex++));
+            Assert.Equal(new HtmlSymbol("fvd", HtmlSymbolType.Text), previousSymbols.ElementAt(orderIndex++));
         }
 
         [Fact]
@@ -85,7 +89,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             var tokenizer = CreateContentTokenizer("asdf--fvd");
 
             // Act
-            Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
+            var symbols = new Stack<HtmlSymbol>();
             var symbolFound = tokenizer.LookaheadUntil((s, p) =>
             {
                 symbols.Push(s);
@@ -107,7 +111,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             var tokenizer = CreateContentTokenizer("asdf--fvd");
 
             // Act
-            Stack<HtmlSymbol> symbols = new Stack<HtmlSymbol>();
+            var symbols = new Stack<HtmlSymbol>();
             var symbolFound = tokenizer.LookaheadUntil((s, p) =>
             {
                 symbols.Push(s);

From e8eb3b7b1c7c373f36febe6cd7e6a8351da7cfd2 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Fri, 9 Mar 2018 11:52:23 -0800
Subject: [PATCH 32/34] Added extra test to cover extra dash in closing comment

---
 .../Legacy/HtmlBlockTest.cs                               | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
index 5d3d46a831..3abd53b105 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlBlockTest.cs
@@ -333,7 +333,13 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         [Fact]
         public void ParseBlockSupportsCommentAsBlock()
         {
-            ParseBlockTest("<!-- foo -->", new MarkupBlock( BlockFactory.HtmlCommentBlock(" foo ")));
+            ParseBlockTest("<!-- foo -->", new MarkupBlock(BlockFactory.HtmlCommentBlock(" foo ")));
+        }
+
+        [Fact]
+        public void ParseBlockSupportsCommentWithExtraDashAsBlock()
+        {
+            ParseBlockTest("<!-- foo --->", new MarkupBlock(BlockFactory.HtmlCommentBlock(" foo -")));
         }
 
         [Fact]

From 3e22c169304a8c23bb108dbf063056ae4b890cd4 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Fri, 9 Mar 2018 17:18:57 -0800
Subject: [PATCH 33/34] Added extra tests for non-covered scenarios: - For
 older version of Razor the HTML comments will be complained about by
 TahHelperRewriter - RazorParserFeatureFlags tests now ensure that
 AllowHtmlCommentsInTagHelpers is true in 2.1 version  and false in older
 versions - Added extra test for IsHtmlCommentAhead to make sure Razor code
 transition is allowed in comment tag - Moved the unallowed html comment
 ending to a static array.

---
 .../Legacy/HtmlMarkupParser.cs                |  7 ++-
 .../Legacy/HtmlMarkupParserTests.cs           | 10 ++++
 .../Legacy/TagHelperParseTreeRewriterTest.cs  | 59 +++++++++++++++++--
 .../RazorParserFeatureFlagsTest.cs            |  2 +
 4 files changed, 71 insertions(+), 7 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index 39841d4835..48c79c83e1 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -12,6 +12,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
     {
         private const string ScriptTagName = "script";
 
+        private static readonly HtmlSymbol[] nonAllowedHtmlCommentEnding = new[] { new HtmlSymbol("-", HtmlSymbolType.Text), new HtmlSymbol("!", HtmlSymbolType.Bang), new HtmlSymbol("<", HtmlSymbolType.OpenAngle) };
+
         private static readonly char[] ValidAfterTypeAttributeNameCharacters = { ' ', '\t', '\r', '\n', '\f', '=' };
         private SourceLocation _lastTagStart = SourceLocation.Zero;
         private HtmlSymbol _bufferedOpenAngle;
@@ -649,16 +651,15 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         internal static bool IsCommentContentDisallowed(IEnumerable<HtmlSymbol> sequence)
         {
             var reversedSequence = sequence.Reverse();
-            var disallowEnding = new[] { new HtmlSymbol("-", HtmlSymbolType.Text), new HtmlSymbol("!", HtmlSymbolType.Bang), new HtmlSymbol("<", HtmlSymbolType.OpenAngle) };
             var index = 0;
             foreach (var item in reversedSequence)
             {
-                if (!item.Equals(disallowEnding[index++]))
+                if (!item.Equals(nonAllowedHtmlCommentEnding[index++]))
                 {
                     return false;
                 }
 
-                if (index == disallowEnding.Length)
+                if (index == nonAllowedHtmlCommentEnding.Length)
                 {
                     return true;
                 }
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs
index c3e0cb87e1..a40ec2e422 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs
@@ -133,6 +133,16 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
             Assert.False(sut.IsHtmlCommentAhead());
         }
 
+        [Fact]
+        public void IsHtmlCommentAhead_ReturnsTrueForCommentWithCodeInside()
+        {
+            // Arrange
+            var sut = CreateTestParserForContent("-- not closed @DateTime.Now comment-->");
+
+            // Act & Assert
+            Assert.True(sut.IsHtmlCommentAhead());
+        }
+
         [Fact]
         public void IsCommentContentDisallowed_ReturnsFalseForAllowedContent()
         {
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
index 425b728716..3f37c82c4d 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs
@@ -1111,7 +1111,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         [Fact]
         public void Rewrite_AllowsSimpleHtmlCommentsAsChildren()
         {
-            // Arrangestring documentContent,
+            // Arrange
             IEnumerable<string> allowedChildren = new List<string> { "b" };
             string literal = "asdf";
             string commentOutput = "Hello World";
@@ -1148,10 +1148,61 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                 Array.Empty<RazorDiagnostic>());
         }
 
+        [Fact]
+        public void Rewrite_DoesntAllowSimpleHtmlCommentsAsChildrenWhenFeatureFlagIsOff()
+        {
+            // Arrange
+            Func<string, string, string, int, int, RazorDiagnostic> nestedTagError =
+                    (childName, parentName, allowed, location, length) =>
+                    RazorDiagnosticFactory.CreateTagHelper_InvalidNestedTag(
+                        new SourceSpan(absoluteIndex: location, lineIndex: 0, characterIndex: location, length: length), childName, parentName, allowed);
+            Func<string, string, int, int, RazorDiagnostic> nestedContentError =
+                (parentName, allowed, location, length) =>
+                RazorDiagnosticFactory.CreateTagHelper_CannotHaveNonTagContent(
+                    new SourceSpan(absoluteIndex: location, lineIndex: 0, characterIndex: location, length: length), parentName, allowed);
+
+            IEnumerable<string> allowedChildren = new List<string> { "b" };
+            string comment1 = "Hello";
+            string expectedOutput = $"<p><!--{comment1}--></p>";
+
+            var pTagHelperBuilder = TagHelperDescriptorBuilder
+                .Create("PTagHelper", "SomeAssembly")
+                .TagMatchingRuleDescriptor(rule => rule.RequireTagName("p"));
+            foreach (var childTag in allowedChildren)
+            {
+                pTagHelperBuilder.AllowChildTag(childTag);
+            }
+
+            var descriptors = new TagHelperDescriptor[]
+            {
+                pTagHelperBuilder.Build()
+            };
+
+            var factory = new SpanFactory();
+            var blockFactory = new BlockFactory(factory);
+
+            var expectedMarkup = new MarkupBlock(
+                new MarkupTagHelperBlock("p",
+                    blockFactory.HtmlCommentBlock(comment1)));
+
+            // Act & Assert
+            EvaluateData(
+                descriptors,
+                expectedOutput,
+                expectedMarkup,
+                new[]
+                {
+                    nestedContentError("p", "b", 3, 4),
+                    nestedContentError("p", "b", 7, 5),
+                    nestedContentError("p", "b", 12, 3),
+                },
+                featureFlags: RazorParserFeatureFlags.Create(RazorLanguageVersion.Version_2_0));
+        }
+
         [Fact]
         public void Rewrite_FailsForContentWithCommentsAsChildren()
         {
-            // Arrangestring documentContent,
+            // Arrange
             Func<string, string, string, int, int, RazorDiagnostic> nestedTagError =
                     (childName, parentName, allowed, location, length) =>
                     RazorDiagnosticFactory.CreateTagHelper_InvalidNestedTag(
@@ -1203,7 +1254,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         [Fact]
         public void Rewrite_AllowsRazorCommentsAsChildren()
         {
-            // Arrangestring documentContent,
+            // Arrange
             IEnumerable<string> allowedChildren = new List<string> { "b" };
             string literal = "asdf";
             string commentOutput = $"@*{literal}*@";
@@ -1248,7 +1299,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         [Fact]
         public void Rewrite_AllowsRazorMarkupInHtmlComment()
         {
-            // Arrangestring documentContent,
+            // Arrange
             IEnumerable<string> allowedChildren = new List<string> { "b" };
             string literal = "asdf";
             string part1 = "Hello ";
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/RazorParserFeatureFlagsTest.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/RazorParserFeatureFlagsTest.cs
index db57a33fdf..cfdb9f023d 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/RazorParserFeatureFlagsTest.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/RazorParserFeatureFlagsTest.cs
@@ -16,6 +16,7 @@ namespace Microsoft.AspNetCore.Razor.Language
 
             // Assert
             Assert.True(context.AllowMinimizedBooleanTagHelperAttributes);
+            Assert.True(context.AllowHtmlCommentsInTagHelpers);
         }
 
         [Fact]
@@ -26,6 +27,7 @@ namespace Microsoft.AspNetCore.Razor.Language
 
             // Assert
             Assert.False(context.AllowMinimizedBooleanTagHelperAttributes);
+            Assert.False(context.AllowHtmlCommentsInTagHelpers);
         }
     }
 }

From ae94c3c4524dda877fd4c3d3b893157c314f0435 Mon Sep 17 00:00:00 2001
From: Artak Mkrtchyan <artakm@corp.microsoft.com>
Date: Fri, 9 Mar 2018 18:18:16 -0800
Subject: [PATCH 34/34] - Updated naming for methods to be more intuitive. -
 Added extra tests for clarity - Added extra comments to clarify complex areas

---
 .../Legacy/BlockKindInternal.cs               |  1 -
 .../Legacy/HtmlMarkupParser.cs                | 40 +++++++++++--------
 .../Legacy/HtmlSymbol.cs                      |  2 +
 .../Legacy/HtmlMarkupParserTests.cs           | 40 ++++++++++++-------
 4 files changed, 51 insertions(+), 32 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/BlockKindInternal.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/BlockKindInternal.cs
index 9f9886164c..6c37427ca7 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/BlockKindInternal.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/BlockKindInternal.cs
@@ -19,7 +19,6 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         // Special
         Comment = 8,
         Tag = 9,
-
         HtmlComment = 10
     }
 }
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
index 48c79c83e1..a23adbb28f 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlMarkupParser.cs
@@ -12,7 +12,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
     {
         private const string ScriptTagName = "script";
 
-        private static readonly HtmlSymbol[] nonAllowedHtmlCommentEnding = new[] { new HtmlSymbol("-", HtmlSymbolType.Text), new HtmlSymbol("!", HtmlSymbolType.Bang), new HtmlSymbol("<", HtmlSymbolType.OpenAngle) };
+        private static readonly HtmlSymbol[] nonAllowedHtmlCommentEnding = new[] { HtmlSymbol.Hyphen, new HtmlSymbol("!", HtmlSymbolType.Bang), new HtmlSymbol("<", HtmlSymbolType.OpenAngle) };
+        private static readonly HtmlSymbol[] singleHyphenArray = new[] { HtmlSymbol.Hyphen };
 
         private static readonly char[] ValidAfterTypeAttributeNameCharacters = { ' ', '\t', '\r', '\n', '\f', '=' };
         private SourceLocation _lastTagStart = SourceLocation.Zero;
@@ -506,7 +507,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
                         while (!EndOfFile)
                         {
                             SkipToAndParseCode(HtmlSymbolType.DoubleHyphen);
-                            var lastDoubleHyphen = AcceptAllButLastDoubleHypens();
+                            var lastDoubleHyphen = AcceptAllButLastDoubleHyphens();
 
                             if (At(HtmlSymbolType.CloseAngle))
                             {
@@ -543,7 +544,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return false;
         }
 
-        protected HtmlSymbol AcceptAllButLastDoubleHypens()
+        protected HtmlSymbol AcceptAllButLastDoubleHyphens()
         {
             var lastDoubleHyphen = CurrentSymbol;
             AcceptWhile(s =>
@@ -558,9 +559,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             });
 
             NextToken();
-            EnsureCurrent();
 
-            if (At(HtmlSymbolType.Text) && IsDashSymbol(CurrentSymbol))
+            if (At(HtmlSymbolType.Text) && IsHyphen(CurrentSymbol))
             {
                 // Doing this here to maintain the order of symbols
                 if (!NextIs(HtmlSymbolType.CloseAngle))
@@ -575,9 +575,9 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             return lastDoubleHyphen;
         }
 
-        internal static bool IsDashSymbol(HtmlSymbol symbol)
+        internal static bool IsHyphen(HtmlSymbol symbol)
         {
-            return string.Equals(symbol.Content, "-", StringComparison.Ordinal);
+            return symbol.Equals(HtmlSymbol.Hyphen);
         }
 
         protected bool IsHtmlCommentAhead()
@@ -589,7 +589,10 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
              * 1. The string "<!--"
              * 2. Optionally, text, with the additional restriction that the text
              *      2.1 must not start with the string ">" nor start with the string "->"
-             *      2.2 nor contain the strings "<!--", "-->", or "--!>"
+             *      2.2 nor contain the strings
+             *          2.2.1 "<!--"
+             *          2.2.2 "-->" // As we will be treating this as a comment ending, there is no need to handle this case at all.
+             *          2.2.3 "--!>"
              *      2.3 nor end with the string "<!-".
              * 3. The string "-->"
              * 
@@ -601,37 +604,42 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             }
 
             // Check condition 2.1
-            if (NextIs(HtmlSymbolType.CloseAngle) || NextIs(next => IsDashSymbol(next) && NextIs(HtmlSymbolType.CloseAngle)))
+            if (NextIs(HtmlSymbolType.CloseAngle) || NextIs(next => IsHyphen(next) && NextIs(HtmlSymbolType.CloseAngle)))
             {
                 return false;
             }
 
             // Check condition 2.2
             var isValidComment = false;
-            LookaheadUntil((s, p) =>
+            LookaheadUntil((symbol, prevSymbols) =>
             {
-                if (s.Type == HtmlSymbolType.DoubleHyphen)
+                if (symbol.Type == HtmlSymbolType.DoubleHyphen)
                 {
                     if (NextIs(HtmlSymbolType.CloseAngle))
                     {
                         // Check condition 2.3: We're at the end of a comment. Check to make sure the text ending is allowed.
-                        isValidComment = !IsCommentContentDisallowed(p);
+                        isValidComment = !IsCommentContentEndingInvalid(prevSymbols);
                         return true;
                     }
-                    else if (NextIs(ns => IsDashSymbol(ns) && NextIs(HtmlSymbolType.CloseAngle)))
+                    else if (NextIs(ns => IsHyphen(ns) && NextIs(HtmlSymbolType.CloseAngle)))
                     {
-                        // This is also a valid closing comment case, as the dashes lookup is treated with DoubleHyphen symbols first.
+                        // Check condition 2.3: we're at the end of a comment, which has an extra dash.
+                        // Need to treat the dash as part of the content and check the ending.
+                        // However, that case would have already been checked as part of check from 2.2.1 which
+                        // would already fail this iteration and we wouldn't get here
                         isValidComment = true;
                         return true;
                     }
                     else if (NextIs(ns => ns.Type == HtmlSymbolType.Bang && NextIs(HtmlSymbolType.CloseAngle)))
                     {
+                        // This is condition 2.2.3
                         isValidComment = false;
                         return true;
                     }
                 }
-                else if (s.Type == HtmlSymbolType.OpenAngle)
+                else if (symbol.Type == HtmlSymbolType.OpenAngle)
                 {
+                    // Checking condition 2.2.1
                     if (NextIs(ns => ns.Type == HtmlSymbolType.Bang && NextIs(HtmlSymbolType.DoubleHyphen)))
                     {
                         isValidComment = false;
@@ -648,7 +656,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
         /// <summary>
         /// Verifies, that the sequence doesn't end with the "&lt;!-" HtmlSymbols. Note, the first symbol is an opening bracket symbol
         /// </summary>
-        internal static bool IsCommentContentDisallowed(IEnumerable<HtmlSymbol> sequence)
+        internal static bool IsCommentContentEndingInvalid(IEnumerable<HtmlSymbol> sequence)
         {
             var reversedSequence = sequence.Reverse();
             var index = 0;
diff --git a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlSymbol.cs b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlSymbol.cs
index f41f323d1d..217e293704 100644
--- a/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlSymbol.cs
+++ b/src/Microsoft.AspNetCore.Razor.Language/Legacy/HtmlSymbol.cs
@@ -8,6 +8,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 {
     internal class HtmlSymbol : SymbolBase<HtmlSymbolType>
     {
+        internal static readonly HtmlSymbol Hyphen = new HtmlSymbol("-", HtmlSymbolType.Text);
+
         public HtmlSymbol(string content, HtmlSymbolType type)
             : base(content, type, RazorDiagnostic.EmptyArray)
         {
diff --git a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs
index a40ec2e422..cc12a33914 100644
--- a/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs
+++ b/test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/HtmlMarkupParserTests.cs
@@ -24,23 +24,23 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
 
         [Theory]
         [MemberData(nameof(NonDashSymbols))]
-        public void IsDashSymbol_ReturnsFalseForNonDashSymbol(object symbol)
+        public void IsHyphen_ReturnsFalseForNonDashSymbol(object symbol)
         {
             // Arrange
             var convertedSymbol = (HtmlSymbol)symbol;
 
             // Act & Assert
-            Assert.False(HtmlMarkupParser.IsDashSymbol(convertedSymbol));
+            Assert.False(HtmlMarkupParser.IsHyphen(convertedSymbol));
         }
 
         [Fact]
-        public void IsDashSymbol_ReturnsTrueForADashSymbol()
+        public void IsHyphen_ReturnsTrueForADashSymbol()
         {
             // Arrange
             var dashSymbol = new HtmlSymbol("-", HtmlSymbolType.Text);
 
             // Act & Assert
-            Assert.True(HtmlMarkupParser.IsDashSymbol(dashSymbol));
+            Assert.True(HtmlMarkupParser.IsHyphen(dashSymbol));
         }
 
         [Fact]
@@ -50,7 +50,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
             var sut = CreateTestParserForContent("-->");
 
             // Act
-            var symbol = sut.AcceptAllButLastDoubleHypens();
+            var symbol = sut.AcceptAllButLastDoubleHyphens();
 
             // Assert
             Assert.Equal(doubleHyphenSymbol, symbol);
@@ -65,12 +65,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
             var sut = CreateTestParserForContent("--->");
 
             // Act
-            var symbol = sut.AcceptAllButLastDoubleHypens();
+            var symbol = sut.AcceptAllButLastDoubleHyphens();
 
             // Assert
             Assert.Equal(doubleHyphenSymbol, symbol);
             Assert.True(sut.At(HtmlSymbolType.CloseAngle));
-            Assert.True(HtmlMarkupParser.IsDashSymbol(sut.PreviousSymbol));
+            Assert.True(HtmlMarkupParser.IsHyphen(sut.PreviousSymbol));
         }
 
         [Fact]
@@ -103,6 +103,16 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
             Assert.True(sut.IsHtmlCommentAhead());
         }
 
+        [Fact]
+        public void IsHtmlCommentAhead_ReturnsFalseForContentWithBadEndingAndExtraDash()
+        {
+            // Arrange
+            var sut = CreateTestParserForContent("-- Some comment content in here <!--->");
+
+            // Act & Assert
+            Assert.False(sut.IsHtmlCommentAhead());
+        }
+
         [Fact]
         public void IsHtmlCommentAhead_ReturnsTrueForValidCommentTagWithExtraInfoAfter()
         {
@@ -144,36 +154,36 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
         }
 
         [Fact]
-        public void IsCommentContentDisallowed_ReturnsFalseForAllowedContent()
+        public void IsCommentContentEndingInvalid_ReturnsFalseForAllowedContent()
         {
             // Arrange
             var expectedSymbol1 = new HtmlSymbol("a", HtmlSymbolType.Text);
             var sequence = Enumerable.Range((int)'a', 26).Select(item => new HtmlSymbol(((char)item).ToString(), HtmlSymbolType.Text));
 
             // Act & Assert
-            Assert.False(HtmlMarkupParser.IsCommentContentDisallowed(sequence));
+            Assert.False(HtmlMarkupParser.IsCommentContentEndingInvalid(sequence));
         }
 
         [Fact]
-        public void IsCommentContentDisallowed_ReturnsTrueForDisallowedContent()
+        public void IsCommentContentEndingInvalid_ReturnsTrueForDisallowedContent()
         {
             // Arrange
             var expectedSymbol1 = new HtmlSymbol("a", HtmlSymbolType.Text);
             var sequence = new[] { new HtmlSymbol("<", HtmlSymbolType.OpenAngle), new HtmlSymbol("!", HtmlSymbolType.Bang), new HtmlSymbol("-", HtmlSymbolType.Text) };
 
             // Act & Assert
-            Assert.True(HtmlMarkupParser.IsCommentContentDisallowed(sequence));
+            Assert.True(HtmlMarkupParser.IsCommentContentEndingInvalid(sequence));
         }
 
         [Fact]
-        public void IsCommentContentDisallowed_ReturnsFalseForEmptyContent()
+        public void IsCommentContentEndingInvalid_ReturnsFalseForEmptyContent()
         {
             // Arrange
             var expectedSymbol1 = new HtmlSymbol("a", HtmlSymbolType.Text);
             var sequence = Array.Empty<HtmlSymbol>();
 
             // Act & Assert
-            Assert.False(HtmlMarkupParser.IsCommentContentDisallowed(sequence));
+            Assert.False(HtmlMarkupParser.IsCommentContentEndingInvalid(sequence));
         }
 
         private class TestHtmlMarkupParser : HtmlMarkupParser
@@ -193,9 +203,9 @@ namespace Microsoft.AspNetCore.Razor.Language.Test.Legacy
                 this.EnsureCurrent();
             }
 
-            public new HtmlSymbol AcceptAllButLastDoubleHypens()
+            public new HtmlSymbol AcceptAllButLastDoubleHyphens()
             {
-                return base.AcceptAllButLastDoubleHypens();
+                return base.AcceptAllButLastDoubleHyphens();
             }
 
             public override void BuildSpan(SpanBuilder span, SourceLocation start, string content)