Add TagHelper parse level opt-out character '!'.

- Added the ability to opt-out of TagHelper parsing by adding a '!' to the beginning of a tag name.
- Modified parsing logic to allow bangs in tags.
- Bangs in tags are removed from output always and are handled as meta code.

#187

src/Microsoft.AspNet.Razor.Runtime/Properties/Resources.Designer.cs

@@ -75,19 +75,19 @@ namespace Microsoft.AspNet.Razor.Runtime
         }
 
         /// <summary>
-        /// Parameter {0} must not contain null tag names.
+        /// Tag name cannot be null or whitespace.
         /// </summary>
-        internal static string HtmlElementNameAttribute_AdditionalTagsCannotContainNull
+        internal static string HtmlElementNameAttribute_ElementNameCannotBeNullOrWhitespace
         {
-            get { return GetString("HtmlElementNameAttribute_AdditionalTagsCannotContainNull"); }
+            get { return GetString("HtmlElementNameAttribute_ElementNameCannotBeNullOrWhitespace"); }
         }
 
         /// <summary>
-        /// Parameter {0} must not contain null tag names.
+        /// Tag name cannot be null or whitespace.
         /// </summary>
-        internal static string FormatHtmlElementNameAttribute_AdditionalTagsCannotContainNull(object p0)
+        internal static string FormatHtmlElementNameAttribute_ElementNameCannotBeNullOrWhitespace()
         {
-            return string.Format(CultureInfo.CurrentCulture, GetString("HtmlElementNameAttribute_AdditionalTagsCannotContainNull"), p0);
+            return GetString("HtmlElementNameAttribute_ElementNameCannotBeNullOrWhitespace");
         }
 
         /// <summary>
@@ -122,6 +122,22 @@ namespace Microsoft.AspNet.Razor.Runtime
             return string.Format(CultureInfo.CurrentCulture, GetString("TagHelperDescriptorResolver_EncounteredUnexpectedError"), p0, p1, p2);
         }
 
+        /// <summary>
+        /// Tag helpers cannot target element name '{0}' because it contains a '{1}' character.
+        /// </summary>
+        internal static string HtmlElementNameAttribute_InvalidElementName
+        {
+            get { return GetString("HtmlElementNameAttribute_InvalidElementName"); }
+        }
+
+        /// <summary>
+        /// Tag helpers cannot target element name '{0}' because it contains a '{1}' character.
+        /// </summary>
+        internal static string FormatHtmlElementNameAttribute_InvalidElementName(object p0, object p1)
+        {
+            return string.Format(CultureInfo.CurrentCulture, GetString("HtmlElementNameAttribute_InvalidElementName"), p0, p1);
+        }
+
         private static string GetString(string name, params string[] formatterNames)
         {
             var value = _resourceManager.GetString(name);

src/Microsoft.AspNet.Razor.Runtime/Resources.resx

@@ -129,8 +129,8 @@
   <data name="ScopeManager_EndCannotBeCalledWithoutACallToBegin" xml:space="preserve">
     <value>Must call '{2}.{1}' before calling '{2}.{0}'.</value>
   </data>
-  <data name="HtmlElementNameAttribute_AdditionalTagsCannotContainNull" xml:space="preserve">
+  <data name="HtmlElementNameAttribute_ElementNameCannotBeNullOrWhitespace" xml:space="preserve">
-    <value>Parameter {0} must not contain null tag names.</value>
+    <value>Tag name cannot be null or whitespace.</value>
   </data>
   <data name="ArgumentCannotBeNullOrEmpty" xml:space="preserve">
     <value>The value cannot be null or empty.</value>
@@ -138,4 +138,7 @@
   <data name="TagHelperDescriptorResolver_EncounteredUnexpectedError" xml:space="preserve">
     <value>Encountered an unexpected error when attempting to resolve tag helper directive '{0}' with value '{1}'. Error: {2}</value>
   </data>
+  <data name="HtmlElementNameAttribute_InvalidElementName" xml:space="preserve">
+    <value>Tag helpers cannot target element name '{0}' because it contains a '{1}' character.</value>
+  </data>
 </root>

src/Microsoft.AspNet.Razor.Runtime/TagHelpers/HtmlElementNameAttribute.cs

@@ -19,6 +19,8 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// <param name="tag">The HTML tag name for the <see cref="TagHelper"/> to target.</param>
         public HtmlElementNameAttribute([NotNull] string tag)
         {
+            ValidateTagName(tag, nameof(tag));
+
             Tags = new[] { tag };
         }
 
@@ -29,12 +31,12 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// <param name="additionalTags">Additional HTML tag names for the <see cref="TagHelper"/> to target.</param>
         public HtmlElementNameAttribute([NotNull] string tag, [NotNull] params string[] additionalTags)
         {
-            if (additionalTags.Contains(null))
+            ValidateTagName(tag, nameof(tag));
+
+            foreach (var tagName in additionalTags)
             {
-                throw new ArgumentNullException(
+                ValidateTagName(tagName, nameof(additionalTags));
-                    nameof(additionalTags),
+            }
-                    Resources.FormatHtmlElementNameAttribute_AdditionalTagsCannotContainNull(nameof(additionalTags)));
-            };
 
             var allTags = new List<string>(additionalTags);
             allTags.Add(tag);
@@ -45,6 +47,23 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// <summary>
         /// An <see cref="IEnumerable{string}"/> of tag names for the <see cref="TagHelper"/> to target.
         /// </summary>
-        public IEnumerable<string> Tags { get; private set; }
+        public IEnumerable<string> Tags { get; }
+
+        private static void ValidateTagName(string tagName, string parameterName)
+        {
+            if (string.IsNullOrWhiteSpace(tagName))
+            {
+                throw new ArgumentException(
+                    Resources.HtmlElementNameAttribute_ElementNameCannotBeNullOrWhitespace,
+                    parameterName);
+            }
+
+            if (tagName.Contains('!'))
+            {
+                throw new ArgumentException(
+                    Resources.FormatHtmlElementNameAttribute_InvalidElementName(tagName, '!'),
+                    parameterName);
+            }
+        }
     }
 }

src/Microsoft.AspNet.Razor/Parser/HtmlMarkupParser.Block.cs

@@ -133,7 +133,9 @@ namespace Microsoft.AspNet.Razor.Parser
                 IDisposable tagBlockWrapper = null;
                 try
                 {
-                    if (!EndOfFile && !AtSpecialTag)
+                    var atSpecialTag = AtSpecialTag;
+
+                    if (!EndOfFile && !atSpecialTag)
                     {
                         // Start a Block tag.  This is used to wrap things like <p> or <a class="btn"> etc.
                         tagBlockWrapper = Context.StartBlock(BlockType.Tag);
@@ -157,7 +159,7 @@ namespace Microsoft.AspNet.Razor.Parser
                         }
                         else
                         {
-                            complete = AfterTagStart(tagStart, tags, tagBlockWrapper);
+                            complete = AfterTagStart(tagStart, tags, atSpecialTag, tagBlockWrapper);
                         }
                     }
 
@@ -187,6 +189,7 @@ namespace Microsoft.AspNet.Razor.Parser
 
         private bool AfterTagStart(SourceLocation tagStart,
                                    Stack<Tuple<HtmlSymbol, SourceLocation>> tags,
+                                   bool atSpecialTag,
                                    IDisposable tagBlockWrapper)
         {
             if (!EndOfFile)
@@ -197,9 +200,16 @@ namespace Microsoft.AspNet.Razor.Parser
                         // End Tag
                         return EndTag(tagStart, tags, tagBlockWrapper);
                     case HtmlSymbolType.Bang:
-                        // Comment
+                        // Comment, CDATA, DOCTYPE, or a parser-escaped HTML tag.
-                        Accept(_bufferedOpenAngle);
+                        if (atSpecialTag)
-                        return BangTag();
+                        {
+                            Accept(_bufferedOpenAngle);
+                            return BangTag();
+                        }
+                        else
+                        {
+                            goto default;
+                        }
                     case HtmlSymbolType.QuestionMark:
                         // XML PI
                         Accept(_bufferedOpenAngle);
@@ -275,30 +285,48 @@ namespace Microsoft.AspNet.Razor.Parser
         {
             // Accept "/" and move next
             Assert(HtmlSymbolType.ForwardSlash);
-            var solidus = CurrentSymbol;
+            var forwardSlash = CurrentSymbol;
             if (!NextToken())
             {
                 Accept(_bufferedOpenAngle);
-                Accept(solidus);
+                Accept(forwardSlash);
                 return false;
             }
             else
             {
-                var tagName = String.Empty;
+                var tagName = string.Empty;
-                if (At(HtmlSymbolType.Text))
+                HtmlSymbol bangSymbol = null;
+
+                if (At(HtmlSymbolType.Bang))
+                {
+                    bangSymbol = CurrentSymbol;
+
+                    var nextSymbol = Lookahead(count: 1);
+
+                    if (nextSymbol != null && nextSymbol.Type == HtmlSymbolType.Text)
+                    {
+                        tagName = "!" + nextSymbol.Content;
+                    }
+                }
+                else if (At(HtmlSymbolType.Text))
                 {
                     tagName = CurrentSymbol.Content;
                 }
+
                 var matched = RemoveTag(tags, tagName, tagStart);
 
                 if (tags.Count == 0 &&
-                    String.Equals(tagName, SyntaxConstants.TextTagName, StringComparison.OrdinalIgnoreCase) &&
+                    // Note tagName may contain a '!' escape character. This ensures </!text> doesn't match here. 
+                    // </!text> tags are treated like any other escaped HTML end tag.
+                    string.Equals(tagName, SyntaxConstants.TextTagName, StringComparison.OrdinalIgnoreCase) &&
                     matched)
                 {
-                    return EndTextTag(solidus, tagBlockWrapper);
+                    return EndTextTag(forwardSlash, tagBlockWrapper);
                 }
                 Accept(_bufferedOpenAngle);
-                Accept(solidus);
+                Accept(forwardSlash);
+
+                OptionalBangEscape();
 
                 AcceptUntil(HtmlSymbolType.CloseAngle);
 
@@ -347,14 +375,22 @@ namespace Microsoft.AspNet.Razor.Parser
             return seenCloseAngle;
         }
 
-        // Special tags include <! and <? tags
+        // Special tags include <!--, <!DOCTYPE, <![CDATA and <? tags
         private bool AtSpecialTag
         {
             get
             {
-                return (At(HtmlSymbolType.OpenAngle) &&
+                if (At(HtmlSymbolType.OpenAngle))
-                       (NextIs(HtmlSymbolType.Bang) ||
+                {
-                        NextIs(HtmlSymbolType.QuestionMark)));
+                    if (NextIs(HtmlSymbolType.Bang))
+                    {
+                        return !IsBangEscape(lookahead: 1);
+                    }
+
+                    return NextIs(HtmlSymbolType.QuestionMark);
+                }
+
+                return false;
             }
         }
 
@@ -651,20 +687,41 @@ namespace Microsoft.AspNet.Razor.Parser
 
         private bool StartTag(Stack<Tuple<HtmlSymbol, SourceLocation>> tags, IDisposable tagBlockWrapper)
         {
-            // If we're at text, it's the name, otherwise the name is ""
+            HtmlSymbol bangSymbol = null;
-            HtmlSymbol tagName;
+            HtmlSymbol potentialTagNameSymbol;
-            if (At(HtmlSymbolType.Text))
+
+            if (At(HtmlSymbolType.Bang))
             {
-                tagName = CurrentSymbol;
+                bangSymbol = CurrentSymbol;
+
+                potentialTagNameSymbol = Lookahead(count: 1);
             }
             else
             {
-                tagName = new HtmlSymbol(CurrentLocation, String.Empty, HtmlSymbolType.Unknown);
+                potentialTagNameSymbol = CurrentSymbol;
+            }
+
+            HtmlSymbol tagName;
+
+            if (potentialTagNameSymbol == null || potentialTagNameSymbol.Type != HtmlSymbolType.Text)
+            {
+                tagName = new HtmlSymbol(potentialTagNameSymbol.Start, string.Empty, HtmlSymbolType.Unknown);
+            }
+            else if (bangSymbol != null)
+            {
+                tagName = new HtmlSymbol(bangSymbol.Start, "!" + potentialTagNameSymbol.Content, HtmlSymbolType.Text);
+            }
+            else
+            {
+                tagName = potentialTagNameSymbol;
             }
 
             Tuple<HtmlSymbol, SourceLocation> tag = Tuple.Create(tagName, _lastTagStart);
 
-            if (tags.Count == 0 && String.Equals(tag.Item1.Content, SyntaxConstants.TextTagName, StringComparison.OrdinalIgnoreCase))
+            if (tags.Count == 0 &&
+                // Note tagName may contain a '!' escape character. This ensures <!text> doesn't match here. 
+                // <!text> tags are treated like any other escaped HTML start tag.
+                string.Equals(tag.Item1.Content, SyntaxConstants.TextTagName, StringComparison.OrdinalIgnoreCase))
             {
                 Output(SpanKind.Markup);
                 Span.CodeGenerator = SpanCodeGenerator.Null;
@@ -709,7 +766,9 @@ namespace Microsoft.AspNet.Razor.Parser
 
                 return true;
             }
+
             Accept(_bufferedOpenAngle);
+            OptionalBangEscape();
             Optional(HtmlSymbolType.Text);
             return RestOfTag(tag, tags, tagBlockWrapper);
         }

src/Microsoft.AspNet.Razor/Parser/HtmlMarkupParser.Document.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using Microsoft.AspNet.Razor.Generator;
 using Microsoft.AspNet.Razor.Parser.SyntaxTree;
 using Microsoft.AspNet.Razor.Tokenizer.Symbols;
 
@@ -42,58 +43,69 @@ namespace Microsoft.AspNet.Razor.Parser
             {
                 if (NextIs(HtmlSymbolType.Bang))
                 {
-                    AcceptAndMoveNext(); // Accept '<'
+                    // Checking to see if we meet the conditions of a special '!' tag: <!DOCTYPE, <![CDATA[, <!--.
-                    BangTag();
+                    if (!IsBangEscape(lookahead: 1))
+                    {
+                        AcceptAndMoveNext(); // Accept '<'
+                        BangTag();
+                        return;
+                    }
+
+                    // We should behave like a normal tag that has a parser escape, fall through to the normal 
+                    // tag logic.
                 }
                 else if (NextIs(HtmlSymbolType.QuestionMark))
                 {
                     AcceptAndMoveNext(); // Accept '<'
                     XmlPI();
+                    return;
+                }
+
+                Output(SpanKind.Markup);
+
+                // Start tag block
+                var tagBlock = Context.StartBlock(BlockType.Tag);
+
+                AcceptAndMoveNext(); // Accept '<'
+
+                if (!At(HtmlSymbolType.ForwardSlash))
+                {
+                    OptionalBangEscape();
+
+                    // Parsing a start tag
+                    var scriptTag = At(HtmlSymbolType.Text) &&
+                                    string.Equals(CurrentSymbol.Content, "script", StringComparison.OrdinalIgnoreCase);
+                    Optional(HtmlSymbolType.Text);
+                    TagContent(); // Parse the tag, don't care about the content
+                    Optional(HtmlSymbolType.ForwardSlash);
+                    Optional(HtmlSymbolType.CloseAngle);
+
+                    if (scriptTag)
+                    {
+                        Output(SpanKind.Markup);
+                        tagBlock.Dispose();
+
+                        SkipToEndScriptAndParseCode();
+                        return;
+                    }
                 }
                 else
                 {
-                    Output(SpanKind.Markup);
+                    // Parsing an end tag
+                    // This section can accept things like: '</p  >' or '</p>' etc.
+                    Optional(HtmlSymbolType.ForwardSlash);
 
-                    // Start tag block
+                    // Whitespace here is invalid (according to the spec)
-                    var tagBlock = Context.StartBlock(BlockType.Tag);
+                    OptionalBangEscape();
-
+                    Optional(HtmlSymbolType.Text);
-                    AcceptAndMoveNext(); // Accept '<'
+                    AcceptAll(HtmlSymbolType.WhiteSpace);
-
+                    Optional(HtmlSymbolType.CloseAngle);
-                    if (!At(HtmlSymbolType.ForwardSlash))
-                    {
-                        // Parsing a start tag
-                        var scriptTag = At(HtmlSymbolType.Text) &&
-                                        string.Equals(CurrentSymbol.Content, "script", StringComparison.OrdinalIgnoreCase);
-                        Optional(HtmlSymbolType.Text);
-                        TagContent(); // Parse the tag, don't care about the content
-                        Optional(HtmlSymbolType.ForwardSlash);
-                        Optional(HtmlSymbolType.CloseAngle);
-
-                        if (scriptTag)
-                        {
-                            Output(SpanKind.Markup);
-                            tagBlock.Dispose();
-
-                            SkipToEndScriptAndParseCode();
-                            return;
-                        }
-                    }
-                    else
-                    {
-                        // Parsing an end tag
-                        // This section can accept things like: '</p  >' or '</p>' etc.
-                        Optional(HtmlSymbolType.ForwardSlash);
-                        // Whitespace here is invalid (according to the spec)
-                        Optional(HtmlSymbolType.Text);
-                        AcceptAll(HtmlSymbolType.WhiteSpace);
-                        Optional(HtmlSymbolType.CloseAngle);
-                    }
-
-                    Output(SpanKind.Markup);
-
-                    // End tag block
-                    tagBlock.Dispose();
                 }
+
+                Output(SpanKind.Markup);
+
+                // End tag block
+                tagBlock.Dispose();
             }
         }
     }

src/Microsoft.AspNet.Razor/Parser/HtmlMarkupParser.cs

@@ -184,5 +184,38 @@ namespace Microsoft.AspNet.Razor.Parser
             Initialize(Span);
             NextToken();
         }
+
+        private bool IsBangEscape(int lookahead)
+        {
+            var potentialBang = Lookahead(lookahead);
+
+            if (potentialBang != null &&
+                potentialBang.Type == HtmlSymbolType.Bang)
+            {
+                var afterBang = Lookahead(lookahead + 1);
+
+                return afterBang != null &&
+                    afterBang.Type == HtmlSymbolType.Text &&
+                    !string.Equals(afterBang.Content, "DOCTYPE", StringComparison.OrdinalIgnoreCase);
+            }
+
+            return false;
+        }
+
+        private void OptionalBangEscape()
+        {
+            if (IsBangEscape(lookahead: 0))
+            {
+                Output(SpanKind.Markup);
+
+                // Accept the parser escape character '!'.
+                Assert(HtmlSymbolType.Bang);
+                AcceptAndMoveNext();
+
+                // Setup the metacode span that we will be outputing.
+                Span.CodeGenerator = SpanCodeGenerator.Null;
+                Output(SpanKind.MetaCode, AcceptedCharacters.None);
+            }
+        }
     }
 }

src/Microsoft.AspNet.Razor/Parser/TokenizerBackedParser.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using Microsoft.AspNet.Razor.Parser.SyntaxTree;
 using Microsoft.AspNet.Razor.Text;
@@ -75,6 +76,43 @@ namespace Microsoft.AspNet.Razor.Parser
             }
         }
 
+        protected TSymbol Lookahead(int count)
+        {
+            if (count < 0)
+            {
+                throw new ArgumentOutOfRangeException(nameof(count));
+            }
+            else if (count == 0)
+            {
+                return CurrentSymbol;
+            }
+
+            // We add 1 in order to store the current symbol.
+            var symbols = new TSymbol[count + 1];
+            var currentSymbol = CurrentSymbol;
+
+            symbols[0] = currentSymbol;
+
+            // We need to look forward "count" many times.
+            for (var i = 1; i <= count; i++)
+            {
+                NextToken();
+                symbols[i] = CurrentSymbol;
+            }
+
+            // Restore Tokenizer's location to where it was pointing before the look-ahead.
+            for (var i = count; 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 symbols[count];
+        }
+
         protected internal bool NextToken()
         {
             PreviousSymbol = CurrentSymbol;