Change `[RestrictChildren]` to allow non-`TagHelper` tags.

- Updated the `TagHelperParseTreeRewriter` loosen child restrictions to non-`TagHelper` HTML elements.
- Updated tests to showcase that non-`TagHelper` elements are allowed to be restricted.
- Added an additional test case to showcase sub-sub nesting of non-`TagHelper` restricted children.

#543

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

@@ -19,10 +19,10 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// Instantiates a new instance of the <see cref="RestrictChildrenAttribute"/> class.
         /// </summary>
         /// <param name="childTag">
-        /// The tag name of an element allowed as a child. Tag helpers must target the element.
+        /// The tag name of an element allowed as a child.
         /// </param>
         /// <param name="childTags">
-        /// Additional names of elements allowed as children. Tag helpers must target all such elements.
+        /// Additional names of elements allowed as children.
         /// </param>
         public RestrictChildrenAttribute(string childTag, params string[] childTags)
         {
@@ -35,7 +35,7 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         }
 
         /// <summary>
-        /// Get the names of elements allowed as children. Tag helpers must target all such elements.
+        /// Get the names of elements allowed as children.
         /// </summary>
         public IEnumerable<string> ChildTags { get; }
     }

src/Microsoft.AspNet.Razor/Parser/TagHelpers/TagHelperParseTreeRewriter.cs

@@ -81,10 +81,10 @@ namespace Microsoft.AspNet.Razor.Parser.TagHelpers.Internal
                         }
                         else
                         {
-                            TrackTagBlock(childBlock);
-
                             // Non-TagHelper tag.
-                            ValidateParentTagHelperAllowsPlainTag(childBlock, context.ErrorSink);
+                            ValidateParentAllowsPlainTag(childBlock, context.ErrorSink);
+
+                            TrackTagBlock(childBlock);
                         }
 
                         // If we get to here it means that we're a normal html tag.  No need to iterate any deeper into
@@ -99,7 +99,7 @@ namespace Microsoft.AspNet.Razor.Parser.TagHelpers.Internal
                 }
                 else
                 {
-                    ValidateParentTagHelperAllowsContent((Span)child, context.ErrorSink);
+                    ValidateParentAllowsContent((Span)child, context.ErrorSink);
                 }
 
                 // At this point the child is a Span or Block with Type BlockType.Tag that doesn't happen to be a
@@ -197,7 +197,7 @@ namespace Microsoft.AspNet.Razor.Parser.TagHelpers.Internal
                     return false;
                 }
 
-                ValidateParentTagHelperAllowsTagHelper(tagName, tagBlock, context.ErrorSink);
+                ValidateParentAllowsTagHelper(tagName, tagBlock, context.ErrorSink);
                 ValidateDescriptors(descriptors, tagName, tagBlock, context.ErrorSink);
 
                 // We're in a start TagHelper block.
@@ -277,7 +277,7 @@ namespace Microsoft.AspNet.Razor.Parser.TagHelpers.Internal
                     // can't recover it means there was no corresponding tag helper start tag.
                     if (TryRecoverTagHelper(tagName, tagBlock, context))
                     {
-                        ValidateParentTagHelperAllowsTagHelper(tagName, tagBlock, context.ErrorSink);
+                        ValidateParentAllowsTagHelper(tagName, tagBlock, context.ErrorSink);
                         ValidateTagSyntax(tagName, tagBlock, context);
 
                         // Successfully recovered, move onto the next element.
@@ -335,10 +335,22 @@ namespace Microsoft.AspNet.Razor.Parser.TagHelpers.Internal
             return attributeNames;
         }
 
-        private void ValidateParentTagHelperAllowsContent(Span child, ErrorSink errorSink)
+        private bool HasAllowedChildren()
         {
-            var allowedChildren = _currentTagHelperTracker?.AllowedChildren;
+            var currentTracker = _trackerStack.Count > 0 ? _trackerStack.Peek() : null;
-            if (allowedChildren != null)
+
+            // If the current tracker is not a TagHelper then there's no AllowedChildren to enforce.
+            if (currentTracker == null || !currentTracker.IsTagHelper)
+            {
+                return false;
+            }
+
+            return _currentTagHelperTracker.AllowedChildren != null;
+        }
+
+        private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
+        {
+            if (HasAllowedChildren())
             {
                 var content = child.Content;
                 if (!string.IsNullOrWhiteSpace(content))
@@ -347,6 +359,7 @@ namespace Microsoft.AspNet.Razor.Parser.TagHelpers.Internal
                     var whitespace = content.Substring(0, content.Length - trimmedStart.Length);
                     var errorStart = SourceLocation.Advance(child.Start, whitespace);
                     var length = trimmedStart.TrimEnd().Length;
+                    var allowedChildren = _currentTagHelperTracker.AllowedChildren;
                     var allowedChildrenString = string.Join(", ", allowedChildren);
                     errorSink.OnError(
                         errorStart,
@@ -358,31 +371,32 @@ namespace Microsoft.AspNet.Razor.Parser.TagHelpers.Internal
             }
         }
 
-        private void ValidateParentTagHelperAllowsPlainTag(Block tagBlock, ErrorSink errorSink)
+        private void ValidateParentAllowsPlainTag(Block tagBlock, ErrorSink errorSink)
         {
-            if (_currentTagHelperTracker?.AllowedChildren != null)
+            var tagName = GetTagName(tagBlock);
+
+            // Treat partial tags such as '</' which have no tag names as content.
+            if (string.IsNullOrEmpty(tagName))
             {
-                var tagName = GetTagName(tagBlock);
+                Debug.Assert(tagBlock.Children.First() is Span);
 
-                // Treat partial tags such as '</' which have no tag names as content based errors.
+                ValidateParentAllowsContent((Span)tagBlock.Children.First(), errorSink);
-                if (string.IsNullOrEmpty(tagName))
+                return;
-                {
+            }
-                    Debug.Assert(tagBlock.Children.First() is Span);
 
-                    ValidateParentTagHelperAllowsContent(tagBlock.Children.First() as Span, errorSink);
+            var currentTracker = _trackerStack.Count > 0 ? _trackerStack.Peek() : null;
-                    return;
-                }
 
+            if (HasAllowedChildren() &&
+                !_currentTagHelperTracker.AllowedChildren.Contains(tagName, StringComparer.OrdinalIgnoreCase))
+            {
                 OnAllowedChildrenTagError(_currentTagHelperTracker, tagName, tagBlock, errorSink);
             }
         }
 
-        private void ValidateParentTagHelperAllowsTagHelper(string tagName, Block tagBlock, ErrorSink errorSink)
+        private void ValidateParentAllowsTagHelper(string tagName, Block tagBlock, ErrorSink errorSink)
         {
-            var currentlyAllowedChildren = _currentTagHelperTracker?.PrefixedAllowedChildren;
+            if (HasAllowedChildren() &&
-
+                !_currentTagHelperTracker.PrefixedAllowedChildren.Contains(tagName, StringComparer.OrdinalIgnoreCase))
-            if (currentlyAllowedChildren != null &&
-                !currentlyAllowedChildren.Contains(tagName, StringComparer.OrdinalIgnoreCase))
             {
                 OnAllowedChildrenTagError(_currentTagHelperTracker, tagName, tagBlock, errorSink);
             }

src/Microsoft.AspNet.Razor/Properties/RazorResources.Designer.cs

@@ -1531,7 +1531,7 @@ namespace Microsoft.AspNet.Razor
         }
 
         /// <summary>
-        /// The &lt;{0}&gt; tag is not allowed by parent &lt;{1}&gt; tag helper. Only child tag helper(s) targeting tag name(s) '{2}' are allowed.
+        /// The &lt;{0}&gt; tag is not allowed by parent &lt;{1}&gt; tag helper. Only child tags with name(s) '{2}' are allowed.
         /// </summary>
         internal static string TagHelperParseTreeRewriter_InvalidNestedTag
         {
@@ -1539,7 +1539,7 @@ namespace Microsoft.AspNet.Razor
         }
 
         /// <summary>
-        /// The &lt;{0}&gt; tag is not allowed by parent &lt;{1}&gt; tag helper. Only child tag helper(s) targeting tag name(s) '{2}' are allowed.
+        /// The &lt;{0}&gt; tag is not allowed by parent &lt;{1}&gt; tag helper. Only child tags with name(s) '{2}' are allowed.
         /// </summary>
         internal static string FormatTagHelperParseTreeRewriter_InvalidNestedTag(object p0, object p1, object p2)
         {

src/Microsoft.AspNet.Razor/RazorResources.resx

@@ -423,7 +423,7 @@ Instead, wrap the contents of the block in "{{}}":
     <value>The parent &lt;{0}&gt; tag helper does not allow non-tag content. Only child tag helper(s) targeting tag name(s) '{1}' are allowed.</value>
   </data>
   <data name="TagHelperParseTreeRewriter_InvalidNestedTag" xml:space="preserve">
-    <value>The &lt;{0}&gt; tag is not allowed by parent &lt;{1}&gt; tag helper. Only child tag helper(s) targeting tag name(s) '{2}' are allowed.</value>
+    <value>The &lt;{0}&gt; tag is not allowed by parent &lt;{1}&gt; tag helper. Only child tags with name(s) '{2}' are allowed.</value>
   </data>
   <data name="ParseError_HelperDirectiveNotAvailable" xml:space="preserve">
     <value>The {0} directive is not supported.</value>

src/Microsoft.AspNet.Razor/TagHelpers/TagHelperDescriptor.cs

@@ -158,7 +158,7 @@ namespace Microsoft.AspNet.Razor.TagHelpers
         }
 
         /// <summary>
-        /// Get the names of elements allowed as children. Tag helpers must target all such elements.
+        /// Get the names of elements allowed as children.
         /// </summary>
         /// <remarks><c>null</c> indicates all children are allowed.</remarks>
         public IEnumerable<string> AllowedChildren { get; set; }

test/Microsoft.AspNet.Razor.Test/TagHelpers/TagHelperParseTreeRewriterTest.cs

@@ -661,18 +661,6 @@ namespace Microsoft.AspNet.Razor.Test.TagHelpers
                     lineIndex: 1,
                     columnIndex: 5,
                     length: 6),
-                new RazorError(
-                    RazorResources.FormatTagHelperParseTreeRewriter_CannotHaveNonTagContent("p", "br"),
-                    absoluteIndex: 23 + newLineLength * 2,
-                    lineIndex: 2,
-                    columnIndex: 8,
-                    length: 5),
-                new RazorError(
-                    RazorResources.FormatTagHelperParseTreeRewriter_InvalidNestedTag("strong", "p", "br"),
-                    absoluteIndex: 34 + newLineLength * 3,
-                    lineIndex: 3,
-                    columnIndex: 5,
-                    length: 6),
             };
             var expectedOutput = new MarkupBlock(
                 new MarkupTagHelperBlock("p",
@@ -711,13 +699,7 @@ namespace Microsoft.AspNet.Razor.Test.TagHelpers
                     absoluteIndex: 18,
                     lineIndex: 0,
                     columnIndex: 18,
-                    length: 6),
+                    length: 6)
-                new RazorError(
-                    RazorResources.FormatTagHelperParseTreeRewriter_InvalidNestedTag("strong", "strong", "br"),
-                    absoluteIndex: 27,
-                    lineIndex: 0,
-                    columnIndex: 27,
-                    length: 6),
             };
             var expectedOutput = new MarkupBlock(
                 new MarkupTagHelperBlock("strong",
@@ -973,8 +955,6 @@ namespace Microsoft.AspNet.Razor.Test.TagHelpers
                             nestedContentError("strong", "strong", 11, 6),
                             nestedTagError("br", "strong", "strong", 18, 2),
                             nestedTagError("em", "strong", "strong", 22, 2),
-                            nestedContentError("strong", "strong", 25, 11),
-                            nestedTagError("em", "strong", "strong", 38, 2),
                             nestedTagError("br", "p", "strong", 51, 2),
                             nestedContentError("p", "strong", 56, 9)
                         }
@@ -995,13 +975,6 @@ namespace Microsoft.AspNet.Razor.Test.TagHelpers
                                 factory.Markup("Something"))),
                         new[]
                         {
-                            nestedTagError("custom", "p", "custom", 4, 6),
-                            nestedContentError("p", "custom", 11, 6),
-                            nestedTagError("br", "p", "custom", 18, 2),
-                            nestedTagError("em", "p", "custom", 22, 2),
-                            nestedContentError("p", "custom", 25, 11),
-                            nestedTagError("em", "p", "custom", 38, 2),
-                            nestedTagError("custom", "p", "custom", 43, 6),
                             nestedTagError("br", "p", "custom", 51, 2),
                             nestedContentError("p", "custom", 56, 9)
                         }
@@ -1027,7 +1000,26 @@ namespace Microsoft.AspNet.Razor.Test.TagHelpers
                         {
                             nestedContentError("p", "custom", 3, 1),
                         }
-                    }
+                    },
+                    {
+                        "<p><custom><br>:<strong><strong>Hello</strong></strong>:<input></custom></p>",
+                        new[] { "custom", "strong" },
+                        new MarkupBlock(
+                            new MarkupTagHelperBlock("p",
+                                blockFactory.MarkupTagBlock("<custom>"),
+                                new MarkupTagHelperBlock("br", TagMode.StartTagOnly),
+                                factory.Markup(":"),
+                                new MarkupTagHelperBlock("strong",
+                                    new MarkupTagHelperBlock("strong",
+                                        factory.Markup("Hello"))),
+                                factory.Markup(":"),
+                                blockFactory.MarkupTagBlock("<input>"),
+                                blockFactory.MarkupTagBlock("</custom>"))),
+                        new[]
+                        {
+                            nestedContentError("strong", "custom, strong", 32, 5),
+                        }
+                    },
                 };
             }
         }