Rewrite of code rendering context

src/Microsoft.AspNetCore.Razor.Language/CodeGeneration/CodeRenderingContext.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.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Language.Intermediate;
 
 namespace Microsoft.AspNetCore.Razor.Language.CodeGeneration
@@ -18,11 +19,15 @@ namespace Microsoft.AspNetCore.Razor.Language.CodeGeneration
         public abstract string DocumentKind { get; }
 
         public abstract ItemCollection Items { get; }
+        
+        public abstract IEnumerable<IntermediateNode> Ancestors { get; }
 
         public abstract IntermediateNodeWriter NodeWriter { get; }
 
         public abstract RazorCodeGenerationOptions Options { get; }
 
+        public abstract IntermediateNode Parent { get; }
+
         public abstract RazorSourceDocument SourceDocument { get; }
 
         public abstract Scope CreateScope();
@@ -56,48 +61,5 @@ namespace Microsoft.AspNetCore.Razor.Language.CodeGeneration
                 _context.EndScope();
             }
         }
-
-
-        // All bits below here are temporary
-
-        #region Temporary TagHelper bits
-
-        internal TagHelperRenderingContext TagHelperRenderingContext { get; set; }
-
-        internal TagHelperRenderingContextScope Push(TagHelperRenderingContext context)
-        {
-            if (context == null)
-            {
-                throw new ArgumentNullException(nameof(context));
-            }
-
-            var scope = new TagHelperRenderingContextScope(this, TagHelperRenderingContext);
-            TagHelperRenderingContext = context;
-            return scope;
-        }
-
-        internal struct TagHelperRenderingContextScope : IDisposable
-        {
-            private readonly CodeRenderingContext _context;
-            private readonly TagHelperRenderingContext _renderingContext;
-
-            public TagHelperRenderingContextScope(CodeRenderingContext context, TagHelperRenderingContext renderingContext)
-            {
-                if (context == null)
-                {
-                    throw new ArgumentNullException(nameof(context));
-                }
-
-                _context = context;
-                _renderingContext = renderingContext;
-            }
-
-            public void Dispose()
-            {
-                _context.TagHelperRenderingContext = _renderingContext;
-            }
-        }
-
-        #endregion
     }
 }

src/Microsoft.AspNetCore.Razor.Language/CodeGeneration/DefaultCodeRenderingContext.cs

@@ -10,9 +10,9 @@ namespace Microsoft.AspNetCore.Razor.Language.CodeGeneration
 {
     internal class DefaultCodeRenderingContext : CodeRenderingContext
     {
+        private readonly Stack<IntermediateNode> _ancestors;
         private readonly RazorCodeDocument _codeDocument;
         private readonly DocumentIntermediateNode _documentNode;
-
         private readonly List<ScopeInternal> _scopes;
 
         public DefaultCodeRenderingContext(
@@ -52,12 +52,11 @@ namespace Microsoft.AspNetCore.Razor.Language.CodeGeneration
             _documentNode = documentNode;
             Options = options;
 
+            _ancestors = new Stack<IntermediateNode>();
             Diagnostics = new RazorDiagnosticCollection();
             Items = new ItemCollection();
             LineMappings = new List<LineMapping>();
 
-            TagHelperRenderingContext = new TagHelperRenderingContext();
-
             var diagnostics = _documentNode.GetAllDiagnostics();
             for (var i = 0; i < diagnostics.Count; i++)
             {
@@ -81,6 +80,10 @@ namespace Microsoft.AspNetCore.Razor.Language.CodeGeneration
         // This will be initialized by the document writer when the context is 'live'.
         public IntermediateNodeVisitor Visitor { get; set; }
 
+        public override IEnumerable<IntermediateNode> Ancestors => _ancestors;
+
+        internal Stack<IntermediateNode> AncestorsInternal => _ancestors;
+
         public override CodeWriter CodeWriter { get; }
 
         public override RazorDiagnosticCollection Diagnostics { get; }
@@ -95,6 +98,8 @@ namespace Microsoft.AspNetCore.Razor.Language.CodeGeneration
 
         public override RazorCodeGenerationOptions Options { get; }
 
+        public override IntermediateNode Parent => _ancestors.Count == 0 ? null : _ancestors.Peek();
+
         public override RazorSourceDocument SourceDocument => _codeDocument.Source;
 
         private ScopeInternal Current => _scopes[_scopes.Count - 1];
@@ -154,10 +159,14 @@ namespace Microsoft.AspNetCore.Razor.Language.CodeGeneration
                 throw new ArgumentNullException(nameof(node));
             }
 
+            _ancestors.Push(node);
+
             for (var i = 0; i < node.Children.Count; i++)
             {
                 Visitor.Visit(node.Children[i]);
             }
+
+            _ancestors.Pop();
         }
 
         public override void RenderNode(IntermediateNode node)

src/Microsoft.AspNetCore.Razor.Language/CodeGeneration/DefaultDocumentWriter.cs

@@ -200,12 +200,7 @@ namespace Microsoft.AspNetCore.Razor.Language.CodeGeneration
 
             public override void VisitTagHelper(TagHelperIntermediateNode node)
             {
-                var tagHelperRenderingContext = new TagHelperRenderingContext();
+                VisitDefault(node);
-
-                using (Context.Push(tagHelperRenderingContext))
-                {
-                    VisitDefault(node);
-                }
             }
 
             public override void VisitDefault(IntermediateNode node)

src/Microsoft.AspNetCore.Razor.Language/Extensions/DefaultTagHelperTargetExtension.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.Globalization;
 using System.Linq;
 using System.Text;
@@ -75,6 +76,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
 
         public void WriteTagHelperBody(CodeRenderingContext context, DefaultTagHelperBodyIntermediateNode node)
         {
+            if (context.Parent as TagHelperIntermediateNode == null)
+            {
+                var message = Resources.FormatIntermediateNodes_InvalidParentNode(node.GetType(), typeof(TagHelperIntermediateNode));
+                throw new InvalidOperationException(message);
+            }
+
             if (DesignTime)
             {
                 context.RenderChildren(node);
@@ -121,6 +128,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
 
         public void WriteTagHelperCreate(CodeRenderingContext context, DefaultTagHelperCreateIntermediateNode node)
         {
+            if (context.Parent as TagHelperIntermediateNode == null)
+            {
+                var message = Resources.FormatIntermediateNodes_InvalidParentNode(node.GetType(), typeof(TagHelperIntermediateNode));
+                throw new InvalidOperationException(message);
+            }
+
             context.CodeWriter
                 .WriteStartAssignment(node.Field)
                 .Write(CreateTagHelperMethodName)
@@ -137,6 +150,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
 
         public void WriteTagHelperExecute(CodeRenderingContext context, DefaultTagHelperExecuteIntermediateNode node)
         {
+            if (context.Parent as TagHelperIntermediateNode == null)
+            {
+                var message = Resources.FormatIntermediateNodes_InvalidParentNode(node.GetType(), typeof(TagHelperIntermediateNode));
+                throw new InvalidOperationException(message);
+            }
+
             if (!DesignTime)
             {
                 context.CodeWriter
@@ -178,6 +197,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
 
         public void WriteTagHelperHtmlAttribute(CodeRenderingContext context, DefaultTagHelperHtmlAttributeIntermediateNode node)
         {
+            if (context.Parent as TagHelperIntermediateNode == null)
+            {
+                var message = Resources.FormatIntermediateNodes_InvalidParentNode(node.GetType(), typeof(TagHelperIntermediateNode));
+                throw new InvalidOperationException(message);
+            }
+
             if (DesignTime)
             {
                 context.RenderChildren(node);
@@ -261,22 +286,25 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
 
         public void WriteTagHelperProperty(CodeRenderingContext context, DefaultTagHelperPropertyIntermediateNode node)
         {
-            var tagHelperRenderingContext = context.TagHelperRenderingContext;
+            var tagHelperNode = context.Parent as TagHelperIntermediateNode;
-            var propertyName = node.BoundAttribute.GetPropertyName();
+            if (context.Parent == null)
-            var propertyValueAccessor = GetTagHelperPropertyAccessor(node.IsIndexerNameMatch, node.Field, node.AttributeName, node.BoundAttribute);
+            {
+                var message = Resources.FormatIntermediateNodes_InvalidParentNode(node.GetType(), typeof(TagHelperIntermediateNode));
+                throw new InvalidOperationException(message);
+            }
 
             if (!DesignTime)
             {
                 // Ensure that the property we're trying to set has initialized its dictionary bound properties.
                 if (node.IsIndexerNameMatch &&
-                    tagHelperRenderingContext.VerifiedPropertyDictionaries.Add($"{node.TagHelper.GetTypeName()}.{propertyName}"))
+                    object.ReferenceEquals(FindFirstUseOfIndexer(tagHelperNode, node), node))
                 {
                     // Throw a reasonable Exception at runtime if the dictionary property is null.
                     context.CodeWriter
                         .Write("if (")
                         .Write(node.Field)
                         .Write(".")
-                        .Write(propertyName)
+                        .Write(node.Property)
                         .WriteLine(" == null)");
                     using (context.CodeWriter.BuildScope())
                     {
@@ -290,34 +318,40 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
                             .WriteParameterSeparator()
                             .WriteStringLiteral(node.TagHelper.GetTypeName())
                             .WriteParameterSeparator()
-                            .WriteStringLiteral(propertyName)
+                            .WriteStringLiteral(node.Property)
                             .WriteEndMethodInvocation(endLine: false)   // End of method call
                             .WriteEndMethodInvocation();   // End of new expression / throw statement
                     }
                 }
             }
 
-            if (tagHelperRenderingContext.RenderedBoundAttributes.TryGetValue(node.AttributeName, out var previousValueAccessor))
+            // If this is not the first use of the attribute value, we need to evaluate the expression and assign it to
+            // the tag helper property.
+            //
+            // Otherwise, the value has already been computed and assigned to another tag helper. We just need to
+            // copy from that tag helper to this one.
+            //
+            // This is important because we can't evaluate the expression twice due to side-effects.
+            var firstUseOfAttribute = FindFirstUseOfAttribute(tagHelperNode, node);
+            if (!object.ReferenceEquals(firstUseOfAttribute, node))
             {
+                // If we get here, this value has already been used. We just need to copy the value.
                 context.CodeWriter
-                    .WriteStartAssignment(propertyValueAccessor)
+                    .WriteStartAssignment(GetPropertyAccessor(node))
-                    .Write(previousValueAccessor)
+                    .Write(GetPropertyAccessor(firstUseOfAttribute))
                     .WriteLine(";");
 
                 return;
             }
-            else
-            {
-                tagHelperRenderingContext.RenderedBoundAttributes[node.AttributeName] = propertyValueAccessor;
-            }
 
+            // If we get there, this is the first time seeing this property so we need to evaluate the expression.
             if (node.BoundAttribute.IsStringProperty || (node.IsIndexerNameMatch && node.BoundAttribute.IsIndexerStringProperty))
             {
                 if (DesignTime)
                 {
                     context.RenderChildren(node);
 
-                    context.CodeWriter.WriteStartAssignment(propertyValueAccessor);
+                    context.CodeWriter.WriteStartAssignment(GetPropertyAccessor(node));
                     if (node.Children.Count == 1 && node.Children.First() is HtmlContentIntermediateNode htmlNode)
                     {
                         var content = GetContent(htmlNode);
@@ -341,7 +375,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
                     context.CodeWriter
                         .WriteStartAssignment(StringValueBufferVariableName)
                         .WriteMethodInvocation(EndWriteTagHelperAttributeMethodName)
-                        .WriteStartAssignment(propertyValueAccessor)
+                        .WriteStartAssignment(GetPropertyAccessor(node))
                         .Write(StringValueBufferVariableName)
                         .WriteLine(";");
                 }
@@ -355,7 +389,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
 
                     using (context.CodeWriter.BuildLinePragma(node.Source))
                     {
-                        var assignmentPrefixLength = propertyValueAccessor.Length + " = ".Length;
+                        var accessor = GetPropertyAccessor(node);
+                        var assignmentPrefixLength = accessor.Length + " = ".Length;
                         if (node.BoundAttribute.IsEnum &&
                             node.Children.Count == 1 &&
                             node.Children.First() is IntermediateToken token &&
@@ -369,7 +404,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
                             }
 
                             context.CodeWriter
-                                .WriteStartAssignment(propertyValueAccessor)
+                                .WriteStartAssignment(accessor)
                                 .Write("global::")
                                 .Write(node.BoundAttribute.TypeName)
                                 .Write(".");
@@ -381,7 +416,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
                                 context.CodeWriter.WritePadding(assignmentPrefixLength, node.Source, context);
                             }
 
-                            context.CodeWriter.WriteStartAssignment(propertyValueAccessor);
+                            context.CodeWriter.WriteStartAssignment(GetPropertyAccessor(node));
                         }
 
                         RenderTagHelperAttributeInline(context, node, node.Source);
@@ -393,7 +428,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
                 {
                     using (context.CodeWriter.BuildLinePragma(node.Source))
                     {
-                        context.CodeWriter.WriteStartAssignment(propertyValueAccessor);
+                        context.CodeWriter.WriteStartAssignment(GetPropertyAccessor(node));
 
                         if (node.BoundAttribute.IsEnum &&
                             node.Children.Count == 1 &&
@@ -422,7 +457,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
                         ExecutionContextAddTagHelperAttributeMethodName)
                     .WriteStringLiteral(node.AttributeName)
                     .WriteParameterSeparator()
-                    .Write(propertyValueAccessor)
+                    .Write(GetPropertyAccessor(node))
                     .WriteParameterSeparator()
                     .Write($"global::Microsoft.AspNetCore.Razor.TagHelpers.HtmlAttributeValueStyle.{node.AttributeStructure}")
                     .WriteEndMethodInvocation();
@@ -548,6 +583,45 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
             }
         }
 
+        private static DefaultTagHelperPropertyIntermediateNode FindFirstUseOfIndexer(
+            TagHelperIntermediateNode tagHelperNode,
+            DefaultTagHelperPropertyIntermediateNode propertyNode)
+        {
+            Debug.Assert(tagHelperNode.Children.Contains(propertyNode));
+            Debug.Assert(propertyNode.IsIndexerNameMatch);
+
+            for (var i = 0; i < tagHelperNode.Children.Count; i++)
+            {
+                if (tagHelperNode.Children[i] is DefaultTagHelperPropertyIntermediateNode otherPropertyNode &&
+                    otherPropertyNode.TagHelper.Equals(propertyNode.TagHelper) &&
+                    otherPropertyNode.BoundAttribute.Equals(propertyNode.BoundAttribute) &&
+                    otherPropertyNode.IsIndexerNameMatch)
+                {
+                    return otherPropertyNode;
+                }
+            }
+
+            // This is unreachable, we should find 'propertyNode' in the list of children.
+            throw new InvalidOperationException();
+        }
+
+        private static DefaultTagHelperPropertyIntermediateNode FindFirstUseOfAttribute(
+            TagHelperIntermediateNode tagHelperNode,
+            DefaultTagHelperPropertyIntermediateNode propertyNode)
+        {
+            for (var i = 0; i < tagHelperNode.Children.Count; i++)
+            {
+                if (tagHelperNode.Children[i] is DefaultTagHelperPropertyIntermediateNode otherPropertyNode &&
+                    string.Equals(otherPropertyNode.AttributeName, propertyNode.AttributeName, StringComparison.Ordinal))
+                {
+                    return otherPropertyNode;
+                }
+            }
+
+            // This is unreachable, we should find 'propertyNode' in the list of children.
+            throw new InvalidOperationException();
+        }
+
         private string GetContent(HtmlContentIntermediateNode node)
         {
             var builder = new StringBuilder();
@@ -562,17 +636,13 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
             return builder.ToString();
         }
 
-        private static string GetTagHelperPropertyAccessor(
+        private static string GetPropertyAccessor(DefaultTagHelperPropertyIntermediateNode node)
-            bool isIndexerNameMatch,
-            string tagHelperVariableName,
-            string attributeName,
-            BoundAttributeDescriptor descriptor)
         {
-            var propertyAccessor = $"{tagHelperVariableName}.{descriptor.GetPropertyName()}";
+            var propertyAccessor = $"{node.Field}.{node.Property}";
 
-            if (isIndexerNameMatch)
+            if (node.IsIndexerNameMatch)
             {
-                var dictionaryKey = attributeName.Substring(descriptor.IndexerNamePrefix.Length);
+                var dictionaryKey = node.AttributeName.Substring(node.BoundAttribute.IndexerNamePrefix.Length);
                 propertyAccessor += $"[\"{dictionaryKey}\"]";
             }
 

src/Microsoft.AspNetCore.Razor.Language/Extensions/PreallocatedAttributeTargetExtension.cs

@@ -2,7 +2,9 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Diagnostics;
 using Microsoft.AspNetCore.Razor.Language.CodeGeneration;
+using Microsoft.AspNetCore.Razor.Language.Intermediate;
 
 namespace Microsoft.AspNetCore.Razor.Language.Extensions
 {
@@ -50,6 +52,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
 
         public void WriteTagHelperHtmlAttribute(CodeRenderingContext context, PreallocatedTagHelperHtmlAttributeIntermediateNode node)
         {
+            if (context.Parent as TagHelperIntermediateNode == null)
+            {
+                var message = Resources.FormatIntermediateNodes_InvalidParentNode(node.GetType(), typeof(TagHelperIntermediateNode));
+                throw new InvalidOperationException(message);
+            }
+
             context.CodeWriter
                 .WriteStartInstanceMethodInvocation(ExecutionContextVariableName, ExecutionContextAddHtmlAttributeMethodName)
                 .Write(node.VariableName)
@@ -75,20 +83,23 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
 
         public void WriteTagHelperProperty(CodeRenderingContext context, PreallocatedTagHelperPropertyIntermediateNode node)
         {
-            var propertyName = node.BoundAttribute.GetPropertyName();
+            var tagHelperNode = context.Parent as TagHelperIntermediateNode;
-            var propertyValueAccessor = GetTagHelperPropertyAccessor(node.IsIndexerNameMatch, node.Field, node.AttributeName, node.BoundAttribute);
+            if (tagHelperNode == null)
-            var attributeValueAccessor = $"{node.VariableName}.Value" /* ORIGINAL: TagHelperAttributeValuePropertyName */;
+            {
+                var message = Resources.FormatIntermediateNodes_InvalidParentNode(node.GetType(), typeof(TagHelperIntermediateNode));
+                throw new InvalidOperationException(message);
+            }
 
             // Ensure that the property we're trying to set has initialized its dictionary bound properties.
             if (node.IsIndexerNameMatch &&
-                context.TagHelperRenderingContext.VerifiedPropertyDictionaries.Add($"{node.TagHelper.GetTypeName()}.{propertyName}"))
+                object.ReferenceEquals(FindFirstUseOfIndexer(tagHelperNode, node), node))
             {
                 // Throw a reasonable Exception at runtime if the dictionary property is null.
                 context.CodeWriter
                     .Write("if (")
                     .Write(node.Field)
                     .Write(".")
-                    .Write(propertyName)
+                    .Write(node.Property)
                     .WriteLine(" == null)");
                 using (context.CodeWriter.BuildScope())
                 {
@@ -102,33 +113,51 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
                         .WriteParameterSeparator()
                         .WriteStringLiteral(node.TagHelper.GetTypeName())
                         .WriteParameterSeparator()
-                        .WriteStringLiteral(propertyName)
+                        .WriteStringLiteral(node.Property)
                         .WriteEndMethodInvocation(endLine: false)   // End of method call
                         .WriteEndMethodInvocation();   // End of new expression / throw statement
                 }
             }
 
             context.CodeWriter
-                .WriteStartAssignment(propertyValueAccessor)
+                .WriteStartAssignment(GetPropertyAccessor(node))
                 .Write("(string)")
-                .Write(attributeValueAccessor)
+                .Write($"{node.VariableName}.Value")
                 .WriteLine(";")
                 .WriteStartInstanceMethodInvocation(ExecutionContextVariableName, ExecutionContextAddTagHelperAttributeMethodName)
                 .Write(node.VariableName)
                 .WriteEndMethodInvocation();
         }
 
-        private static string GetTagHelperPropertyAccessor(
+        private static PreallocatedTagHelperPropertyIntermediateNode FindFirstUseOfIndexer(
-            bool isIndexerNameMatch,
+            TagHelperIntermediateNode tagHelperNode,
-            string tagHelperVariableName,
+            PreallocatedTagHelperPropertyIntermediateNode propertyNode)
-            string attributeName,
-            BoundAttributeDescriptor descriptor)
         {
-            var propertyAccessor = $"{tagHelperVariableName}.{descriptor.GetPropertyName()}";
+            Debug.Assert(tagHelperNode.Children.Contains(propertyNode));
+            Debug.Assert(propertyNode.IsIndexerNameMatch);
 
-            if (isIndexerNameMatch)
+            for (var i = 0; i < tagHelperNode.Children.Count; i++)
             {
-                var dictionaryKey = attributeName.Substring(descriptor.IndexerNamePrefix.Length);
+                if (tagHelperNode.Children[i] is PreallocatedTagHelperPropertyIntermediateNode otherPropertyNode &&
+                    otherPropertyNode.TagHelper.Equals(propertyNode.TagHelper) &&
+                    otherPropertyNode.BoundAttribute.Equals(propertyNode.BoundAttribute) &&
+                    otherPropertyNode.IsIndexerNameMatch)
+                {
+                    return otherPropertyNode;
+                }
+            }
+
+            // This is unreachable, we should find 'propertyNode' in the list of children.
+            throw new InvalidOperationException();
+        }
+
+        private static string GetPropertyAccessor(PreallocatedTagHelperPropertyIntermediateNode node)
+        {
+            var propertyAccessor = $"{node.Field}.{node.Property}";
+
+            if (node.IsIndexerNameMatch)
+            {
+                var dictionaryKey = node.AttributeName.Substring(node.BoundAttribute.IndexerNamePrefix.Length);
                 propertyAccessor += $"[\"{dictionaryKey}\"]";
             }
 

src/Microsoft.AspNetCore.Razor.Language/Properties/Resources.Designer.cs

@@ -584,6 +584,20 @@ namespace Microsoft.AspNetCore.Razor.Language
         internal static string FormatRenderingContextRequiresDelegate(object p0, object p1)
             => string.Format(CultureInfo.CurrentCulture, GetString("RenderingContextRequiresDelegate"), p0, p1);
 
+        /// <summary>
+        /// The '{0}' node type can only be used as a direct child of a '{1}' node.
+        /// </summary>
+        internal static string IntermediateNodes_InvalidParentNode
+        {
+            get => GetString("IntermediateNodes_InvalidParentNode");
+        }
+
+        /// <summary>
+        /// The '{0}' node type can only be used as a direct child of a '{1}' node.
+        /// </summary>
+        internal static string FormatIntermediateNodes_InvalidParentNode(object p0, object p1)
+            => string.Format(CultureInfo.CurrentCulture, GetString("IntermediateNodes_InvalidParentNode"), p0, p1);
+
         private static string GetString(string name, params string[] formatterNames)
         {
             var value = _resourceManager.GetString(name);

src/Microsoft.AspNetCore.Razor.Language/Resources.resx

@@ -240,4 +240,7 @@
   <data name="RenderingContextRequiresDelegate" xml:space="preserve">
     <value>The '{0}' requires a '{1}' delegate to be set.</value>
   </data>
+  <data name="IntermediateNodes_InvalidParentNode" xml:space="preserve">
+    <value>The '{0}' node type can only be used as a direct child of a '{1}' node.</value>
+  </data>
 </root>

test/Microsoft.AspNetCore.Razor.Language.Test/Extensions/DefaultTagHelperTargetExtensionTest.cs

@@ -71,6 +71,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
             var extension = new DefaultTagHelperTargetExtension() { DesignTime = true };
             var context = TestCodeRenderingContext.CreateDesignTime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperBodyIntermediateNode()
             {
                 Children =
@@ -78,6 +79,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
                     new CSharpExpressionIntermediateNode(),
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperBody(context, node);
@@ -98,6 +101,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
             var extension = new DefaultTagHelperTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperBodyIntermediateNode()
             {
                 Children =
@@ -107,6 +111,8 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
                 TagMode = TagMode.SelfClosing,
                 TagName = "p",
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperBody(context, node);
@@ -130,11 +136,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
             var extension = new DefaultTagHelperTargetExtension() { DesignTime = true };
             var context = TestCodeRenderingContext.CreateDesignTime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperCreateIntermediateNode()
             {
                 Field = "__TestNamespace_MyTagHelper",
                 Type = "TestNamespace.MyTagHelper",
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperCreate(context, node);
@@ -155,11 +164,14 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
             var extension = new DefaultTagHelperTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperCreateIntermediateNode()
             {
                 Field = "__TestNamespace_MyTagHelper",
                 Type = "TestNamespace.MyTagHelper",
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperCreate(context, node);
@@ -181,7 +193,10 @@ __tagHelperExecutionContext.Add(__TestNamespace_MyTagHelper);
             var extension = new DefaultTagHelperTargetExtension() { DesignTime = true };
             var context = TestCodeRenderingContext.CreateDesignTime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperExecuteIntermediateNode();
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperExecute(context, node);
@@ -201,7 +216,10 @@ __tagHelperExecutionContext.Add(__TestNamespace_MyTagHelper);
             var extension = new DefaultTagHelperTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperExecuteIntermediateNode();
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperExecute(context, node);
@@ -228,6 +246,7 @@ __tagHelperExecutionContext = __tagHelperScopeManager.End();
             var extension = new DefaultTagHelperTargetExtension() { DesignTime = true };
             var context = TestCodeRenderingContext.CreateDesignTime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperHtmlAttributeIntermediateNode()
             {
                 AttributeName = "name",
@@ -244,6 +263,8 @@ __tagHelperExecutionContext = __tagHelperScopeManager.End();
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperHtmlAttribute(context, node);
@@ -265,6 +286,7 @@ Render Children
             var extension = new DefaultTagHelperTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperHtmlAttributeIntermediateNode()
             {
                 AttributeName = "name",
@@ -277,6 +299,8 @@ Render Children
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperHtmlAttribute(context, node);
@@ -300,6 +324,7 @@ __tagHelperExecutionContext.AddHtmlAttribute(""name"", Html.Raw(__tagHelperStrin
             var extension = new DefaultTagHelperTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperHtmlAttributeIntermediateNode()
             {
                 AttributeName = "name",
@@ -316,6 +341,8 @@ __tagHelperExecutionContext.AddHtmlAttribute(""name"", Html.Raw(__tagHelperStrin
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperHtmlAttribute(context, node);
@@ -339,6 +366,7 @@ EndAddHtmlAttributeValues(__tagHelperExecutionContext);
             var extension = new DefaultTagHelperTargetExtension() { DesignTime = true };
             var context = TestCodeRenderingContext.CreateDesignTime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperPropertyIntermediateNode()
             {
                 AttributeName = "bound",
@@ -356,6 +384,8 @@ EndAddHtmlAttributeValues(__tagHelperExecutionContext);
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -377,6 +407,7 @@ __InputTagHelper.StringProp = ""value"";
             var extension = new DefaultTagHelperTargetExtension() { DesignTime = true };
             var context = TestCodeRenderingContext.CreateDesignTime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperPropertyIntermediateNode()
             {
                 AttributeName = "bound",
@@ -394,6 +425,8 @@ __InputTagHelper.StringProp = ""value"";
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -415,6 +448,7 @@ __InputTagHelper.StringProp = string.Empty;
             var extension = new DefaultTagHelperTargetExtension() { DesignTime = true };
             var context = TestCodeRenderingContext.CreateDesignTime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperPropertyIntermediateNode()
             {
                 AttributeName = "bound",
@@ -433,6 +467,8 @@ __InputTagHelper.StringProp = string.Empty;
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -450,6 +486,50 @@ __InputTagHelper.IntProp = 32;
                 ignoreLineEndingDifferences: true);
         }
 
+        // If a value is bound to multiple tag helpers, we want to make sure to only render the first
+        // occurrence of the expression due to side-effects.
+        [Fact]
+        public void WriteTagHelperProperty_DesignTime_NonStringProperty_SecondUseOfAttribute()
+        {
+            // Arrange
+            var extension = new DefaultTagHelperTargetExtension() { DesignTime = true };
+            var context = TestCodeRenderingContext.CreateDesignTime();
+
+            var tagHelperNode = new TagHelperIntermediateNode();
+            var node1 = new DefaultTagHelperPropertyIntermediateNode()
+            {
+                // We only look at the attribute name here.
+                AttributeName = "bound",
+                Field = "__OtherTagHelper",
+                Property = "IntProp",
+            };
+            var node2 = new DefaultTagHelperPropertyIntermediateNode()
+            {
+                AttributeName = "bound",
+                AttributeStructure = AttributeStructure.DoubleQuotes,
+                BoundAttribute = IntPropertyTagHelper.BoundAttributes.Single(),
+                Field = "__InputTagHelper",
+                IsIndexerNameMatch = false,
+                Property = "IntProp",
+                TagHelper = IntPropertyTagHelper,
+                Source = Span,
+            };
+            tagHelperNode.Children.Add(node1);
+            tagHelperNode.Children.Add(node2);
+            Push(context, tagHelperNode);
+
+            // Act
+            extension.WriteTagHelperProperty(context, node2);
+
+            // Assert
+            var csharp = context.CodeWriter.Builder.ToString();
+            Assert.Equal(
+@"__InputTagHelper.IntProp = __OtherTagHelper.IntProp;
+",
+                csharp,
+                ignoreLineEndingDifferences: true);
+        }
+
         [Fact]
         public void WriteTagHelperProperty_DesignTime_NonStringProperty_RendersCorrectly_WithoutLocation()
         {
@@ -457,6 +537,7 @@ __InputTagHelper.IntProp = 32;
             var extension = new DefaultTagHelperTargetExtension() { DesignTime = true };
             var context = TestCodeRenderingContext.CreateDesignTime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperPropertyIntermediateNode()
             {
                 AttributeName = "bound",
@@ -474,6 +555,8 @@ __InputTagHelper.IntProp = 32;
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -494,6 +577,7 @@ __InputTagHelper.IntProp = 32;
             var extension = new DefaultTagHelperTargetExtension() { DesignTime = true };
             var context = TestCodeRenderingContext.CreateDesignTime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperPropertyIntermediateNode()
             {
                 AttributeName = "foo-bound",
@@ -512,6 +596,8 @@ __InputTagHelper.IntProp = 32;
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -536,6 +622,7 @@ __InputTagHelper.IntIndexer[""bound""] = 32;
             var extension = new DefaultTagHelperTargetExtension() { DesignTime = true };
             var context = TestCodeRenderingContext.CreateDesignTime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperPropertyIntermediateNode()
             {
                 AttributeName = "foo-bound",
@@ -553,6 +640,8 @@ __InputTagHelper.IntIndexer[""bound""] = 32;
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -573,6 +662,7 @@ __InputTagHelper.IntIndexer[""bound""] = 32;
             var extension = new DefaultTagHelperTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperPropertyIntermediateNode()
             {
                 AttributeName = "bound",
@@ -590,6 +680,8 @@ __InputTagHelper.IntIndexer[""bound""] = 32;
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -616,6 +708,7 @@ __tagHelperExecutionContext.AddTagHelperAttribute(""bound"", __InputTagHelper.St
             var extension = new DefaultTagHelperTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperPropertyIntermediateNode()
             {
                 AttributeName = "bound",
@@ -634,6 +727,8 @@ __tagHelperExecutionContext.AddTagHelperAttribute(""bound"", __InputTagHelper.St
                     }
                 },
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -652,6 +747,50 @@ __tagHelperExecutionContext.AddTagHelperAttribute(""bound"", __InputTagHelper.In
                 ignoreLineEndingDifferences: true);
         }
 
+        // If a value is bound to multiple tag helpers, we want to make sure to only render the first
+        // occurrence of the expression due to side-effects.
+        [Fact]
+        public void WriteTagHelperProperty_Runtime_NonStringProperty_SecondUseOfAttribute()
+        {
+            // Arrange
+            var extension = new DefaultTagHelperTargetExtension();
+            var context = TestCodeRenderingContext.CreateRuntime();
+
+            var tagHelperNode = new TagHelperIntermediateNode();
+            var node1 = new DefaultTagHelperPropertyIntermediateNode()
+            {
+                // We only look at the attribute name here.
+                AttributeName = "bound",
+                Field = "__OtherTagHelper",
+                Property = "IntProp",
+            };
+            var node2 = new DefaultTagHelperPropertyIntermediateNode()
+            {
+                AttributeName = "bound",
+                AttributeStructure = AttributeStructure.DoubleQuotes,
+                BoundAttribute = IntPropertyTagHelper.BoundAttributes.Single(),
+                Field = "__InputTagHelper",
+                IsIndexerNameMatch = false,
+                Property = "IntProp",
+                TagHelper = IntPropertyTagHelper,
+                Source = Span,
+            };
+            tagHelperNode.Children.Add(node1);
+            tagHelperNode.Children.Add(node2);
+            Push(context, tagHelperNode);
+
+            // Act
+            extension.WriteTagHelperProperty(context, node2);
+
+            // Assert
+            var csharp = context.CodeWriter.Builder.ToString();
+            Assert.Equal(
+@"__InputTagHelper.IntProp = __OtherTagHelper.IntProp;
+",
+                csharp,
+                ignoreLineEndingDifferences: true);
+        }
+
         [Fact]
         public void WriteTagHelperProperty_Runtime_NonStringProperty_RendersCorrectly_WithoutLocation()
         {
@@ -659,6 +798,7 @@ __tagHelperExecutionContext.AddTagHelperAttribute(""bound"", __InputTagHelper.In
             var extension = new DefaultTagHelperTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperPropertyIntermediateNode()
             {
                 AttributeName = "bound",
@@ -676,6 +816,8 @@ __tagHelperExecutionContext.AddTagHelperAttribute(""bound"", __InputTagHelper.In
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -697,6 +839,7 @@ __tagHelperExecutionContext.AddTagHelperAttribute(""bound"", __InputTagHelper.In
             var extension = new DefaultTagHelperTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperPropertyIntermediateNode()
             {
                 AttributeName = "foo-bound",
@@ -715,6 +858,8 @@ __tagHelperExecutionContext.AddTagHelperAttribute(""bound"", __InputTagHelper.In
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -729,6 +874,71 @@ __tagHelperExecutionContext.AddTagHelperAttribute(""bound"", __InputTagHelper.In
 #line 3 ""test.cshtml""
 __InputTagHelper.IntIndexer[""bound""] = 32;
 
+#line default
+#line hidden
+__tagHelperExecutionContext.AddTagHelperAttribute(""foo-bound"", __InputTagHelper.IntIndexer[""bound""], global::Microsoft.AspNetCore.Razor.TagHelpers.HtmlAttributeValueStyle.DoubleQuotes);
+",
+                csharp,
+                ignoreLineEndingDifferences: true);
+        }
+
+        [Fact] // We should only emit the validation code for the first use of an indexer property.
+        public void WriteTagHelperProperty_Runtime_NonStringIndexer_MultipleValues()
+        {
+            // Arrange
+            var extension = new DefaultTagHelperTargetExtension();
+            var context = TestCodeRenderingContext.CreateRuntime();
+
+            var tagHelperNode = new TagHelperIntermediateNode();
+            var node1 = new DefaultTagHelperPropertyIntermediateNode()
+            {
+                AttributeName = "foo-first",
+                AttributeStructure = AttributeStructure.DoubleQuotes,
+                BoundAttribute = IntIndexerTagHelper.BoundAttributes.Single(),
+                Field = "__InputTagHelper",
+                IsIndexerNameMatch = true,
+                Property = "IntIndexer",
+                TagHelper = IntIndexerTagHelper,
+                Source = Span,
+                Children =
+                {
+                    new CSharpExpressionIntermediateNode()
+                    {
+                        Children = { new IntermediateToken { Kind = IntermediateToken.TokenKind.CSharp, Content = "17", } },
+                    }
+                }
+            };
+            var node2 = new DefaultTagHelperPropertyIntermediateNode()
+            {
+                AttributeName = "foo-bound",
+                AttributeStructure = AttributeStructure.DoubleQuotes,
+                BoundAttribute = IntIndexerTagHelper.BoundAttributes.Single(),
+                Field = "__InputTagHelper",
+                IsIndexerNameMatch = true,
+                Property = "IntIndexer",
+                TagHelper = IntIndexerTagHelper,
+                Source = Span,
+                Children =
+                {
+                    new CSharpExpressionIntermediateNode()
+                    {
+                        Children = { new IntermediateToken { Kind = IntermediateToken.TokenKind.CSharp, Content = "32", } },
+                    }
+                }
+            };
+            tagHelperNode.Children.Add(node1);
+            tagHelperNode.Children.Add(node2);
+            Push(context, tagHelperNode);
+
+            // Act
+            extension.WriteTagHelperProperty(context, node2);
+
+            // Assert
+            var csharp = context.CodeWriter.Builder.ToString();
+            Assert.Equal(
+@"#line 3 ""test.cshtml""
+__InputTagHelper.IntIndexer[""bound""] = 32;
+
 #line default
 #line hidden
 __tagHelperExecutionContext.AddTagHelperAttribute(""foo-bound"", __InputTagHelper.IntIndexer[""bound""], global::Microsoft.AspNetCore.Razor.TagHelpers.HtmlAttributeValueStyle.DoubleQuotes);
@@ -744,6 +954,7 @@ __tagHelperExecutionContext.AddTagHelperAttribute(""foo-bound"", __InputTagHelpe
             var extension = new DefaultTagHelperTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new DefaultTagHelperPropertyIntermediateNode()
             {
                 AttributeName = "foo-bound",
@@ -761,6 +972,8 @@ __tagHelperExecutionContext.AddTagHelperAttribute(""foo-bound"", __InputTagHelpe
                     }
                 }
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -785,7 +998,7 @@ __tagHelperExecutionContext.AddTagHelperAttribute(""foo-bound"", __InputTagHelpe
             // Arrange
             var extension = new DefaultTagHelperTargetExtension() { DesignTime = true };
             var context = TestCodeRenderingContext.CreateDesignTime();
-
+            
             var node = new DefaultTagHelperRuntimeIntermediateNode();
 
             // Act
@@ -805,7 +1018,7 @@ __tagHelperExecutionContext.AddTagHelperAttribute(""foo-bound"", __InputTagHelpe
             // Arrange
             var extension = new DefaultTagHelperTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
-
+            
             var node = new DefaultTagHelperRuntimeIntermediateNode();
 
             // Act
@@ -837,6 +1050,11 @@ private global::Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperScopeMana
                 ignoreLineEndingDifferences: true);
         }
 
+        private static void Push(CodeRenderingContext context, TagHelperIntermediateNode node)
+        {
+            ((DefaultCodeRenderingContext)context).AncestorsInternal.Push(node);
+        }
+
         private static DocumentIntermediateNode Lower(RazorCodeDocument codeDocument)
         {
             var engine = RazorEngine.Create();

test/Microsoft.AspNetCore.Razor.Language.Test/Extensions/PreallocatedAttributeTargetExtensionTest.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using Microsoft.AspNetCore.Razor.Language.CodeGeneration;
+using Microsoft.AspNetCore.Razor.Language.Intermediate;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Razor.Language.Extensions
@@ -9,7 +10,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
     public class PreallocatedAttributeTargetExtensionTest
     {
         [Fact]
-        public void WriteDeclarePreallocatedTagHelperHtmlAttribute_RendersCorrectly()
+        public void WriteTagHelperHtmlAttributeValue_RendersCorrectly()
         {
             // Arrange
             var extension = new PreallocatedAttributeTargetExtension();
@@ -36,7 +37,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
         }
 
         [Fact]
-        public void WriteDeclarePreallocatedTagHelperHtmlAttribute_Minimized_RendersCorrectly()
+        public void WriteTagHelperHtmlAttributeValue_Minimized_RendersCorrectly()
         {
             // Arrange
             var extension = new PreallocatedAttributeTargetExtension();
@@ -63,16 +64,19 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
         }
 
         [Fact]
-        public void WriteAddPreallocatedTagHelperHtmlAttribute_RendersCorrectly()
+        public void WriteTagHelperHtmlAttribute_RendersCorrectly()
         {
             // Arrange
             var extension = new PreallocatedAttributeTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new PreallocatedTagHelperHtmlAttributeIntermediateNode()
             {
                 VariableName = "_tagHelper1"
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperHtmlAttribute(context, node);
@@ -87,12 +91,12 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
         }
 
         [Fact]
-        public void WriteDeclarePreallocatedTagHelperAttribute_RendersCorrectly()
+        public void WriteTagHelperPropertyValue_RendersCorrectly()
         {
             // Arrange
             var extension = new PreallocatedAttributeTargetExtension();
             var context = TestCodeRenderingContext.CreateRuntime();
-
+            
             var node = new PreallocatedTagHelperPropertyValueIntermediateNode()
             {
                 AttributeName = "Foo",
@@ -114,7 +118,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
         }
 
         [Fact]
-        public void WriteSetPreallocatedTagHelperProperty_RendersCorrectly()
+        public void WriteTagHelperProperty_RendersCorrectly()
         {
             // Arrange
             var extension = new PreallocatedAttributeTargetExtension();
@@ -124,7 +128,6 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
             tagHelperBuilder.TypeName("FooTagHelper");
 
             var builder = new DefaultBoundAttributeDescriptorBuilder(tagHelperBuilder, TagHelperConventions.DefaultKind);
-
             builder
                 .Name("Foo")
                 .TypeName("System.String")
@@ -132,13 +135,17 @@ namespace Microsoft.AspNetCore.Razor.Language.Extensions
 
             var descriptor = builder.Build();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new PreallocatedTagHelperPropertyIntermediateNode()
             {
                 AttributeName = descriptor.Name,
-                Field = "__FooTagHelper",
-                VariableName = "_tagHelper1",
                 BoundAttribute = descriptor,
+                Field = "__FooTagHelper",
+                Property = "FooProp",
+                VariableName = "_tagHelper1",
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -164,7 +171,6 @@ __tagHelperExecutionContext.AddTagHelperAttribute(_tagHelper1);
             tagHelperBuilder.TypeName("FooTagHelper");
 
             var builder = new DefaultBoundAttributeDescriptorBuilder(tagHelperBuilder, TagHelperConventions.DefaultKind);
-
             builder
                 .Name("Foo")
                 .TypeName("System.Collections.Generic.Dictionary<System.String, System.String>")
@@ -173,6 +179,7 @@ __tagHelperExecutionContext.AddTagHelperAttribute(_tagHelper1);
 
             var descriptor = builder.Build();
 
+            var tagHelperNode = new TagHelperIntermediateNode();
             var node = new PreallocatedTagHelperPropertyIntermediateNode()
             {
                 AttributeName = "pre-Foo",
@@ -180,8 +187,11 @@ __tagHelperExecutionContext.AddTagHelperAttribute(_tagHelper1);
                 VariableName = "_tagHelper1",
                 BoundAttribute = descriptor,
                 IsIndexerNameMatch = true,
+                Property = "FooProp",
                 TagHelper = tagHelperBuilder.Build(),
             };
+            tagHelperNode.Children.Add(node);
+            Push(context, tagHelperNode);
 
             // Act
             extension.WriteTagHelperProperty(context, node);
@@ -199,5 +209,68 @@ __tagHelperExecutionContext.AddTagHelperAttribute(_tagHelper1);
                 csharp,
                 ignoreLineEndingDifferences: true);
         }
+
+        [Fact]
+        public void WriteSetPreallocatedTagHelperProperty_IndexerAttribute_MultipleValues()
+        {
+            // Arrange
+            var extension = new PreallocatedAttributeTargetExtension();
+            var context = TestCodeRenderingContext.CreateRuntime();
+
+            var tagHelperBuilder = new DefaultTagHelperDescriptorBuilder(TagHelperConventions.DefaultKind, "FooTagHelper", "Test");
+            tagHelperBuilder.TypeName("FooTagHelper");
+
+            var builder = new DefaultBoundAttributeDescriptorBuilder(tagHelperBuilder, TagHelperConventions.DefaultKind);
+            builder
+                .Name("Foo")
+                .TypeName("System.Collections.Generic.Dictionary<System.String, System.String>")
+                .AsDictionaryAttribute("pre-", "System.String")
+                .PropertyName("FooProp");
+
+            var boundAttribute = builder.Build();
+            var tagHelper = tagHelperBuilder.Build();
+
+            var tagHelperNode = new TagHelperIntermediateNode();
+            var node1 = new PreallocatedTagHelperPropertyIntermediateNode()
+            {
+                AttributeName = "pre-Bar",
+                Field = "__FooTagHelper",
+                VariableName = "_tagHelper0s",
+                BoundAttribute = boundAttribute,
+                IsIndexerNameMatch = true,
+                Property = "FooProp",
+                TagHelper = tagHelper,
+            };
+            var node2 = new PreallocatedTagHelperPropertyIntermediateNode()
+            {
+                AttributeName = "pre-Foo",
+                Field = "__FooTagHelper",
+                VariableName = "_tagHelper1",
+                BoundAttribute = boundAttribute,
+                IsIndexerNameMatch = true,
+                Property = "FooProp",
+                TagHelper = tagHelper,
+            };
+            tagHelperNode.Children.Add(node1);
+            tagHelperNode.Children.Add(node2);
+            Push(context, tagHelperNode);
+
+            // Act
+            extension.WriteTagHelperProperty(context, node2);
+
+            // Assert
+            var csharp = context.CodeWriter.Builder.ToString();
+            Assert.Equal(
+@"__FooTagHelper.FooProp[""Foo""] = (string)_tagHelper1.Value;
+__tagHelperExecutionContext.AddTagHelperAttribute(_tagHelper1);
+",
+                csharp,
+                ignoreLineEndingDifferences: true);
+        }
+
+        private static void Push(CodeRenderingContext context, TagHelperIntermediateNode node)
+        {
+            ((DefaultCodeRenderingContext)context).AncestorsInternal.Push(node);
+        }
     }
 }

test/Microsoft.AspNetCore.Razor.Language.Test/TestFiles/IntegrationTests/CodeGenerationIntegrationTest/PrefixedAttributeTagHelpers_Runtime.codegen.cs

@@ -181,6 +181,10 @@ __TestNamespace_InputTagHelper1.IntDictionaryProperty["pepper"] = 98;
             __tagHelperExecutionContext.AddTagHelperAttribute(__tagHelperAttribute_5);
             __TestNamespace_InputTagHelper2.StringDictionaryProperty["paprika"] = (string)__tagHelperAttribute_5.Value;
             __tagHelperExecutionContext.AddTagHelperAttribute(__tagHelperAttribute_5);
+            if (__TestNamespace_InputTagHelper1.StringDictionaryProperty == null)
+            {
+                throw new InvalidOperationException(InvalidTagHelperIndexerAssignment("string-prefix-cumin", "TestNamespace.InputTagHelper1", "StringDictionaryProperty"));
+            }
             BeginWriteTagHelperAttribute();
             WriteLiteral("literate ");
 #line 21 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/PrefixedAttributeTagHelpers.cshtml"
@@ -192,6 +196,10 @@ __TestNamespace_InputTagHelper1.IntDictionaryProperty["pepper"] = 98;
             __tagHelperStringValueBuffer = EndWriteTagHelperAttribute();
             __TestNamespace_InputTagHelper1.StringDictionaryProperty["cumin"] = __tagHelperStringValueBuffer;
             __tagHelperExecutionContext.AddTagHelperAttribute("string-prefix-cumin", __TestNamespace_InputTagHelper1.StringDictionaryProperty["cumin"], global::Microsoft.AspNetCore.Razor.TagHelpers.HtmlAttributeValueStyle.DoubleQuotes);
+            if (__TestNamespace_InputTagHelper2.StringDictionaryProperty == null)
+            {
+                throw new InvalidOperationException(InvalidTagHelperIndexerAssignment("string-prefix-cumin", "TestNamespace.InputTagHelper2", "StringDictionaryProperty"));
+            }
             __TestNamespace_InputTagHelper2.StringDictionaryProperty["cumin"] = __TestNamespace_InputTagHelper1.StringDictionaryProperty["cumin"];
             await __tagHelperRunner.RunAsync(__tagHelperExecutionContext);
             if (!__tagHelperExecutionContext.Output.IsContentModified)