Add indexer null-check for preallocated tag helper attributes

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

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using Microsoft.AspNetCore.Razor.Language.Intermediate;
 using Microsoft.AspNetCore.Razor.Language.Legacy;
 
@@ -18,6 +19,8 @@ namespace Microsoft.AspNetCore.Razor.Language.CodeGeneration
 
         public string ExecutionContextAddTagHelperAttributeMethodName { get; set; } = "AddTagHelperAttribute";
 
+        public string FormatInvalidIndexerAssignmentMethodName { get; set; } = "InvalidTagHelperIndexerAssignment";
+
         public void WriteDeclarePreallocatedTagHelperHtmlAttribute(CSharpRenderingContext context, DeclarePreallocatedTagHelperHtmlAttributeIRNode node)
         {
             context.Writer
@@ -74,8 +77,39 @@ namespace Microsoft.AspNetCore.Razor.Language.CodeGeneration
         public void WriteSetPreallocatedTagHelperProperty(CSharpRenderingContext context, SetPreallocatedTagHelperPropertyIRNode node)
         {
             var tagHelperVariableName = GetTagHelperVariableName(node.TagHelperTypeName);
+            var propertyName = node.Descriptor.GetPropertyName();
             var propertyValueAccessor = GetTagHelperPropertyAccessor(node.IsIndexerNameMatch, tagHelperVariableName, node.AttributeName, node.Descriptor);
             var attributeValueAccessor = $"{node.VariableName}.Value" /* ORIGINAL: TagHelperAttributeValuePropertyName */;
+
+            // Ensure that the property we're trying to set has initialized its dictionary bound properties.
+            if (node.IsIndexerNameMatch &&
+                context.TagHelperRenderingContext.VerifiedPropertyDictionaries.Add($"{node.TagHelperTypeName}.{propertyName}"))
+            {
+                // Throw a reasonable Exception at runtime if the dictionary property is null.
+                context.Writer
+                    .Write("if (")
+                    .Write(tagHelperVariableName)
+                    .Write(".")
+                    .Write(propertyName)
+                    .WriteLine(" == null)");
+                using (context.Writer.BuildScope())
+                {
+                    // System is in Host.NamespaceImports for all MVC scenarios. No need to generate FullName
+                    // of InvalidOperationException type.
+                    context.Writer
+                        .Write("throw ")
+                        .WriteStartNewObject(nameof(InvalidOperationException))
+                        .WriteStartMethodInvocation(FormatInvalidIndexerAssignmentMethodName)
+                        .WriteStringLiteral(node.AttributeName)
+                        .WriteParameterSeparator()
+                        .WriteStringLiteral(node.TagHelperTypeName)
+                        .WriteParameterSeparator()
+                        .WriteStringLiteral(propertyName)
+                        .WriteEndMethodInvocation(endLine: false)   // End of method call
+                        .WriteEndMethodInvocation();   // End of new expression / throw statement
+                }
+            }
+
             context.Writer
                 .WriteStartAssignment(propertyValueAccessor)
                 .Write("(string)")

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

@@ -324,7 +324,7 @@ namespace Microsoft.AspNetCore.Razor.Language.CodeGeneration
 
             // Ensure that the property we're trying to set has initialized its dictionary bound properties.
             if (node.IsIndexerNameMatch &&
-                tagHelperRenderingContext.VerifiedPropertyDictionaries.Add(propertyName))
+                tagHelperRenderingContext.VerifiedPropertyDictionaries.Add($"{node.TagHelperTypeName}.{propertyName}"))
             {
                 // Throw a reasonable Exception at runtime if the dictionary property is null.
                 context.Writer

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

@@ -171,7 +171,8 @@ __tagHelperExecutionContext.AddTagHelperAttribute(_tagHelper1);
             var extension = new PreallocatedAttributeTargetExtension();
             var context = new CSharpRenderingContext()
             {
-                Writer = new CSharpCodeWriter()
+                Writer = new CSharpCodeWriter(),
+                TagHelperRenderingContext = new TagHelperRenderingContext()
             };
 
             var descriptor = BoundAttributeDescriptorBuilder
@@ -197,7 +198,11 @@ __tagHelperExecutionContext.AddTagHelperAttribute(_tagHelper1);
             // Assert
             var csharp = context.Writer.Builder.ToString();
             Assert.Equal(
-@"__FooTagHelper.FooProp[""Foo""] = (string)_tagHelper1.Value;
+@"if (__FooTagHelper.FooProp == null)
+{
+    throw new InvalidOperationException(InvalidTagHelperIndexerAssignment(""pre-Foo"", ""FooTagHelper"", ""FooProp""));
+}
+__FooTagHelper.FooProp[""Foo""] = (string)_tagHelper1.Value;
 __tagHelperExecutionContext.AddTagHelperAttribute(_tagHelper1);
 ",
                 csharp,

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

@@ -105,6 +105,10 @@ __TestNamespace_InputTagHelper1.IntDictionaryProperty["garlic"] = 37;
 #line default
 #line hidden
             __tagHelperExecutionContext.AddTagHelperAttribute("int-prefix-garlic", __TestNamespace_InputTagHelper1.IntDictionaryProperty["garlic"], global::Microsoft.AspNetCore.Razor.TagHelpers.HtmlAttributeValueStyle.DoubleQuotes);
+            if (__TestNamespace_InputTagHelper2.IntDictionaryProperty == null)
+            {
+                throw new InvalidOperationException(InvalidTagHelperIndexerAssignment("int-prefix-garlic", "TestNamespace.InputTagHelper2", "IntDictionaryProperty"));
+            }
             __TestNamespace_InputTagHelper2.IntDictionaryProperty["garlic"] = __TestNamespace_InputTagHelper1.IntDictionaryProperty["garlic"];
 #line 17 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/PrefixedAttributeTagHelpers.cshtml"
 __TestNamespace_InputTagHelper1.IntProperty = 42;
@@ -140,6 +144,10 @@ __TestNamespace_InputTagHelper1.IntProperty = 42;
                 throw new InvalidOperationException(InvalidTagHelperIndexerAssignment("int-prefix-grabber", "TestNamespace.InputTagHelper2", "IntDictionaryProperty"));
             }
             __TestNamespace_InputTagHelper2.IntDictionaryProperty["grabber"] = __TestNamespace_InputTagHelper1.IntProperty;
+            if (__TestNamespace_InputTagHelper1.IntDictionaryProperty == null)
+            {
+                throw new InvalidOperationException(InvalidTagHelperIndexerAssignment("int-prefix-salt", "TestNamespace.InputTagHelper1", "IntDictionaryProperty"));
+            }
 #line 19 "TestFiles/IntegrationTests/CodeGenerationIntegrationTest/PrefixedAttributeTagHelpers.cshtml"
 __TestNamespace_InputTagHelper1.IntDictionaryProperty["salt"] = 37;
 
@@ -157,16 +165,20 @@ __TestNamespace_InputTagHelper1.IntDictionaryProperty["pepper"] = 98;
             __tagHelperExecutionContext.AddHtmlAttribute(__tagHelperAttribute_3);
             __TestNamespace_InputTagHelper1.StringProperty = (string)__tagHelperAttribute_4.Value;
             __tagHelperExecutionContext.AddTagHelperAttribute(__tagHelperAttribute_4);
+            if (__TestNamespace_InputTagHelper2.StringDictionaryProperty == null)
+            {
+                throw new InvalidOperationException(InvalidTagHelperIndexerAssignment("string-prefix-grabber", "TestNamespace.InputTagHelper2", "StringDictionaryProperty"));
+            }
             __TestNamespace_InputTagHelper2.StringDictionaryProperty["grabber"] = (string)__tagHelperAttribute_4.Value;
             __tagHelperExecutionContext.AddTagHelperAttribute(__tagHelperAttribute_4);
+            if (__TestNamespace_InputTagHelper1.StringDictionaryProperty == null)
+            {
+                throw new InvalidOperationException(InvalidTagHelperIndexerAssignment("string-prefix-paprika", "TestNamespace.InputTagHelper1", "StringDictionaryProperty"));
+            }
             __TestNamespace_InputTagHelper1.StringDictionaryProperty["paprika"] = (string)__tagHelperAttribute_5.Value;
             __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"
@@ -204,9 +216,21 @@ __TestNamespace_InputTagHelper1.IntDictionaryProperty["value"] = 37;
 #line default
 #line hidden
             __tagHelperExecutionContext.AddTagHelperAttribute("int-prefix-value", __TestNamespace_InputTagHelper1.IntDictionaryProperty["value"], global::Microsoft.AspNetCore.Razor.TagHelpers.HtmlAttributeValueStyle.DoubleQuotes);
+            if (__TestNamespace_InputTagHelper2.IntDictionaryProperty == null)
+            {
+                throw new InvalidOperationException(InvalidTagHelperIndexerAssignment("int-prefix-value", "TestNamespace.InputTagHelper2", "IntDictionaryProperty"));
+            }
             __TestNamespace_InputTagHelper2.IntDictionaryProperty["value"] = __TestNamespace_InputTagHelper1.IntDictionaryProperty["value"];
+            if (__TestNamespace_InputTagHelper1.StringDictionaryProperty == null)
+            {
+                throw new InvalidOperationException(InvalidTagHelperIndexerAssignment("string-prefix-thyme", "TestNamespace.InputTagHelper1", "StringDictionaryProperty"));
+            }
             __TestNamespace_InputTagHelper1.StringDictionaryProperty["thyme"] = (string)__tagHelperAttribute_6.Value;
             __tagHelperExecutionContext.AddTagHelperAttribute(__tagHelperAttribute_6);
+            if (__TestNamespace_InputTagHelper2.StringDictionaryProperty == null)
+            {
+                throw new InvalidOperationException(InvalidTagHelperIndexerAssignment("string-prefix-thyme", "TestNamespace.InputTagHelper2", "StringDictionaryProperty"));
+            }
             __TestNamespace_InputTagHelper2.StringDictionaryProperty["thyme"] = (string)__tagHelperAttribute_6.Value;
             __tagHelperExecutionContext.AddTagHelperAttribute(__tagHelperAttribute_6);
             await __tagHelperRunner.RunAsync(__tagHelperExecutionContext);