Addressed feedback

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

@@ -139,6 +139,53 @@ public void WriteSetTagHelperProperty_NonStringAttribute_RendersCorrectly()
 @"#line 3 ""test.cshtml""
 __InputTagHelper.FooProp = 42;
 
+#line default
+#line hidden
+",
+                csharp,
+                ignoreLineEndingDifferences: true);
+        }
+
+        [Fact]
+        public void WriteSetTagHelperProperty_IndexerAttribute_RendersCorrectly()
+        {
+            // Arrange
+            var descriptors = new[]
+            {
+                CreateTagHelperDescriptor(
+                    tagName: "input",
+                    typeName: "InputTagHelper",
+                    assemblyName: "TestAssembly",
+                    attributes: new Action<ITagHelperBoundAttributeDescriptorBuilder>[]
+                    {
+                        builder => builder
+                            .Name("bound")
+                            .PropertyName("FooProp")
+                            .TypeName("System.Collections.Generic.Dictionary<System.String, System.Int32>")
+                            .AsDictionary("foo-", "System.Int32"),
+                    })
+            };
+            var engine = RazorEngine.Create(builder => builder.AddTagHelpers(descriptors));
+            var content = @"
+@addTagHelper *, TestAssembly
+<input foo-bound=""42"" />";
+            var sourceDocument = TestRazorSourceDocument.Create(content);
+            var codeDocument = RazorCodeDocument.Create(sourceDocument);
+            var irDocument = Lower(codeDocument, engine);
+            var node = irDocument.Children.Last().Children[2] as SetTagHelperPropertyIRNode;
+
+            var writer = new DesignTimeTagHelperWriter();
+            var context = GetCSharpRenderingContext(writer, codeDocument);
+
+            // Act
+            writer.WriteSetTagHelperProperty(context, node);
+
+            // Assert
+            var csharp = context.Writer.Builder.ToString();
+            Assert.Equal(
+@"#line 3 ""test.cshtml""
+__InputTagHelper.FooProp[""bound""] = 42;
+
 #line default
 #line hidden
 ",

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

@@ -316,6 +316,8 @@ public void WriteSetTagHelperProperty_RendersCorrectly()
 
             // Assert
             var csharp = context.Writer.Builder.ToString();
+
+            // The attribute value is not rendered inline because we are not using the preallocated writer.
             Assert.Equal(
 @"BeginWriteTagHelperAttribute();
 Render Children