De-dupe TagHelperDescriptors based on Type for rendering.

- This can occur if you have multiple [TargetElement] attributes that overlap. Ultimately the descriptor is the same because its the same type, just the required attributes differ.
- Added tests to validate.

#326

src/Microsoft.AspNet.Razor/Generator/Compiler/CodeBuilder/CSharp/CSharpTagHelperCodeRenderer.cs

@@ -5,7 +5,6 @@
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
-using Microsoft.AspNet.Razor.Parser.SyntaxTree;
 using Microsoft.AspNet.Razor.TagHelpers;
 
 namespace Microsoft.AspNet.Razor.Generator.Compiler.CSharp
@@ -56,11 +55,15 @@ public CSharpTagHelperCodeRenderer([NotNull] IChunkVisitor bodyVisitor,
         /// <param name="chunk">A <see cref="TagHelperChunk"/> to render.</param>
         public void RenderTagHelper(TagHelperChunk chunk)
         {
-            var tagHelperDescriptors = chunk.Descriptors;
+            // Remove any duplicate TagHelperDescriptors that referrence the same type name. Duplicates can occur when
+            // multiple TargetElement attributes are on a TagHelper type and matchs overlap for an HTML element.
+            // Having more than one descriptor with the same TagHelper type results in generated code that runs
+            // the same TagHelper X many times (instead of once) over a single HTML element.
+            var tagHelperDescriptors = chunk.Descriptors.Distinct(TypeNameTagHelperDescriptorComparer.Default);
 
             RenderBeginTagHelperScope(chunk.TagName, chunk.SelfClosing, chunk.Children);
 
-            RenderTagHelpersCreation(chunk);
+            RenderTagHelpersCreation(chunk, tagHelperDescriptors);
 
             var attributeDescriptors = tagHelperDescriptors.SelectMany(descriptor => descriptor.Attributes);
             var boundHTMLAttributes = attributeDescriptors.Select(descriptor => descriptor.Name);
@@ -146,10 +149,10 @@ protected virtual string GenerateUniqueId()
             return Guid.NewGuid().ToString("N");
         }
 
-        private void RenderTagHelpersCreation(TagHelperChunk chunk)
+        private void RenderTagHelpersCreation(
+            TagHelperChunk chunk,
+            IEnumerable<TagHelperDescriptor> tagHelperDescriptors)
         {
-            var tagHelperDescriptors = chunk.Descriptors;
-
             // This is to maintain value accessors for attributes when creating the TagHelpers.
             // Ultimately it enables us to do scenarios like this:
             // myTagHelper1.Foo = DateTime.Now;
@@ -551,5 +554,25 @@ public int GetHashCode(TagHelperAttributeDescriptor descriptor)
                 return StringComparer.OrdinalIgnoreCase.GetHashCode(descriptor.Name);
             }
         }
+
+        private class TypeNameTagHelperDescriptorComparer : IEqualityComparer<TagHelperDescriptor>
+        {
+            public static readonly TypeNameTagHelperDescriptorComparer Default = 
+                new TypeNameTagHelperDescriptorComparer();
+
+            private TypeNameTagHelperDescriptorComparer()
+            {
+            }
+
+            public bool Equals(TagHelperDescriptor descriptorX, TagHelperDescriptor descriptorY)
+            {
+                return string.Equals(descriptorX.TypeName, descriptorY.TypeName, StringComparison.OrdinalIgnoreCase);
+            }
+
+            public int GetHashCode(TagHelperDescriptor descriptor)
+            {
+                return StringComparer.OrdinalIgnoreCase.GetHashCode(descriptor.TypeName);
+            }
+        }
     }
 }

test/Microsoft.AspNet.Razor.Test/Generator/CSharpTagHelperRenderingTest.cs

@@ -19,6 +19,56 @@ private static IEnumerable<TagHelperDescriptor> DefaultPAndInputTagHelperDescrip
         private static IEnumerable<TagHelperDescriptor> PrefixedPAndInputTagHelperDescriptors
             => BuildPAndInputTagHelperDescriptors("THS");
 
+        private static IEnumerable<TagHelperDescriptor> DuplicateTargetTagHelperDescriptors
+        {
+            get
+            {
+                var inputTypePropertyInfo = typeof(TestType).GetProperty("Type");
+                var inputCheckedPropertyInfo = typeof(TestType).GetProperty("Checked");
+                return new[]
+                {
+                    new TagHelperDescriptor(
+                        tagName: "*",
+                        typeName: "CatchAllTagHelper",
+                        assemblyName: "SomeAssembly",
+                        attributes: new TagHelperAttributeDescriptor[]
+                        {
+                            new TagHelperAttributeDescriptor("type", inputTypePropertyInfo)
+                        },
+                        requiredAttributes: new[] { "type" }),
+                    new TagHelperDescriptor(
+                        tagName: "*",
+                        typeName: "CatchAllTagHelper",
+                        assemblyName: "SomeAssembly",
+                        attributes: new TagHelperAttributeDescriptor[]
+                        {
+                            new TagHelperAttributeDescriptor("type", inputTypePropertyInfo),
+                            new TagHelperAttributeDescriptor("checked", inputCheckedPropertyInfo)
+                        },
+                        requiredAttributes: new[] { "type", "checked" }),
+                    new TagHelperDescriptor(
+                        tagName: "input",
+                        typeName: "InputTagHelper",
+                        assemblyName: "SomeAssembly",
+                        attributes: new TagHelperAttributeDescriptor[]
+                        {
+                            new TagHelperAttributeDescriptor("type", inputTypePropertyInfo)
+                        },
+                        requiredAttributes: new[] { "type" }),
+                    new TagHelperDescriptor(
+                        tagName: "input",
+                        typeName: "InputTagHelper",
+                        assemblyName: "SomeAssembly",
+                        attributes: new TagHelperAttributeDescriptor[]
+                        {
+                            new TagHelperAttributeDescriptor("type", inputTypePropertyInfo),
+                            new TagHelperAttributeDescriptor("checked", inputCheckedPropertyInfo)
+                        },
+                        requiredAttributes: new[] { "type", "checked" })
+                };
+            }
+        }
+
         private static IEnumerable<TagHelperDescriptor> AttributeTargetingTagHelperDescriptors
         {
             get
@@ -93,6 +143,13 @@ public static TheoryData TagHelperDescriptorFlowTestData
                         DefaultPAndInputTagHelperDescriptors,
                         false
                     },
+                    {
+                        "DuplicateTargetTagHelper",
+                        "DuplicateTargetTagHelper",
+                        DuplicateTargetTagHelperDescriptors,
+                        DuplicateTargetTagHelperDescriptors,
+                        false
+                    },
                     {
                         "BasicTagHelpers",
                         "BasicTagHelpers.DesignTime",
@@ -410,6 +467,7 @@ public static TheoryData RuntimeTimeTagHelperTestData
                     { "BasicTagHelpers.RemoveTagHelper", DefaultPAndInputTagHelperDescriptors },
                     { "BasicTagHelpers.Prefixed", PrefixedPAndInputTagHelperDescriptors },
                     { "ComplexTagHelpers", DefaultPAndInputTagHelperDescriptors },
+                    { "DuplicateTargetTagHelper", DuplicateTargetTagHelperDescriptors },
                     { "EmptyAttributeTagHelpers", DefaultPAndInputTagHelperDescriptors },
                     { "EscapedTagHelpers", DefaultPAndInputTagHelperDescriptors },
                     { "AttributeTargetingTagHelpers", AttributeTargetingTagHelperDescriptors },

test/Microsoft.AspNet.Razor.Test/TestFiles/CodeGenerator/CS/Output/DuplicateTargetTagHelper.cs

@@ -0,0 +1,48 @@
+#pragma checksum "DuplicateTargetTagHelper.cshtml" "{ff1816ec-aa5e-4d10-87f7-6f4963833460}" "9cd2f5a40be40d26a0756bf6a74cee58bd13927f"
+namespace TestOutput
+{
+    using Microsoft.AspNet.Razor.Runtime.TagHelpers;
+    using System;
+    using System.Threading.Tasks;
+
+    public class DuplicateTargetTagHelper
+    {
+        #line hidden
+        #pragma warning disable 0414
+        private TagHelperContent __tagHelperStringValueBuffer = null;
+        #pragma warning restore 0414
+        private TagHelperExecutionContext __tagHelperExecutionContext = null;
+        private TagHelperRunner __tagHelperRunner = null;
+        private TagHelperScopeManager __tagHelperScopeManager = new TagHelperScopeManager();
+        private InputTagHelper __InputTagHelper = null;
+        private CatchAllTagHelper __CatchAllTagHelper = null;
+        #line hidden
+        public DuplicateTargetTagHelper()
+        {
+        }
+
+        #pragma warning disable 1998
+        public override async Task ExecuteAsync()
+        {
+            __tagHelperRunner = __tagHelperRunner ?? new TagHelperRunner();
+            Instrumentation.BeginContext(33, 2, true);
+            WriteLiteral("\r\n");
+            Instrumentation.EndContext();
+            __tagHelperExecutionContext = __tagHelperScopeManager.Begin("input", true, "test", async() => {
+            }
+            , StartTagHelperWritingScope, EndTagHelperWritingScope);
+            __InputTagHelper = CreateTagHelper<InputTagHelper>();
+            __tagHelperExecutionContext.Add(__InputTagHelper);
+            __InputTagHelper.Type = "checkbox";
+            __tagHelperExecutionContext.AddTagHelperAttribute("type", __InputTagHelper.Type);
+            __CatchAllTagHelper = CreateTagHelper<CatchAllTagHelper>();
+            __tagHelperExecutionContext.Add(__CatchAllTagHelper);
+            __CatchAllTagHelper.Type = __InputTagHelper.Type;
+            __tagHelperExecutionContext.AddHtmlAttribute("checked", "true");
+            __tagHelperExecutionContext.Output = await __tagHelperRunner.RunAsync(__tagHelperExecutionContext);
+            await WriteTagHelperAsync(__tagHelperExecutionContext);
+            __tagHelperExecutionContext = __tagHelperScopeManager.End();
+        }
+        #pragma warning restore 1998
+    }
+}

test/Microsoft.AspNet.Razor.Test/TestFiles/CodeGenerator/CS/Source/DuplicateTargetTagHelper.cshtml

@@ -0,0 +1,3 @@
+@addTagHelper "something, nice"
+
+<input type="checkbox" checked="true" />