Add `HtmlAttributeNotBoundAttribute`

- #182
- ignore otherwise-bound (i.e. `public`) properties in tag helpers

nits:
- add more `TagHelperDescriptorFactory` tests e.g. of `internal` properties
- remove `private` setter from `HtmlAttributeNameAttribute`
- use `null` propagation to shorten `IsAccessibleProperty` expression
- clean up some trailing whitespace

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

@@ -28,6 +28,6 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         /// <summary>
         /// HTML attribute name of the associated property.
         /// </summary>
-        public string Name { get; private set; }
+        public string Name { get; }
     }
 }

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

@@ -0,0 +1,21 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
+{
+    /// <summary>
+    /// Indicates the associated <see cref="ITagHelper"/> property should not be bound to HTML attributes.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = false)]
+    public sealed class HtmlAttributeNotBoundAttribute : Attribute
+    {
+        /// <summary>
+        /// Instantiates a new instance of the <see cref="HtmlAttributeNotBoundAttribute"/> class.
+        /// </summary>
+        public HtmlAttributeNotBoundAttribute()
+        {
+        }
+    }
+}

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

@@ -203,7 +203,7 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         }
 
         private static IEnumerable<TagHelperAttributeDescriptor> GetAttributeDescriptors(
-            Type type, 
+            Type type,
             ErrorSink errorSink)
         {
             var accessibleProperties = type.GetRuntimeProperties().Where(IsAccessibleProperty);
@@ -226,12 +226,12 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
             Type parentType,
             ErrorSink errorSink)
         {
-            // data-* attributes are explicitly not implemented by user agents and are not intended for use on 
+            // data-* attributes are explicitly not implemented by user agents and are not intended for use on
             // the server; therefore it's invalid for TagHelpers to bind to them.
             if (attributeDescriptor.Name.StartsWith(DataDashPrefix, StringComparison.OrdinalIgnoreCase))
             {
                 errorSink.OnError(
-                    SourceLocation.Zero, 
+                    SourceLocation.Zero,
                     Resources.FormatTagHelperDescriptorFactory_InvalidBoundAttributeName(
                         attributeDescriptor.PropertyName,
                         parentType.FullName,
@@ -255,10 +255,10 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
 
         private static bool IsAccessibleProperty(PropertyInfo property)
         {
-            return property.GetMethod != null &&
+            // Accessible properties are those with public getters and setters and without [HtmlAttributeNotBound].
-                   property.GetMethod.IsPublic &&
+            return property.GetMethod?.IsPublic == true &&
-                   property.SetMethod != null &&
+                property.SetMethod?.IsPublic == true &&
-                   property.SetMethod.IsPublic;
+                property.GetCustomAttribute<HtmlAttributeNotBoundAttribute>(inherit: false) == null;
         }
 
         /// <summary>

test/Microsoft.AspNet.Razor.Runtime.Test/TagHelpers/CommonTagHelpers.cs

@@ -23,10 +23,13 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         public string InvalidNoSetAttribute { get { return string.Empty; } }
     }
 
-    public class PrivateAccessorTagHelper : TagHelper
+    public class NonPublicAccessorTagHelper : TagHelper
     {
         public string ValidAttribute { get; set; }
         public string InvalidPrivateSetAttribute { get; private set; }
         public string InvalidPrivateGetAttribute { private get; set; }
+        protected string InvalidProtectedAttribute { get; set; }
+        internal string InvalidInternalAttribute { get; set; }
+        protected internal string InvalidProtectedInternalAttribute { get; set; }
     }
 }

test/Microsoft.AspNet.Razor.Runtime.Test/TagHelpers/TagHelperDescriptorFactoryTest.cs

@@ -443,11 +443,11 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         {
             // Arrange
             var errorSink = new ErrorSink();
-            var validProperty = typeof(PrivateAccessorTagHelper).GetProperty(
+            var validProperty = typeof(NonPublicAccessorTagHelper).GetProperty(
-                nameof(PrivateAccessorTagHelper.ValidAttribute));
+                nameof(NonPublicAccessorTagHelper.ValidAttribute));
             var expectedDescriptor = new TagHelperDescriptor(
-                "private-accessor",
+                "non-public-accessor",
-                typeof(PrivateAccessorTagHelper).FullName,
+                typeof(NonPublicAccessorTagHelper).FullName,
                 AssemblyName,
                 new[] {
                     new TagHelperAttributeDescriptor(
@@ -457,7 +457,7 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
             // Act
             var descriptors = TagHelperDescriptorFactory.CreateDescriptors(
                 AssemblyName,
-                typeof(PrivateAccessorTagHelper),
+                typeof(NonPublicAccessorTagHelper),
                 errorSink);
 
             // Assert
@@ -466,6 +466,51 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
             Assert.Equal(expectedDescriptor, descriptor, CaseSensitiveTagHelperDescriptorComparer.Default);
         }
 
+        [Fact]
+        public void CreateDescriptor_DoesNotIncludePropertiesWithNotBound()
+        {
+            // Arrange
+            var errorSink = new ErrorSink();
+            var boundProperty = typeof(NotBoundAttributeTagHelper).GetProperty(
+                nameof(NotBoundAttributeTagHelper.BoundProperty));
+            var expectedDescriptor = new TagHelperDescriptor(
+                "not-bound-attribute",
+                typeof(NotBoundAttributeTagHelper).FullName,
+                AssemblyName,
+                new[]
+                {
+                    new TagHelperAttributeDescriptor("bound-property", boundProperty)
+                });
+
+            // Act
+            var descriptors = TagHelperDescriptorFactory.CreateDescriptors(
+                AssemblyName,
+                typeof(NotBoundAttributeTagHelper),
+                errorSink);
+
+            // Assert
+            Assert.Empty(errorSink.Errors);
+            var descriptor = Assert.Single(descriptors);
+            Assert.Equal(expectedDescriptor, descriptor, CaseSensitiveTagHelperDescriptorComparer.Default);
+        }
+
+        [Fact(Skip = "#364")]
+        public void CreateDescriptor_AddsErrorForTagHelperWithDuplicateAttributeNames()
+        {
+            // Arrange
+            var errorSink = new ErrorSink();
+
+            // Act
+            var descriptors = TagHelperDescriptorFactory.CreateDescriptors(
+                AssemblyName,
+                typeof(DuplicateAttributeNameTagHelper),
+                errorSink);
+
+            // Assert
+            Assert.Empty(descriptors);
+            var error = Assert.Single(errorSink.Errors);
+        }
+
         [Fact]
         public void CreateDescriptor_ResolvesMultipleTagHelperDescriptorsFromSingleType()
         {
@@ -867,7 +912,7 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
             {
                 var errorFormat = "Invalid tag helper bound property '{0}.{1}'. Tag helpers cannot bind to HTML " +
                     "attributes beginning with 'data-'.";
-                
+
                 // type, expectedAttributeDescriptors, expectedErrors
                 return new TheoryData<Type, IEnumerable<TagHelperAttributeDescriptor>, string[]>
                 {
@@ -1049,6 +1094,26 @@ namespace Microsoft.AspNet.Razor.Runtime.TagHelpers
         {
         }
 
+        private class DuplicateAttributeNameTagHelper
+        {
+            public string MyNameIsLegion { get; set; }
+
+            [HtmlAttributeName("my-name-is-legion")]
+            public string Fred { get; set; }
+        }
+
+        private class NotBoundAttributeTagHelper
+        {
+            public string BoundProperty { get; set; }
+
+            [HtmlAttributeNotBound]
+            public string NotBoundProperty { get; set; }
+
+            [HtmlAttributeName("unused")]
+            [HtmlAttributeNotBound]
+            public string NamedNotBoundProperty { get; set; }
+        }
+
         private class OverriddenAttributeTagHelper
         {
             [HtmlAttributeName("SomethingElse")]