[Fixes #5207] Support IsIndexer for ViewComponent tag helpers

src/Microsoft.AspNetCore.Mvc.Core/Properties/AssemblyInfo.cs

@@ -6,7 +6,6 @@ using System.Resources;
 using System.Runtime.CompilerServices;
 
 [assembly: InternalsVisibleTo("Microsoft.AspNetCore.Mvc.Core.Test, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
-[assembly: InternalsVisibleTo("Microsoft.AspNetCore.Mvc.Razor.Test, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
 [assembly: InternalsVisibleTo("DynamicProxyGenAssembly2, PublicKey=0024000004800000940000000602000000240000525341310004000001000100c547cac37abd99c8db225ef2f6c8a3602f3b3606cc9891605d02baa56104f4cfc0734aa39b93bf7852f7d9266654753cc297e7d2edfe0bac1cdcf9f717241550e0a7b191195b7667bb4f64bcb8e2121380fd1d9d46ad2d92d2d15605093924cceaf74c4861eff62abf69b9291ed0a340e113be11e6a7d3113e92484cf7045cc7")]
 [assembly: AssemblyMetadata("Serviceable", "True")]
 [assembly: NeutralResourcesLanguage("en-us")]

src/Microsoft.AspNetCore.Mvc.Razor.Host/Internal/ViewComponentTagHelperChunkVisitor.cs

@@ -131,9 +131,23 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Host.Internal
                 $"global::{_context.ViewContextTypeName}",
                 ViewContextVariable);
 
+            var indexerAttributes = descriptor.Attributes.Where(a => a.IsIndexer);
+
             foreach (var attribute in descriptor.Attributes)
             {
+                if (attribute.IsIndexer)
+                {
+                    continue;
+                }
+
                 Writer.WriteAutoPropertyDeclaration("public", attribute.TypeName, attribute.PropertyName);
+
+                if (indexerAttributes.Any(a => string.Equals(a.PropertyName, attribute.PropertyName, StringComparison.Ordinal)))
+                {
+                    Writer.Write(" = ")
+                        .WriteStartNewObject(attribute.TypeName)
+                        .WriteEndMethodInvocation();
+                }
             }
         }
 
@@ -173,7 +187,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Host.Internal
 
         private string[] GetMethodParameters(TagHelperDescriptor descriptor)
         {
-            var propertyNames = descriptor.Attributes.Select(attribute => attribute.PropertyName);
+            var propertyNames = descriptor.Attributes.Where(a => !a.IsIndexer).Select(attribute => attribute.PropertyName);
             var joinedPropertyNames = string.Join(", ", propertyNames);
             var parametersString = $" new {{ { joinedPropertyNames } }}";
 

src/Microsoft.AspNetCore.Mvc.Razor/Internal/ViewComponentTagHelperDescriptorFactory.cs

@@ -10,6 +10,7 @@ using Microsoft.AspNetCore.Mvc.Razor.Host;
 using Microsoft.AspNetCore.Mvc.ViewComponents;
 using Microsoft.AspNetCore.Razor.Compilation.TagHelpers;
 using Microsoft.AspNetCore.Razor.Runtime.TagHelpers;
+using Microsoft.Extensions.Internal;
 
 namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 {
@@ -89,6 +90,8 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
         {
             var methodParameters = viewComponentDescriptor.MethodInfo.GetParameters();
             var attributeDescriptors = new List<TagHelperAttributeDescriptor>();
+            var indexerDescriptors = new List<TagHelperAttributeDescriptor>();
+            var requiredAttributeDescriptors = new List<TagHelperRequiredAttributeDescriptor>();
 
             foreach (var parameter in methodParameters)
             {
@@ -105,14 +108,53 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
                 descriptor.IsIndexer = false;
 
                 attributeDescriptors.Add(descriptor);
+
+                var indexerDescriptor = GetIndexerAttributeDescriptor(parameter, lowerKebabName);
+                if (indexerDescriptor != null)
+                {
+                    indexerDescriptors.Add(indexerDescriptor);
+                }
+                else
+                {
+                    // Set required attributes only for non-indexer attributes. Indexer attributes can't be required attributes
+                    // because there are two ways of setting values for the attribute.
+                    requiredAttributeDescriptors.Add(new TagHelperRequiredAttributeDescriptor
+                    {
+                        Name = lowerKebabName
+                    });
+                }
             }
 
+            attributeDescriptors.AddRange(indexerDescriptors);
             tagHelperDescriptor.Attributes = attributeDescriptors;
-            tagHelperDescriptor.RequiredAttributes = tagHelperDescriptor.Attributes.Select(
+            tagHelperDescriptor.RequiredAttributes = requiredAttributeDescriptors;
-                attribute => new TagHelperRequiredAttributeDescriptor
+        }
-                {
+
-                    Name = attribute.Name
+        private TagHelperAttributeDescriptor GetIndexerAttributeDescriptor(ParameterInfo parameter, string name)
-                });
+        {
+            var dictionaryTypeArguments = ClosedGenericMatcher.ExtractGenericInterface(
+                parameter.ParameterType,
+                typeof(IDictionary<,>))
+                ?.GenericTypeArguments
+                .Select(t => t.IsGenericParameter ? null : t)
+                .ToArray();
+
+            if (dictionaryTypeArguments?[0] != typeof(string))
+            {
+                return null;
+            }
+
+            var type = dictionaryTypeArguments[1];
+            var descriptor = new TagHelperAttributeDescriptor
+            {
+                Name = name + "-",
+                PropertyName = parameter.Name,
+                TypeName = GetCSharpTypeName(type),
+                IsEnum = type.GetTypeInfo().IsEnum,
+                IsIndexer = true
+            };
+
+            return descriptor;
         }
 
         private string GetTagName(ViewComponentDescriptor descriptor)

src/Microsoft.AspNetCore.Mvc.Razor/project.json

@@ -26,6 +26,10 @@
     "Microsoft.AspNetCore.Mvc.ViewFeatures": "1.1.0-*",
     "Microsoft.CodeAnalysis.CSharp": "1.3.0",
     "Microsoft.Extensions.FileProviders.Composite": "1.1.0-*",
+    "Microsoft.Extensions.ClosedGenericMatcher.Sources": {
+      "version": "1.1.0-*",
+      "type": "build"
+    },
     "Microsoft.Extensions.HashCodeCombiner.Sources": {
       "version": "1.1.0-*",
       "type": "build"

src/Microsoft.AspNetCore.Mvc.ViewFeatures/Properties/AssemblyInfo.cs

@@ -6,7 +6,6 @@ using System.Resources;
 using System.Runtime.CompilerServices;
 
 [assembly: InternalsVisibleTo("Microsoft.AspNetCore.Mvc.ViewFeatures.Test, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
-[assembly: InternalsVisibleTo("Microsoft.AspNetCore.Mvc.Razor.Test, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
 [assembly: InternalsVisibleTo("Microsoft.AspNetCore.Mvc.Formatters.Xml.Test, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
 [assembly: InternalsVisibleTo("DynamicProxyGenAssembly2, PublicKey=0024000004800000940000000602000000240000525341310004000001000100c547cac37abd99c8db225ef2f6c8a3602f3b3606cc9891605d02baa56104f4cfc0734aa39b93bf7852f7d9266654753cc297e7d2edfe0bac1cdcf9f717241550e0a7b191195b7667bb4f64bcb8e2121380fd1d9d46ad2d92d2d15605093924cceaf74c4861eff62abf69b9291ed0a340e113be11e6a7d3113e92484cf7045cc7")]
 [assembly: AssemblyMetadata("Serviceable", "True")]

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/Internal/ChunkVisitorTestFactory.cs

@@ -44,6 +44,10 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Host
                 GetTagHelperChunk("Baz"),
                 GetNestedViewComponentTagHelperChunk("Foo", visitedTagHelperChunks),
                 GetViewComponentTagHelperChunk("Bar", visitedTagHelperChunks),
+                GetIndexerViewComponentTagHelperChunk(
+                    "Bee",
+                    visitedTagHelperChunks,
+                    "System.Collections.Generic.Dictionary<global::System.String, global::System.Collections.Generic.List<global::System.Int32>>"),
             };
         }
 
@@ -120,5 +124,52 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Host
 
             return tagHelperChunk;
         }
+
+        private static TagHelperChunk GetIndexerViewComponentTagHelperChunk(string name, bool visitedTagHelperChunks, string attributeTypeName)
+        {
+            var typeName = visitedTagHelperChunks ? $"{_testNamespace}.{_testClass}.{name}Type" : $"{name}Type";
+
+            var attribute = new TagHelperAttributeDescriptor
+            {
+                Name = "attribute",
+                PropertyName = "Attribute",
+                TypeName = attributeTypeName
+            };
+
+            var indexerAttribute = new TagHelperAttributeDescriptor
+            {
+                Name = attribute.Name + "-",
+                PropertyName = attribute.PropertyName,
+                TypeName = attributeTypeName,
+                IsIndexer = true
+            };
+
+            var tagHelperDescriptor = new TagHelperDescriptor
+            {
+                AssemblyName = $"{name}Assembly",
+                TagName = name.ToLowerInvariant(),
+                TypeName = typeName,
+                Attributes = new[]
+                {
+                    attribute,
+                    indexerAttribute
+                }
+            };
+
+            tagHelperDescriptor.PropertyBag.Add(
+                ViewComponentTagHelperDescriptorConventions.ViewComponentNameKey,
+                name);
+
+            var tagHelperChunk = new TagHelperChunk(
+                $"vc:{name.ToLowerInvariant()}",
+                TagMode.SelfClosing,
+                new List<TagHelperAttributeTracker>(),
+                new[]
+                {
+                    tagHelperDescriptor
+                });
+
+            return tagHelperChunk;
+        }
     }
 }

test/Microsoft.AspNetCore.Mvc.Razor.Host.Test/TestFiles/Output/Runtime/GeneratedViewComponentTagHelperClasses.cs

@@ -36,3 +36,23 @@ public class __Generated__BarViewComponentTagHelper : Microsoft.AspNetCore.Razor
         output.Content.SetHtmlContent(viewContent);
     }
 }
+[Microsoft.AspNetCore.Razor.TagHelpers.HtmlTargetElementAttribute("bee")]
+public class __Generated__BeeViewComponentTagHelper : Microsoft.AspNetCore.Razor.TagHelpers.TagHelper
+{
+    private readonly global::Microsoft.AspNetCore.Mvc.IViewComponentHelper _viewComponentHelper = null;
+    public __Generated__BeeViewComponentTagHelper(global::Microsoft.AspNetCore.Mvc.IViewComponentHelper viewComponentHelper)
+    {
+        _viewComponentHelper = viewComponentHelper;
+    }
+    [Microsoft.AspNetCore.Razor.TagHelpers.HtmlAttributeNotBoundAttribute, global::Microsoft.AspNetCore.Mvc.ViewFeatures.ViewContextAttribute]
+    public global::Microsoft.AspNetCore.Mvc.Rendering.ViewContext ViewContext { get; set; }
+    public System.Collections.Generic.Dictionary<global::System.String, global::System.Collections.Generic.List<global::System.Int32>> Attribute { get; set; }
+     = new System.Collections.Generic.Dictionary<global::System.String, global::System.Collections.Generic.List<global::System.Int32>>();
+    public override async global::System.Threading.Tasks.Task ProcessAsync(Microsoft.AspNetCore.Razor.TagHelpers.TagHelperContext context, Microsoft.AspNetCore.Razor.TagHelpers.TagHelperOutput output)
+    {
+        (_viewComponentHelper as global::Microsoft.AspNetCore.Mvc.ViewFeatures.IViewContextAware)?.Contextualize(ViewContext);
+        var viewContent = await _viewComponentHelper.InvokeAsync("Bee",  new { Attribute });
+        output.TagName = null;
+        output.Content.SetHtmlContent(viewContent);
+    }
+}

test/Microsoft.AspNetCore.Mvc.Razor.Test/Internal/DefaultTagHelperActivatorTest.cs

@@ -46,7 +46,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
         {
             var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
             var metadataProvider = new EmptyModelMetadataProvider();
-            var viewData = new ViewDataDictionary(metadataProvider);
+            var viewData = new ViewDataDictionary(metadataProvider, new ModelStateDictionary());
             var viewContext = new ViewContext(
                 actionContext,
                 Mock.Of<IView>(),

test/Microsoft.AspNetCore.Mvc.Razor.Test/Internal/DefaultTagHelperFactoryTest.cs

@@ -158,7 +158,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
         {
             var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
             var metadataProvider = new EmptyModelMetadataProvider();
-            var viewData = new ViewDataDictionary(metadataProvider);
+            var viewData = new ViewDataDictionary(metadataProvider, new ModelStateDictionary());
             var viewContext = new ViewContext(
                 actionContext,
                 Mock.Of<IView>(),

test/Microsoft.AspNetCore.Mvc.Razor.Test/Internal/ViewComponentTagHelperDescriptorFactoryTest.cs

@@ -9,6 +9,7 @@ using Microsoft.AspNetCore.Mvc.Razor.Host;
 using Microsoft.AspNetCore.Mvc.Razor.Internal;
 using Microsoft.AspNetCore.Mvc.ViewComponents;
 using Microsoft.AspNetCore.Razor.Compilation.TagHelpers;
+using Microsoft.AspNetCore.Razor.TagHelpers.Testing;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Mvc.Razor.Test.Internal
@@ -48,7 +49,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Test.Internal
             var descriptors = factory.CreateDescriptors(assemblyName);
 
             // Assert
-            Assert.Equal(expectedDescriptors, descriptors, TagHelperDescriptorComparer.Default);
+            Assert.Equal(expectedDescriptors, descriptors, CaseSensitiveTagHelperDescriptorComparer.Default);
         }
 
         public static TheoryData TypeData
@@ -219,7 +220,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Test.Internal
                         {
                             Name = "test-enum",
                             PropertyName = "testEnum",
-                            TypeName = typeof(TestEnum).FullName,
+                            TypeName = ViewComponentTagHelperDescriptorFactory.GetCSharpTypeName(typeof(TestEnum)),
                             IsEnum = true
                         },
 
@@ -273,14 +274,22 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Test.Internal
                         {
                             Name = "foo",
                             PropertyName = "Foo",
-                            TypeName = "System.Collections.Generic.List<global::System.String>"
+                            TypeName = ViewComponentTagHelperDescriptorFactory.GetCSharpTypeName(typeof(List<string>))
                         },
 
                         new TagHelperAttributeDescriptor
                         {
                             Name = "bar",
                             PropertyName = "Bar",
-                            TypeName = "System.Collections.Generic.Dictionary<global::System.String, global::System.Int32>"
+                            TypeName = ViewComponentTagHelperDescriptorFactory.GetCSharpTypeName(typeof(Dictionary<string, int>))
+                        },
+
+                        new TagHelperAttributeDescriptor
+                        {
+                            Name = "bar-",
+                            PropertyName = "Bar",
+                            TypeName = typeof(int).FullName,
+                            IsIndexer = true
                         }
                     },
                     RequiredAttributes = new List<TagHelperRequiredAttributeDescriptor>
@@ -288,11 +297,6 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Test.Internal
                         new TagHelperRequiredAttributeDescriptor
                         {
                             Name = "foo"
-                        },
-
-                        new TagHelperRequiredAttributeDescriptor
-                        {
-                            Name = "bar"
                         }
                     }
                 };

test/Microsoft.AspNetCore.Mvc.Razor.Test/RazorPageActivatorTest.cs

@@ -66,7 +66,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
             var viewContext = new ViewContext(
                 actionContext,
                 Mock.Of<IView>(),
-                new ViewDataDictionary(new EmptyModelMetadataProvider()),
+                new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary()),
                 Mock.Of<ITempDataDictionary>(),
                 TextWriter.Null,
                 new HtmlHelperOptions());
@@ -117,7 +117,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
             var viewContext = new ViewContext(
                 actionContext,
                 Mock.Of<IView>(),
-                new ViewDataDictionary(new EmptyModelMetadataProvider()),
+                new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary()),
                 Mock.Of<ITempDataDictionary>(),
                 TextWriter.Null,
                 new HtmlHelperOptions());
@@ -159,7 +159,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
             };
 
             var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
-            var viewData = new ViewDataDictionary<object>(new EmptyModelMetadataProvider())
+            var viewData = new ViewDataDictionary<object>(new EmptyModelMetadataProvider(), new ModelStateDictionary())
             {
                 Model = new MyModel()
             };
@@ -208,7 +208,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
             };
 
             var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
-            var viewData = new ViewDataDictionary<MyModel>(new EmptyModelMetadataProvider())
+            var viewData = new ViewDataDictionary<MyModel>(new EmptyModelMetadataProvider(), new ModelStateDictionary())
             {
                 Model = new MyModel()
             };
@@ -257,7 +257,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
             };
 
             var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
-            var viewData = new ViewDataDictionary<object>(new EmptyModelMetadataProvider());
+            var viewData = new ViewDataDictionary<object>(new EmptyModelMetadataProvider(), new ModelStateDictionary());
             var viewContext = new ViewContext(
                 actionContext,
                 Mock.Of<IView>(),
@@ -302,7 +302,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
             var viewContext = new ViewContext(
                 actionContext,
                 Mock.Of<IView>(),
-                new ViewDataDictionary(new EmptyModelMetadataProvider()),
+                new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary()),
                 Mock.Of<ITempDataDictionary>(),
                 TextWriter.Null,
                 new HtmlHelperOptions());
@@ -343,7 +343,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
             var viewContext = new ViewContext(
                 actionContext,
                 Mock.Of<IView>(),
-                new ViewDataDictionary(new EmptyModelMetadataProvider()),
+                new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary()),
                 Mock.Of<ITempDataDictionary>(),
                 TextWriter.Null,
                 new HtmlHelperOptions());

test/Microsoft.AspNetCore.Mvc.Razor.Test/RazorPageCreateModelExpressionTest.cs

@@ -220,7 +220,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
         private static ViewContext CreateViewContext()
         {
             var provider = new TestModelMetadataProvider();
-            var viewData = new ViewDataDictionary<RazorPageCreateModelExpressionModel>(provider);
+            var viewData = new ViewDataDictionary<RazorPageCreateModelExpressionModel>(provider, new ModelStateDictionary());
             var serviceCollection = new ServiceCollection();
             serviceCollection.AddSingleton<IModelMetadataProvider>(provider);
             serviceCollection.AddSingleton<ExpressionTextCache, ExpressionTextCache>();

test/Microsoft.AspNetCore.Mvc.Razor.Test/RazorPageCreateTagHelperTest.cs

@@ -108,7 +108,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
                        .Returns(serviceProvider.Object);
 
             var actionContext = new ActionContext(httpContext.Object, new RouteData(), new ActionDescriptor());
-            var viewData = new ViewDataDictionary(new EmptyModelMetadataProvider());
+            var viewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary());
             var viewContext = new ViewContext(
                 actionContext,
                 Mock.Of<IView>(),

test/Microsoft.AspNetCore.Mvc.Razor.Test/RazorPageTest.cs

@@ -1501,7 +1501,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
             return new ViewContext(
                 actionContext,
                 viewMock.Object,
-                new ViewDataDictionary(new EmptyModelMetadataProvider()),
+                new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary()),
                 Mock.Of<ITempDataDictionary>(),
                 writer,
                 new HtmlHelperOptions());

test/Microsoft.AspNetCore.Mvc.Razor.Test/RazorViewTest.cs

@@ -62,7 +62,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
         public async Task RenderAsync_AsPartial_ActivatesViews_WithThePassedInViewContext()
         {
             // Arrange
-            var viewData = new ViewDataDictionary(new EmptyModelMetadataProvider());
+            var viewData = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary());
             var page = new TestableRazorPage(v =>
             {
                 // viewData is assigned to ViewContext by the activator
@@ -1672,7 +1672,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
             return new ViewContext(
                 actionContext,
                 view,
-                new ViewDataDictionary(new EmptyModelMetadataProvider()),
+                new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary()),
                 Mock.Of<ITempDataDictionary>(),
                 new StringWriter(),
                 new HtmlHelperOptions());

test/Microsoft.AspNetCore.Mvc.Razor.Test/project.json

@@ -22,6 +22,10 @@
     "Microsoft.AspNetCore.Mvc.DataAnnotations": "1.1.0-*",
     "Microsoft.AspNetCore.Mvc.Formatters.Xml": "1.1.0-*",
     "Microsoft.AspNetCore.Mvc.Razor": "1.1.0-*",
+    "Microsoft.AspNetCore.Razor.TagHelpers.Testing.Sources": {
+      "version": "1.1.0-*",
+      "type": "build"
+    },
     "Microsoft.AspNetCore.Mvc.TestCommon": {
       "version": "1.1.0-*",
       "type": "build"

test/WebSites/TagHelpersWebSite/Views/Home/ViewComponentTagHelpers.cshtml

@@ -7,6 +7,7 @@
 }
 
 <vc:generic items="dict"></vc:generic>
+<vc:generic items-foo="items"></vc:generic>
 <vc:dan jacket-color="Green" /><br />
 <div>
     <vc:copyright website="example.com" year="year" bold></vc:copyright>