Add back support for AddTagHelpersAsServices

This doesn't go through the Razor tag helper discovery pipeline because
this can really only ever work for ITagHelper based taghelpers. So
there's really no point in reusing that logic, which would be hard
anyway.

src/Microsoft.AspNetCore.Mvc.Razor/DependencyInjection/MvcRazorMvcCoreBuilderExtensions.cs

@@ -67,6 +67,11 @@ private static void AddRazorViewEngineFeatureProviders(IMvcCoreBuilder builder)
                 builder.PartManager.FeatureProviders.Add(new MetadataReferenceFeatureProvider());
             }
 
+            if (!builder.PartManager.FeatureProviders.OfType<TagHelperFeatureProvider>().Any())
+            {
+                builder.PartManager.FeatureProviders.Add(new TagHelperFeatureProvider());
+            }
+
             if (!builder.PartManager.FeatureProviders.OfType<ViewsFeatureProvider>().Any())
             {
                 builder.PartManager.FeatureProviders.Add(new ViewsFeatureProvider());

src/Microsoft.AspNetCore.Mvc.Razor/TagHelpers/TagHelperFeatureProvider.cs

@@ -0,0 +1,43 @@
+// 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.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using Microsoft.AspNetCore.Mvc.ApplicationParts;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.TagHelpers
+{
+    public class TagHelperFeatureProvider : IApplicationFeatureProvider<TagHelperFeature>
+    {
+        public void PopulateFeature(IEnumerable<ApplicationPart> parts, TagHelperFeature feature)
+        {
+            foreach (var part in parts)
+            {
+                if (IncludePart(part) && part is IApplicationPartTypeProvider typeProvider)
+                {
+                    foreach (var type in typeProvider.Types)
+                    {
+                        var typeInfo = type.GetTypeInfo();
+                        if (IncludeType(typeInfo) && !feature.TagHelpers.Contains(typeInfo))
+                        {
+                            feature.TagHelpers.Add(typeInfo);
+                        }
+                    }
+                }
+            }
+        }
+
+        protected virtual bool IncludePart(ApplicationPart part) => true;
+
+        protected virtual bool IncludeType(TypeInfo type)
+        {
+            // We don't need to check visibility here, that's handled by the type provider.
+            return
+                typeof(ITagHelper).GetTypeInfo().IsAssignableFrom(type) &&
+                !type.IsAbstract &&
+                !type.IsGenericType;
+        }
+    }
+}

test/Microsoft.AspNetCore.Mvc.FunctionalTests/TagHelpersFromServicesTest.cs

@@ -16,7 +16,7 @@ public TagHelpersFromServicesTest(MvcTestFixture<ControllersFromServicesWebSite.
 
         public HttpClient Client { get; }
 
-        [Fact(Skip = "Workaround for https://github.com/aspnet/Mvc/issues/5768.")]
+        [Fact]
         public async Task TagHelpersWithConstructorInjectionAreCreatedAndActivated()
         {
             // Arrange

test/Microsoft.AspNetCore.Mvc.Razor.Test/DependencyInjection/MvcRazorMvcBuilderExtensionsTest.cs

@@ -47,7 +47,7 @@ public void AddTagHelpersAsServices_RegistersDiscoveredTagHelpers()
                 typeof(TestTagHelperOne),
                 typeof(TestTagHelperTwo)));
 
-            manager.FeatureProviders.Add(new TestFeatureProvider());
+            manager.FeatureProviders.Add(new TagHelperFeatureProvider());
 
             var builder = new MvcBuilder(services, manager);
 
@@ -78,16 +78,5 @@ private class TestTagHelperOne : TagHelper
         private class TestTagHelperTwo : TagHelper
         {
         }
-
-        private class TestFeatureProvider : IApplicationFeatureProvider<TagHelperFeature>
-        {
-            public void PopulateFeature(IEnumerable<ApplicationPart> parts, TagHelperFeature feature)
-            {
-                foreach (var type in parts.OfType<IApplicationPartTypeProvider>().SelectMany(tp => tp.Types))
-                {
-                    feature.TagHelpers.Add(type);
-                }
-            }
-        }
     }
 }

test/Microsoft.AspNetCore.Mvc.Razor.Test/DependencyInjection/MvcRazorMvcCoreBuilderExtensionsTest.cs

@@ -9,7 +9,6 @@
 using Microsoft.AspNetCore.Mvc.Razor.Compilation;
 using Microsoft.AspNetCore.Mvc.Razor.Internal;
 using Microsoft.AspNetCore.Mvc.Razor.TagHelpers;
-using Microsoft.AspNetCore.Razor.Runtime.TagHelpers;
 using Microsoft.AspNetCore.Razor.TagHelpers;
 using Microsoft.Extensions.DependencyInjection;
 using Moq;

test/Microsoft.AspNetCore.Mvc.Test/MvcServiceCollectionExtensionsTest.cs

@@ -214,6 +214,7 @@ public void AddMvcTwice_DoesNotAddApplicationFeatureProvidersTwice()
                 feature => Assert.IsType<ControllerFeatureProvider>(feature),
                 feature => Assert.IsType<ViewComponentFeatureProvider>(feature),
                 feature => Assert.IsType<MetadataReferenceFeatureProvider>(feature),
+                feature => Assert.IsType<TagHelperFeatureProvider>(feature),
                 feature => Assert.IsType<ViewsFeatureProvider>(feature),
                 feature => Assert.IsType<CompiledPageFeatureProvider>(feature));
         }