[Fixes #4087] Add support for AddTagHelpersAsServices()

src/Microsoft.AspNetCore.Mvc.Razor.Host/MvcRazorHost.cs

@@ -143,9 +143,12 @@ public MvcRazorHost(string root)
         /// Initializes a new instance of <see cref="MvcRazorHost"/> using the specified <paramref name="chunkTreeCache"/>.
         /// </summary>
         /// <param name="chunkTreeCache">An <see cref="IChunkTreeCache"/> rooted at the application base path.</param>
-        public MvcRazorHost(IChunkTreeCache chunkTreeCache)
+        /// <param name="resolver">The <see cref="ITagHelperDescriptorResolver"/> used to resolve tag helpers on razor views.</param>
+        public MvcRazorHost(IChunkTreeCache chunkTreeCache, ITagHelperDescriptorResolver resolver)
             : this(chunkTreeCache, new RazorPathNormalizer())
         {
+
+            TagHelperDescriptorResolver = resolver;
         }
 
         /// <inheritdoc />

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

@@ -6,7 +6,10 @@
 using System.Reflection;
 using Microsoft.AspNetCore.Mvc.Razor;
 using Microsoft.AspNetCore.Mvc.Razor.Compilation;
+using Microsoft.AspNetCore.Mvc.Razor.Internal;
+using Microsoft.AspNetCore.Mvc.Razor.TagHelpers;
 using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Razor.Runtime.TagHelpers;
 using Microsoft.AspNetCore.Razor.TagHelpers;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 
@@ -41,6 +44,28 @@ public static IMvcBuilder AddRazorOptions(
             return builder;
         }
 
+        /// <summary>
+        /// Registers tag helpers as services and changes the existing <see cref="ITagHelperActivator"/>
+        /// for an <see cref="ServiceBasedTagHelperActivator"/>.
+        /// </summary>
+        /// <param name="builder">The <see cref="IMvcBuilder"/> instance this method extends.</param>
+        /// <returns>The <see cref="IMvcBuilder"/> instance this method extends.</returns>
+        public static IMvcBuilder AddTagHelpersAsServices(this IMvcBuilder builder)
+        {
+            var feature = new TagHelperFeature();
+            builder.PartManager.PopulateFeature(feature);
+
+            foreach (var type in feature.TagHelpers.Select(t => t.AsType()))
+            {
+                builder.Services.TryAddTransient(type, type);
+            }
+
+            builder.Services.Replace(ServiceDescriptor.Transient<ITagHelperActivator, ServiceBasedTagHelperActivator>());
+            builder.Services.Replace(ServiceDescriptor.Transient<ITagHelperTypeResolver, FeatureTagHelperTypeResolver>());
+
+            return builder;
+        }
+
         /// <summary>
         /// Adds an initialization callback for a given <typeparamref name="TTagHelper"/>.
         /// </summary>

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

@@ -2,17 +2,20 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Linq;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.AspNetCore.Mvc.Razor;
 using Microsoft.AspNetCore.Mvc.Razor.Compilation;
 using Microsoft.AspNetCore.Mvc.Razor.Directives;
 using Microsoft.AspNetCore.Mvc.Razor.Internal;
+using Microsoft.AspNetCore.Mvc.Razor.TagHelpers;
 using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Razor.Compilation.TagHelpers;
+using Microsoft.AspNetCore.Razor.Runtime.TagHelpers;
 using Microsoft.AspNetCore.Razor.TagHelpers;
 using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.Extensions.Options;
-using Microsoft.Extensions.PlatformAbstractions;
 
 namespace Microsoft.Extensions.DependencyInjection
 {
@@ -26,10 +29,19 @@ public static IMvcCoreBuilder AddRazorViewEngine(this IMvcCoreBuilder builder)
             }
 
             builder.AddViews();
+            AddRazorViewEngineFeatureProviders(builder);
             AddRazorViewEngineServices(builder.Services);
             return builder;
         }
 
+        private static void AddRazorViewEngineFeatureProviders(IMvcCoreBuilder builder)
+        {
+            if (!builder.PartManager.FeatureProviders.OfType<TagHelperFeatureProvider>().Any())
+            {
+                builder.PartManager.FeatureProviders.Add(new TagHelperFeatureProvider());
+            }
+        }
+
         public static IMvcCoreBuilder AddRazorViewEngine(
             this IMvcCoreBuilder builder,
             Action<RazorViewEngineOptions> setupAction)
@@ -45,6 +57,8 @@ public static IMvcCoreBuilder AddRazorViewEngine(
             }
 
             builder.AddViews();
+
+            AddRazorViewEngineFeatureProviders(builder);
             AddRazorViewEngineServices(builder.Services);
 
             if (setupAction != null)
@@ -55,6 +69,28 @@ public static IMvcCoreBuilder AddRazorViewEngine(
             return builder;
         }
 
+        /// <summary>
+        /// Registers discovered tag helpers as services and changes the existing <see cref="ITagHelperActivator"/>
+        /// for an <see cref="ServiceBasedTagHelperActivator"/>.
+        /// </summary>
+        /// <param name="builder">The <see cref="IMvcCoreBuilder"/> instance this method extends.</param>
+        /// <returns>The <see cref="IMvcCoreBuilder"/> instance this method extends.</returns>
+        public static IMvcCoreBuilder AddTagHelpersAsServices(this IMvcCoreBuilder builder)
+        {
+            var feature = new TagHelperFeature();
+            builder.PartManager.PopulateFeature(feature);
+
+            foreach (var type in feature.TagHelpers.Select(t => t.AsType()))
+            {
+                builder.Services.TryAddTransient(type, type);
+            }
+
+            builder.Services.Replace(ServiceDescriptor.Transient<ITagHelperActivator, ServiceBasedTagHelperActivator>());
+            builder.Services.Replace(ServiceDescriptor.Transient<ITagHelperTypeResolver, FeatureTagHelperTypeResolver>());
+
+            return builder;
+        }
+
         /// <summary>
         /// Adds an initialization callback for a given <typeparamref name="TTagHelper"/>.
         /// </summary>
@@ -116,14 +152,20 @@ internal static void AddRazorViewEngineServices(IServiceCollection services)
                 return new DefaultChunkTreeCache(accessor.FileProvider);
             }));
 
+            services.TryAddTransient<ITagHelperDescriptorResolver, TagHelperDescriptorResolver>();
+
+            services.TryAddTransient<ITagHelperTypeResolver, TagHelperTypeResolver>();
+            services.TryAddTransient<ITagHelperDescriptorFactory>(s => new TagHelperDescriptorFactory(designTime: false));
+
             // Caches compilation artifacts across the lifetime of the application.
             services.TryAddSingleton<ICompilerCacheProvider, DefaultCompilerCacheProvider>();
 
             // In the default scenario the following services are singleton by virtue of being initialized as part of
             // creating the singleton RazorViewEngine instance.
             services.TryAddTransient<IRazorPageFactoryProvider, DefaultRazorPageFactoryProvider>();
             services.TryAddTransient<IRazorCompilationService, RazorCompilationService>();
-            services.TryAddTransient<IMvcRazorHost, MvcRazorHost>();
+
+            services.TryAddTransient<IMvcRazorHost,MvcRazorHost>();
 
             // This caches Razor page activation details that are valid for the lifetime of the application.
             services.TryAddSingleton<IRazorPageActivator, RazorPageActivator>();

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

@@ -0,0 +1,28 @@
+// 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;
+using Microsoft.AspNetCore.Mvc.Rendering;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.Internal
+{
+    /// <summary>
+    /// A <see cref="ITagHelperActivator"/> that retrieves tag helpers as services from the request's
+    /// <see cref="IServiceProvider"/>.
+    /// </summary>
+    public class ServiceBasedTagHelperActivator : ITagHelperActivator
+    {
+        /// <inheritdoc />
+        public TTagHelper Create<TTagHelper>(ViewContext context) where TTagHelper : ITagHelper
+        {
+            if (context == null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            return context.HttpContext.RequestServices.GetRequiredService<TTagHelper>();
+        }
+    }
+}

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

@@ -0,0 +1,86 @@
+// 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;
+using System.Collections.Generic;
+using Microsoft.AspNetCore.Razor;
+using Microsoft.AspNetCore.Mvc.ApplicationParts;
+using Microsoft.AspNetCore.Razor.Runtime.TagHelpers;
+using System.Reflection;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.TagHelpers
+{
+    /// <summary>
+    /// Resolves tag helper types from the <see cref="ApplicationPartManager.ApplicationParts"/>
+    /// of the application.
+    /// </summary>
+    public class FeatureTagHelperTypeResolver : ITagHelperTypeResolver
+    {
+        private readonly ApplicationPartManager _manager;
+
+        /// <summary>
+        /// Initializes a new <see cref="FeatureTagHelperTypeResolver"/> instance.
+        /// </summary>
+        /// <param name="manager">The <see cref="ApplicationPartManager"/> of the application.</param>
+        public FeatureTagHelperTypeResolver(ApplicationPartManager manager)
+        {
+            if (manager == null)
+            {
+                throw new ArgumentNullException(nameof(manager));
+            }
+
+            _manager = manager;
+
+        }
+
+        /// <inheritdoc />
+        public IEnumerable<Type> Resolve(string assemblyName, SourceLocation documentLocation, ErrorSink errorSink)
+        {
+            if (assemblyName == null)
+            {
+                throw new ArgumentNullException(nameof(assemblyName));
+            }
+
+            if (errorSink == null)
+            {
+                throw new ArgumentNullException(nameof(errorSink));
+            }
+
+            var parsedName = new AssemblyName(assemblyName);
+            Assembly assembly;
+            try
+            {
+                assembly = Assembly.Load(parsedName);
+            }
+            catch (Exception ex)
+            {
+                errorSink.OnError(
+                    documentLocation,
+                    string.Format(
+                        "Cannot resolve TagHelper containing assembly '{0}'.Error: {1}",
+                        parsedName.Name,
+                        ex.Message),
+                    assemblyName.Length);
+
+                return Type.EmptyTypes;
+            }
+
+            var feature = new TagHelperFeature();
+            _manager.PopulateFeature(feature);
+
+            var results = new List<Type>();
+            for (int i = 0; i < feature.TagHelpers.Count; i++)
+            {
+                var tagHelper = feature.TagHelpers[i];
+                var tagHelperAssembly = tagHelper.Assembly;
+
+                if (tagHelperAssembly.Equals(assembly))
+                {
+                    results.Add(tagHelper.AsType());
+                }
+            }
+
+            return results;
+        }
+    }
+}

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

@@ -0,0 +1,21 @@
+// 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.Reflection;
+using Microsoft.AspNetCore.Mvc.ApplicationParts;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.TagHelpers
+{
+    /// <summary>
+    /// The list of tag helper types in an MVC application. The <see cref="TagHelperFeature"/> can be populated
+    /// using the <see cref="ApplicationPartManager"/> that is available during startup at <see cref="IMvcBuilder.PartManager"/>
+    /// and <see cref="IMvcCoreBuilder.PartManager"/> or at a later stage by requiring the <see cref="ApplicationPartManager"/>
+    /// as a dependency in a component.
+    /// </summary>
+    public class TagHelperFeature
+    {
+        public IList<TypeInfo> TagHelpers { get; } = new List<TypeInfo>();
+    }
+}

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

@@ -0,0 +1,28 @@
+// 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 Microsoft.AspNetCore.Mvc.ApplicationParts;
+using Microsoft.AspNetCore.Razor.Runtime.TagHelpers;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.TagHelpers
+{
+    /// <summary>
+    /// Discovers tag helpers from a list of <see cref="ApplicationPart"/> instances.
+    /// </summary>
+    public class TagHelperFeatureProvider : IApplicationFeatureProvider<TagHelperFeature>
+    {
+        /// <inheritdoc />
+        public void PopulateFeature(IEnumerable<ApplicationPart> parts, TagHelperFeature feature)
+        {
+            foreach (var type in parts.OfType<IApplicationPartTypeProvider>().SelectMany(p => p.Types))
+            {
+                if (TagHelperConventions.IsTagHelper(type) && ! feature.TagHelpers.Contains(type))
+                {
+                    feature.TagHelpers.Add(type);
+                }
+            }
+        }
+    }
+}

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

@@ -4,12 +4,15 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Net.Http;
 using System.Reflection;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Mvc.ApplicationParts;
 using Microsoft.AspNetCore.Mvc.Controllers;
 using Microsoft.AspNetCore.Mvc.Infrastructure;
+using Microsoft.AspNetCore.Mvc.Razor.Compilation;
+using Microsoft.AspNetCore.Mvc.TagHelpers;
 using Microsoft.AspNetCore.Mvc.ViewComponents;
 using Microsoft.AspNetCore.TestHost;
 using Microsoft.AspNetCore.Testing;

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

@@ -0,0 +1,34 @@
+// 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.Net.Http;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.FunctionalTests
+{
+    public class TagHelpersFromServicesTest : IClassFixture<MvcTestFixture<ControllersFromServicesWebSite.Startup>>
+    {
+        public TagHelpersFromServicesTest(MvcTestFixture<ControllersFromServicesWebSite.Startup> fixture)
+        {
+            Client = fixture.Client;
+        }
+
+        public HttpClient Client { get; }
+
+        [Fact]
+        public async Task TagHelpersWithConstructorInjectionAreCreatedAndActivated()
+        {
+            // Arrange
+            var expected = "3";
+            var request = new HttpRequestMessage(HttpMethod.Get, "http://localhost/another/inservicestaghelper");
+
+            // Act
+            var response = await Client.SendAsync(request);
+            var responseText = await response.Content.ReadAsStringAsync();
+
+            // Assert
+            Assert.Equal(expected, responseText.Trim());
+        }
+    }
+}