Added design time support for ViewComponent TagHelpers

src/Microsoft.AspNetCore.Razor.Design/Internal/AssemblyTagHelperDescriptorResolver.cs

@@ -4,16 +4,26 @@
 using System;
 using System.Collections.Generic;
 using System.Globalization;
+using System.Linq;
+using System.Reflection;
 using Microsoft.AspNetCore.Razor.Compilation.TagHelpers;
 using Microsoft.AspNetCore.Razor.Runtime.TagHelpers;
+using Microsoft.Extensions.DependencyInjection;
 
 namespace Microsoft.AspNetCore.Razor.Design.Internal
 {
     public class AssemblyTagHelperDescriptorResolver
     {
-        private readonly TagHelperDescriptorFactory _descriptorFactory = new TagHelperDescriptorFactory(designTime: true);
+        private const string TypeFullName = "Microsoft.AspNetCore.Mvc.DesignTimeMvcServiceCollectionProvider";
+        private const string MvcAssemblyName = "Microsoft.AspNetCore.Mvc";
+        private const string MethodName = "PopulateServiceCollection";
+
+        private readonly TagHelperDescriptorFactory _tagHelperDescriptorFactory;
         private readonly TagHelperTypeResolver _tagHelperTypeResolver;
 
+        private bool _isInitialized;
+        private Action<IServiceCollection, string> _populateMethodDelegate;
+
         public AssemblyTagHelperDescriptorResolver()
             : this(new TagHelperTypeResolver())
         {
@@ -22,6 +32,7 @@ public AssemblyTagHelperDescriptorResolver()
         public AssemblyTagHelperDescriptorResolver(TagHelperTypeResolver tagHelperTypeResolver)
         {
             _tagHelperTypeResolver = tagHelperTypeResolver;
+            _tagHelperDescriptorFactory = new TagHelperDescriptorFactory(designTime: true);
         }
 
         public static int DefaultProtocolVersion { get; } = 1;
@@ -35,19 +46,7 @@ public IEnumerable<TagHelperDescriptor> Resolve(string assemblyName, ErrorSink e
                 throw new ArgumentNullException(nameof(assemblyName));
             }
 
-            if (ProtocolVersion == 1)
-            {
-                var tagHelperTypes = GetTagHelperTypes(assemblyName, errorSink);
-                var tagHelperDescriptors = new List<TagHelperDescriptor>();
-                foreach (var tagHelperType in tagHelperTypes)
-                {
-                    var descriptors = _descriptorFactory.CreateDescriptors(assemblyName, tagHelperType, errorSink);
-                    tagHelperDescriptors.AddRange(descriptors);
-                }
-
-                return tagHelperDescriptors;
-            }
-            else
+            if (ProtocolVersion != 1)
             {
                 // Unknown protocol
                 throw new InvalidOperationException(
@@ -56,6 +55,39 @@ public IEnumerable<TagHelperDescriptor> Resolve(string assemblyName, ErrorSink e
                         DesignResources.InvalidProtocolValue,
                         typeof(TagHelperDescriptor).FullName, ProtocolVersion));
             }
+
+            EnsureMvcInitialized();
+
+            ITagHelperDescriptorResolver resolver;
+            if (_populateMethodDelegate != null)
+            {
+                var serviceCollection = new ServiceCollection();
+                serviceCollection.AddSingleton<ITagHelperTypeResolver>(_tagHelperTypeResolver);
+                serviceCollection.AddSingleton<ITagHelperDescriptorFactory>(_tagHelperDescriptorFactory);
+
+                // Populate the service collection
+                _populateMethodDelegate(serviceCollection, assemblyName);
+
+                var services = serviceCollection.BuildServiceProvider();
+                resolver = services.GetRequiredService<ITagHelperDescriptorResolver>();
+            }
+            else
+            {
+                // MVC assembly does not exist. Manually create the resolver.
+                resolver = new TagHelperDescriptorResolver(_tagHelperTypeResolver, _tagHelperDescriptorFactory);
+            }
+
+            var directiveDescriptors = new[]
+            {
+                new TagHelperDirectiveDescriptor
+                {
+                    DirectiveText = $"*, {assemblyName}"
+                }
+            };
+            var context = new TagHelperDescriptorResolutionContext(directiveDescriptors, errorSink);
+            var descriptors = resolver.Resolve(context);
+
+            return descriptors;
         }
 
         /// <summary>
@@ -65,5 +97,34 @@ protected virtual IEnumerable<Type> GetTagHelperTypes(string assemblyName, Error
         {
             return _tagHelperTypeResolver.Resolve(assemblyName, SourceLocation.Zero, errorSink);
         }
+
+        private void EnsureMvcInitialized()
+        {
+            if (_isInitialized)
+            {
+                return;
+            }
+
+            _isInitialized = true;
+
+            var providerClass = Type.GetType($"{TypeFullName}, {MvcAssemblyName}");
+
+            // Get the method from the type
+            var populateMethod = providerClass?.GetMethods(BindingFlags.Public | BindingFlags.Static)
+                .FirstOrDefault(methodInfo =>
+                {
+                    if (string.Equals(MethodName, methodInfo.Name, StringComparison.Ordinal))
+                    {
+                        var methodParams = methodInfo.GetParameters();
+                        return methodParams.Length == 2
+                            && methodParams[0].ParameterType.Equals(typeof(IServiceCollection))
+                            && methodParams[1].ParameterType.Equals(typeof(string));
+                    }
+                    return false;
+                });
+
+            _populateMethodDelegate = (Action<IServiceCollection, string>) populateMethod
+                ?.CreateDelegate(typeof(Action<IServiceCollection, string>));
+        }
     }
 }

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

@@ -38,6 +38,7 @@
   "dependencies": {
     "Microsoft.AspNetCore.Razor.Runtime": "1.1.0-*",
     "Microsoft.Extensions.CommandLineUtils": "1.1.0-*",
+    "Microsoft.Extensions.DependencyInjection": "1.1.0-*",
     "Newtonsoft.Json": "9.0.1"
   },
   "frameworks": {
@@ -49,6 +50,10 @@
         }
       }
     },
-    "net451": {}
+    "net451": {
+      "frameworkAssemblies": {
+        "System.Runtime": ""
+      }
+    }
   }
 }