Decouple tooling from MVC assemblies

benchmarks/Microsoft.AspNetCore.Razor.Performance/Microsoft.AspNetCore.Razor.Performance.csproj

@@ -10,14 +10,12 @@
 
   <ItemGroup>
     <ProjectReference Include="..\..\src\Microsoft.AspNetCore.Mvc.Razor.Extensions\Microsoft.AspNetCore.Mvc.Razor.Extensions.csproj" />
+    <ProjectReference Include="..\..\src\Microsoft.CodeAnalysis.Razor.Workspaces\Microsoft.CodeAnalysis.Razor.Workspaces.csproj" />
   </ItemGroup>
 
   <ItemGroup>
-    <Compile Include="..\..\src\Microsoft.VisualStudio.LanguageServices.Razor\RazorDiagnosticJsonConverter.cs">
+    <Compile Include="..\..\src\Microsoft.VisualStudio.LanguageServices.Razor\Serialization\*.cs">
-      <Link>Shared\RazorDiagnosticJsonConverter.cs</Link>
+      <Link>Serialization\%(FileName)%(Extension)</Link>
-    </Compile>
-    <Compile Include="..\..\src\Microsoft.VisualStudio.LanguageServices.Razor\TagHelperDescriptorJsonConverter.cs">
-      <Link>Shared\TagHelperDescriptorJsonConverter.cs</Link>
     </Compile>
   </ItemGroup>
 

benchmarks/Microsoft.AspNetCore.Razor.Performance/TagHelperSerializationBenchmark.cs

@@ -7,7 +7,7 @@ using System.IO;
 using System.Text;
 using BenchmarkDotNet.Attributes;
 using Microsoft.AspNetCore.Razor.Language;
-using Microsoft.VisualStudio.LanguageServices.Razor;
+using Microsoft.VisualStudio.LanguageServices.Razor.Serialization;
 using Newtonsoft.Json;
 
 namespace Microsoft.AspNetCore.Razor.Performance

src/Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X/ExtensionInitializer.cs

@@ -0,0 +1,29 @@
+// 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.Razor.Language;
+
+namespace Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X
+{
+    internal class ExtensionInitializer : RazorExtensionInitializer
+    {
+        public override void Initialize(RazorProjectEngineBuilder builder)
+        {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
+            if (builder.Configuration.ConfigurationName == "MVC-1.0")
+            {
+                RazorExtensions.Register(builder);
+            }
+            else if (builder.Configuration.ConfigurationName == "MVC-1.1")
+            {
+                RazorExtensions.Register(builder);
+                RazorExtensions.RegisterViewComponentTagHelpers(builder);
+            }
+        }
+    }
+}

src/Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X/Properties/AssemblyInfo.cs

@@ -2,5 +2,10 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.Runtime.CompilerServices;
+using Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X;
+using Microsoft.AspNetCore.Razor.Language;
+
+[assembly: ProvideRazorExtensionInitializer("MVC-1.0", typeof(ExtensionInitializer))]
+[assembly: ProvideRazorExtensionInitializer("MVC-1.1", typeof(ExtensionInitializer))]
 
 [assembly: InternalsVisibleTo("Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X.Test, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]

src/Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X/RazorExtensions.cs

@@ -45,6 +45,8 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X
                 throw new ArgumentNullException(nameof(builder));
             }
 
+            builder.Features.Add(new ViewComponentTagHelperDescriptorProvider());
+
             builder.Features.Add(new ViewComponentTagHelperPass());
             builder.AddTargetExtension(new ViewComponentTagHelperTargetExtension());
         }
@@ -88,6 +90,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X
 
             EnsureDesignTime(builder);
 
+            builder.Features.Add(new ViewComponentTagHelperDescriptorProvider());
             builder.Features.Add(new ViewComponentTagHelperPass());
             builder.AddTargetExtension(new ViewComponentTagHelperTargetExtension());
         }

src/Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X/ViewComponentTypeVisitor.cs

@@ -24,10 +24,9 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X
                 var symbol = compilation.GetAssemblyOrModuleSymbol(reference) as IAssemblySymbol;
                 if (symbol != null)
                 {
-                    if (string.Equals(symbol.Identity.Name, ViewComponentTypes.Assembly, StringComparison.Ordinal) &&
+                    if (string.Equals(symbol.Identity.Name, ViewComponentTypes.Assembly, StringComparison.Ordinal))
-                        symbol.Identity.Version > ViewComponentTypes.AssemblyVersion)
                     {
-                        enabled = true;
+                        enabled = symbol.Identity.Version >= ViewComponentTypes.AssemblyVersion;
                         break;
                     }
                 }

src/Microsoft.AspNetCore.Mvc.Razor.Extensions/RazorExtensions.cs

@@ -61,6 +61,8 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Extensions
             InheritsDirective.Register(builder);
             SectionDirective.Register(builder);
 
+            builder.Features.Add(new ViewComponentTagHelperDescriptorProvider());
+
             builder.AddTargetExtension(new ViewComponentTagHelperTargetExtension());
             builder.AddTargetExtension(new TemplateTargetExtension()
             {

src/Microsoft.AspNetCore.Mvc.Razor.Extensions/ViewComponentTypeVisitor.cs

@@ -10,31 +10,14 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Extensions
 {
     internal class ViewComponentTypeVisitor : SymbolVisitor
     {
-        private static readonly Version SupportedVCTHMvcVersion = new Version(1, 1);
-
         private readonly INamedTypeSymbol _viewComponentAttribute;
         private readonly INamedTypeSymbol _nonViewComponentAttribute;
         private readonly List<INamedTypeSymbol> _results;
 
         public static ViewComponentTypeVisitor Create(Compilation compilation, List<INamedTypeSymbol> results)
         {
-            var enabled = false;
+            var vcAttribute = compilation.GetTypeByMetadataName(ViewComponentTypes.ViewComponentAttribute);
-            foreach (var reference in compilation.References)
+            var nonVCAttribute = compilation.GetTypeByMetadataName(ViewComponentTypes.NonViewComponentAttribute);
-            {
-                var symbol = compilation.GetAssemblyOrModuleSymbol(reference) as IAssemblySymbol;
-                if (symbol != null)
-                {
-                    if (string.Equals(symbol.Identity.Name, ViewComponentTypes.Assembly, StringComparison.Ordinal) &&
-                        symbol.Identity.Version > ViewComponentTypes.AssemblyVersion)
-                    {
-                        enabled = true;
-                        break;
-                    }
-                }
-            }
-
-            var vcAttribute = enabled ? compilation.GetTypeByMetadataName(ViewComponentTypes.ViewComponentAttribute) : null;
-            var nonVCAttribute = enabled ? compilation.GetTypeByMetadataName(ViewComponentTypes.NonViewComponentAttribute) : null;
             return new ViewComponentTypeVisitor(vcAttribute, nonVCAttribute, results);
         }
 

src/Microsoft.CodeAnalysis.Razor.Workspaces/FallbackProjectEngineFactory.cs

@@ -0,0 +1,37 @@
+// 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.Composition;
+using Microsoft.AspNetCore.Razor.Language;
+
+namespace Microsoft.CodeAnalysis.Razor
+{
+    [Export(typeof(IFallbackProjectEngineFactory))]
+    internal class FallbackProjectEngineFactory : IFallbackProjectEngineFactory
+    {
+        public RazorProjectEngine Create(RazorConfiguration configuration, RazorProjectFileSystem fileSystem, Action<RazorProjectEngineBuilder> configure)
+        {
+            if (configuration == null)
+            {
+                throw new ArgumentNullException(nameof(configuration));
+            }
+
+            if (fileSystem == null)
+            {
+                throw new ArgumentNullException(nameof(fileSystem));
+            }
+
+            // This is a very basic implementation that will provide reasonable support without crashing.
+            // If the user falls into this situation, ideally they can realize that something is wrong and take
+            // action.
+            //
+            // This has no support for:
+            // - Tag Helpers
+            // - Imports
+            // - Default Imports
+            // - and will have a very limited set of directives
+            return RazorProjectEngine.Create(configuration, fileSystem, configure);
+        }
+    }
+}

src/Microsoft.CodeAnalysis.Razor.Workspaces/IFallbackProjectEngineFactory.cs

@@ -0,0 +1,10 @@
+// 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.
+
+namespace Microsoft.CodeAnalysis.Razor
+{
+    // Used to create the 'fallback' project engine when we don't have a custom implementation.
+    internal interface IFallbackProjectEngineFactory : IProjectEngineFactory
+    {
+    }
+}

src/Microsoft.CodeAnalysis.Razor.Workspaces/ProjectSystem/ProjectSnapshotManagerExtensions.cs

@@ -13,7 +13,7 @@ namespace Microsoft.CodeAnalysis.Razor.ProjectSystem
             for (var i = 0; i< projects.Count; i++)
             {
                 var project = projects[i];
-                if (string.Equals(filePath, project.WorkspaceProject.FilePath, StringComparison.OrdinalIgnoreCase))
+                if (FilePathComparer.Instance.Equals(filePath, project.FilePath))
                 {
                     return project;
                 }

src/Microsoft.CodeAnalysis.Razor.Workspaces/Properties/AssemblyInfo.cs

@@ -2,7 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.Runtime.CompilerServices;
-
+[assembly: InternalsVisibleTo("Microsoft.AspNetCore.Razor.Performance, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
 [assembly: InternalsVisibleTo("Microsoft.CodeAnalysis.Razor.Workspaces.Test, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
 [assembly: InternalsVisibleTo("Microsoft.CodeAnalysis.Remote.Razor, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
 [assembly: InternalsVisibleTo("Microsoft.VisualStudio.Editor.Razor, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]

src/Microsoft.CodeAnalysis.Razor.Workspaces/RazorProjectEngineFactoryService.cs

@@ -4,11 +4,20 @@
 using System;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.CodeAnalysis.Host;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
 
 namespace Microsoft.CodeAnalysis.Razor
 {
     internal abstract class RazorProjectEngineFactoryService : ILanguageService
     {
-        public abstract RazorProjectEngine Create(string projectPath, Action<RazorProjectEngineBuilder> configure);
+        public abstract IProjectEngineFactory FindFactory(ProjectSnapshot project);
+
+        public abstract IProjectEngineFactory FindSerializableFactory(ProjectSnapshot project);
+
+        public abstract RazorProjectEngine Create(ProjectSnapshot project, Action<RazorProjectEngineBuilder> configure);
+
+        public abstract RazorProjectEngine Create(ProjectSnapshot project, RazorProjectFileSystem fileSystem, Action<RazorProjectEngineBuilder> configure);
+
+        public abstract RazorProjectEngine Create(string directoryPath, Action<RazorProjectEngineBuilder> configure);
     }
 }

src/Microsoft.CodeAnalysis.Razor.Workspaces/TagHelperResolutionResult.cs

@@ -1,6 +1,7 @@
 // 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.Language;
 
@@ -8,6 +9,8 @@ namespace Microsoft.CodeAnalysis.Razor
 {
     public sealed class TagHelperResolutionResult
     {
+        internal static TagHelperResolutionResult Empty = new TagHelperResolutionResult(Array.Empty<TagHelperDescriptor>(), Array.Empty<RazorDiagnostic>());
+
         public TagHelperResolutionResult(IReadOnlyList<TagHelperDescriptor> descriptors, IReadOnlyList<RazorDiagnostic> diagnostics)
         {
             Descriptors = descriptors;

src/Microsoft.CodeAnalysis.Razor.Workspaces/TagHelperResolver.cs

@@ -1,14 +1,57 @@
 // 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 System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.CodeAnalysis.Host;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
 
 namespace Microsoft.CodeAnalysis.Razor
 {
     internal abstract class TagHelperResolver : ILanguageService
     {
-        public abstract Task<TagHelperResolutionResult> GetTagHelpersAsync(Project project, CancellationToken cancellationToken);
+        public abstract Task<TagHelperResolutionResult> GetTagHelpersAsync(ProjectSnapshot project, CancellationToken cancellationToken = default);
+
+        protected virtual async Task<TagHelperResolutionResult> GetTagHelpersAsync(ProjectSnapshot project, RazorProjectEngine engine)
+        {
+            if (project == null)
+            {
+                throw new ArgumentNullException(nameof(project));
+            }
+
+            if (engine == null)
+            {
+                throw new ArgumentNullException(nameof(engine));
+            }
+
+            if (project.WorkspaceProject == null)
+            {
+                return TagHelperResolutionResult.Empty;
+            }
+
+            var providers = engine.Engine.Features.OfType<ITagHelperDescriptorProvider>().ToArray();
+            if (providers.Length == 0)
+            {
+                return TagHelperResolutionResult.Empty;
+            }
+
+            var results = new List<TagHelperDescriptor>();
+            var context = TagHelperDescriptorProviderContext.Create(results);
+
+            var compilation = await project.WorkspaceProject.GetCompilationAsync().ConfigureAwait(false);
+            context.SetCompilation(compilation);
+
+            for (var i = 0; i < providers.Length; i++)
+            {
+                var provider = providers[i];
+                provider.Execute(context);
+            }
+
+            return new TagHelperResolutionResult(results, Array.Empty<RazorDiagnostic>());
+        }
     }
 }

src/Microsoft.CodeAnalysis.Remote.Razor/DefaultTagHelperResolver.cs

@@ -1,54 +0,0 @@
-// 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.Threading;
-using System.Threading.Tasks;
-using Microsoft.AspNetCore.Mvc.Razor.Extensions;
-using Microsoft.AspNetCore.Razor.Language;
-using Microsoft.CodeAnalysis.Razor;
-
-namespace Microsoft.CodeAnalysis.Remote.Razor
-{
-    internal class DefaultTagHelperResolver : TagHelperResolver
-    {
-        public DefaultTagHelperResolver(bool designTime)
-        {
-            DesignTime = designTime;
-        }
-
-        public bool DesignTime { get; }
-
-        private TagHelperResolutionResult GetTagHelpers(Compilation compilation)
-        {
-            var descriptors = new List<TagHelperDescriptor>();
-
-            var providers = new ITagHelperDescriptorProvider[]
-            {
-                new DefaultTagHelperDescriptorProvider() { DesignTime = DesignTime, },
-                new ViewComponentTagHelperDescriptorProvider(),
-            };
-
-            var results = new List<TagHelperDescriptor>();
-            var context = TagHelperDescriptorProviderContext.Create(results);
-            context.SetCompilation(compilation);
-
-            for (var i = 0; i < providers.Length; i++)
-            {
-                var provider = providers[i];
-                provider.Execute(context);
-            }
-
-            var diagnostics = new List<RazorDiagnostic>();
-            var resolutionResult = new TagHelperResolutionResult(results, diagnostics);
-
-            return resolutionResult;
-        }
-
-        public override async Task<TagHelperResolutionResult> GetTagHelpersAsync(Project project, CancellationToken cancellationToken)
-        {
-            var compilation = await project.GetCompilationAsync(cancellationToken).ConfigureAwait(false);
-            return GetTagHelpers(compilation);
-        }
-    }
-}

src/Microsoft.CodeAnalysis.Remote.Razor/Microsoft.CodeAnalysis.Remote.Razor.csproj

@@ -7,12 +7,13 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <Compile Include="..\Microsoft.VisualStudio.LanguageServices.Razor\RazorDiagnosticJsonConverter.cs" />
+    <Compile Include="..\Microsoft.VisualStudio.LanguageServices.Razor\Serialization\*.cs">
+      <Link>Serialization\%(FileName)%(Extension)</Link>
+    </Compile>
   </ItemGroup>
 
   <ItemGroup>
     <ProjectReference Include="..\Microsoft.CodeAnalysis.Razor.Workspaces\Microsoft.CodeAnalysis.Razor.Workspaces.csproj" />
-    <ProjectReference Include="..\Microsoft.AspNetCore.Mvc.Razor.Extensions\Microsoft.AspNetCore.Mvc.Razor.Extensions.csproj" />
     <ProjectReference Include="..\Microsoft.AspNetCore.Razor.Language\Microsoft.AspNetCore.Razor.Language.csproj" />
   </ItemGroup>
 

src/Microsoft.CodeAnalysis.Remote.Razor/RazorLanguageService.cs

@@ -10,34 +10,22 @@ using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.CodeAnalysis.Razor;
-using Microsoft.VisualStudio.LanguageServices.Razor;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
 
 namespace Microsoft.CodeAnalysis.Remote.Razor
 {
-    internal class RazorLanguageService : ServiceHubServiceBase
+    internal class RazorLanguageService : RazorServiceBase
     {
         public RazorLanguageService(Stream stream, IServiceProvider serviceProvider)
-            : base(serviceProvider, stream)
+            : base(stream, serviceProvider)
         {
-            Rpc.JsonSerializer.Converters.Add(new RazorDiagnosticJsonConverter());
-
-            // Due to this issue - https://github.com/dotnet/roslyn/issues/16900#issuecomment-277378950
-            // We need to manually start the RPC connection. Otherwise we'd be opting ourselves into 
-            // race condition prone call paths.
-            Rpc.StartListening();
         }
 
-        public async Task<TagHelperResolutionResult> GetTagHelpersAsync(Guid projectIdBytes, string projectDebugName, CancellationToken cancellationToken = default(CancellationToken))
+        public async Task<TagHelperResolutionResult> GetTagHelpersAsync(ProjectSnapshotHandle projectHandle, string factoryTypeName, CancellationToken cancellationToken = default)
         {
-            var projectId = ProjectId.CreateFromSerialized(projectIdBytes, projectDebugName);
+            var project = await GetProjectSnapshotAsync(projectHandle, cancellationToken).ConfigureAwait(false);
 
-            var solution = await GetSolutionAsync(cancellationToken).ConfigureAwait(false);
+            return await RazorServices.TagHelperResolver.GetTagHelpersAsync(project, factoryTypeName, cancellationToken);
-            var project = solution.GetProject(projectId);
-
-            var resolver = new DefaultTagHelperResolver(designTime: true);
-            var result = await resolver.GetTagHelpersAsync(project, cancellationToken).ConfigureAwait(false);
-
-            return result;
         }
 
         public Task<IEnumerable<DirectiveDescriptor>> GetDirectivesAsync(Guid projectIdBytes, string projectDebugName, CancellationToken cancellationToken = default(CancellationToken))

src/Microsoft.CodeAnalysis.Remote.Razor/RazorServiceBase.cs

@@ -0,0 +1,67 @@
+// 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.IO;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis.Razor;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
+
+namespace Microsoft.CodeAnalysis.Remote.Razor
+{
+    internal abstract class RazorServiceBase : ServiceHubServiceBase
+    {
+        public RazorServiceBase(Stream stream, IServiceProvider serviceProvider)
+            : base(serviceProvider, stream)
+        {
+            RazorServices = new RazorServices();
+
+            Rpc.JsonSerializer.Converters.RegisterRazorConverters();
+
+            // Due to this issue - https://github.com/dotnet/roslyn/issues/16900#issuecomment-277378950
+            // We need to manually start the RPC connection. Otherwise we'd be opting ourselves into 
+            // race condition prone call paths.
+            Rpc.StartListening();
+        }
+
+        protected RazorServices RazorServices { get; }
+
+        protected virtual async Task<ProjectSnapshot> GetProjectSnapshotAsync(ProjectSnapshotHandle projectHandle, CancellationToken cancellationToken)
+        {
+            if (projectHandle == null)
+            {
+                throw new ArgumentNullException(nameof(projectHandle));
+            }
+
+            var solution = await GetSolutionAsync(cancellationToken).ConfigureAwait(false);
+            var workspaceProject = solution.GetProject(projectHandle.WorkspaceProjectId);
+
+            return new SerializedProjectSnapshot(projectHandle.FilePath, projectHandle.Configuration, workspaceProject);
+        }
+
+        private class SerializedProjectSnapshot : ProjectSnapshot
+        {
+            public SerializedProjectSnapshot(string filePath, RazorConfiguration configuration, Project workspaceProject)
+            {
+                FilePath = filePath;
+                Configuration = configuration;
+                WorkspaceProject = workspaceProject;
+
+                IsInitialized = true;
+                Version = VersionStamp.Default;
+            }
+
+            public override RazorConfiguration Configuration { get; }
+
+            public override string FilePath { get; }
+
+            public override bool IsInitialized { get; }
+
+            public override VersionStamp Version { get; }
+
+            public override Project WorkspaceProject { get; }
+        }
+    }
+}

src/Microsoft.CodeAnalysis.Remote.Razor/RazorServices.cs

@@ -0,0 +1,22 @@
+// 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.
+
+namespace Microsoft.CodeAnalysis.Razor
+{
+    // Provides access to Razor language and workspace services that are avialable in the OOP host.
+    //
+    // Since we don't have access to the workspace we only have access to some specific things
+    // that we can construct directly.
+    internal class RazorServices
+    {
+        public RazorServices()
+        {
+            FallbackProjectEngineFactory = new FallbackProjectEngineFactory();
+            TagHelperResolver = new RemoteTagHelperResolver(FallbackProjectEngineFactory);
+        }
+
+        public IFallbackProjectEngineFactory FallbackProjectEngineFactory { get; }
+
+        public RemoteTagHelperResolver TagHelperResolver { get; }
+    }
+}

src/Microsoft.CodeAnalysis.Remote.Razor/RemoteTagHelperResolver.cs

@@ -0,0 +1,84 @@
+// 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.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
+
+namespace Microsoft.CodeAnalysis.Razor
+{
+    internal class RemoteTagHelperResolver : TagHelperResolver
+    {
+        private readonly static RazorConfiguration DefaultConfiguration = FallbackRazorConfiguration.MVC_2_0;
+
+        private readonly IFallbackProjectEngineFactory _fallbackFactory;
+
+        public RemoteTagHelperResolver(IFallbackProjectEngineFactory fallbackFactory)
+        {
+            if (fallbackFactory == null)
+            {
+                throw new ArgumentNullException(nameof(fallbackFactory));
+            }
+
+            _fallbackFactory = fallbackFactory;
+        }
+
+        public override Task<TagHelperResolutionResult> GetTagHelpersAsync(ProjectSnapshot project, CancellationToken cancellationToken = default)
+        {
+            throw new NotImplementedException();
+        }
+
+        public Task<TagHelperResolutionResult> GetTagHelpersAsync(ProjectSnapshot project, string factoryTypeName, CancellationToken cancellationToken = default)
+        {
+            if (project == null)
+            {
+                throw new ArgumentNullException(nameof(project));
+            }
+
+            if (project.Configuration == null || project.WorkspaceProject == null)
+            {
+                return Task.FromResult(TagHelperResolutionResult.Empty);
+            }
+
+            var engine = CreateProjectEngine(project, factoryTypeName);
+            return GetTagHelpersAsync(project, engine);
+        }
+
+        internal RazorProjectEngine CreateProjectEngine(ProjectSnapshot project, string factoryTypeName)
+        {
+            // This section is really similar to the code DefaultProjectEngineFactoryService
+            // but with a few differences that are significant in the remote scenario
+            //
+            // Most notably, we are going to find the Tag Helpers using a compilation, and we have
+            // no editor settings.
+            Action<RazorProjectEngineBuilder> configure = (b) =>
+            {
+                b.Features.Add(new DefaultTagHelperDescriptorProvider() { DesignTime = true });
+            };
+
+            // The default configuration currently matches MVC-2.0. Beyond MVC-2.0 we added SDK support for 
+            // properly detecting project versions, so that's a good version to assume when we can't find a
+            // configuration.
+            var configuration = project?.Configuration ?? DefaultConfiguration;
+
+            // If there's no factory to handle the configuration then fall back to a very basic configuration.
+            //
+            // This will stop a crash from happening in this case (misconfigured project), but will still make
+            // it obvious to the user that something is wrong.
+            var factory = CreateFactory(configuration, factoryTypeName) ?? _fallbackFactory;
+            return factory.Create(configuration, RazorProjectFileSystem.Empty, configure);
+        }
+
+        private IProjectEngineFactory CreateFactory(RazorConfiguration configuration, string factoryTypeName)
+        {
+            if (factoryTypeName == null)
+            {
+                return null;
+            }
+
+            return (IProjectEngineFactory)Activator.CreateInstance(Type.GetType(factoryTypeName, throwOnError: true));
+        }
+    }
+}

src/Microsoft.VisualStudio.Editor.Razor/DefaultProjectEngineFactoryService.cs

@@ -6,8 +6,6 @@ using System.IO;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.CodeAnalysis.Razor;
 using Microsoft.CodeAnalysis.Razor.ProjectSystem;
-using Mvc1_X = Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X;
-using MvcLatest = Microsoft.AspNetCore.Mvc.Razor.Extensions;
 
 namespace Microsoft.VisualStudio.Editor.Razor
 {
@@ -16,58 +14,127 @@ namespace Microsoft.VisualStudio.Editor.Razor
         private readonly static RazorConfiguration DefaultConfiguration = FallbackRazorConfiguration.MVC_2_0;
 
         private readonly ProjectSnapshotManager _projectManager;
+        private readonly IFallbackProjectEngineFactory _defaultFactory;
+        private readonly Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>[] _customFactories;
 
-        public DefaultProjectEngineFactoryService(ProjectSnapshotManager projectManager)
+        public DefaultProjectEngineFactoryService(
+           ProjectSnapshotManager projectManager,
+           IFallbackProjectEngineFactory defaultFactory,
+           Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>[] customFactories)
         {
             if (projectManager == null)
             {
                 throw new ArgumentNullException(nameof(projectManager));
             }
 
+            if (defaultFactory == null)
+            {
+                throw new ArgumentNullException(nameof(defaultFactory));
+            }
+
+            if (customFactories == null)
+            {
+                throw new ArgumentNullException(nameof(customFactories));
+            }
+
             _projectManager = projectManager;
+            _defaultFactory = defaultFactory;
+            _customFactories = customFactories;
         }
 
-        public override RazorProjectEngine Create(string projectPath, Action<RazorProjectEngineBuilder> configure)
+        public override IProjectEngineFactory FindFactory(ProjectSnapshot project)
         {
-            if (projectPath == null)
+            if (project == null)
             {
-                throw new ArgumentNullException(nameof(projectPath));
+                throw new ArgumentNullException(nameof(project));
             }
 
-            // In 15.5 we expect projectPath to be a directory, NOT the path to the csproj.
+            return SelectFactory(project.Configuration ?? DefaultConfiguration, requireSerializable: false);
-            var project = FindProject(projectPath);
-            var configuration = project?.Configuration ?? DefaultConfiguration;
-            var fileSystem = RazorProjectFileSystem.Create(projectPath);
-
-            RazorProjectEngine projectEngine;
-            if (configuration.LanguageVersion.Major == 1)
-            {
-                projectEngine = RazorProjectEngine.Create(configuration, fileSystem, b =>
-                {
-                    configure?.Invoke(b);
-
-                    Mvc1_X.RazorExtensions.Register(b);
-
-                    if (configuration.LanguageVersion.Minor >= 1)
-                    {
-                        Mvc1_X.RazorExtensions.RegisterViewComponentTagHelpers(b);
-                    }
-                });
-            }
-            else
-            {
-                projectEngine = RazorProjectEngine.Create(configuration, fileSystem, b =>
-                {
-                    configure?.Invoke(b);
-
-                    MvcLatest.RazorExtensions.Register(b);
-                });
-            }
-
-            return projectEngine;
         }
 
-        private ProjectSnapshot FindProject(string directory)
+        public override IProjectEngineFactory FindSerializableFactory(ProjectSnapshot project)
+        {
+            if (project == null)
+            {
+                throw new ArgumentNullException(nameof(project));
+            }
+
+            return SelectFactory(project.Configuration ?? DefaultConfiguration, requireSerializable: true);
+        }
+
+        public override RazorProjectEngine Create(ProjectSnapshot project, Action<RazorProjectEngineBuilder> configure)
+        {
+            if (project == null)
+            {
+                throw new ArgumentNullException(nameof(project));
+            }
+
+            return CreateCore(project, RazorProjectFileSystem.Create(Path.GetDirectoryName(project.FilePath)), configure);
+        }
+
+        public override RazorProjectEngine Create(string directoryPath, Action<RazorProjectEngineBuilder> configure)
+        {
+            if (directoryPath == null)
+            {
+                throw new ArgumentNullException(nameof(directoryPath));
+            }
+
+            var project = FindProjectByDirectory(directoryPath);
+            return CreateCore(project, RazorProjectFileSystem.Create(directoryPath), configure);
+        }
+
+        public override RazorProjectEngine Create(ProjectSnapshot project, RazorProjectFileSystem fileSystem, Action<RazorProjectEngineBuilder> configure)
+        {
+            if (project == null)
+            {
+                throw new ArgumentNullException(nameof(project));
+            }
+
+            if (fileSystem == null)
+            {
+                throw new ArgumentNullException(nameof(fileSystem));
+            }
+
+            return CreateCore(project, fileSystem, configure);
+        }
+
+        private RazorProjectEngine CreateCore(ProjectSnapshot project, RazorProjectFileSystem fileSystem, Action<RazorProjectEngineBuilder> configure)
+        {
+            // When we're running in the editor, the editor provides a configure delegate that will include
+            // the editor settings and tag helpers.
+            // 
+            // This service is only used in process in Visual Studio, and any other callers should provide these
+            // things also.
+            configure = configure ?? ((b) => { });
+
+            // The default configuration currently matches MVC-2.0. Beyond MVC-2.0 we added SDK support for 
+            // properly detecting project versions, so that's a good version to assume when we can't find a
+            // configuration.
+            var configuration = project?.Configuration ?? DefaultConfiguration;
+
+            // If there's no factory to handle the configuration then fall back to a very basic configuration.
+            //
+            // This will stop a crash from happening in this case (misconfigured project), but will still make
+            // it obvious to the user that something is wrong.
+            var factory = SelectFactory(configuration) ?? _defaultFactory;
+            return factory.Create(configuration, fileSystem, configure);
+        }
+
+        private IProjectEngineFactory SelectFactory(RazorConfiguration configuration, bool requireSerializable = false)
+        {
+            for (var i = 0; i < _customFactories.Length; i++)
+            {
+                var factory = _customFactories[i];
+                if (string.Equals(configuration.ConfigurationName, factory.Metadata.ConfigurationName))
+                {
+                    return requireSerializable && !factory.Metadata.SupportsSerialization ? null : factory.Value;
+                }
+            }
+
+            return null;
+        }
+
+        private ProjectSnapshot FindProjectByDirectory(string directory)
         {
             directory = NormalizeDirectoryPath(directory);
 
@@ -75,9 +142,9 @@ namespace Microsoft.VisualStudio.Editor.Razor
             for (var i = 0; i < projects.Count; i++)
             {
                 var project = projects[i];
-                if (project.WorkspaceProject?.FilePath != null)
+                if (project.FilePath != null)
                 {
-                    if (string.Equals(directory, NormalizeDirectoryPath(Path.GetDirectoryName(project.WorkspaceProject.FilePath)), StringComparison.OrdinalIgnoreCase))
+                    if (string.Equals(directory, NormalizeDirectoryPath(Path.GetDirectoryName(project.FilePath)), StringComparison.OrdinalIgnoreCase))
                     {
                         return project;
                     }

src/Microsoft.VisualStudio.Editor.Razor/DefaultProjectEngineFactoryServiceFactory.cs

@@ -1,6 +1,10 @@
 // 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 System.Composition;
+using System.Linq;
 using Microsoft.CodeAnalysis.Host;
 using Microsoft.CodeAnalysis.Host.Mef;
 using Microsoft.CodeAnalysis.Razor;
@@ -11,9 +15,34 @@ namespace Microsoft.VisualStudio.Editor.Razor
     [ExportLanguageServiceFactory(typeof(RazorProjectEngineFactoryService), RazorLanguage.Name, ServiceLayer.Default)]
     internal class DefaultProjectEngineFactoryServiceFactory : ILanguageServiceFactory
     {
+        private readonly Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>[] _customFactories;
+        private readonly IFallbackProjectEngineFactory _fallbackFactory;
+
+        [ImportingConstructor]
+        public DefaultProjectEngineFactoryServiceFactory(
+            IFallbackProjectEngineFactory fallbackFactory,
+            [ImportMany] IEnumerable<Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>> customFactories)
+        {
+            if (fallbackFactory == null)
+            {
+                throw new ArgumentNullException(nameof(fallbackFactory));
+            }
+
+            if (customFactories == null)
+            {
+                throw new ArgumentNullException(nameof(customFactories));
+            }
+
+            _fallbackFactory = fallbackFactory;
+            _customFactories = customFactories.ToArray();
+        }
+
         public ILanguageService CreateLanguageService(HostLanguageServices languageServices)
         {
-            return new DefaultProjectEngineFactoryService(languageServices.GetRequiredService<ProjectSnapshotManager>());
+            return new DefaultProjectEngineFactoryService(
+                languageServices.GetRequiredService<ProjectSnapshotManager>(),
+                _fallbackFactory,
+                _customFactories);
         }
     }
 }

src/Microsoft.VisualStudio.Editor.Razor/DefaultTagHelperResolver.cs

@@ -2,59 +2,45 @@
 // 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 System.Threading;
 using System.Threading.Tasks;
-using Microsoft.AspNetCore.Mvc.Razor.Extensions;
 using Microsoft.AspNetCore.Razor.Language;
-using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Razor;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
 
 namespace Microsoft.VisualStudio.Editor.Razor
 {
     internal class DefaultTagHelperResolver : TagHelperResolver
     {
-        // Hack for testability. The view component visitor will normally just no op if we're not referencing
+        private readonly RazorProjectEngineFactoryService _engineFactory;
-        // an appropriate version of MVC.
-        internal bool ForceEnableViewComponentDiscovery { get; set; }
 
-        public override async Task<TagHelperResolutionResult> GetTagHelpersAsync(Project project, CancellationToken cancellationToken)
+        public DefaultTagHelperResolver(RazorProjectEngineFactoryService engineFactory)
+        {
+            if (engineFactory == null)
+            {
+                throw new ArgumentNullException(nameof(engineFactory));
+            }
+
+            _engineFactory = engineFactory;
+        }
+
+        public override Task<TagHelperResolutionResult> GetTagHelpersAsync(ProjectSnapshot project, CancellationToken cancellationToken = default)
         {
             if (project == null)
             {
                 throw new ArgumentNullException(nameof(project));
             }
 
-            var compilation = await project.GetCompilationAsync(cancellationToken).ConfigureAwait(false);
+            if (project.Configuration == null || project.WorkspaceProject == null)
-            var result = GetTagHelpers(compilation);
-            return result;
-        }
-
-        // Internal for testing
-        internal TagHelperResolutionResult GetTagHelpers(Compilation compilation)
-        {
-            var descriptors = new List<TagHelperDescriptor>();
-
-            var providers = new ITagHelperDescriptorProvider[]
             {
-                new DefaultTagHelperDescriptorProvider() { DesignTime = true, },
+                return Task.FromResult(TagHelperResolutionResult.Empty);
-                new ViewComponentTagHelperDescriptorProvider() { ForceEnabled = ForceEnableViewComponentDiscovery },
-            };
-
-            var results = new List<TagHelperDescriptor>();
-            var context = TagHelperDescriptorProviderContext.Create(results);
-            context.SetCompilation(compilation);
-
-            for (var i = 0; i < providers.Length; i++)
-            {
-                var provider = providers[i];
-                provider.Execute(context);
             }
 
-            var diagnostics = new List<RazorDiagnostic>();
+            var engine = _engineFactory.Create(project, RazorProjectFileSystem.Empty, b => 
-            var resolutionResult = new TagHelperResolutionResult(results, diagnostics);
+            {
-
+                b.Features.Add(new DefaultTagHelperDescriptorProvider() { DesignTime = true, });
-            return resolutionResult;
+            });
+            return GetTagHelpersAsync(project, engine);
         }
     }
 }

src/Microsoft.VisualStudio.Editor.Razor/DefaultTagHelperResolverFactory.cs

@@ -14,7 +14,7 @@ namespace Microsoft.VisualStudio.Editor.Razor
     {
         public ILanguageService CreateLanguageService(HostLanguageServices languageServices)
         {
-            return new DefaultTagHelperResolver();
+            return new DefaultTagHelperResolver(languageServices.GetRequiredService<RazorProjectEngineFactoryService>());
         }
     }
 }

src/Microsoft.VisualStudio.Editor.Razor/LegacyProjectEngineFactory_1_0.cs

@@ -0,0 +1,32 @@
+// 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.Reflection;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis.Razor;
+
+namespace Microsoft.VisualStudio.Editor.Razor
+{
+    [ExportCustomProjectEngineFactory("MVC-1.0", SupportsSerialization = true)]
+    internal class LegacyProjectEngineFactory_1_0 : IProjectEngineFactory
+    {
+        private const string AssemblyName = "Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X";
+
+        public RazorProjectEngine Create(RazorConfiguration configuration, RazorProjectFileSystem fileSystem, Action<RazorProjectEngineBuilder> configure)
+        {
+            // Rewrite the assembly name into a full name just like this one, but with the name of the MVC design time assembly.
+            var assemblyName = new AssemblyName(typeof(LegacyProjectEngineFactory_1_0).Assembly.FullName);
+            assemblyName.Name = AssemblyName;
+
+            var extension = new AssemblyExtension(configuration.ConfigurationName, Assembly.Load(assemblyName));
+            var initializer = extension.CreateInitializer();
+
+            return RazorProjectEngine.Create(configuration, fileSystem, b =>
+            {
+                initializer.Initialize(b);
+                configure?.Invoke(b);
+            });
+        }
+    }
+}

src/Microsoft.VisualStudio.Editor.Razor/LegacyProjectEngineFactory_1_1.cs

@@ -0,0 +1,32 @@
+// 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.Reflection;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis.Razor;
+
+namespace Microsoft.VisualStudio.Editor.Razor
+{
+    [ExportCustomProjectEngineFactory("MVC-1.1", SupportsSerialization = true)]
+    internal class LegacyProjectEngineFactory_1_1 : IProjectEngineFactory
+    {
+        private const string AssemblyName = "Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X";
+
+        public RazorProjectEngine Create(RazorConfiguration configuration, RazorProjectFileSystem fileSystem, Action<RazorProjectEngineBuilder> configure)
+        {
+            // Rewrite the assembly name into a full name just like this one, but with the name of the MVC design time assembly.
+            var assemblyName = new AssemblyName(typeof(LegacyProjectEngineFactory_1_1).Assembly.FullName);
+            assemblyName.Name = AssemblyName;
+
+            var extension = new AssemblyExtension(configuration.ConfigurationName, Assembly.Load(assemblyName));
+            var initializer = extension.CreateInitializer();
+
+            return RazorProjectEngine.Create(configuration, fileSystem, b =>
+            {
+                initializer.Initialize(b);
+                configure?.Invoke(b);
+            });
+        }
+    }
+}

src/Microsoft.VisualStudio.Editor.Razor/LegacyProjectEngineFactory_2_0.cs

@@ -0,0 +1,31 @@
+// 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.Reflection;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis.Razor;
+
+namespace Microsoft.VisualStudio.Editor.Razor
+{
+    [ExportCustomProjectEngineFactory("MVC-2.0", SupportsSerialization = true)]
+    internal class LegacyProjectEngineFactory_2_0 : IProjectEngineFactory
+    {
+        private const string AssemblyName = "Microsoft.AspNetCore.Mvc.Razor.Extensions";
+        public RazorProjectEngine Create(RazorConfiguration configuration, RazorProjectFileSystem fileSystem, Action<RazorProjectEngineBuilder> configure)
+        {
+            // Rewrite the assembly name into a full name just like this one, but with the name of the MVC design time assembly.
+            var assemblyName = new AssemblyName(typeof(LegacyProjectEngineFactory_2_0).Assembly.FullName);
+            assemblyName.Name = AssemblyName;
+
+            var extension = new AssemblyExtension(configuration.ConfigurationName, Assembly.Load(assemblyName));
+            var initializer = extension.CreateInitializer();
+
+            return RazorProjectEngine.Create(configuration, fileSystem, b =>
+            {
+                initializer.Initialize(b);
+                configure?.Invoke(b);
+            });
+        }
+    }
+}

src/Microsoft.VisualStudio.Editor.Razor/LegacyProjectEngineFactory_2_1.cs

@@ -0,0 +1,33 @@
+// 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.Reflection;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis.Razor;
+
+namespace Microsoft.VisualStudio.Editor.Razor
+{
+    // Currently we provide a fixed configuration for 2.1, but this is a point-in-time issue. We plan
+    // to make the 2.1 configuration more flexible and less hardcoded.
+    [ExportCustomProjectEngineFactory("MVC-2.1", SupportsSerialization = true)]
+    internal class LegacyProjectEngineFactory_2_1 : IProjectEngineFactory
+    {
+        private const string AssemblyName = "Microsoft.AspNetCore.Mvc.Razor.Extensions";
+        public RazorProjectEngine Create(RazorConfiguration configuration, RazorProjectFileSystem fileSystem, Action<RazorProjectEngineBuilder> configure)
+        {
+            // Rewrite the assembly name into a full name just like this one, but with the name of the MVC design time assembly.
+            var assemblyName = new AssemblyName(typeof(LegacyProjectEngineFactory_2_1).Assembly.FullName);
+            assemblyName.Name = AssemblyName;
+
+            var extension = new AssemblyExtension(configuration.ConfigurationName, Assembly.Load(assemblyName));
+            var initializer = extension.CreateInitializer();
+
+            return RazorProjectEngine.Create(configuration, fileSystem, b =>
+            {
+                initializer.Initialize(b);
+                configure?.Invoke(b);
+            });
+        }
+    }
+}

src/Microsoft.VisualStudio.Editor.Razor/Microsoft.VisualStudio.Editor.Razor.csproj

@@ -14,8 +14,6 @@
 
   <ItemGroup>
     <ProjectReference Include="..\..\src\Microsoft.CodeAnalysis.Razor.Workspaces\Microsoft.CodeAnalysis.Razor.Workspaces.csproj" />
-    <ProjectReference Include="..\Microsoft.AspNetCore.Mvc.Razor.Extensions\Microsoft.AspNetCore.Mvc.Razor.Extensions.csproj" />
-    <ProjectReference Include="..\Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X\Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X.csproj" />
   </ItemGroup>
 
 </Project>

src/Microsoft.VisualStudio.LanguageServices.Razor/Legacy/LegacyTagHelperResolver.cs

@@ -1,11 +1,12 @@
 // 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.ComponentModel.Composition;
-using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Razor;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
 
 namespace Microsoft.VisualStudio.LanguageServices.Razor
 {
@@ -14,23 +15,42 @@ namespace Microsoft.VisualStudio.LanguageServices.Razor
     // use TagHelperResolver.
     // ----------------------------------------------------------------------------------------------------
     [Export(typeof(ITagHelperResolver))]
-    internal class LegacyTagHelperResolver : OOPTagHelperResolver, ITagHelperResolver
+    internal class LegacyTagHelperResolver : ITagHelperResolver
     {
+        private readonly Workspace _workspace;
+
         [ImportingConstructor]
-        public LegacyTagHelperResolver(
+        public LegacyTagHelperResolver([Import(typeof(VisualStudioWorkspace))] Workspace workspace)
-            [Import(typeof(VisualStudioWorkspace))] Workspace workspace)
-            : base(workspace)
         {
+            if (workspace == null)
+            {
+                throw new ArgumentNullException(nameof(workspace));
+            }
+
+            _workspace = workspace;
         }
 
         public Task<TagHelperResolutionResult> GetTagHelpersAsync(Project project)
         {
             if (project == null)
             {
-                throw new System.ArgumentNullException(nameof(project));
+                throw new ArgumentNullException(nameof(project));
             }
 
-            return base.GetTagHelpersAsync(project, CancellationToken.None);
+            if (project.FilePath == null)
+            {
+                return Task.FromResult(TagHelperResolutionResult.Empty);
+            }
+
+            var projectManager = _workspace.Services.GetLanguageServices(RazorLanguage.Name).GetRequiredService<ProjectSnapshotManager>();
+            var projectSnapshot = projectManager.GetProjectWithFilePath(project.FilePath);
+            if (projectSnapshot == null)
+            {
+                return Task.FromResult(TagHelperResolutionResult.Empty);
+            }
+
+            var resolver = _workspace.Services.GetLanguageServices(RazorLanguage.Name).GetRequiredService<TagHelperResolver>();
+            return resolver.GetTagHelpersAsync(projectSnapshot);
         }
     }
 }

src/Microsoft.VisualStudio.LanguageServices.Razor/OOPTagHelperResolver.cs

@@ -6,6 +6,7 @@ using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Razor;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
 using Microsoft.VisualStudio.Editor.Razor;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
@@ -15,53 +16,67 @@ namespace Microsoft.VisualStudio.LanguageServices.Razor
     internal class OOPTagHelperResolver : TagHelperResolver
     {
         private readonly DefaultTagHelperResolver _defaultResolver;
+        private readonly RazorProjectEngineFactoryService _engineFactory;
+        private readonly ErrorReporter _errorReporter;
         private readonly Workspace _workspace;
 
-        public OOPTagHelperResolver(Workspace workspace)
+        public OOPTagHelperResolver(RazorProjectEngineFactoryService engineFactory, ErrorReporter errorReporter, Workspace workspace)
         {
+            if (engineFactory == null)
+            {
+                throw new ArgumentNullException(nameof(engineFactory));
+            }
+
+            if (errorReporter == null)
+            {
+                throw new ArgumentNullException(nameof(errorReporter));
+            }
+
             if (workspace == null)
             {
                 throw new ArgumentNullException(nameof(workspace));
             }
 
+            _engineFactory = engineFactory;
+            _errorReporter = errorReporter;
             _workspace = workspace;
-            _defaultResolver = new DefaultTagHelperResolver();
+
+            _defaultResolver = new DefaultTagHelperResolver(_engineFactory);
         }
 
-        public override async Task<TagHelperResolutionResult> GetTagHelpersAsync(Project project, CancellationToken cancellationToken)
+        public override async Task<TagHelperResolutionResult> GetTagHelpersAsync(ProjectSnapshot project, CancellationToken cancellationToken = default)
         {
             if (project == null)
             {
                 throw new ArgumentNullException(nameof(project));
             }
 
+            if (project.Configuration == null || project.WorkspaceProject == null)
+            {
+                return TagHelperResolutionResult.Empty;
+            }
+
+            // Not every custom factory supports the OOP host. Our priority system should work like this:
+            //
+            // 1. Use custom factory out of process
+            // 2. Use custom factory in process
+            // 3. Use fallback factory in process
+            //
+            // Calling into RazorTemplateEngineFactoryService.Create will accomplish #2 and #3 in one step.
+            var factory = _engineFactory.FindSerializableFactory(project);
+
             try
             {
                 TagHelperResolutionResult result = null;
-
+                if (factory != null)
-                // We're being defensive here because the OOP host can return null for the client/session/operation
-                // when it's disconnected (user stops the process).
-                var client = await RazorLanguageServiceClientFactory.CreateAsync(_workspace, cancellationToken);
-                if (client != null)
                 {
-                    using (var session = await client.CreateSessionAsync(project.Solution))
+                    result = await ResolveTagHelpersOutOfProcessAsync(factory, project);
-                    {
-                        if (session != null)
-                        {
-                            var jsonObject = await session.InvokeAsync<JObject>(
-                                "GetTagHelpersAsync",
-                                new object[] { project.Id.Id, "Foo", },
-                                cancellationToken).ConfigureAwait(false);
-
-                            result = GetTagHelperResolutionResult(jsonObject);
-                        }
-                    }
                 }
 
                 if (result == null)
                 {
                     // Was unable to get tag helpers OOP, fallback to default behavior.
-                    result = await _defaultResolver.GetTagHelpersAsync(project, cancellationToken);
+                    result = await ResolveTagHelpersInProcessAsync(project);
                 }
 
                 return result;
@@ -76,11 +91,61 @@ namespace Microsoft.VisualStudio.LanguageServices.Razor
             }
         }
 
-        private TagHelperResolutionResult GetTagHelperResolutionResult(JObject jsonObject)
+        protected virtual async Task<TagHelperResolutionResult> ResolveTagHelpersOutOfProcessAsync(IProjectEngineFactory factory, ProjectSnapshot project)
+        {
+            // We're being overly defensive here because the OOP host can return null for the client/session/operation
+            // when it's disconnected (user stops the process).
+            //
+            // This will change in the future to an easier to consume API but for VS RTM this is what we have.
+            try
+            {
+                var client = await RazorLanguageServiceClientFactory.CreateAsync(_workspace, CancellationToken.None);
+                if (client != null)
+                {
+                    using (var session = await client.CreateSessionAsync(project.WorkspaceProject.Solution))
+                    {
+                        if (session != null)
+                        {
+                            var args = new object[]
+                            {
+                                Serialize(project),
+                                factory == null ? null : factory.GetType().AssemblyQualifiedName,
+                            };
+
+                            var json = await session.InvokeAsync<JObject>("GetTagHelpersAsync", args, CancellationToken.None).ConfigureAwait(false);
+                            return Deserialize(json);
+                        }
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                // We silence exceptions from the OOP host because we don't want to bring down VS for an OOP failure.
+                // We will retry all failures in process anyway, so if there's a real problem that isn't unique to OOP
+                // then it will report a crash in VS.
+                _errorReporter.ReportError(ex, project);
+            }
+
+            return null;
+        }
+
+        protected virtual Task<TagHelperResolutionResult> ResolveTagHelpersInProcessAsync(ProjectSnapshot project)
+        {
+            return _defaultResolver.GetTagHelpersAsync(project);
+        }
+
+        private JObject Serialize(ProjectSnapshot snapshot)
         {
             var serializer = new JsonSerializer();
-            serializer.Converters.Add(TagHelperDescriptorJsonConverter.Instance);
+            serializer.Converters.RegisterRazorConverters();
-            serializer.Converters.Add(RazorDiagnosticJsonConverter.Instance);
+
+            return JObject.FromObject(snapshot, serializer);
+        }
+
+        private TagHelperResolutionResult Deserialize(JObject jsonObject)
+        {
+            var serializer = new JsonSerializer();
+            serializer.Converters.RegisterRazorConverters();
 
             using (var reader = jsonObject.CreateReader())
             {

src/Microsoft.VisualStudio.LanguageServices.Razor/OOPTagHelperResolverFactory.cs

@@ -14,8 +14,10 @@ namespace Microsoft.VisualStudio.LanguageServices.Razor
     {
         public ILanguageService CreateLanguageService(HostLanguageServices languageServices)
         {
-            var workspace = languageServices.WorkspaceServices.Workspace;
+            return new OOPTagHelperResolver(
-            return new OOPTagHelperResolver(workspace);
+                languageServices.GetRequiredService<RazorProjectEngineFactoryService>(),
+                languageServices.WorkspaceServices.GetRequiredService<ErrorReporter>(),
+                languageServices.WorkspaceServices.Workspace);
         }
     }
 }

src/Microsoft.VisualStudio.LanguageServices.Razor/Serialization/JsonConverterCollectionExtensions.cs

@@ -0,0 +1,27 @@
+// 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.VisualStudio.LanguageServices.Razor.Serialization;
+using Newtonsoft.Json;
+
+namespace Microsoft.CodeAnalysis.Razor
+{
+    internal static class JsonConverterCollectionExtensions
+    {
+        public static void RegisterRazorConverters(this JsonConverterCollection collection)
+        {
+            if (collection == null)
+            {
+                throw new ArgumentNullException(nameof(collection));
+            }
+
+            collection.Add(TagHelperDescriptorJsonConverter.Instance);
+            collection.Add(RazorDiagnosticJsonConverter.Instance);
+            collection.Add(RazorExtensionJsonConverter.Instance);
+            collection.Add(RazorConfigurationJsonConverter.Instance);
+            collection.Add(ProjectSnapshotJsonConverter.Instance);
+            collection.Add(ProjectSnapshotHandleJsonConverter.Instance);
+        }
+    }
+}

src/Microsoft.VisualStudio.LanguageServices.Razor/Serialization/ProjectSnapshotHandle.cs

@@ -0,0 +1,29 @@
+// 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.Razor.Language;
+
+namespace Microsoft.CodeAnalysis.Razor.ProjectSystem
+{
+    internal sealed class ProjectSnapshotHandle
+    {
+        public ProjectSnapshotHandle(string filePath, RazorConfiguration configuration, ProjectId workspaceProjectId)
+        {
+            if (filePath == null)
+            {
+                throw new ArgumentNullException(nameof(filePath));
+            }
+
+            FilePath = filePath;
+            Configuration = configuration;
+            WorkspaceProjectId = workspaceProjectId;
+        }
+
+        public RazorConfiguration Configuration { get; }
+
+        public string FilePath { get; }
+
+        public ProjectId WorkspaceProjectId { get; }
+    }
+}

src/Microsoft.VisualStudio.LanguageServices.Razor/Serialization/ProjectSnapshotHandleJsonConverter.cs

@@ -0,0 +1,73 @@
+// 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.Razor.Language;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor.Serialization
+{
+    internal class ProjectSnapshotHandleJsonConverter : JsonConverter
+    {
+        public static readonly ProjectSnapshotHandleJsonConverter Instance = new ProjectSnapshotHandleJsonConverter();
+
+        public override bool CanConvert(Type objectType)
+        {
+            return typeof(ProjectSnapshotHandle).IsAssignableFrom(objectType);
+        }
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            if (reader.TokenType != JsonToken.StartObject)
+            {
+                return null;
+            }
+
+            var obj = JObject.Load(reader);
+            var filePath = obj[nameof(ProjectSnapshotHandle.FilePath)].Value<string>();
+            var configuration = obj[nameof(ProjectSnapshotHandle.Configuration)].ToObject<RazorConfiguration>(serializer);
+            
+            var id = obj[nameof(ProjectSnapshotHandle.WorkspaceProjectId)].Value<string>();
+            var workspaceProjectId = id == null ? null : ProjectId.CreateFromSerialized(Guid.Parse(id));
+
+            return new ProjectSnapshotHandle(filePath, configuration, workspaceProjectId);
+        }
+
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            var handle = (ProjectSnapshotHandle)value;
+
+            writer.WriteStartObject();
+
+            writer.WritePropertyName(nameof(ProjectSnapshotHandle.FilePath));
+            writer.WriteValue(handle.FilePath);
+
+            if (handle.Configuration == null)
+            {
+                writer.WritePropertyName(nameof(ProjectSnapshotHandle.Configuration));
+                writer.WriteNull();
+            }
+            else
+            {
+                writer.WritePropertyName(nameof(ProjectSnapshotHandle.Configuration));
+                serializer.Serialize(writer, handle.Configuration);
+            }
+
+            if (handle.WorkspaceProjectId == null)
+            {
+                writer.WritePropertyName(nameof(ProjectSnapshotHandle.WorkspaceProjectId));
+                writer.WriteNull();
+            }
+            else
+            {
+                writer.WritePropertyName(nameof(ProjectSnapshotHandle.WorkspaceProjectId));
+                writer.WriteValue(handle.WorkspaceProjectId.Id);
+            }
+
+            writer.WriteEndObject();
+        }
+    }
+}

src/Microsoft.VisualStudio.LanguageServices.Razor/Serialization/ProjectSnapshotJsonConverter.cs

@@ -0,0 +1,40 @@
+// 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.CodeAnalysis.Razor.ProjectSystem;
+using Newtonsoft.Json;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor.Serialization
+{
+    // We can't truly serialize a snapshot because it has access to a Workspace Project\
+    //
+    // Instead we serialize to a ProjectSnapshotHandle and then use that to re-create the snapshot
+    // inside the remote host.
+    internal class ProjectSnapshotJsonConverter : JsonConverter
+    {
+        public static readonly ProjectSnapshotJsonConverter Instance = new ProjectSnapshotJsonConverter();
+
+        public override bool CanRead => false;
+
+        public override bool CanWrite => true;
+        
+        public override bool CanConvert(Type objectType)
+        {
+            return typeof(ProjectSnapshot).IsAssignableFrom(objectType);
+        }
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            throw new NotSupportedException();
+        }
+
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            var project = (ProjectSnapshot)value;
+            var handle = new ProjectSnapshotHandle(project.FilePath, project.Configuration, project.WorkspaceProject?.Id);
+
+            ProjectSnapshotHandleJsonConverter.Instance.WriteJson(writer, handle, serializer);
+        }
+    }
+}

src/Microsoft.VisualStudio.LanguageServices.Razor/Serialization/RazorConfigurationJsonConverter.cs

@@ -0,0 +1,53 @@
+// 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.Razor.Language;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor.Serialization
+{
+    internal class RazorConfigurationJsonConverter : JsonConverter
+    {
+        public static readonly RazorConfigurationJsonConverter Instance = new RazorConfigurationJsonConverter();
+
+        public override bool CanConvert(Type objectType)
+        {
+            return typeof(RazorConfiguration).IsAssignableFrom(objectType);
+        }
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            if (reader.TokenType != JsonToken.StartObject)
+            {
+                return null;
+            }
+
+            var obj = JObject.Load(reader);
+            var configurationName = obj[nameof(RazorConfiguration.ConfigurationName)].Value<string>();
+            var languageVersion = obj[nameof(RazorConfiguration.LanguageVersion)].Value<string>();
+            var extensions = obj[nameof(RazorConfiguration.Extensions)].ToObject<RazorExtension[]>(serializer);
+
+            return RazorConfiguration.Create(RazorLanguageVersion.Parse(languageVersion), configurationName, extensions);
+        }
+
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            var configuration = (RazorConfiguration)value;
+
+            writer.WriteStartObject();
+
+            writer.WritePropertyName(nameof(RazorConfiguration.ConfigurationName));
+            writer.WriteValue(configuration.ConfigurationName);
+
+            writer.WritePropertyName(nameof(RazorConfiguration.LanguageVersion));
+            writer.WriteValue(configuration.LanguageVersion.ToString());
+
+            writer.WritePropertyName(nameof(RazorConfiguration.Extensions));
+            serializer.Serialize(writer, configuration.Extensions);
+
+            writer.WriteEndObject();
+        }
+    }
+}

src/Microsoft.VisualStudio.LanguageServices.Razor/Serialization/RazorDiagnosticJsonConverter.cs

@@ -6,7 +6,7 @@ using Microsoft.AspNetCore.Razor.Language;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
 
-namespace Microsoft.VisualStudio.LanguageServices.Razor
+namespace Microsoft.VisualStudio.LanguageServices.Razor.Serialization
 {
     internal class RazorDiagnosticJsonConverter : JsonConverter
     {

src/Microsoft.VisualStudio.LanguageServices.Razor/Serialization/RazorExtensionJsonConverter.cs

@@ -0,0 +1,45 @@
+// 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.Razor.Language;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor.Serialization
+{
+    internal class RazorExtensionJsonConverter : JsonConverter
+    {
+        public static readonly RazorExtensionJsonConverter Instance = new RazorExtensionJsonConverter();
+
+        public override bool CanConvert(Type objectType)
+        {
+            return typeof(RazorExtension).IsAssignableFrom(objectType);
+        }
+
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            if (reader.TokenType != JsonToken.StartObject)
+            {
+                return null;
+            }
+
+            var obj = JObject.Load(reader);
+            var extensionName = obj[nameof(RazorExtension.ExtensionName)].Value<string>();
+
+            return new SerializedRazorExtension(extensionName);
+        }
+
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            var extension = (RazorExtension)value;
+
+            writer.WriteStartObject();
+
+            writer.WritePropertyName(nameof(RazorExtension.ExtensionName));
+            writer.WriteValue(extension.ExtensionName);
+
+            writer.WriteEndObject();
+        }
+    }
+}

src/Microsoft.VisualStudio.LanguageServices.Razor/Serialization/SerializedRazorExtension.cs

@@ -0,0 +1,23 @@
+// 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.Razor.Language;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor.Serialization
+{
+    internal class SerializedRazorExtension : RazorExtension
+    {
+        public SerializedRazorExtension(string extensionName)
+        {
+            if (extensionName == null)
+            {
+                throw new ArgumentNullException(nameof(extensionName));
+            }
+
+            ExtensionName = extensionName;
+        }
+
+        public override string ExtensionName { get; }
+    }
+}

src/Microsoft.VisualStudio.LanguageServices.Razor/Serialization/TagHelperDescriptorJsonConverter.cs

@@ -7,7 +7,7 @@ using Microsoft.AspNetCore.Razor.Language;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
 
-namespace Microsoft.VisualStudio.LanguageServices.Razor
+namespace Microsoft.VisualStudio.LanguageServices.Razor.Serialization
 {
     internal class TagHelperDescriptorJsonConverter : JsonConverter
     {

test/Microsoft.VisualStudio.Editor.Razor.Test/DefaultProjectEngineFactoryServiceTest.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Linq;
+using System.Reflection;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Razor;
@@ -31,28 +32,62 @@ namespace Microsoft.VisualStudio.Editor.Razor
             HostProject_For_1_0 = new HostProject("/TestPath/SomePath/Test.csproj", FallbackRazorConfiguration.MVC_1_0);
             HostProject_For_1_1 = new HostProject("/TestPath/SomePath/Test.csproj", FallbackRazorConfiguration.MVC_1_1);
             HostProject_For_2_0 = new HostProject("/TestPath/SomePath/Test.csproj", FallbackRazorConfiguration.MVC_2_0);
+
+            HostProject_For_2_1 = new HostProject(
+                "/TestPath/SomePath/Test.csproj", 
+                new ProjectSystemRazorConfiguration(RazorLanguageVersion.Version_2_1, "MVC-2.1", Array.Empty<RazorExtension>()));
+            HostProject_For_UnknownConfiguration = new HostProject(
+                "/TestPath/SomePath/Test.csproj",
+                new ProjectSystemRazorConfiguration(RazorLanguageVersion.Version_2_1, "Blazor-0.1", Array.Empty<RazorExtension>()));
+
+
+            CustomFactories = new Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>[]
+            {
+                new Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>(
+                    () => new LegacyProjectEngineFactory_1_0(),
+                    typeof(LegacyProjectEngineFactory_1_0).GetCustomAttribute<ExportCustomProjectEngineFactoryAttribute>()),
+                new Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>(
+                    () => new LegacyProjectEngineFactory_1_1(),
+                    typeof(LegacyProjectEngineFactory_1_1).GetCustomAttribute<ExportCustomProjectEngineFactoryAttribute>()),
+                new Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>(
+                    () => new LegacyProjectEngineFactory_2_0(),
+                    typeof(LegacyProjectEngineFactory_2_0).GetCustomAttribute<ExportCustomProjectEngineFactoryAttribute>()),
+                new Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>(
+                    () => new LegacyProjectEngineFactory_2_1(),
+                    typeof(LegacyProjectEngineFactory_2_1).GetCustomAttribute<ExportCustomProjectEngineFactoryAttribute>()),
+            };
+
+            FallbackFactory = new FallbackProjectEngineFactory();
         }
 
+        private Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>[] CustomFactories { get; }
+
+        private IFallbackProjectEngineFactory FallbackFactory { get; }
+
         private HostProject HostProject_For_1_0 { get; }
 
         private HostProject HostProject_For_1_1 { get; }
 
         private HostProject HostProject_For_2_0 { get; }
 
+        private HostProject HostProject_For_2_1 { get; }
+
+        private HostProject HostProject_For_UnknownConfiguration { get; }
+
         // We don't actually look at the project, we rely on the ProjectStateManager
         private Project WorkspaceProject { get; }
 
         private Workspace Workspace { get; }
 
         [Fact]
-        public void Create_CreatesTemplateEngine_ForLatest()
+        public void Create_CreatesDesignTimeTemplateEngine_ForVersion2_1()
         {
             // Arrange
             var projectManager = new TestProjectSnapshotManager(Workspace);
-            projectManager.HostProjectAdded(HostProject_For_2_0);
+            projectManager.HostProjectAdded(HostProject_For_2_1);
             projectManager.WorkspaceProjectAdded(WorkspaceProject);
 
-            var factoryService = new DefaultProjectEngineFactoryService(projectManager);
+            var factoryService = new DefaultProjectEngineFactoryService(projectManager, FallbackFactory, CustomFactories);
 
             // Act
             var engine = factoryService.Create("/TestPath/SomePath/", b =>
@@ -62,6 +97,30 @@ namespace Microsoft.VisualStudio.Editor.Razor
 
             // Assert
             Assert.Single(engine.Engine.Features.OfType<MyCoolNewFeature>());
+            Assert.Single(engine.Engine.Features.OfType<MvcLatest.ViewComponentTagHelperDescriptorProvider>());
+            Assert.Single(engine.Engine.Features.OfType<MvcLatest.MvcViewDocumentClassifierPass>());
+            Assert.Single(engine.Engine.Features.OfType<MvcLatest.ViewComponentTagHelperPass>());
+        }
+
+        [Fact]
+        public void Create_CreatesDesignTimeTemplateEngine_ForVersion2_0()
+        {
+            // Arrange
+            var projectManager = new TestProjectSnapshotManager(Workspace);
+            projectManager.HostProjectAdded(HostProject_For_2_0);
+            projectManager.WorkspaceProjectAdded(WorkspaceProject);
+
+            var factoryService = new DefaultProjectEngineFactoryService(projectManager, FallbackFactory, CustomFactories);
+
+            // Act
+            var engine = factoryService.Create("/TestPath/SomePath/", b =>
+            {
+                b.Features.Add(new MyCoolNewFeature());
+            });
+
+            // Assert
+            Assert.Single(engine.Engine.Features.OfType<MyCoolNewFeature>());
+            Assert.Single(engine.Engine.Features.OfType<MvcLatest.ViewComponentTagHelperDescriptorProvider>());
             Assert.Single(engine.Engine.Features.OfType<MvcLatest.MvcViewDocumentClassifierPass>());
             Assert.Single(engine.Engine.Features.OfType<MvcLatest.ViewComponentTagHelperPass>());
         }
@@ -74,7 +133,7 @@ namespace Microsoft.VisualStudio.Editor.Razor
             projectManager.HostProjectAdded(HostProject_For_1_1);
             projectManager.WorkspaceProjectAdded(WorkspaceProject);
 
-            var factoryService = new DefaultProjectEngineFactoryService(projectManager);
+            var factoryService = new DefaultProjectEngineFactoryService(projectManager, FallbackFactory, CustomFactories);
 
             // Act
             var engine = factoryService.Create("/TestPath/SomePath/", b =>
@@ -84,6 +143,7 @@ namespace Microsoft.VisualStudio.Editor.Razor
 
             // Assert
             Assert.Single(engine.Engine.Features.OfType<MyCoolNewFeature>());
+            Assert.Single(engine.Engine.Features.OfType<Mvc1_X.ViewComponentTagHelperDescriptorProvider>());
             Assert.Single(engine.Engine.Features.OfType<Mvc1_X.MvcViewDocumentClassifierPass>());
             Assert.Single(engine.Engine.Features.OfType<Mvc1_X.ViewComponentTagHelperPass>());
         }
@@ -96,7 +156,7 @@ namespace Microsoft.VisualStudio.Editor.Razor
             projectManager.HostProjectAdded(HostProject_For_1_0);
             projectManager.WorkspaceProjectAdded(WorkspaceProject);
 
-            var factoryService = new DefaultProjectEngineFactoryService(projectManager);
+            var factoryService = new DefaultProjectEngineFactoryService(projectManager, FallbackFactory, CustomFactories);
 
             // Act
             var engine = factoryService.Create("/TestPath/SomePath/", b =>
@@ -106,17 +166,18 @@ namespace Microsoft.VisualStudio.Editor.Razor
 
             // Assert
             Assert.Single(engine.Engine.Features.OfType<MyCoolNewFeature>());
-            Assert.Single(engine.Engine.Features.OfType<Mvc1_X.MvcViewDocumentClassifierPass>());
+            Assert.Empty(engine.Engine.Features.OfType<MvcLatest.ViewComponentTagHelperDescriptorProvider>());
-            Assert.Empty(engine.Engine.Features.OfType<Mvc1_X.ViewComponentTagHelperPass>());
+            Assert.Empty(engine.Engine.Features.OfType<MvcLatest.MvcViewDocumentClassifierPass>());
+            Assert.Empty(engine.Engine.Features.OfType<MvcLatest.ViewComponentTagHelperPass>());
         }
 
         [Fact]
-        public void Create_UnknownProjectPath_UsesLatest()
+        public void Create_UnknownProject_UsesVersion2_0()
         {
             // Arrange
             var projectManager = new TestProjectSnapshotManager(Workspace);
 
-            var factoryService = new DefaultProjectEngineFactoryService(projectManager);
+            var factoryService = new DefaultProjectEngineFactoryService(projectManager, FallbackFactory, CustomFactories);
 
             // Act
             var engine = factoryService.Create("/TestPath/DifferentPath/", b =>
@@ -126,30 +187,33 @@ namespace Microsoft.VisualStudio.Editor.Razor
 
             // Assert
             Assert.Single(engine.Engine.Features.OfType<MyCoolNewFeature>());
+            Assert.Single(engine.Engine.Features.OfType<MvcLatest.ViewComponentTagHelperDescriptorProvider>());
             Assert.Single(engine.Engine.Features.OfType<MvcLatest.MvcViewDocumentClassifierPass>());
             Assert.Single(engine.Engine.Features.OfType<MvcLatest.ViewComponentTagHelperPass>());
         }
 
         [Fact]
-        public void Create_MvcReferenceNotFound_UsesLatest()
+        public void Create_ForUnknownConfiguration_UsesFallbackFactory()
         {
             // Arrange
             var projectManager = new TestProjectSnapshotManager(Workspace);
-            projectManager.HostProjectAdded(HostProject_For_2_0);
+            projectManager.HostProjectAdded(HostProject_For_UnknownConfiguration);
             projectManager.WorkspaceProjectAdded(WorkspaceProject);
 
-            var factoryService = new DefaultProjectEngineFactoryService(projectManager);
+            var factoryService = new DefaultProjectEngineFactoryService(projectManager, FallbackFactory, CustomFactories);
 
             // Act
-            var engine = factoryService.Create("/TestPath/DifferentPath/", b =>
+            var engine = factoryService.Create("/TestPath/SomePath/", b =>
             {
                 b.Features.Add(new MyCoolNewFeature());
             });
 
             // Assert
             Assert.Single(engine.Engine.Features.OfType<MyCoolNewFeature>());
-            Assert.Single(engine.Engine.Features.OfType<MvcLatest.MvcViewDocumentClassifierPass>());
+            Assert.Empty(engine.Engine.Features.OfType<DefaultTagHelperDescriptorProvider>());
-            Assert.Single(engine.Engine.Features.OfType<MvcLatest.ViewComponentTagHelperPass>());
+            Assert.Empty(engine.Engine.Features.OfType<MvcLatest.ViewComponentTagHelperDescriptorProvider>());
+            Assert.Empty(engine.Engine.Features.OfType<MvcLatest.MvcViewDocumentClassifierPass>());
+            Assert.Empty(engine.Engine.Features.OfType<MvcLatest.ViewComponentTagHelperPass>());
         }
 
         private class MyCoolNewFeature : IRazorEngineFeature

test/Microsoft.VisualStudio.Editor.Razor.Test/Microsoft.VisualStudio.Editor.Razor.Test.csproj

@@ -10,6 +10,8 @@
 
   <ItemGroup>
     <ProjectReference Include="..\Microsoft.CodeAnalysis.Razor.Workspaces.Test.Common\Microsoft.CodeAnalysis.Razor.Workspaces.Test.Common.csproj" />
+    <ProjectReference Include="..\..\src\Microsoft.AspNetCore.Mvc.Razor.Extensions\Microsoft.AspNetCore.Mvc.Razor.Extensions.csproj" />
+    <ProjectReference Include="..\..\src\Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X\Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X.csproj" />
     <ProjectReference Include="..\Microsoft.VisualStudio.Editor.Razor.Test.Common\Microsoft.VisualStudio.Editor.Razor.Test.Common.csproj" />
   </ItemGroup>
 

test/Microsoft.VisualStudio.LanguageServices.Razor.Test/Microsoft.VisualStudio.LanguageServices.Razor.Test.csproj

@@ -18,6 +18,8 @@
   </ItemGroup>
 
   <ItemGroup>
+    <ProjectReference Include="..\..\src\Microsoft.AspNetCore.Mvc.Razor.Extensions\Microsoft.AspNetCore.Mvc.Razor.Extensions.csproj" />
+    <ProjectReference Include="..\..\src\Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X\Microsoft.AspNetCore.Mvc.Razor.Extensions.Version1_X.csproj" />
     <ProjectReference Include="..\..\src\Microsoft.VisualStudio.LanguageServices.Razor\Microsoft.VisualStudio.LanguageServices.Razor.csproj" />
     <ProjectReference Include="..\..\src\Microsoft.AspNetCore.Razor.Runtime\Microsoft.AspNetCore.Razor.Runtime.csproj" />
     <ProjectReference Include="..\..\src\Microsoft.AspNetCore.Razor\Microsoft.AspNetCore.Razor.csproj" />

test/Microsoft.VisualStudio.LanguageServices.Razor.Test/OOPTagHelperResolverTest.cs

@@ -0,0 +1,177 @@
+// 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.Linq;
+using System.Reflection;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Razor;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
+using Microsoft.VisualStudio.Editor.Razor;
+using Moq;
+using Xunit;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor
+{
+    public class OOPTagHelperResolverTest
+    {
+        public OOPTagHelperResolverTest()
+        {
+            HostProject_For_2_0 = new HostProject("Test.csproj", FallbackRazorConfiguration.MVC_2_0);
+            HostProject_For_NonSerializableConfiguration = new HostProject(
+                "Test.csproj",
+                new ProjectSystemRazorConfiguration(RazorLanguageVersion.Version_2_1, "Blazor-0.1", Array.Empty<RazorExtension>()));
+
+            CustomFactories = new Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>[]
+            {
+                new Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>(
+                    () => new LegacyProjectEngineFactory_2_0(),
+                    typeof(LegacyProjectEngineFactory_2_0).GetCustomAttribute<ExportCustomProjectEngineFactoryAttribute>()),
+
+                // We don't really use this factory, we just use it to ensure that the call is going to go out of process.
+                new Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>(
+                    () => new LegacyProjectEngineFactory_2_1(),
+                    new ExportCustomProjectEngineFactoryAttribute("Blazor-0.1") { SupportsSerialization = false, }),
+            };
+
+            FallbackFactory = new FallbackProjectEngineFactory();
+
+            Workspace = new AdhocWorkspace();
+
+            var info = ProjectInfo.Create(ProjectId.CreateNewId("Test"), VersionStamp.Default, "Test", "Test", LanguageNames.CSharp, filePath: "Test.csproj");
+            WorkspaceProject = Workspace.CurrentSolution.AddProject(info).GetProject(info.Id);
+
+            ErrorReporter = new DefaultErrorReporter();
+            ProjectManager = new TestProjectSnapshotManager(Workspace);
+            EngineFactory = new DefaultProjectEngineFactoryService(ProjectManager, FallbackFactory, CustomFactories);
+        }
+
+        private ErrorReporter ErrorReporter { get; }
+
+        private RazorProjectEngineFactoryService EngineFactory { get; }
+
+        private Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>[] CustomFactories { get; }
+
+        private IFallbackProjectEngineFactory FallbackFactory { get; }
+
+        private HostProject HostProject_For_2_0 { get; }
+
+        private HostProject HostProject_For_NonSerializableConfiguration { get; }
+
+        private ProjectSnapshotManagerBase ProjectManager { get; }
+
+        private Project WorkspaceProject { get; }
+
+        private Workspace Workspace { get; }
+
+        [Fact]
+        public async Task GetTagHelpersAsync_WithNonInitializedProject_Noops()
+        {
+            // Arrange
+            ProjectManager.HostProjectAdded(HostProject_For_2_0);
+
+            var project = ProjectManager.GetProjectWithFilePath("Test.csproj");
+
+            var resolver = new TestTagHelperResolver(EngineFactory, ErrorReporter, Workspace);
+
+            var result = await resolver.GetTagHelpersAsync(project);
+
+            // Assert
+            Assert.Same(TagHelperResolutionResult.Empty, result);
+        }
+
+        [Fact]
+        public async Task GetTagHelpersAsync_WithSerializableCustomFactory_GoesOutOfProcess()
+        {
+            // Arrange
+            ProjectManager.HostProjectAdded(HostProject_For_2_0);
+            ProjectManager.WorkspaceProjectAdded(WorkspaceProject);
+
+            var project = ProjectManager.GetProjectWithFilePath("Test.csproj");
+
+            var resolver = new TestTagHelperResolver(EngineFactory, ErrorReporter, Workspace)
+            {
+                OnResolveOutOfProcess = (f, p) =>
+                {
+                    Assert.Same(CustomFactories[0].Value, f);
+                    Assert.Same(project, p);
+
+                    return Task.FromResult(TagHelperResolutionResult.Empty);
+                },
+            };
+
+            var result = await resolver.GetTagHelpersAsync(project);
+
+            // Assert
+            Assert.Same(TagHelperResolutionResult.Empty, result);      
+        }
+
+        [Fact]
+        public async Task GetTagHelpersAsync_WithNonSerializableCustomFactory_StaysInProcess()
+        {
+            // Arrange
+            ProjectManager.HostProjectAdded(HostProject_For_NonSerializableConfiguration);
+            ProjectManager.WorkspaceProjectAdded(WorkspaceProject);
+
+            var project = ProjectManager.GetProjectWithFilePath("Test.csproj");
+
+            var resolver = new TestTagHelperResolver(EngineFactory, ErrorReporter, Workspace)
+            {
+                OnResolveInProcess = (p) =>
+                {
+                    Assert.Same(project, p);
+
+                    return Task.FromResult(TagHelperResolutionResult.Empty);
+                },
+            };
+
+            var result = await resolver.GetTagHelpersAsync(project);
+
+            // Assert
+            Assert.Same(TagHelperResolutionResult.Empty, result);
+
+        }
+
+        private class TestTagHelperResolver : OOPTagHelperResolver
+        {
+            public TestTagHelperResolver(RazorProjectEngineFactoryService engineFactory, ErrorReporter errorReporter, Workspace workspace) 
+                : base(engineFactory, errorReporter, workspace)
+            {
+            }
+
+            public Func<IProjectEngineFactory, ProjectSnapshot, Task<TagHelperResolutionResult>> OnResolveOutOfProcess { get; set; }
+
+            public Func<ProjectSnapshot, Task<TagHelperResolutionResult>> OnResolveInProcess { get; set; }
+
+            protected override Task<TagHelperResolutionResult> ResolveTagHelpersOutOfProcessAsync(IProjectEngineFactory factory, ProjectSnapshot project)
+            {
+                Assert.NotNull(OnResolveOutOfProcess);
+                return OnResolveOutOfProcess(factory, project);
+            }
+
+            protected override Task<TagHelperResolutionResult> ResolveTagHelpersInProcessAsync(ProjectSnapshot project)
+            {
+                Assert.NotNull(OnResolveInProcess);
+                return OnResolveInProcess(project);
+            }
+        }
+        private class TestProjectSnapshotManager : DefaultProjectSnapshotManager
+        {
+            public TestProjectSnapshotManager(Workspace workspace)
+                : base(
+                      Mock.Of<ForegroundDispatcher>(),
+                      Mock.Of<ErrorReporter>(),
+                      Mock.Of<ProjectSnapshotWorker>(),
+                      Enumerable.Empty<ProjectSnapshotChangeTrigger>(),
+                      workspace)
+            {
+            }
+
+            protected override void NotifyBackgroundWorker(ProjectSnapshotUpdateContext context)
+            {
+            }
+        }
+    }
+}

test/Microsoft.VisualStudio.LanguageServices.Razor.Test/Serialization/ProjectSnapshotHandleSerializationTest.cs

@@ -0,0 +1,73 @@
+// 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.Linq;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Razor;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
+using Newtonsoft.Json;
+using Xunit;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor.Serialization
+{
+    public class ProjectSnapshotHandleSerializationTest
+    {
+        public ProjectSnapshotHandleSerializationTest()
+        {
+            var converters = new JsonConverterCollection();
+            converters.RegisterRazorConverters();
+            Converters = converters.ToArray();
+        }
+
+        public JsonConverter[] Converters { get; }
+
+        [Fact]
+        public void ProjectSnapshotHandleJsonConverter_Serialization_CanKindaRoundTrip()
+        {
+            // Arrange
+            var snapshot = new ProjectSnapshotHandle(
+                "Test.csproj",
+                new ProjectSystemRazorConfiguration(
+                RazorLanguageVersion.Version_1_1,
+                    "Test",
+                    new[]
+                    {
+                        new ProjectSystemRazorExtension("Test-Extension1"),
+                        new ProjectSystemRazorExtension("Test-Extension2"),
+                    }),
+                ProjectId.CreateFromSerialized(Guid.NewGuid(), "Test"));
+
+            // Act
+            var json = JsonConvert.SerializeObject(snapshot, Converters);
+            var obj = JsonConvert.DeserializeObject<ProjectSnapshotHandle>(json, Converters);
+
+            // Assert
+            Assert.Equal(snapshot.FilePath, obj.FilePath);
+            Assert.Equal(snapshot.Configuration.ConfigurationName, obj.Configuration.ConfigurationName);
+            Assert.Collection(
+                snapshot.Configuration.Extensions, 
+                e => Assert.Equal("Test-Extension1", e.ExtensionName),
+                e => Assert.Equal("Test-Extension2", e.ExtensionName));
+            Assert.Equal(snapshot.Configuration.LanguageVersion, obj.Configuration.LanguageVersion);
+            Assert.Equal(snapshot.WorkspaceProjectId.Id, obj.WorkspaceProjectId.Id);
+        }
+
+        [Fact]
+        public void ProjectSnapshotHandleJsonConverter_SerializationWithNulls_CanKindaRoundTrip()
+        {
+            // Arrange
+            var snapshot = new ProjectSnapshotHandle("Test.csproj", null, null);
+
+            // Act
+            var json = JsonConvert.SerializeObject(snapshot, Converters);
+            var obj = JsonConvert.DeserializeObject<ProjectSnapshotHandle>(json, Converters);
+
+            // Assert
+            Assert.Equal(snapshot.FilePath, obj.FilePath);
+            Assert.Null(obj.Configuration);
+            Assert.Null(obj.WorkspaceProjectId);
+        }
+    }
+}

test/Microsoft.VisualStudio.LanguageServices.Razor.Test/Serialization/RazorConfigurationSerializationTest.cs

@@ -0,0 +1,50 @@
+// 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.Linq;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis.Razor;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
+using Newtonsoft.Json;
+using Xunit;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor.Serialization
+{
+    public class RazorConfigurationSerializationTest
+    {
+        public RazorConfigurationSerializationTest()
+        {
+            var converters = new JsonConverterCollection();
+            converters.RegisterRazorConverters();
+            Converters = converters.ToArray();
+        }
+
+        public JsonConverter[] Converters { get; }
+
+        [Fact]
+        public void RazorConfigurationJsonConverter_Serialization_CanRoundTrip()
+        {
+            // Arrange
+            var configuration = new ProjectSystemRazorConfiguration(
+                RazorLanguageVersion.Version_1_1,
+                "Test",
+                new[]
+                {
+                    new ProjectSystemRazorExtension("Test-Extension1"),
+                    new ProjectSystemRazorExtension("Test-Extension2"),
+                });
+
+            // Act
+            var json = JsonConvert.SerializeObject(configuration, Converters);
+            var obj = JsonConvert.DeserializeObject<RazorConfiguration>(json, Converters);
+
+            // Assert
+            Assert.Equal(configuration.ConfigurationName, obj.ConfigurationName);
+            Assert.Collection(
+                configuration.Extensions, 
+                e => Assert.Equal("Test-Extension1", e.ExtensionName),
+                e => Assert.Equal("Test-Extension2", e.ExtensionName));
+            Assert.Equal(configuration.LanguageVersion, obj.LanguageVersion);
+        }
+    }
+}

test/Microsoft.VisualStudio.LanguageServices.Razor.Test/Serialization/RazorExtensionSerializationTest.cs

@@ -0,0 +1,38 @@
+// 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.Linq;
+using Microsoft.AspNetCore.Razor.Language;
+using Microsoft.CodeAnalysis.Razor;
+using Microsoft.CodeAnalysis.Razor.ProjectSystem;
+using Newtonsoft.Json;
+using Xunit;
+
+namespace Microsoft.VisualStudio.LanguageServices.Razor.Serialization
+{
+    public class RazorExtensionSerializationTest
+    {
+        public RazorExtensionSerializationTest()
+        {
+            var converters = new JsonConverterCollection();
+            converters.RegisterRazorConverters();
+            Converters = converters.ToArray();
+        }
+
+        public JsonConverter[] Converters { get; }
+
+        [Fact]
+        public void RazorExensionJsonConverter_Serialization_CanRoundTrip()
+        {
+            // Arrange
+            var extension = new ProjectSystemRazorExtension("Test");
+
+            // Act
+            var json = JsonConvert.SerializeObject(extension, Converters);
+            var obj = JsonConvert.DeserializeObject<RazorExtension>(json, Converters);
+
+            // Assert
+            Assert.Equal(extension.ExtensionName, obj.ExtensionName);
+        }
+    }
+}

test/Microsoft.VisualStudio.LanguageServices.Razor.Test/Serialization/TagHelperDescriptorSerializationTest.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Language.Legacy;
+using Microsoft.VisualStudio.LanguageServices.Razor.Serialization;
 using Newtonsoft.Json;
 using Xunit;
 

tooling/Microsoft.VisualStudio.RazorExtension/RazorInfo/RazorInfoViewModel.cs

@@ -177,7 +177,8 @@ namespace Microsoft.VisualStudio.RazorExtension.RazorInfo
                     .Select(reference => reference.Display)
                     .Select(filter => Path.GetFileNameWithoutExtension(filter));
                 var projectFilters = project.AllProjectReferences.Select(filter => solution.GetProject(filter.ProjectId).AssemblyName);
-                var resolutionResult = await _tagHelperResolver.GetTagHelpersAsync(project, CancellationToken.None);
+
+                var resolutionResult = await _tagHelperResolver.GetTagHelpersAsync(projectViewModel.Snapshot.Project);
 
                 var files = GetCshtmlDocuments(project);