Use package without MEF dependency for GitHubPane

The package that hosts GitHubPane mustn't initialize MEF (even on a background thread).

Author: jcansdale

src/GitHub.Exports/Settings/Guids.cs

@@ -13,6 +13,7 @@ public static class Guids
         public const string CodeContainerProviderId = "6CE146CB-EF57-4F2C-A93F-5BA685317660";
         public const string InlineReviewsPackageId = "248325BE-4A2D-4111-B122-E7D59BF73A35";
         public const string PullRequestStatusPackageId = "5121BEC6-1088-4553-8453-0DDC7C8E2238";
+        public const string GitHubPanePackageId = "0A40459D-6B6D-4110-B6CE-EC83C0BC6A09";
         public const string TeamExplorerWelcomeMessage = "C529627F-8AA6-4FDB-82EB-4BFB7DB753C3";
         public const string LoginManagerId = "7BA2071A-790A-4F95-BE4A-0EEAA5928AAF";
 

src/GitHub.VisualStudio/GitHub.VisualStudio.csproj

@@ -315,6 +315,7 @@
     <Compile Include="Commands\ShowGitHubPaneCommand.cs" />
     <Compile Include="Commands\OpenPullRequestsCommand.cs" />
     <Compile Include="GitContextPackage.cs" />
+    <Compile Include="GitHubPanePackage.cs" />
     <Compile Include="IServiceProviderPackage.cs" />
     <Compile Include="Helpers\ActiveDocumentSnapshot.cs" />
     <Compile Include="Commands\AddConnectionCommand.cs" />

src/GitHub.VisualStudio/GitHubPackage.cs

@@ -28,7 +28,6 @@ namespace GitHub.VisualStudio
     [Guid(Guids.guidGitHubPkgString)]
     [ProvideMenuResource("Menus.ctmenu", 1)]
     [ProvideAutoLoad(Guids.UIContext_Git, PackageAutoLoadFlags.BackgroundLoad)]
-    [ProvideToolWindow(typeof(GitHubPane), Orientation = ToolWindowOrientation.Right, Style = VsDockStyle.Tabbed, Window = EnvDTE.Constants.vsWindowKindSolutionExplorer)]
     [ProvideOptionPage(typeof(OptionsPage), "GitHub for Visual Studio", "General", 0, 0, supportsAutomation: true)]
     public class GitHubPackage : AsyncMenuPackage
     {
@@ -137,7 +136,7 @@ public async Task<IGitHubPaneViewModel> ShowGitHubPane()
             }
 
             var gitHubPane = (GitHubPane)pane;
-            var viewModel = (IGitHubPaneViewModel)((FrameworkElement)gitHubPane.View).DataContext;
+            var viewModel = (IGitHubPaneViewModel)(gitHubPane.View).DataContext;
             await viewModel.InitializeAsync(pane);
             return viewModel;
         }

src/GitHub.VisualStudio/GitHubPanePackage.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Runtime.InteropServices;
+using GitHub.VisualStudio.UI;
+using Microsoft.VisualStudio.Shell;
+
+namespace GitHub.VisualStudio
+{
+    /// <summary>
+    /// This is the host package for the <see cref="GitHubPane"/> tool window.
+    /// </summary>
+    /// <remarks>
+    /// This package mustn't use MEF.
+    /// See: https://github.com/github/VisualStudio/issues/1550
+    /// </remarks>
+    [PackageRegistration(UseManagedResourcesOnly = true, AllowsBackgroundLoading = true)]
+    [Guid(Guids.GitHubPanePackageId)]
+    [ProvideToolWindow(typeof(GitHubPane), Orientation = ToolWindowOrientation.Right,
+        Style = VsDockStyle.Tabbed, Window = EnvDTE.Constants.vsWindowKindSolutionExplorer)]
+    public sealed class GitHubPanePackage : AsyncPackage
+    {
+    }
+}