Make sure only one instance of a service is created

IVSServices and ITeamExplorerServices have methods that depend on types
from specific versions of TeamFoundation. Unfortunately, because the
class itself doesn't depend on any TeamFoundation types, it can be
happily instantiated by the runtime, which means that there would be two
instances of each of these MEF exports floating around, which of course
silently crashes the MEF loading of any other types that depend on these
services in their constructors.

We need to make sure that any service exported by these
TeamFoundation-specific projects have fields/properties/constructors
that depend on TeamFoundation types, so that they will not be
instantiated if the VS they're running on is a different version.

Author: shana

src/GitHub.TeamFoundation.14/Services/TeamExplorerServices.cs

@@ -13,6 +13,14 @@ public class TeamExplorerServices : ITeamExplorerServices
     {
         readonly IServiceProvider serviceProvider;
 
+        /// <summary>
+        /// This MEF export requires specific versions of TeamFoundation. ITeamExplorerNotificationManager is declared here so
+        /// that instances of this type cannot be created if the TeamFoundation dlls are not available
+        /// (otherwise we'll have multiple instances of ITeamExplorerServices exports, and that would be Bad(tm))
+        /// </summary>
+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1823:AvoidUnusedPrivateFields")]
+        ITeamExplorerNotificationManager manager;
+
         [ImportingConstructor]
         public TeamExplorerServices([Import(typeof(SVsServiceProvider))] IServiceProvider serviceProvider)
         {
@@ -21,31 +29,31 @@ public TeamExplorerServices([Import(typeof(SVsServiceProvider))] IServiceProvide
 
         public void ShowMessage(string message)
         {
-            var manager = serviceProvider.TryGetService<ITeamExplorer>() as ITeamExplorerNotificationManager;
+            manager = serviceProvider.TryGetService<ITeamExplorer>() as ITeamExplorerNotificationManager;
             manager?.ShowNotification(message, NotificationType.Information, NotificationFlags.None, null, default(Guid));
         }
 
         public void ShowMessage(string message, ICommand command)
         {
-            var manager = serviceProvider.TryGetService<ITeamExplorer>() as ITeamExplorerNotificationManager;
+            manager = serviceProvider.TryGetService<ITeamExplorer>() as ITeamExplorerNotificationManager;
             manager?.ShowNotification(message, NotificationType.Information, NotificationFlags.None, command, default(Guid));
         }
 
         public void ShowWarning(string message)
         {
-            var manager = serviceProvider.TryGetService<ITeamExplorer>() as ITeamExplorerNotificationManager;
+            manager = serviceProvider.TryGetService<ITeamExplorer>() as ITeamExplorerNotificationManager;
             manager?.ShowNotification(message, NotificationType.Warning, NotificationFlags.None, null, default(Guid));
         }
 
         public void ShowError(string message)
         {
-            var manager = serviceProvider.TryGetService<ITeamExplorer>() as ITeamExplorerNotificationManager;
+            manager = serviceProvider.TryGetService<ITeamExplorer>() as ITeamExplorerNotificationManager;
             manager?.ShowNotification(message, NotificationType.Error, NotificationFlags.None, null, default(Guid));
         }
 
         public void ClearNotifications()
         {
-            var manager = serviceProvider.TryGetService<ITeamExplorer>() as ITeamExplorerNotificationManager;
+            manager = serviceProvider.TryGetService<ITeamExplorer>() as ITeamExplorerNotificationManager;
             manager?.ClearNotifications();
         }
     }

src/GitHub.TeamFoundation.14/Services/VSServices.cs

@@ -23,6 +23,14 @@ public class VSServices : IVSServices
     {
         readonly IUIProvider serviceProvider;
 
+        /// <summary>
+        /// This MEF export requires specific versions of TeamFoundation. IGitExt is declared here so
+        /// that instances of this type cannot be created if the TeamFoundation dlls are not available
+        /// (otherwise we'll have multiple instances of IVSServices exports, and that would be Bad(tm))
+        /// </summary>
+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1823:AvoidUnusedPrivateFields")]
+        IGitExt gitExtService;
+
         [ImportingConstructor]
         public VSServices(IUIProvider serviceProvider)
         {
@@ -56,8 +64,8 @@ public void Clone(string cloneUrl, string clonePath, bool recurseSubmodules)
 
         IGitRepositoryInfo GetRepoFromVS()
         {
-            var gitExt = serviceProvider.GetService<IGitExt>();
-            return gitExt.ActiveRepositories.FirstOrDefault();
+            gitExtService = serviceProvider.GetService<IGitExt>();
+            return gitExtService.ActiveRepositories.FirstOrDefault();
         }
 
         public LibGit2Sharp.IRepository GetActiveRepo()