Workspace: Prevent DocumentIds from changing on configuration change

It's possible for events like device (dis)connect to make several quick
calls to `ActiveConfigurationChanged`, some of which would be canceled,
ultimately causing old `DocumentId` data to get lost during project
reload.

Creating new `DocumentId`s could break multiple Roslyn services such as
intellisense. This change makes the whole process more robust so that
`DocumentId` data does not get lost.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/915494

3 files changed, 41 insertions, 10 deletions

diff --git a/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.TypeSystem/MonoDevelopWorkspace.ProjectData.cs b/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.TypeSystem/MonoDevelopWorkspace.ProjectData.cs
index 3d62435d25..52d2088c81 100644
--- a/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.TypeSystem/MonoDevelopWorkspace.ProjectData.cs
+++ b/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.TypeSystem/MonoDevelopWorkspace.ProjectData.cs
@@ -46,11 +46,17 @@ namespace MonoDevelop.Ide.TypeSystem
 				this.projectId = projectId;
 				workspaceRef = new WeakReference<MonoDevelopWorkspace> (ws);
 				DocumentData = new DocumentMap (projectId);
-				this.metadataReferences = new List<MonoDevelopMetadataReference> (metadataReferences.Length);
+				this.metadataReferences = new List<MonoDevelopMetadataReference> (metadataReferences);
+			}
+
+			internal void Connect ()
+			{
+				if (!workspaceRef.TryGetTarget (out var ws))
+					return;
 
-				lock (this.metadataReferences) {
+				lock (metadataReferences) {
 					foreach (var metadataReference in metadataReferences) {
-						AddMetadataReference_NoLock (metadataReference, ws);
+						metadataReference.SnapshotUpdated += OnMetadataReferenceUpdated;
 					}
 				}
 			}
diff --git a/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.TypeSystem/MonoDevelopWorkspace.ProjectDataMap.cs b/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.TypeSystem/MonoDevelopWorkspace.ProjectDataMap.cs
index bd6fedc593..a9a7bd2d5d 100644
--- a/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.TypeSystem/MonoDevelopWorkspace.ProjectDataMap.cs
+++ b/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.TypeSystem/MonoDevelopWorkspace.ProjectDataMap.cs
@@ -202,14 +202,33 @@ namespace MonoDevelop.Ide.TypeSystem
 				}
 			}
 
-			internal ProjectData CreateData (ProjectId id, ImmutableArray<MonoDevelopMetadataReference> metadataReferences)
+			/// <summary>
+			/// Construct, connect to, and return a new <see cref="ProjectData"/> based on
+			/// <paramref name="metadataReferences"/>. This replaces any old <see cref="ProjectData"/> for
+			/// <paramref name="id"/>.
+			/// </summary>
+			internal ProjectData ReplaceData (ProjectId id, ImmutableArray<MonoDevelopMetadataReference> metadataReferences, out ProjectData oldData)
+			{
+				var result = new ProjectData (id, metadataReferences, Workspace);
+				ReplaceData (id, result, out oldData);
+				return result;
+			}
+
+			/// <summary>
+			/// Remove the old <see cref="ProjectData"/> for <paramref name="id"/>, replace it with
+			/// <paramref name="newData"/>, and and connect to <paramref name="newData"/>.
+			/// </summary>
+			internal void ReplaceData (ProjectId id, ProjectData newData, out ProjectData oldData)
 			{
 				lock (updatingProjectDataLock) {
-					var result = new ProjectData (id, metadataReferences, Workspace);
-					projectDataMap [id] = result;
-					return result;
+					oldData = RemoveData (id);
+					if (newData != null) {
+						newData.Connect ();
+						projectDataMap [id] = newData;
+					}
 				}
 			}
+
 			internal ProjectId[] GetProjectIds ()
 			{
 				lock (updatingProjectDataLock) {
diff --git a/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.TypeSystem/MonoDevelopWorkspace.ProjectSystemHandler.cs b/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.TypeSystem/MonoDevelopWorkspace.ProjectSystemHandler.cs
index 2399816b3b..b2446f8ac2 100644
--- a/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.TypeSystem/MonoDevelopWorkspace.ProjectSystemHandler.cs
+++ b/main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.TypeSystem/MonoDevelopWorkspace.ProjectSystemHandler.cs
@@ -144,12 +144,14 @@ namespace MonoDevelop.Ide.TypeSystem
 				try {
 					await workspace.LoadLock.WaitAsync ().ConfigureAwait (false);
 					//when reloading e.g. after a save, preserve document IDs
-					oldProjectData = projectMap.RemoveData (projectId);
-					projectData = projectMap.CreateData (projectId, cacheInfo.References);
+					projectData = projectMap.ReplaceData (projectId, cacheInfo.References, out oldProjectData);
 
 					var documents = await CreateDocuments (projectData, p, token, cacheInfo.SourceFiles, oldProjectData).ConfigureAwait (false);
-					if (documents == null)
+					if (documents == null) {
+						// Restore old document data if cancellation happens here.
+						projectMap.ReplaceData (projectId, oldProjectData, out _);
 						return null;
+					}
 
 					mainDocuments = documents.Item1;
 					additionalDocuments = documents.Item2;
@@ -157,6 +159,10 @@ namespace MonoDevelop.Ide.TypeSystem
 					workspace.LoadLock.Release ();
 				}
 
+				if (token.IsCancellationRequested || mainDocuments == null) {
+					return null;
+				}
+
 				// TODO: Pass in the WorkspaceMetadataFileReferenceResolver
 				var info = ProjectInfo.Create (
 					projectId,