[Core] Fix references not saved on installing NuGet packages

The fix applied in commit c459d3c6388d667be6aaf10d466d3367a95555bd
now means that Project.ReevaluateProject can be called at the same
time as NuGet packages are being installed if those NuGet packages
contains MSBuild imports. When creating a new Xamarin.Forms project
references are added to the Android project at the same time that
the ReevaluateProject method is called, indirectly when the type
system calls GetSourceFilesAsync and causes the CoreCompileDependsOn
targets to be run. During the call to MSBuildProject.EvaluateAsync,
which the ReevaluateProject method awaits on, the UI thread can be
used to add a new reference to the project. If the project is not
saved the MSBuildProject is not updated so the LoadProjectItems
was removing the references added to the project since they do not
exist in the evaluated items. When the project is then saved by the
NuGet addin the reference is not in the .csproj file.

Now items added to the project whilst MSBuildProject.EvaluateAsync
is called in ReevaluteProject are captured and LoadProjectItems
takes these into account to ensure they are not lost.

Fixes VSTS #586393 Getting multiple errors on building Forms App

1 files changed, 28 insertions, 2 deletions

diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/Project.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/Project.cs
index ff4e9112c5..141ebcaedc 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/Project.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/Project.cs
@@ -2326,6 +2326,12 @@ namespace MonoDevelop.Projects
 					throw new InvalidOperationException (it.GetType ().Name + " already belongs to a project");
 				it.Project = this;
 			}
+
+			if (monitorItemsModifiedDuringReevaluation) {
+				if (itemsAddedDuringReevaluation == null)
+					itemsAddedDuringReevaluation = ImmutableList.CreateBuilder<ProjectItem> ();
+				itemsAddedDuringReevaluation.AddRange (objs);
+			}
 		
 			NotifyModified ("Items");
 			if (ProjectItemAdded != null)
@@ -2346,6 +2352,9 @@ namespace MonoDevelop.Projects
 			NotifyFileRemovedFromProject (objs.OfType<ProjectFile> ());
 		}
 
+		bool monitorItemsModifiedDuringReevaluation;
+		internal ImmutableList<ProjectItem>.Builder itemsAddedDuringReevaluation;
+
 		internal void NotifyFileChangedInProject (ProjectFile file)
 		{
 			OnFileChangedInProject (new ProjectFileEventArgs (this, file));
@@ -2955,9 +2964,16 @@ namespace MonoDevelop.Projects
 					}
 				}
 			}
-			if (IsReevaluating)
+			if (IsReevaluating) {
+				if (itemsAddedDuringReevaluation != null) {
+					// Handle new items added whilst re-evaluating the MSBuildProject.
+					foreach (var item in itemsAddedDuringReevaluation) {
+						unusedItems.Remove (item);
+						localItems.Add (item);
+					}
+				}
 				Items.SetItems (localItems, newItems, unusedItems);
-			else
+			} else
 				Items.AddRange (localItems);
 		}
 
@@ -4012,6 +4028,12 @@ namespace MonoDevelop.Projects
 		{
 			return BindTask (ct => Runtime.RunInMainThread (async () => {
 				using (await writeProjectLock.EnterAsync ()) {
+
+					if (modifiedInMemory) {
+						await Task.Run (() => WriteProject (monitor));
+						modifiedInMemory = false;
+					}
+
 					var oldCapabilities = new HashSet<string> (projectCapabilities);
 					bool oldSupportsExecute = SupportsExecute ();
 
@@ -4019,7 +4041,9 @@ namespace MonoDevelop.Projects
 						IsReevaluating = true;
 
 						// Reevaluate the msbuild project
+						monitorItemsModifiedDuringReevaluation = true;
 						await sourceProject.EvaluateAsync ();
+						monitorItemsModifiedDuringReevaluation = false;
 
 						// Loads minimal data required to instantiate extensions and prepare for project loading
 						InitBeforeProjectExtensionLoad ();
@@ -4031,6 +4055,8 @@ namespace MonoDevelop.Projects
 
 					} finally {
 						IsReevaluating = false;
+						monitorItemsModifiedDuringReevaluation = false;
+						itemsAddedDuringReevaluation = null;
 					}
 
 					if (resetCachedCompileItems)