Add test that verifies imports are only loaded once

Fixes VSTS #591651 - Project model evaluation contention

3 files changed, 57 insertions, 2 deletions

diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects.MSBuild/DefaultMSBuildEngine.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects.MSBuild/DefaultMSBuildEngine.cs
index 874b441b06..c8543e34c6 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects.MSBuild/DefaultMSBuildEngine.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects.MSBuild/DefaultMSBuildEngine.cs
@@ -42,6 +42,9 @@ namespace MonoDevelop.Projects.MSBuild
 	{
 		Dictionary<FilePath, LoadedProjectInfo> loadedProjects = new Dictionary<FilePath, LoadedProjectInfo> ();
 
+		// For test purposes.
+		internal static Func<MSBuildProject, MSBuildEvaluationContext> GetEvaluationContext = null;
+
 		class LoadedProjectInfo
 		{
 			public MSBuildProject Project;
@@ -152,9 +155,9 @@ namespace MonoDevelop.Projects.MSBuild
 
 				if (pi.NeedsLoad) {
 					LogBeginProjectFileLoad (context, fileName);
+					pi.LastWriteTime = File.GetLastWriteTimeUtc (fileName);
 					pi.Project.Load (fileName, new MSBuildXmlReader { ForEvaluation = true });
 					pi.NeedsLoad = false;
-					pi.LastWriteTime = File.GetLastWriteTimeUtc (fileName);
 					LogEndProjectFileLoad (context);
 				}
 
@@ -218,7 +221,7 @@ namespace MonoDevelop.Projects.MSBuild
 			pi.ReferencedProjects = new List<MSBuildProject> ();
 
 			try {
-				var context = new MSBuildEvaluationContext ();
+				var context = GetEvaluationContext?.Invoke (pi.Project) ?? new MSBuildEvaluationContext ();
 				foreach (var p in pi.GlobalProperties) {
 					context.SetPropertyValue (p.Key, p.Value);
 					StoreProperty (pi, p.Key, p.Value, p.Value);
diff --git a/main/tests/MonoDevelop.Core.Tests/MonoDevelop.Projects/MSBuildProjectTests.cs b/main/tests/MonoDevelop.Core.Tests/MonoDevelop.Projects/MSBuildProjectTests.cs
index ce45cc9365..2f9f0de492 100644
--- a/main/tests/MonoDevelop.Core.Tests/MonoDevelop.Projects/MSBuildProjectTests.cs
+++ b/main/tests/MonoDevelop.Core.Tests/MonoDevelop.Projects/MSBuildProjectTests.cs
@@ -57,6 +57,56 @@ namespace MonoDevelop.Projects
 			return p;
 		}
 
+		class CustomLogger : MSBuildEngineLogger
+		{
+			internal Dictionary<string, int> loadTasks = new Dictionary<string, int> ();
+			internal Dictionary<string, int> evalTasks = new Dictionary<string, int> ();
+
+			static void IncValue (Dictionary<string, int> tasks, string project)
+			{
+				tasks.TryGetValue (project, out int count);
+				tasks [project] = ++count;
+			}
+
+			public override void LogMessage (string s)
+			{
+				Dictionary<string, int> tasks;
+
+				if (s.StartsWith ("Load Project:", StringComparison.Ordinal)) {
+					tasks = loadTasks;
+				} else if (s.StartsWith ("Evaluate Project:", StringComparison.Ordinal)) {
+					tasks = evalTasks;
+				} else
+					return;
+				
+				IncValue (tasks, s);
+			}
+		}
+
+		[Test]
+		public void ImportsLoadedAndEvaluatedOnlyOnce ()
+		{
+			try {
+				using (var p = LoadProject ()) {
+					CustomLogger log = null;
+
+					DefaultMSBuildEngine.GetEvaluationContext = proj => {
+						if (proj != p)
+							return null;
+						
+						log = new CustomLogger ();
+						return new MSBuildEvaluationContext { Log = log };
+					};
+
+					p.Evaluate ();
+					Assert.That (log.loadTasks.Values, Is.All.EqualTo (1));
+					Assert.That (log.evalTasks.Values, Is.All.EqualTo (1));
+				}
+			} finally {
+				DefaultMSBuildEngine.GetEvaluationContext = null;
+			}
+		}
+
 		[Test]
 		public void Properties ()
 		{
diff --git a/main/tests/test-projects/msbuild-project-test/test.csproj b/main/tests/test-projects/msbuild-project-test/test.csproj
index a73d66a032..e7029dff67 100755
--- a/main/tests/test-projects/msbuild-project-test/test.csproj
+++ b/main/tests/test-projects/msbuild-project-test/test.csproj
@@ -68,5 +68,7 @@
   </ItemGroup>
   <Target Name="Conditioned" Condition="false"></Target>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
+  <!-- Imported twice for verification -->
+  <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <Import Project="extra.csproj" />
 </Project>