Merge pull request #31049 from...

Merge pull request #31049 from jasonmalinowski/fix-project-reference-conversion-during-project-unload

Make sure we convert project references back on project removal

src/VisualStudio/CSharp/Test/ProjectSystemShim/CPS/CSharpReferencesTests.cs

@@ -85,6 +85,29 @@ IEnumerable<PortableExecutableReference> GetProject3MetadataReferences()
             }
         }
 
+
+        [WpfFact]
+        [Trait(Traits.Feature, Traits.Features.ProjectSystemShims)]
+        public void RemoveProjectConvertsProjectReferencesBack()
+        {
+            using (var environment = new TestEnvironment())
+            {
+                var project1 = CreateCSharpCPSProject(environment, "project1", commandLineArguments: @"/out:c:\project1.dll");
+                var project2 = CreateCSharpCPSProject(environment, "project2");
+
+                // Add project reference as metadata reference: since this is known to be the output path of project1, the metadata reference is converted to a project reference
+                project2.AddMetadataReference(@"c:\project1.dll", new MetadataReferenceProperties());
+                Assert.Single(environment.Workspace.CurrentSolution.GetProject(project2.Id).AllProjectReferences);
+
+                // Remove project1. project2's reference should have been converted back
+                project1.Dispose();
+                Assert.Empty(environment.Workspace.CurrentSolution.GetProject(project2.Id).AllProjectReferences);
+                Assert.Single(environment.Workspace.CurrentSolution.GetProject(project2.Id).MetadataReferences);
+
+                project2.Dispose();
+            }
+        }
+
         [WpfFact]
         [Trait(Traits.Feature, Traits.Features.ProjectSystemShims)]
         public void AddRemoveAnalyzerReference_CPS()

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.cs

@@ -1288,18 +1288,29 @@ public void ApplyBatchChangeToProject(ProjectId projectId, Func<CodeAnalysis.Sol
             }
         }
 
-        private Dictionary<ProjectId, ProjectReferenceInformation> _projectReferenceInfo = new Dictionary<ProjectId, ProjectReferenceInformation>();
+        private Dictionary<ProjectId, ProjectReferenceInformation> _projectReferenceInfoMap = new Dictionary<ProjectId, ProjectReferenceInformation>();
 
         private ProjectReferenceInformation GetReferenceInfo_NoLock(ProjectId projectId)
         {
-            return _projectReferenceInfo.GetOrAdd(projectId, _ => new ProjectReferenceInformation());
+            return _projectReferenceInfoMap.GetOrAdd(projectId, _ => new ProjectReferenceInformation());
         }
 
         protected internal override void OnProjectRemoved(ProjectId projectId)
         {
             lock (_gate)
             {
-                _projectReferenceInfo.Remove(projectId);
+                if (_projectReferenceInfoMap.TryGetValue(projectId, out var projectReferenceInfo))
+                {
+                    // If we still had any output paths, we'll want to remove them to cause conversion back to metadata references.
+                    // The call below implicitly is modifying the collection we've fetched, so we'll make a copy.
+                    foreach (var outputPath in projectReferenceInfo.OutputPaths.ToList())
+                    {
+                        RemoveProjectOutputPath(projectId, outputPath);
+                    }
+
+                    _projectReferenceInfoMap.Remove(projectId);
+                }
+
                 _projectToGuidMap = _projectToGuidMap.Remove(projectId);
                 _projectToHierarchyMap = _projectToHierarchyMap.Remove(projectId);
 
@@ -1390,6 +1401,11 @@ private void ConvertMetadataReferencesToProjectReferences_NoLock(ProjectId proje
             SetSolutionAndRaiseWorkspaceChanged_NoLock(modifiedSolution, projectIdsChanged);
         }
 
+        /// <summary>
+        /// Finds all projects that had a project reference to <paramref name="projectId"/> and convert it back to a metadata reference.
+        /// </summary>
+        /// <param name="projectId">The <see cref="ProjectId"/> of the project being referenced.</param>
+        /// <param name="outputPath">The output path of the given project to remove the link to.</param>
         private void ConvertProjectReferencesToMetadataReferences_NoLock(ProjectId projectId, string outputPath)
         {
             var modifiedSolution = this.CurrentSolution;