Correct change detection when projects not supporting EnC are added/removed

src/EditorFeatures/Test/EditAndContinue/EditAndContinueWorkspaceServiceTests.cs

@@ -1852,7 +1852,7 @@ public async Task SemanticError()
         [Fact]
         public async Task HasChanges()
         {
-            using var _ = CreateWorkspace(out var solution, out var service);
+            using var _ = CreateWorkspace(out var solution, out var service, [typeof(NoCompilationLanguageService)]);
 
             var pathA = Path.Combine(TempRoot.Root, "A.cs");
             var pathB = Path.Combine(TempRoot.Root, "B.cs");
@@ -1903,6 +1903,17 @@ public async Task HasChanges()
             // remove a project:
             Assert.True(await EditSession.HasChangesAsync(solution, solution.RemoveProject(projectD.Id), CancellationToken.None));
 
+            // add a project that doesn't support EnC:
+
+            oldSolution = solution;
+            var projectE = solution.AddProject("E", "E", NoCompilationConstants.LanguageName);
+            solution = projectE.Solution;
+
+            Assert.False(await EditSession.HasChangesAsync(oldSolution, solution, CancellationToken.None));
+
+            // remove a project that doesn't support EnC:
+            Assert.False(await EditSession.HasChangesAsync(solution, oldSolution, CancellationToken.None));
+
             EndDebuggingSession(debuggingSession);
         }
 
@@ -3677,9 +3688,7 @@ public async Task ActiveStatements_SyntaxErrorOrOutOfSyncDocument(bool isOutOfSy
         [CombinatorialData]
         public async Task ActiveStatements_ForeignDocument(bool withPath, bool designTimeOnly)
         {
-            var composition = FeaturesTestCompositions.Features.AddParts(typeof(NoCompilationLanguageService));
-
-            using var _ = CreateWorkspace(out var solution, out var service, new[] { typeof(NoCompilationLanguageService) });
+            using var _ = CreateWorkspace(out var solution, out var service, [typeof(NoCompilationLanguageService)]);
 
             var project = solution.AddProject("dummy_proj", "dummy_proj", designTimeOnly ? LanguageNames.CSharp : NoCompilationConstants.LanguageName);
             var filePath = withPath ? Path.Combine(TempRoot.Root, "test.cs") : null;

src/Features/Core/Portable/EditAndContinue/EditSession.cs

@@ -290,22 +290,36 @@ public static async ValueTask<bool> HasChangesAsync(Solution oldSolution, Soluti
                 return false;
             }
 
-            if (oldSolution.ProjectIds.Count != newSolution.ProjectIds.Count)
-            {
-                return true;
-            }
-
             foreach (var newProject in newSolution.Projects)
             {
+                if (!newProject.SupportsEditAndContinue())
+                {
+                    continue;
+                }
+
                 var oldProject = oldSolution.GetProject(newProject.Id);
                 if (oldProject == null || await HasChangedOrAddedDocumentsAsync(oldProject, newProject, changedOrAddedDocuments: null, cancellationToken).ConfigureAwait(false))
                 {
+                    // project added or has changes
+                    return true;
+                }
+            }
+
+            foreach (var oldProject in oldSolution.Projects)
+            {
+                if (!oldProject.SupportsEditAndContinue())
+                {
+                    continue;
+                }
+
+                var newProject = newSolution.GetProject(oldProject.Id);
+                if (newProject == null)
+                {
+                    // project removed
                     return true;
                 }
             }
 
-            // The number of projects in both solution is the same and there are no new projects and no changes in existing projects.
-            // Therefore there are no changes.
             return false;
         }