Address review comments

src/EditorFeatures/Core/Implementation/IntelliSense/AsyncCompletion/CompletionSource.cs

@@ -201,19 +201,23 @@ internal CompletionSource(ITextView textView, IThreadingContext threadingContext
                 return new AsyncCompletionData.CompletionContext(ImmutableArray<VSCompletionItem>.Empty);
             }
 
+            ImmutableArray<VSCompletionItem> items;
             var filterCache = PooledDictionary<string, AsyncCompletionData.CompletionFilter>.GetInstance();
-
             var itemsBuilder = new ArrayBuilder<VSCompletionItem>(completionList.Items.Length);
-            foreach (var roslynItem in completionList.Items)
+            try
             {
-                cancellationToken.ThrowIfCancellationRequested();
-                var item = Convert(document, roslynItem, completionService, filterCache);
-                itemsBuilder.Add(item);
+                foreach (var roslynItem in completionList.Items)
+                {
+                    cancellationToken.ThrowIfCancellationRequested();
+                    var item = Convert(document, roslynItem, completionService, filterCache);
+                    itemsBuilder.Add(item);
+                }
+            }
+            finally
+            {
+                filterCache.Free();
+                items = itemsBuilder.ToImmutableAndFree();
             }
-
-            filterCache.Free();
-
-            var items = itemsBuilder.ToImmutableAndFree();
 
             var suggestionItemOptions = completionList.SuggestionModeItem != null
                     ? new AsyncCompletionData.SuggestionItemOptions(

src/Features/Core/Portable/Completion/Providers/AbstractTypeImportCompletionProvider.cs

@@ -68,7 +68,7 @@ private async Task AddCompletionItemsAsync(CompletionContext completionContext,
 
             // Get completion items from current project. 
             var compilation = await project.GetCompilationAsync(cancellationToken).ConfigureAwait(false);
-            await typeImportCompletionService.GetTopLevelTypesFromProjectAsync(project, HandlePublicAndInternalItem, cancellationToken)
+            await typeImportCompletionService.GetTopLevelTypesAsync(project, HandlePublicAndInternalItem, cancellationToken)
                 .ConfigureAwait(false); 
 
             // Get completion items from source references.
@@ -79,18 +79,14 @@ await typeImportCompletionService.GetTopLevelTypesFromProjectAsync(project, Hand
                 var referencedProject = project.Solution.GetProject(projectReference.ProjectId);
                 var referencedCompilation = await referencedProject.GetCompilationAsync(cancellationToken).ConfigureAwait(false);
 
-                await typeImportCompletionService.GetTopLevelTypesFromProjectAsync(
+                await typeImportCompletionService.GetTopLevelTypesAsync(
                     referencedProject,
                     GetHandler(compilation.Assembly, referencedCompilation.Assembly),
                     cancellationToken).ConfigureAwait(false);
             }
 
             // Get completion items from PE references.
-            var peReferences = project.MetadataReferences
-                .Where(reference => reference is PortableExecutableReference)
-                .Cast<PortableExecutableReference>();
-
-            foreach (var peReference in peReferences)
+            foreach (var peReference in project.MetadataReferences.OfType<PortableExecutableReference>())
             {
                 cancellationToken.ThrowIfCancellationRequested();
 

src/Features/Core/Portable/Completion/Providers/TypeImportCompletionService.cs

@@ -21,16 +21,16 @@ internal interface ITypeImportCompletionService : IWorkspaceService
         /// getting types from source only, so the project must support compilation. 
         /// For getting types from PE, use <see cref="GetTopLevelTypesFromPEReference"/>.
         /// </summary>
-        Task GetTopLevelTypesFromProjectAsync(
+        Task GetTopLevelTypesAsync(
             Project project,
-            Action<TypeImportCompletionItemInfo> handleAccessibleItem,
+            Action<TypeImportCompletionItemInfo> handleItem,
             CancellationToken cancellationToken);
 
         void GetTopLevelTypesFromPEReference(
             Solution solution,
             Compilation compilation,
             PortableExecutableReference peReference,
-            Action<TypeImportCompletionItemInfo> handleAccessibleItem,
+            Action<TypeImportCompletionItemInfo> handleItem,
             CancellationToken cancellationToken);
     }
 
@@ -85,7 +85,7 @@ public Service(ConcurrentDictionary<string, ReferenceCacheEntry> peReferenceCach
                 _projectItemsCache = projectReferenceCache;
             }
 
-            public async Task GetTopLevelTypesFromProjectAsync(
+            public async Task GetTopLevelTypesAsync(
                 Project project,
                 Action<TypeImportCompletionItemInfo> handleItem,
                 CancellationToken cancellationToken)
@@ -96,6 +96,8 @@ public Service(ConcurrentDictionary<string, ReferenceCacheEntry> peReferenceCach
                 }
 
                 var compilation = await project.GetCompilationAsync(cancellationToken).ConfigureAwait(false);
+
+                // Since we only need top level types from source, therefore we only care if source symbol checksum changes.
                 var checksum = await SymbolTreeInfo.GetSourceSymbolsChecksumAsync(project, cancellationToken).ConfigureAwait(false);
 
                 GetAccessibleTopLevelTypesWorker(