Fix C# "speculative T" completion to appear properly in linked document...

Fix C# "speculative T" completion to appear properly in linked document scenarios, fixing failing unit test

Additionally, this change audits calls to GetUnionItemsFromDocumentAndLinkedDocumentsAsync to avoid redundant awaits.

src/Features/CSharp/Portable/Completion/CompletionProviders/SnippetCompletionProvider.cs

@@ -62,9 +62,9 @@ public override async Task ProduceCompletionListAsync(CompletionListContext cont
                     return;
                 }
 
-                var snippetCompletionItems = await document.GetUnionResultsFromDocumentAndLinks(
+                var snippetCompletionItems = await document.GetUnionItemsFromDocumentAndLinkedDocumentsAsync(
                     UnionCompletionItemComparer.Instance,
-                    async (d, c) => await GetSnippetsForDocumentAsync(d, position, workspace, c).ConfigureAwait(false),
+                    (d, c) => GetSnippetsForDocumentAsync(d, position, workspace, c),
                     cancellationToken).ConfigureAwait(false);
 
                 context.AddItems(snippetCompletionItems);

src/Features/CSharp/Portable/Completion/CompletionProviders/SpeculativeTCompletionProvider.cs

@@ -31,7 +31,11 @@ public override async Task ProduceCompletionListAsync(CompletionListContext cont
             var position = context.Position;
             var cancellationToken = context.CancellationToken;
 
-            if (await ShouldShowSpeculativeTCompletionItem(document, position, cancellationToken).ConfigureAwait(false))
+            var showSpeculativeT = await document.IsValidContextForDocumentOrLinkedDocumentsAsync(
+                (doc, ct) => ShouldShowSpeculativeTCompletionItemAsync(doc, position, ct),
+                cancellationToken).ConfigureAwait(false);
+
+            if (showSpeculativeT)
             {
                 var text = await document.GetTextAsync(cancellationToken).ConfigureAwait(false);
                 var filterSpan = this.GetTextChangeSpan(text, position);
@@ -41,7 +45,7 @@ public override async Task ProduceCompletionListAsync(CompletionListContext cont
             }
         }
 
-        private async Task<bool> ShouldShowSpeculativeTCompletionItem(Document document, int position, CancellationToken cancellationToken)
+        private async Task<bool> ShouldShowSpeculativeTCompletionItemAsync(Document document, int position, CancellationToken cancellationToken)
         {
             var syntaxTree = await document.GetSyntaxTreeAsync(cancellationToken).ConfigureAwait(false);
             if (syntaxTree.IsInNonUserCode(position, cancellationToken) ||

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

@@ -54,9 +54,9 @@ public override async Task ProduceCompletionListAsync(CompletionListContext cont
 
             using (Logger.LogBlock(FunctionId.Completion_KeywordCompletionProvider_GetItemsWorker, cancellationToken))
             {
-                var keywords = await document.GetUnionResultsFromDocumentAndLinks(
+                var keywords = await document.GetUnionItemsFromDocumentAndLinkedDocumentsAsync(
                     s_comparer,
-                    async (doc, ct) => await RecommendKeywordsAsync(doc, position, ct).ConfigureAwait(false),
+                    (doc, ct) => RecommendKeywordsAsync(doc, position, ct),
                     cancellationToken).ConfigureAwait(false);
 
                 var text = await document.GetTextAsync(cancellationToken).ConfigureAwait(false);

src/Features/Core/Portable/Shared/Extensions/DocumentExtensions.cs

@@ -35,7 +35,7 @@ public static bool ShouldHideAdvancedMembers(this Document document)
             return document.WithSyntaxRoot(newRoot);
         }
 
-        public static async Task<IEnumerable<T>> GetUnionResultsFromDocumentAndLinks<T>(
+        public static async Task<IEnumerable<T>> GetUnionItemsFromDocumentAndLinkedDocumentsAsync<T>(
             this Document document,
             IEqualityComparer<T> comparer,
             Func<Document, CancellationToken, Task<IEnumerable<T>>> getItemsWorker,
@@ -61,5 +61,28 @@ public static bool ShouldHideAdvancedMembers(this Document document)
 
             return totalItems;
         }
+
+        public static async Task<bool> IsValidContextForDocumentOrLinkedDocumentsAsync(
+            this Document document,
+            Func<Document, CancellationToken, Task<bool>> contextChecker,
+            CancellationToken cancellationToken)
+        {
+            if (await contextChecker(document, cancellationToken).ConfigureAwait(false))
+            {
+                return true;
+            }
+
+            var solution = document.Project.Solution;
+            foreach (var linkedDocumentId in document.GetLinkedDocumentIds())
+            {
+                var linkedDocument = solution.GetDocument(linkedDocumentId);
+                if (await contextChecker(linkedDocument, cancellationToken).ConfigureAwait(false))
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
     }
 }