Add telemetry for VS item cache

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

@@ -15,6 +15,9 @@ internal enum ActionInfo
             CommitWithTypeImportCompletionEnabled,
             CommitTypeImportCompletionItem,
 
+            RoslynCompletionItemsCached,
+            VSCompletionItemsCacheHit,
+
             // For targeted type completion
             SessionHasTargetTypeFilterEnabled,
 
@@ -30,6 +33,12 @@ internal enum ActionInfo
             CommitItemWithTargetTypeFilter,
         }
 
+        internal static void LogRoslynCompletionItemsCached(int count) =>
+            s_logAggregator.IncreaseCountBy((int)ActionInfo.RoslynCompletionItemsCached, count);
+
+        internal static void LogVSCompletionItemsCacheHit(int count) =>
+            s_logAggregator.IncreaseCountBy((int)ActionInfo.VSCompletionItemsCacheHit, count);
+
         internal static void LogSessionWithTypeImportCompletionEnabled() =>
             s_logAggregator.IncreaseCount((int)ActionInfo.SessionWithTypeImportCompletionEnabled);
 

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

@@ -269,6 +269,9 @@ static void CheckForExperimentStatus(ITextView textView, Document document)
                 session.Properties.AddProperty(ExcludedCommitCharacters, excludedCommitCharacters);
             }
 
+            AsyncCompletionLogger.LogRoslynCompletionItemsCached(RoslynCompletionItemsCached);
+            AsyncCompletionLogger.LogVSCompletionItemsCacheHit(VSCompletionItemsCacheHitCount);
+
             return new AsyncCompletionData.CompletionContext(
                 items,
                 suggestionItemOptions,
@@ -315,13 +318,23 @@ public async Task<object> GetDescriptionAsync(IAsyncCompletionSession session, V
             }
         }
 
+        private int VSCompletionItemsCacheHitCount { get; set; }
+
+        private int RoslynCompletionItemsCached { get; set; }
+
         private VSCompletionItem Convert(
             Document document,
             RoslynCompletionItem roslynItem)
         {
-            if (roslynItem.IsCached && s_roslynItemToVsItem.TryGetValue(roslynItem, out var vsItem))
+            if (roslynItem.IsCached)
             {
-                return vsItem;
+                RoslynCompletionItemsCached++;
+
+                if (s_roslynItemToVsItem.TryGetValue(roslynItem, out var vsItem))
+                {
+                    VSCompletionItemsCacheHitCount++;
+                    return vsItem;
+                }
             }
 
             var imageId = roslynItem.Tags.GetFirstGlyph().GetImageId();