Single instance the completion helpers so we can cache data across completion calls.

src/EditorFeatures/Core/Implementation/IntelliSense/Completion/Controller.Session_FilterModel.cs

@@ -208,6 +208,16 @@ internal partial class Session
                     return HandleDeletionTrigger(model, filterResults);
                 }
 
+                return HandleNormalFiltering(model, filterReason, textSnapshot, document, helper, recentItems, itemToFilterText, filterResults);
+            }
+
+            private Model HandleNormalFiltering(
+                Model model, CompletionFilterReason filterReason, 
+                ITextSnapshot textSnapshot, Document document, 
+                CompletionHelper helper, ImmutableArray<string> recentItems, 
+                Dictionary<CompletionItem, string> itemToFilterText, 
+                List<FilterResult> filterResults)
+            {
                 // Not deletion.  Defer to the language to decide which item it thinks best
                 // matches the text typed so far.
 
@@ -238,8 +248,8 @@ internal partial class Session
                 // like "WriteLine" since no filter text has actually been provided.  HOwever,
                 // if "Console.WriteL$$" is typed, then we do want "WriteLine" to be committed.
                 var matchingItemCount = filterResults.Where(t => t.MatchedFilterText).Count();
-                var isUnique = bestCompletionItem != null && 
-                    matchingItemCount == 1 && 
+                var isUnique = bestCompletionItem != null &&
+                    matchingItemCount == 1 &&
                     itemToFilterText[bestCompletionItem].Length > 0;
 
                 var result = model.WithFilteredItems(filterResults.Select(r => r.PresentationItem).AsImmutable())

src/Features/Core/Portable/Completion/CompletionHelper.cs

@@ -10,35 +10,33 @@
 
 namespace Microsoft.CodeAnalysis.Completion
 {
-    internal class CompletionHelper
+    internal sealed class CompletionHelper
     {
+        private static readonly CompletionHelper CaseSensitiveInstance = new CompletionHelper(isCaseSensitive: true);
+        private static readonly CompletionHelper CaseInsensitiveInstance = new CompletionHelper(isCaseSensitive: false);
+
         private readonly object _gate = new object();
         private readonly Dictionary<string, PatternMatcher> _patternMatcherMap = new Dictionary<string, PatternMatcher>();
         private readonly Dictionary<string, PatternMatcher> _fallbackPatternMatcherMap = new Dictionary<string, PatternMatcher>();
         private static readonly CultureInfo EnUSCultureInfo = new CultureInfo("en-US");
         private readonly bool _isCaseSensitive;
 
-        protected CompletionHelper(bool isCaseSensitive)
+        private CompletionHelper(bool isCaseSensitive)
         {
             _isCaseSensitive = isCaseSensitive;
         }
 
         public static CompletionHelper GetHelper(Workspace workspace, string language)
         {
+            var isCaseSensitive = true;
             var ls = workspace.Services.GetLanguageServices(language);
             if (ls != null)
             {
-                var factory = ls.GetService<CompletionHelperFactory>();
-                if (factory != null)
-                {
-                    return factory.CreateCompletionHelper();
-                }
-
                 var syntaxFacts = ls.GetService<ISyntaxFactsService>();
-                return new CompletionHelper(syntaxFacts?.IsCaseSensitive ?? true);
+                isCaseSensitive = syntaxFacts?.IsCaseSensitive ?? true;
             }
 
-            return null;
+            return isCaseSensitive ? CaseSensitiveInstance : CaseInsensitiveInstance;
         }
 
         public static CompletionHelper GetHelper(Document document)
@@ -62,12 +60,6 @@ public bool MatchesFilterText(CompletionItem item, string filterText)
             return GetMatch(item, filterText) != null;
         }
 
-        private static int GetRecentItemIndex(ImmutableArray<string> recentItems, CompletionItem item)
-        {
-            var index = recentItems.IndexOf(item.DisplayText);
-            return -index;
-        }
-
         private PatternMatch? GetMatch(CompletionItem item, string filterText)
         {
             return GetMatch(item, filterText, includeMatchSpans: false);

src/Features/Core/Portable/Completion/CompletionHelperFactory.cs

-// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
-
-using Microsoft.CodeAnalysis.Host;
-
-namespace Microsoft.CodeAnalysis.Completion
-{
-    internal abstract class CompletionHelperFactory : ILanguageService
-    {
-        public abstract CompletionHelper CreateCompletionHelper();
-    }
-}
\ No newline at end of file

src/Features/Core/Portable/Features.csproj

@@ -168,7 +168,6 @@
     <Compile Include="Completion\CompletionDescription.cs" />
     <Compile Include="Completion\CompletionFilterReason.cs" />
     <Compile Include="Completion\CompletionHelper.cs" />
-    <Compile Include="Completion\CompletionHelperFactory.cs" />
     <Compile Include="Completion\CompletionItem.cs" />
     <Compile Include="Completion\CompletionItemFilter.cs" />
     <Compile Include="Completion\CompletionItemRules.cs" />