Move method off of CompletionHelper.

src/EditorFeatures/Core/Extensibility/Completion/CompletionHelper.cs

@@ -375,46 +375,6 @@ private static bool TextTypedSoFarMatchesItem(CompletionItem item, char ch, stri
                 item.FilterText.StartsWith(textTypedWithChar, StringComparison.CurrentCultureIgnoreCase);
         }
 
-        /// <summary>
-        /// Returns true if the character typed should be used to filter the specified completion
-        /// item.  A character will be checked to see if it should filter an item.  If not, it will be
-        /// checked to see if it should commit that item.  If it does neither, then completion will
-        /// be dismissed.
-        /// </summary>
-        public virtual bool IsFilterCharacter(CompletionItem item, char ch, string textTypedSoFar)
-        {
-            // general rule: if the filtering text exactly matches the start of the item then it must be a filter character
-            if (TextTypedSoFarMatchesItem(item, ch, textTypedSoFar))
-            {
-                return false;
-            }
-
-            foreach (var rule in item.Rules.FilterCharacterRules)
-            {
-                switch (rule.Kind)
-                {
-                    case CharacterSetModificationKind.Add:
-                        if (rule.Characters.Contains(ch))
-                        {
-                            return true;
-                        }
-                        continue;
-
-                    case CharacterSetModificationKind.Remove:
-                        if (rule.Characters.Contains(ch))
-                        {
-                            return false;
-                        }
-                        continue;
-
-                    case CharacterSetModificationKind.Replace:
-                        return rule.Characters.Contains(ch);
-                }
-            }
-
-            return false;
-        }
-
         private static StringComparison GetComparision(bool isCaseSensitive)
         {
             return isCaseSensitive? StringComparison.CurrentCulture: StringComparison.CurrentCultureIgnoreCase;

src/EditorFeatures/Core/Implementation/IntelliSense/Completion/Controller_TypeChar.cs

@@ -337,11 +337,46 @@ private bool IsFilterCharacter(char ch)
                 return char.IsLetterOrDigit(ch);
             }
 
-            var helper = GetCompletionHelper();
-            if (helper != null)
+            var filterText = GetCurrentFilterText(model, model.SelectedItem.Item);
+            return IsFilterCharacter(model.SelectedItem.Item, ch, filterText);
+        }
+
+        private static bool TextTypedSoFarMatchesItem(CompletionItem item, char ch, string textTypedSoFar)
+        {
+            var textTypedWithChar = textTypedSoFar + ch;
+            return item.DisplayText.StartsWith(textTypedWithChar, StringComparison.CurrentCultureIgnoreCase) ||
+                item.FilterText.StartsWith(textTypedWithChar, StringComparison.CurrentCultureIgnoreCase);
+        }
+
+        private bool IsFilterCharacter(CompletionItem item, char ch, string filterText)
+        {
+            // general rule: if the filtering text exactly matches the start of the item then it must be a filter character
+            if (TextTypedSoFarMatchesItem(item, ch, textTypedSoFar: filterText))
             {
-                var filterText = GetCurrentFilterText(model, model.SelectedItem.Item);
-                return helper.IsFilterCharacter(model.SelectedItem.Item, ch, filterText);
+                return false;
+            }
+
+            foreach (var rule in item.Rules.FilterCharacterRules)
+            {
+                switch (rule.Kind)
+                {
+                    case CharacterSetModificationKind.Add:
+                        if (rule.Characters.Contains(ch))
+                        {
+                            return true;
+                        }
+                        continue;
+
+                    case CharacterSetModificationKind.Remove:
+                        if (rule.Characters.Contains(ch))
+                        {
+                            return false;
+                        }
+                        continue;
+
+                    case CharacterSetModificationKind.Replace:
+                        return rule.Characters.Contains(ch);
+                }
             }
 
             return false;