Add async to the list of class element completion keyword and refactoring according to feedback

src/harness/fourslash.ts

@@ -3426,7 +3426,8 @@ namespace FourSlashInterface {
             "readonly",
             "get",
             "set",
-            "constructor"
+            "constructor",
+            "async"
         ];
 
         constructor(protected state: FourSlash.TestState, private negative = false) {

src/services/completions.ts

@@ -618,7 +618,8 @@ namespace ts.Completions {
 
             if (classLikeContainer = tryGetClassLikeCompletionContainer(contextToken)) {
                 // cursor inside class declaration
-                return tryGetClassLikeCompletionSymbols(classLikeContainer);
+                getGetClassLikeCompletionSymbols(classLikeContainer);
+                return true;
             }
 
             if (jsxContainer = tryGetContainingJsxElement(contextToken)) {
@@ -929,7 +930,7 @@ namespace ts.Completions {
          *
          * @returns true if 'symbols' was successfully populated; false otherwise.
          */
-        function tryGetClassLikeCompletionSymbols(classLikeDeclaration: ClassLikeDeclaration): boolean {
+        function getGetClassLikeCompletionSymbols(classLikeDeclaration: ClassLikeDeclaration) {
             // We're looking up possible property names from parent type.
             isMemberCompletion = true;
             // Declaring new property/method/accessor
@@ -965,8 +966,6 @@ namespace ts.Completions {
                         baseProperty =>  baseProperty.getDeclarations() && !(getDeclarationModifierFlagsFromSymbol(baseProperty) & ModifierFlags.Private));
                 }
             }
-
-            return true;
         }
 
         /**
@@ -1431,6 +1430,7 @@ namespace ts.Completions {
             case SyntaxKind.ReadonlyKeyword:
             case SyntaxKind.GetKeyword:
             case SyntaxKind.SetKeyword:
+            case SyntaxKind.AsyncKeyword:
                 return true;
         }
     }

tests/cases/fourslash/completionEntryForClassMembers.ts

@@ -84,6 +84,9 @@
 ////class M extends B {
 ////    private static identi/*classThatStartedWritingIdentifierAfterPrivateStaticModifier*/
 ////}
+////class N extends B {
+////    async /*classThatHasWrittenAsyncKeyword*/
+////}
 
 const allowedKeywordCount = verify.allowedClassElementKeywords.length;
 type CompletionInfo = [string, string];
@@ -171,6 +174,7 @@ const classInstanceElementLocations = [
     "classThatStartedWritingIdentifierOfGetAccessor",
     "classThatStartedWritingIdentifierOfSetAccessor",
     "classThatStartedWritingIdentifierAfterModifier",
+    "classThatHasWrittenAsyncKeyword"
 ];
 verifyClassElementLocations(instanceMemberInfo, classInstanceElementLocations);