Merge pull request #14657 from erikmcc/master

Allow export default abstract class. Related to issue 3792.

src/compiler/parser.ts

@@ -1267,6 +1267,7 @@ namespace ts {
         function nextTokenIsClassOrFunctionOrAsync(): boolean {
             nextToken();
             return token() === SyntaxKind.ClassKeyword || token() === SyntaxKind.FunctionKeyword ||
+                (token() === SyntaxKind.AbstractKeyword && lookAhead(nextTokenIsClassKeywordOnSameLine)) ||
                 (token() === SyntaxKind.AsyncKeyword && lookAhead(nextTokenIsFunctionKeywordOnSameLine));
         }
 
@@ -4661,6 +4662,11 @@ namespace ts {
             return tokenIsIdentifierOrKeyword(token()) && !scanner.hasPrecedingLineBreak();
         }
 
+        function nextTokenIsClassKeywordOnSameLine() {
+            nextToken();
+            return token() === SyntaxKind.ClassKeyword && !scanner.hasPrecedingLineBreak();
+        }
+
         function nextTokenIsFunctionKeywordOnSameLine() {
             nextToken();
             return token() === SyntaxKind.FunctionKeyword && !scanner.hasPrecedingLineBreak();