From c5fd2f14f38d669f604f8cb40af8f3e0d747c600 Mon Sep 17 00:00:00 2001
From: Anders Hejlsberg <andersh@microsoft.com>
Date: Mon, 18 Dec 2017 18:30:34 -0800
Subject: [PATCH] Parse xxx? as JSDoc type when not followed by token that
 starts type

---
 src/compiler/parser.ts | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
index debb4be67ba..9c4aba68a37 100644
--- a/src/compiler/parser.ts
+++ b/src/compiler/parser.ts
@@ -1477,6 +1477,11 @@ namespace ts {
             return isStartOfExpression();
         }
 
+        function nextTokenIsStartOfType() {
+            nextToken();
+            return isStartOfType();
+        }
+
         // True if positioned at a list terminator
         function isListTerminator(kind: ParsingContext): boolean {
             if (token() === SyntaxKind.EndOfFileToken) {
@@ -2767,8 +2772,8 @@ namespace ts {
                         type = createJSDocPostfixType(SyntaxKind.JSDocNonNullableType, type);
                         break;
                     case SyntaxKind.QuestionToken:
-                        // only parse postfix ? inside jsdoc, otherwise it is a conditional type
-                        if (!(contextFlags & NodeFlags.JSDoc)) {
+                        // If not in JSDoc and next token is start of a type we have a conditional type
+                        if (!(contextFlags & NodeFlags.JSDoc) && lookAhead(nextTokenIsStartOfType)) {
                             return type;
                         }
                         type = createJSDocPostfixType(SyntaxKind.JSDocNullableType, type);