[parser] Allow escaped async in for-of

Bug: v8:11722
Change-Id: I34569071d74f0fe68b30cf3a596ea944440f1fec
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2864703Reviewed-by: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74361}

src/parsing/parser-base.h

@@ -5986,7 +5986,8 @@ typename ParserBase<Impl>::StatementT ParserBase<Impl>::ParseForStatement(
       expression = ParseExpressionCoverGrammar();
       // `for (async of` is disallowed but `for (async.x of` is allowed, so
       // check if the token is ASYNC after parsing the expression.
-      bool expression_is_async = scanner()->current_token() == Token::ASYNC;
+      bool expression_is_async = scanner()->current_token() == Token::ASYNC &&
+                                 !scanner()->literal_contains_escapes();
       // Initializer is reference followed by in/of.
       lhs_end_pos = end_position();
       is_for_each = CheckInOrOf(&for_info.mode);

test/cctest/test-parsing.cc

@@ -7157,6 +7157,16 @@ TEST(ForOfExpressionError) {
   RunParserSyncTest(context_data, data, kError);
 }
 
+TEST(ForOfAsync) {
+  const char* context_data[][2] = {{"", ""},
+                                   {"'use strict';", ""},
+                                   {"function foo(){ 'use strict';", "}"},
+                                   {nullptr, nullptr}};
+
+  const char* data[] = {"for(\\u0061sync of []) {}", nullptr};
+
+  RunParserSyncTest(context_data, data, kSuccess);
+}
 
 TEST(InvalidUnicodeEscapes) {
   const char* context_data[][2] = {