[parser] Relex restriction on reserved words

src/parsing/parser-base.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_PARSING_PARSER_BASE_H
 #define V8_PARSING_PARSER_BASE_H
 
 #include "src/ast/scopes.h"
 #include "src/bailout-reason.h"
 #include "src/hashmap.h"
@@ skipping 3225 matching lines @@
 
 template <class Traits>
 bool ParserBase<Traits>::IsNextLetKeyword() {
   DCHECK(peek() == Token::LET);
   Token::Value next_next = PeekAhead();
   switch (next_next) {
     case Token::LBRACE:
     case Token::LBRACK:
     case Token::IDENTIFIER:
     case Token::STATIC:
-    case Token::LET:  // Yes, you can do let let = ... in sloppy mode
+    case Token::LET:  // `let let;` is disallowed by static semantics, but the
+                      // token must be first interpreted as a keyword in order
+                      // for those semantics to apply. This ensures that ASI is
+                      // not honored when a LineTerminator separates the
+                      // tokens.
     case Token::YIELD:
     case Token::AWAIT:
     case Token::ASYNC:
       return true;
+    case Token::FUTURE_STRICT_RESERVED_WORD:
+      return is_sloppy(language_mode());
     default:
       return false;
   }
 }
 
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseArrowFunctionLiteral(
     bool accept_IN, const FormalParametersT& formal_parameters, bool is_async,
     const ExpressionClassifier& formals_classifier, bool* ok) {
@@ skipping 326 matching lines @@
     has_seen_constructor_ = true;
     return;
   }
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PARSING_PARSER_BASE_H