harmony-scoping: Allow 'const' iteration variables in strict mode.

src/preparser.cc

 // Copyright 2011 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.
 
 #include <cmath>
 
 #include "src/allocation.h"
 #include "src/base/logging.h"
 #include "src/conversions-inl.h"
 #include "src/conversions.h"
@@ skipping 391 matching lines @@
   //
   // ConstDeclaration ::
   //   const ConstBinding (',' ConstBinding)* ';'
   // ConstBinding ::
   //   Identifier '=' AssignmentExpression
   //
   // TODO(ES6):
   // ConstBinding ::
   //   BindingPattern '=' AssignmentExpression
   bool require_initializer = false;
+  bool is_strict_const = false;
   if (peek() == Token::VAR) {
     Consume(Token::VAR);
   } else if (peek() == Token::CONST) {
     // TODO(ES6): The ES6 Draft Rev4 section 12.2.2 reads:
     //
     // ConstDeclaration : const ConstBinding (',' ConstBinding)* ';'
     //
     // * It is a Syntax Error if the code that matches this production is not
     //   contained in extended code.
     //
     // However disallowing const in sloppy mode will break compatibility with
     // existing pages. Therefore we keep allowing const with the old
     // non-harmony semantics in sloppy mode.
     Consume(Token::CONST);
     if (strict_mode() == STRICT) {
       if (allow_harmony_scoping()) {
         if (var_context != kSourceElement && var_context != kForStatement) {
           ReportMessageAt(scanner()->peek_location(), "unprotected_const");
           *ok = false;
           return Statement::Default();
         }
-        require_initializer = true;
+        is_strict_const = true;
+        require_initializer = var_context != kForStatement;
       } else {
         Scanner::Location location = scanner()->peek_location();
         ReportMessageAt(location, "strict_const");
         *ok = false;
         return Statement::Default();
       }
     }
   } else if (peek() == Token::LET && strict_mode() == STRICT) {
     Consume(Token::LET);
     if (var_context != kSourceElement && var_context != kForStatement) {
       ReportMessageAt(scanner()->peek_location(), "unprotected_let");
       *ok = false;
       return Statement::Default();
     }
   } else {
     *ok = false;
     return Statement::Default();
   }
 
   // The scope of a var/const declared variable anywhere inside a function
   // is the entire function (ECMA-262, 3rd, 10.1.3, and 12.2). The scope
   // of a let declared variable is the scope of the immediately enclosing
   // block.
   int nvars = 0;  // the number of variables declared
   do {
     // Parse variable name.
     if (nvars > 0) Consume(Token::COMMA);
     ParseIdentifier(kDontAllowEvalOrArguments, CHECK_OK);
     nvars++;
-    if (peek() == Token::ASSIGN || require_initializer) {
+    if (peek() == Token::ASSIGN || require_initializer ||
+        (is_strict_const && peek() == Token::COMMA)) {

[rossberg, 2014/10/23 09:44:54]

I don't understand this condition. If it is true, you always will produce a
syntax error on the next line. Is that intentional? If so, perhaps put in an
explanatory comment (or refactor).

[Dmitry Lomov (no reviews), 2014/10/23 10:33:34]

Yes, intentional. Comment added.

       Expect(Token::ASSIGN, CHECK_OK);
       ParseAssignmentExpression(var_context != kForStatement, CHECK_OK);
       if (decl_props != NULL) *decl_props = kHasInitializers;
     }
   } while (peek() == Token::COMMA);
 
   if (num_decl != NULL) *num_decl = nvars;
   return Statement::Default();
 }
 
@@ skipping 197 matching lines @@
 
 PreParser::Statement PreParser::ParseForStatement(bool* ok) {
   // ForStatement ::
   //   'for' '(' Expression? ';' Expression? ';' Expression? ')' Statement
 
   Expect(Token::FOR, CHECK_OK);
   Expect(Token::LPAREN, CHECK_OK);
   if (peek() != Token::SEMICOLON) {
     if (peek() == Token::VAR || peek() == Token::CONST ||
         (peek() == Token::LET && strict_mode() == STRICT)) {
-      bool is_let = peek() == Token::LET;
+      bool is_let_or_strict_const =

[rossberg, 2014/10/23 09:44:54]

Nit: how about naming this 'is_lexical'?

[Dmitry Lomov (no reviews), 2014/10/23 10:33:34]

Done.

+          peek() == Token::LET ||
+          (peek() == Token::CONST && strict_mode() == STRICT);
       int decl_count;
       VariableDeclarationProperties decl_props = kHasNoInitializers;
       ParseVariableDeclarations(
           kForStatement, &decl_props, &decl_count, CHECK_OK);
       bool has_initializers = decl_props == kHasInitializers;
-      bool accept_IN = decl_count == 1 && !(is_let && has_initializers);
+      bool accept_IN =
+          decl_count == 1 && !(is_let_or_strict_const && has_initializers);
       bool accept_OF = !has_initializers;
       if (accept_IN && CheckInOrOf(accept_OF)) {
         ParseExpression(true, CHECK_OK);
         Expect(Token::RPAREN, CHECK_OK);
 
         ParseStatement(CHECK_OK);
         return Statement::Default();
       }
     } else {
       Expression lhs = ParseExpression(false, CHECK_OK);
@@ skipping 236 matching lines @@
   ParseIdentifier(kAllowEvalOrArguments, CHECK_OK);
   ParseArguments(ok);
 
   return Expression::Default();
 }
 
 #undef CHECK_OK
 
 
 } }  // v8::internal