[es6] emit error when for-in loop declarations are initialized in strict mode

src/preparser.cc

Index: src/preparser.cc
diff --git a/src/preparser.cc b/src/preparser.cc
index 5a6a094f6af52b7ba025e9d4ff9c0450499497f7..f145d7681902d3d098830579791b738da5a2f256 100644
--- a/src/preparser.cc
+++ b/src/preparser.cc
@@ -410,10 +410,8 @@ PreParser::Statement PreParser::ParseVariableStatement(
   // VariableStatement ::
   //   VariableDeclarations ';'
 
-  Statement result = ParseVariableDeclarations(var_context,
-                                               NULL,
-                                               NULL,
-                                               CHECK_OK);
+  Statement result =
+      ParseVariableDeclarations(var_context, NULL, NULL, NULL, CHECK_OK);
   ExpectSemicolon(CHECK_OK);
   return result;
 }
@@ -426,9 +424,8 @@ PreParser::Statement PreParser::ParseVariableStatement(
 // of 'for-in' loops.
 PreParser::Statement PreParser::ParseVariableDeclarations(
     VariableDeclarationContext var_context,
-    VariableDeclarationProperties* decl_props,
-    int* num_decl,
-    bool* ok) {
+    VariableDeclarationProperties* decl_props, int* num_decl,
+    Scanner::Location* first_initializer_loc, bool* ok) {
   // VariableDeclarations ::
   //   ('var' | 'const') (Identifier ('=' AssignmentExpression)?)+[',']
   //
@@ -482,16 +479,25 @@ PreParser::Statement PreParser::ParseVariableDeclarations(
   // of a let declared variable is the scope of the immediately enclosing
   // block.
   int nvars = 0;  // the number of variables declared
+  bool initializer_recorded = false;
   do {
     // Parse variable name.
     if (nvars > 0) Consume(Token::COMMA);
     ParseIdentifier(kDontAllowEvalOrArguments, CHECK_OK);
+    Scanner::Location variable_loc = scanner()->location();
     nvars++;
     if (peek() == Token::ASSIGN || require_initializer ||
         // require initializers for multiple consts.
         (is_strict_const && peek() == Token::COMMA)) {
       Expect(Token::ASSIGN, CHECK_OK);
       ParseAssignmentExpression(var_context != kForStatement, CHECK_OK);
+
+      variable_loc.end_pos = scanner()->location().end_pos;
+      if (first_initializer_loc && !initializer_recorded) {
+        *first_initializer_loc = variable_loc;
+        initializer_recorded = true;
+      }
+
       if (decl_props != NULL) *decl_props = kHasInitializers;
     }
   } while (peek() == Token::COMMA);
@@ -735,13 +741,26 @@ PreParser::Statement PreParser::ParseForStatement(bool* ok) {
                         (peek() == Token::CONST && is_strict(language_mode()));
       int decl_count;
       VariableDeclarationProperties decl_props = kHasNoInitializers;
-      ParseVariableDeclarations(
-          kForStatement, &decl_props, &decl_count, CHECK_OK);
+      Scanner::Location first_initializer_loc = Scanner::Location::invalid();
+      ParseVariableDeclarations(kForStatement, &decl_props, &decl_count,
+                                &first_initializer_loc, CHECK_OK);
       bool has_initializers = decl_props == kHasInitializers;
       bool accept_IN = decl_count == 1 && !(is_lexical && has_initializers);
-      bool accept_OF = !has_initializers;
+      bool accept_OF = true;
       if (accept_IN && CheckInOrOf(accept_OF, &visit_mode, ok)) {
         if (!*ok) return Statement::Default();
+        if (first_initializer_loc.IsValid() &&
+            (is_strict(language_mode()) ||
+             visit_mode == ForEachStatement::ITERATE)) {
+          if (visit_mode == ForEachStatement::ITERATE) {
+            ReportMessageAt(first_initializer_loc, "for_of_loop_initializer");
+          } else {
+            ReportMessageAt(first_initializer_loc,
+                            "strict_for_in_loop_initializer");
+          }
+          *ok = false;
+          return Statement::Default();
+        }
         ParseExpression(true, CHECK_OK);
         Expect(Token::RPAREN, CHECK_OK);
         ParseSubStatement(CHECK_OK);