Block scoped const variables.

src/preparser.cc

Index: src/preparser.cc
diff --git a/src/preparser.cc b/src/preparser.cc
index 492ae7b214df79b0d804d35bc0a8c0ab5872d3fc..86d9d9bd34e50a1c06b045024348470b8ce82cf8 100644
--- a/src/preparser.cc
+++ b/src/preparser.cc
@@ -125,12 +125,18 @@ PreParser::Statement PreParser::ParseSourceElement(bool* ok) {
   // In harmony mode we allow additionally the following productions
   // SourceElement:
   //    LetDeclaration
+  //    ConstDeclaration
 
   switch (peek()) {
     case i::Token::FUNCTION:
       return ParseFunctionDeclaration(ok);
     case i::Token::LET:
       return ParseVariableStatement(kSourceElement, ok);
+    case i::Token::CONST:
+      if (harmony_scoping_) {
+        return ParseHarmonyConstDeclaration(ok);
+      }
+      // FALLTHROUGH
     default:
       return ParseStatement(ok);
   }
@@ -335,6 +341,15 @@ PreParser::Statement PreParser::ParseVariableDeclarations(
   if (peek() == i::Token::VAR) {
     Consume(i::Token::VAR);
   } else if (peek() == i::Token::CONST) {
+    if (harmony_scoping_) {
+      ASSERT(var_context == kForStatement ||
+             var_context == kStatement);
+      i::Scanner::Location location = scanner_->peek_location();
+      ReportMessageAt(location.beg_pos, location.end_pos,
+                      "unprotected_const", NULL);
+      *ok = false;
+      return Statement::Default();
+    }
     if (strict_mode()) {
       i::Scanner::Location location = scanner_->peek_location();
       ReportMessageAt(location, "strict_const", NULL);
@@ -386,6 +401,39 @@ PreParser::Statement PreParser::ParseVariableDeclarations(
 }
 
 
+PreParser::Statement PreParser::ParseHarmonyConstDeclaration(bool* ok) {
+  // ES6 Draft Rev3
+  //
+  // ConstDeclaration ::
+  //   const ConstBinding (',' ConstBinding)* ';'
+  // ConstBinding ::
+  //   Identifier '=' AssignmentExpression
+  //
+  // TODO(ES6):
+  // ConstBinding ::
+  //   BindingPattern '=' AssignmentExpression
+
+  Consume(i::Token::CONST);
+  do {
+    // Parse variable name.
+    Identifier identifier  = ParseIdentifier(CHECK_OK);
+    if (!identifier.IsValidStrictVariable()) {
+      StrictModeIdentifierViolation(scanner_->location(),
+                                    "strict_var_name",
+                                    identifier,
+                                    ok);
+      return Statement::Default();
+    }
+
+    Expect(i::Token::ASSIGN, CHECK_OK);
+    ParseAssignmentExpression(false, CHECK_OK);
+  } while (Check(i::Token::COMMA));
+
+  ExpectSemicolon(CHECK_OK);
+  return Statement::Default();
+}
+
+
 PreParser::Statement PreParser::ParseExpressionOrLabelledStatement(bool* ok) {
   // ExpressionStatement | LabelledStatement ::
   //   Expression ';'