[es6] implement default/optional parameters (WIP / comments)

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 905 matching lines @@
   Scanner::Location eval_args_error_loc = Scanner::Location::invalid();
   Scanner::Location dupe_error_loc = Scanner::Location::invalid();
   Scanner::Location reserved_error_loc = Scanner::Location::invalid();
 
   bool is_rest = false;
   bool done = arity_restriction == FunctionLiteral::GETTER_ARITY ||
       (peek() == Token::RPAREN &&
        arity_restriction != FunctionLiteral::SETTER_ARITY);
   while (!done) {
     bool is_strict_reserved = false;
+    int rest_pos;
     is_rest = peek() == Token::ELLIPSIS && allow_harmony_rest_params();
     if (is_rest) {
       Consume(Token::ELLIPSIS);
+      rest_pos = position();
     }
 
     Identifier param_name =
         ParseIdentifierOrStrictReservedWord(&is_strict_reserved, CHECK_OK);
     if (!eval_args_error_loc.IsValid() && param_name.IsEvalOrArguments()) {
       eval_args_error_loc = scanner()->location();
     }
     if (!reserved_error_loc.IsValid() && is_strict_reserved) {
       reserved_error_loc = scanner()->location();
     }
 
     int prev_value = scanner()->FindSymbol(&duplicate_finder, 1);
 
     if (!dupe_error_loc.IsValid() && prev_value != 0) {
       dupe_error_loc = scanner()->location();
     }
 
+    if (peek() == Token::ASSIGN) {
+      Consume(Token::ASSIGN);
+      static const bool accept_IN = true;
+      ExpressionT defaultValue = ParseAssignmentExpression(accept_IN, CHECK_OK);
+      if (is_rest) {
+        ReportMessageAt(Scanner::Location(rest_pos, scanner()->location().end_pos), "rest_param_default");
+        *ok = false;
+        return Expression::Default();
+      }
+      // Default value is not needed in pre-parser.
+      USE(defaultValue);
+    }
+
     if (arity_restriction == FunctionLiteral::SETTER_ARITY) break;
     done = (peek() == Token::RPAREN);
     if (!done) {
       if (is_rest) {
         ReportMessageAt(scanner()->peek_location(), "param_after_rest");
         *ok = false;
         return Expression::Default();
       }
       Expect(Token::COMMA, CHECK_OK);
     }
@@ skipping 118 matching lines @@
 
   DCHECK(!spread_pos.IsValid());
 
   return Expression::Default();
 }
 
 #undef CHECK_OK
 
 
 } }  // v8::internal