[es6] Fix default parameters in arrow functions

src/parser.cc

 // 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.
 
 #include "src/parser.h"
 
 #include "src/api.h"
 #include "src/ast.h"
 #include "src/ast-literal-reindexer.h"
 #include "src/bailout-reason.h"
@@ skipping 3886 matching lines @@
 
   bool is_rest = expr->IsSpread();
   if (is_rest) {
     expr = expr->AsSpread()->expression();
     parameters->has_rest = true;
   }
   if (parameters->is_simple) {
     parameters->is_simple = !is_rest && expr->IsVariableProxy();
   }
 
+  Expression* initializer = nullptr;
   if (expr->IsVariableProxy()) {
     // When the formal parameter was originally seen, it was parsed as a
     // VariableProxy and recorded as unresolved in the scope.  Here we undo that
     // parse-time side-effect for parameters that are single-names (not
     // patterns; for patterns that happens uniformly in
     // PatternRewriter::VisitVariableProxy).
     parser_->scope_->RemoveUnresolved(expr->AsVariableProxy());
-  }
-
-  Expression* initializer = nullptr;
-  if (!is_rest && parser_->allow_harmony_default_parameters() &&
-      parser_->Check(Token::ASSIGN)) {
-    ExpressionClassifier init_classifier;
-    initializer =
-        parser_->ParseAssignmentExpression(true, &init_classifier, ok);
-    if (!*ok) return;
-    parser_->ValidateExpression(&init_classifier, ok);
-    if (!*ok) return;
-    parameters->is_simple = false;
+  } else if (expr->IsAssignment()) {
+    Assignment* assignment = expr->AsAssignment();
+    DCHECK(parser_->allow_harmony_default_parameters());
+    DCHECK(!assignment->is_compound());
+    initializer = assignment->value();
+    expr = assignment->target();
   }
 
   AddFormalParameter(parameters, expr, initializer, is_rest);
 }
 
 
 void ParserTraits::ParseArrowFunctionFormalParameterList(
     ParserFormalParameters* parameters, Expression* expr,
     const Scanner::Location& params_loc,
     Scanner::Location* duplicate_loc, bool* ok) {
@@ skipping 2135 matching lines @@
 Expression* Parser::SpreadCallNew(Expression* function,
                                   ZoneList<v8::internal::Expression*>* args,
                                   int pos) {
   args->InsertAt(0, function, zone());
 
   return factory()->NewCallRuntime(
       ast_value_factory()->reflect_construct_string(), NULL, args, pos);
 }
 }  // namespace internal
 }  // namespace v8