[es6] support AssignmentPattern as LHS in for-in/of loops

src/parsing/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 938 matching lines @@
           *ok = false;
           return Statement::Default();
         }
         ParseExpression(true, CHECK_OK);
         Expect(Token::RPAREN, CHECK_OK);
         ParseSubStatement(CHECK_OK);
         return Statement::Default();
       }
     } else {
       int lhs_beg_pos = peek_position();
-      Expression lhs = ParseExpression(false, CHECK_OK);
+      ExpressionClassifier classifier;
+      Expression lhs = ParseExpression(false, &classifier, CHECK_OK);
       int lhs_end_pos = scanner()->location().end_pos;
       is_let_identifier_expression =
           lhs.IsIdentifier() && lhs.AsIdentifier().IsLet();
       if (CheckInOrOf(&mode, ok)) {
         if (!*ok) return Statement::Default();
-        lhs = CheckAndRewriteReferenceExpression(
-            lhs, lhs_beg_pos, lhs_end_pos, MessageTemplate::kInvalidLhsInFor,
-            kSyntaxError, CHECK_OK);
+        bool is_destructuring =
+            allow_harmony_destructuring_assignment() &&
+            (lhs->IsArrayLiteral() || lhs->IsObjectLiteral());
+        if (is_destructuring) {
+          ValidateAssignmentPattern(&classifier, CHECK_OK);

[adamk, 2015/12/10 19:23:33]

Please add a few tests to test-parsing.cc to make sure we have preparser
coverage here.

+        } else {
+          ValidateExpression(&classifier, CHECK_OK);
+          lhs = CheckAndRewriteReferenceExpression(
+              lhs, lhs_beg_pos, lhs_end_pos, MessageTemplate::kInvalidLhsInFor,
+              kSyntaxError, CHECK_OK);
+        }
         ParseExpression(true, CHECK_OK);
         Expect(Token::RPAREN, CHECK_OK);
         ParseSubStatement(CHECK_OK);
         return Statement::Default();
       }
     }
   }
 
   // Parsed initializer at this point.
   // Detect attempts at 'let' declarations in sloppy mode.
@@ skipping 289 matching lines @@
     Expect(Token::RBRACE, CHECK_OK);
     return PreParserExpression::Default();
   }
 }
 
 #undef CHECK_OK
 
 
 }  // namespace internal
 }  // namespace v8