[parser] Fix scopes in rewriting of for-of and destructuring assignments.

src/parsing/pattern-rewriter.cc

 // Copyright 2015 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/ast/ast.h"
 #include "src/messages.h"
 #include "src/parsing/parameter-initializer-rewriter.h"
 #include "src/parsing/parser.h"
 
 namespace v8 {
@@ skipping 568 matching lines @@
       loop->Initialize(condition, body);
     }
 
     block_->statements()->Add(loop, zone());
     RecurseIntoSubpattern(spread->expression(),
                           factory()->NewVariableProxy(array));
   }
 
   Expression* closing_condition = factory()->NewUnaryOperation(
       Token::NOT, factory()->NewVariableProxy(done), nopos);
-  parser_->FinalizeIteratorUse(completion, closing_condition, iterator, block_,
-                               target);
+
+  // Since assignments are being rewritten at the end of parsing, scope() may
+  // already have been removed by FinalizeBlockScope in the meantime.  In that
+  // case, find the first outer non-removed scope.

[Dan Ehrenberg, 2016/11/22 16:07:00]

Should we put this logic to find the appropriate non-deleted scope at the
entrypoint to the rewriter, rather than in its usage here? I wonder if there are
other bugs lurking or possible to create in the future where we use a scope
that's actually deleted (the call to NewTemporary() seems saved just because we
never delete closure scopes right now, though).

[neis, 2016/11/23 12:51:08]

Done.

+  Scope* real_scope = scope();
+  while (real_scope != nullptr && real_scope->HasBeenRemoved()) {
+    real_scope = real_scope->outer_scope();
+  }
+  DCHECK_NOT_NULL(real_scope);

[Toon Verwaest, 2016/11/22 08:30:18]

What about moving this into an aptly named helper function?

[neis, 2016/11/23 12:51:08]

Done.

+
+  parser_->FinalizeIteratorUse(real_scope, completion, closing_condition,
+                               iterator, block_, target);
   block_ = target;
 }
 
 
 void Parser::PatternRewriter::VisitArrayLiteral(ArrayLiteral* node) {
   Variable* temp_var = nullptr;
   VisitArrayLiteral(node, &temp_var);
 }
 
 
@@ skipping 86 matching lines @@
 NOT_A_PATTERN(TryFinallyStatement)
 NOT_A_PATTERN(UnaryOperation)
 NOT_A_PATTERN(VariableDeclaration)
 NOT_A_PATTERN(WhileStatement)
 NOT_A_PATTERN(WithStatement)
 NOT_A_PATTERN(Yield)
 
 #undef NOT_A_PATTERN
 }  // namespace internal
 }  // namespace v8