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

src/parsing/pattern-rewriter.cc

Index: src/parsing/pattern-rewriter.cc
diff --git a/src/parsing/pattern-rewriter.cc b/src/parsing/pattern-rewriter.cc
index 21b1cec69655c092b3c4e822ed3d14dd6987ccb6..217b8da08532df9b6413698bdbebf2689a92787f 100644
--- a/src/parsing/pattern-rewriter.cc
+++ b/src/parsing/pattern-rewriter.cc
@@ -586,8 +586,18 @@ void Parser::PatternRewriter::VisitArrayLiteral(ArrayLiteral* node,
 
   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;
 }