Fix corner case in iterator finalization for array destructuring.

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 425 matching lines @@
     if (value->IsSpread()) {
       spread = value->AsSpread();
       break;
     }
 
     PatternContext context = SetInitializerContextIfNeeded(value);
 
     // if (!done) {
     //   done = true;  // If .next, .done or .value throws, don't close.
     //   result = IteratorNext(iterator);
-    //   v = (done = result.done) ? undefined : result.value;
+    //   if (result.done) {
+    //     v = undefined;
+    //   } else {
+    //     v = result.value;
+    //     done = false;
+    //   }
     // }
-    Statement* if_statement;
+    Statement* if_not_done;
     {
+      auto result_done = factory()->NewProperty(
+          factory()->NewVariableProxy(result),
+          factory()->NewStringLiteral(ast_value_factory()->done_string(),
+                                      RelocInfo::kNoPosition),
+          RelocInfo::kNoPosition);
+
+      auto assign_undefined = factory()->NewAssignment(
+          Token::ASSIGN, factory()->NewVariableProxy(v),
+          factory()->NewUndefinedLiteral(RelocInfo::kNoPosition),
+          RelocInfo::kNoPosition);
+
+      auto assign_value = factory()->NewAssignment(
+          Token::ASSIGN, factory()->NewVariableProxy(v),
+          factory()->NewProperty(
+              factory()->NewVariableProxy(result),
+              factory()->NewStringLiteral(ast_value_factory()->value_string(),
+                                          RelocInfo::kNoPosition),
+              RelocInfo::kNoPosition),
+          RelocInfo::kNoPosition);
+
+      auto unset_done = factory()->NewAssignment(
+          Token::ASSIGN, factory()->NewVariableProxy(done),
+          factory()->NewBooleanLiteral(false, RelocInfo::kNoPosition),
+          RelocInfo::kNoPosition);
+
+      auto inner_else =
+          factory()->NewBlock(nullptr, 2, true, RelocInfo::kNoPosition);
+      inner_else->statements()->Add(
+          factory()->NewExpressionStatement(assign_value, nopos), zone());
+      inner_else->statements()->Add(
+          factory()->NewExpressionStatement(unset_done, nopos), zone());
+
+      auto inner_if = factory()->NewIfStatement(
+          result_done,
+          factory()->NewExpressionStatement(assign_undefined, nopos),
+          inner_else, nopos);
+
       auto next_block =
           factory()->NewBlock(nullptr, 3, true, RelocInfo::kNoPosition);
-
       next_block->statements()->Add(
           factory()->NewExpressionStatement(
               factory()->NewAssignment(
                   Token::ASSIGN, factory()->NewVariableProxy(done),
                   factory()->NewBooleanLiteral(true, nopos), nopos),
               nopos),
           zone());
-
       next_block->statements()->Add(
           factory()->NewExpressionStatement(
               parser_->BuildIteratorNextResult(
                   factory()->NewVariableProxy(iterator), result,
                   RelocInfo::kNoPosition),
               RelocInfo::kNoPosition),
           zone());
+      next_block->statements()->Add(inner_if, zone());
 
-      auto assign_to_done = factory()->NewAssignment(
-          Token::ASSIGN, factory()->NewVariableProxy(done),
-          factory()->NewProperty(
-              factory()->NewVariableProxy(result),
-              factory()->NewStringLiteral(ast_value_factory()->done_string(),
-                                          RelocInfo::kNoPosition),
-              RelocInfo::kNoPosition),
-          RelocInfo::kNoPosition);
-      auto next_value = factory()->NewConditional(
-          assign_to_done,
-          factory()->NewUndefinedLiteral(RelocInfo::kNoPosition),
-          factory()->NewProperty(
-              factory()->NewVariableProxy(result),
-              factory()->NewStringLiteral(ast_value_factory()->value_string(),
-                                          RelocInfo::kNoPosition),
-              RelocInfo::kNoPosition),
-          RelocInfo::kNoPosition);
-      next_block->statements()->Add(
-          factory()->NewExpressionStatement(
-              factory()->NewAssignment(Token::ASSIGN,
-                                       factory()->NewVariableProxy(v),
-                                       next_value, RelocInfo::kNoPosition),
-              RelocInfo::kNoPosition),
-          zone());
-
-      if_statement = factory()->NewIfStatement(
+      if_not_done = factory()->NewIfStatement(
           factory()->NewUnaryOperation(Token::NOT,
                                        factory()->NewVariableProxy(done),
                                        RelocInfo::kNoPosition),
           next_block, factory()->NewEmptyStatement(RelocInfo::kNoPosition),
           RelocInfo::kNoPosition);
     }
-    block_->statements()->Add(if_statement, zone());
+    block_->statements()->Add(if_not_done, zone());
 
     if (!(value->IsLiteral() && value->AsLiteral()->raw_value()->IsTheHole())) {
       if (FLAG_harmony_iterator_close) {
         // completion = kAbruptCompletion;
         Expression* proxy = factory()->NewVariableProxy(completion);
         Expression* assignment = factory()->NewAssignment(
             Token::ASSIGN, proxy,
             factory()->NewSmiLiteral(kAbruptCompletion, nopos), nopos);
         block_->statements()->Add(
             factory()->NewExpressionStatement(assignment, nopos), zone());
@@ skipping 171 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