[es6] Fix completion values of for loops with lexical variables

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/v8.h"
 
 #include "src/api.h"
 #include "src/ast.h"
 #include "src/bailout-reason.h"
 #include "src/base/platform/platform.h"
@@ skipping 3204 matching lines @@
   // We rewrite a for statement of the form
   //
   //  labels: for (let/const x = i; cond; next) body
   //
   // into
   //
   //  {
   //    let/const x = i;
   //    temp_x = x;
   //    first = 1;
+  //    undefined;
   //    outer: for (;;) {
-  //      let/const x = temp_x;
-  //      if (first == 1) {
-  //        first = 0;
-  //      } else {
-  //        next;
+  //      { // This block's only function is to ensure that the statements it
+  //        // contains do not affect the normal completion value. This is
+  //        // accomplished by setting its ignore_completion_value bit.
+  //        // No new lexical scope is introduced, so lexically scoped variables
+  //        // declared here will be scoped to the outer for loop.
+  //        let/const x = temp_x;
+  //        if (first == 1) {
+  //          first = 0;
+  //        } else {
+  //          next;
+  //        }
+  //        flag = 1;
   //      }
-  //      flag = 1;
   //      labels: for (; flag == 1; flag = 0, temp_x = x) {
   //        if (cond) {
   //          body
   //        } else {
   //          break outer;
   //        }
   //      }
   //      if (flag == 1) {
   //        break;
   //      }
@@ skipping 32 matching lines @@
     first = scope_->DeclarationScope()->NewTemporary(temp_name);
     VariableProxy* first_proxy = factory()->NewVariableProxy(first);
     Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
     Assignment* assignment = factory()->NewAssignment(
         Token::ASSIGN, first_proxy, const1, RelocInfo::kNoPosition);
     Statement* assignment_statement =
         factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition);
     outer_block->AddStatement(assignment_statement, zone());
   }
 
+  // make statement: undefined;
+  outer_block->AddStatement(
+      factory()->NewExpressionStatement(
+          factory()->NewUndefinedLiteral(RelocInfo::kNoPosition),
+          RelocInfo::kNoPosition),
+      zone());
+
   // Make statement: outer: for (;;)
   // Note that we don't actually create the label, or set this loop up as an
   // explicit break target, instead handing it directly to those nodes that
   // need to know about it. This should be safe because we don't run any code
   // in this function that looks up break targets.
   ForStatement* outer_loop =
       factory()->NewForStatement(NULL, RelocInfo::kNoPosition);
   outer_block->AddStatement(outer_loop, zone());
 
   outer_block->set_scope(for_scope);
   scope_ = inner_scope;
 
-  Block* inner_block = factory()->NewBlock(NULL, names->length() + 4, false,
-                                           RelocInfo::kNoPosition);
+  Block* inner_block =
+      factory()->NewBlock(NULL, 3, false, RelocInfo::kNoPosition);
+  Block* ignore_completion_block = factory()->NewBlock(
+      NULL, names->length() + 2, true, RelocInfo::kNoPosition);
   ZoneList<Variable*> inner_vars(names->length(), zone());
   // For each let variable x:
   //    make statement: let/const x = temp_x.
   VariableMode mode = is_const ? CONST : LET;
   for (int i = 0; i < names->length(); i++) {
     VariableProxy* proxy = NewUnresolved(names->at(i), mode);
     Declaration* declaration = factory()->NewVariableDeclaration(
         proxy, mode, scope_, RelocInfo::kNoPosition);
     Declare(declaration, true, CHECK_OK);
     inner_vars.Add(declaration->proxy()->var(), zone());
     VariableProxy* temp_proxy = factory()->NewVariableProxy(temps.at(i));
     Assignment* assignment =
         factory()->NewAssignment(is_const ? Token::INIT_CONST : Token::INIT_LET,
                                  proxy, temp_proxy, RelocInfo::kNoPosition);
     Statement* assignment_statement =
         factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition);
     DCHECK(init->position() != RelocInfo::kNoPosition);
     proxy->var()->set_initializer_position(init->position());
-    inner_block->AddStatement(assignment_statement, zone());
+    ignore_completion_block->AddStatement(assignment_statement, zone());
   }
 
   // Make statement: if (first == 1) { first = 0; } else { next; }
   if (next) {
     DCHECK(first);
     Expression* compare = NULL;
     // Make compare expression: first == 1.
     {
       Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
       VariableProxy* first_proxy = factory()->NewVariableProxy(first);
       compare = factory()->NewCompareOperation(Token::EQ, first_proxy, const1,
                                                RelocInfo::kNoPosition);
     }
     Statement* clear_first = NULL;
     // Make statement: first = 0.
     {
       VariableProxy* first_proxy = factory()->NewVariableProxy(first);
       Expression* const0 = factory()->NewSmiLiteral(0, RelocInfo::kNoPosition);
       Assignment* assignment = factory()->NewAssignment(
           Token::ASSIGN, first_proxy, const0, RelocInfo::kNoPosition);
       clear_first =
           factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition);
     }
     Statement* clear_first_or_next = factory()->NewIfStatement(
         compare, clear_first, next, RelocInfo::kNoPosition);
-    inner_block->AddStatement(clear_first_or_next, zone());
+    ignore_completion_block->AddStatement(clear_first_or_next, zone());
   }
 
   Variable* flag = scope_->DeclarationScope()->NewTemporary(temp_name);
   // Make statement: flag = 1.
   {
     VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
     Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
     Assignment* assignment = factory()->NewAssignment(
         Token::ASSIGN, flag_proxy, const1, RelocInfo::kNoPosition);
     Statement* assignment_statement =
         factory()->NewExpressionStatement(assignment, RelocInfo::kNoPosition);
-    inner_block->AddStatement(assignment_statement, zone());
+    ignore_completion_block->AddStatement(assignment_statement, zone());
   }
-
+  inner_block->AddStatement(ignore_completion_block, zone());
   // Make cond expression for main loop: flag == 1.
   Expression* flag_cond = NULL;
   {
     Expression* const1 = factory()->NewSmiLiteral(1, RelocInfo::kNoPosition);
     VariableProxy* flag_proxy = factory()->NewVariableProxy(flag);
     flag_cond = factory()->NewCompareOperation(Token::EQ, flag_proxy, const1,
                                                RelocInfo::kNoPosition);
   }
 
   // Create chain of expressions "flag = 0, temp_x = x, ..."
@@ skipping 27 matching lines @@
   // Make statement: if (cond) { body; } else { break outer; }
   Statement* body_or_stop = body;
   if (cond) {
     Statement* stop =
         factory()->NewBreakStatement(outer_loop, RelocInfo::kNoPosition);
     body_or_stop =
         factory()->NewIfStatement(cond, body, stop, cond->position());
   }
 
   // Make statement: labels: for (; flag == 1; flag = 0, temp_x = x)
-  // Note that we re-use the original loop node, which retains it labels
+  // Note that we re-use the original loop node, which retains its labels
   // and ensures that any break or continue statements in body point to
   // the right place.
   loop->Initialize(NULL, flag_cond, compound_next_statement, body_or_stop);
   inner_block->AddStatement(loop, zone());
 
   // Make statement: if (flag == 1) { break; }
   {
     Expression* compare = NULL;
     // Make compare expresion: flag == 1.
     {
@@ skipping 2403 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