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

src/parsing/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/parsing/parser.h"
 
 #include "src/api.h"
 #include "src/ast/ast.h"
 #include "src/ast/ast-expression-visitor.h"
 #include "src/ast/ast-literal-reindexer.h"
@@ skipping 3308 matching lines @@
       Runtime::kThrowIteratorResultNotAnObject, throw_arguments, pos);
 
   return factory()->NewBinaryOperation(
       Token::AND,
       factory()->NewUnaryOperation(Token::NOT, is_spec_object_call, pos),
       throw_call, pos);
 }
 
 
 void Parser::InitializeForEachStatement(ForEachStatement* stmt,
-                                        Expression* each,
-                                        Expression* subject,
-                                        Statement* body) {
+                                        Expression* each, Expression* subject,
+                                        Statement* body,
+                                        bool is_destructuring) {
   ForOfStatement* for_of = stmt->AsForOfStatement();
 
   if (for_of != NULL) {
     Variable* iterator = scope_->NewTemporary(
         ast_value_factory()->dot_iterator_string());
     Variable* result = scope_->NewTemporary(
         ast_value_factory()->dot_result_string());
 
     Expression* assign_iterator;
     Expression* next_result;
@@ skipping 30 matching lines @@
 
     // each = result.value
     {
       Expression* value_literal = factory()->NewStringLiteral(
           ast_value_factory()->value_string(), RelocInfo::kNoPosition);
       Expression* result_proxy = factory()->NewVariableProxy(result);
       Expression* result_value = factory()->NewProperty(
           result_proxy, value_literal, RelocInfo::kNoPosition);
       assign_each = factory()->NewAssignment(Token::ASSIGN, each, result_value,
                                              RelocInfo::kNoPosition);
+      if (is_destructuring) {
+        DCHECK(allow_harmony_destructuring_assignment());
+        bool ok = true;
+        auto rewrite =
+            factory()->NewRewritableAssignmentExpression(assign_each);

[adamk, 2015/12/10 17:28:03]

Making the callers here and below construct a RewritableAssignmentExpression is
a little ugly. Can you add a new entry point to PatternRewriter that
encapsulates this, taking an Expression and returning the rewritten one?

[caitp (gmail), 2015/12/10 18:19:35]

Done

+        PatternRewriter::RewriteDestructuringAssignment(this, rewrite, scope_,
+                                                        &ok);
+        DCHECK(ok);

[adamk, 2015/12/10 17:28:03]

It looks like all callers of RewriteDestructuringAssignment do a DCHECK. Can you
remove the ok argument and do that DCHECK to the end of
RewriteDestructuringAssignment?

[caitp (gmail), 2015/12/10 18:19:36]

Done.

+        assign_each = rewrite->expression();
+      }
     }
 
     for_of->Initialize(each, subject, body,
                        assign_iterator,
                        next_result,
                        result_done,
                        assign_each);
   } else {
+    if (is_destructuring) {
+      Variable* temp =
+          scope_->NewTemporary(ast_value_factory()->dot_result_string());

[adamk, 2015/12/10 17:28:03]

dot_result_string has a special usage (for completion value stuff). How about
just the empty string?

[caitp (gmail), 2015/12/10 18:19:36]

I think this is the completion-correct model, and matches what we do for for-of
loops. But, I've changed it to the empty string, let me know if you change your
mind

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

If there's a reason for it to be .result, I'd expect there's some test that
should catch it. Otherwise I'd always prefer empty string to make clear there's
no reason for .result.

+      VariableProxy* temp_proxy = factory()->NewVariableProxy(temp);
+      bool ok = true;
+      auto rewrite =
+          factory()->NewRewritableAssignmentExpression(factory()->NewAssignment(
+              Token::ASSIGN, each, temp_proxy, RelocInfo::kNoPosition));
+      PatternRewriter::RewriteDestructuringAssignment(this, rewrite, scope_,
+                                                      &ok);
+      DCHECK(ok);
+      auto block =
+          factory()->NewBlock(nullptr, 2, false, RelocInfo::kNoPosition);
+      block->statements()->Add(
+          factory()->NewExpressionStatement(rewrite->expression(),
+                                            RelocInfo::kNoPosition),
+          zone());
+      block->statements()->Add(body, zone());
+      body = block;
+      each = factory()->NewVariableProxy(temp);
+    }
     stmt->Initialize(each, subject, body);
   }
 }
 
 
 Statement* Parser::DesugarLexicalBindingsInForStatement(
     Scope* inner_scope, bool is_const, ZoneList<const AstRawString*>* names,
     ForStatement* loop, Statement* init, Expression* cond, Statement* next,
     Statement* body, bool* ok) {
   // ES6 13.7.4.8 specifies that on each loop iteration the let variables are
@@ skipping 364 matching lines @@
               each_initialization_block, &descriptor, &decl,
               IsLexicalVariableMode(descriptor.mode) ? &lexical_bindings
                                                      : nullptr,
               CHECK_OK);
         }
 
         body_block->statements()->Add(each_initialization_block, zone());
         body_block->statements()->Add(body, zone());
         VariableProxy* temp_proxy =
             factory()->NewVariableProxy(temp, each_beg_pos, each_end_pos);
-        InitializeForEachStatement(loop, temp_proxy, enumerable, body_block);
+        InitializeForEachStatement(loop, temp_proxy, enumerable, body_block,
+                                   false);
         scope_ = for_scope;
         body_scope->set_end_position(scanner()->location().end_pos);
         body_scope = body_scope->FinalizeBlockScope();
         if (body_scope != nullptr) {
           body_block->set_scope(body_scope);
         }
 
         // Create a TDZ for any lexically-bound names.
         if (IsLexicalVariableMode(parsing_result.descriptor.mode)) {
           DCHECK_NULL(init_block);
@@ skipping 30 matching lines @@
         }
       } else {
         init = parsing_result.BuildInitializationBlock(
             IsLexicalVariableMode(parsing_result.descriptor.mode)
                 ? &lexical_bindings
                 : nullptr,
             CHECK_OK);
       }
     } else {
       int lhs_beg_pos = peek_position();
-      Expression* expression = ParseExpression(false, CHECK_OK);
+      ExpressionClassifier classifier;
+      Expression* expression = ParseExpression(false, &classifier, CHECK_OK);
       int lhs_end_pos = scanner()->location().end_pos;
       ForEachStatement::VisitMode mode;
       is_let_identifier_expression =
           expression->IsVariableProxy() &&
           expression->AsVariableProxy()->raw_name() ==
               ast_value_factory()->let_string();
 
       if (CheckInOrOf(&mode, ok)) {
         if (!*ok) return nullptr;
-        expression = this->CheckAndRewriteReferenceExpression(
-            expression, lhs_beg_pos, lhs_end_pos,
-            MessageTemplate::kInvalidLhsInFor, kSyntaxError, CHECK_OK);
+        bool is_destructuring =
+            allow_harmony_destructuring_assignment() &&
+            (expression->IsArrayLiteral() || expression->IsObjectLiteral());
+        if (is_destructuring) {
+          ValidateAssignmentPattern(&classifier, CHECK_OK);
+        } else {
+          ValidateExpression(&classifier, CHECK_OK);
+          expression = this->CheckAndRewriteReferenceExpression(
+              expression, lhs_beg_pos, lhs_end_pos,
+              MessageTemplate::kInvalidLhsInFor, kSyntaxError, CHECK_OK);
+        }
 
         ForEachStatement* loop =
             factory()->NewForEachStatement(mode, labels, stmt_pos);
         Target target(&this->target_stack_, loop);
 
         Expression* enumerable = ParseExpression(true, CHECK_OK);
         Expect(Token::RPAREN, CHECK_OK);
 
         // Make a block around the statement in case a lexical binding
         // is introduced, e.g. by a FunctionDeclaration.
         // This block must not use for_scope as its scope because if a
         // lexical binding is introduced which overlaps with the for-in/of,
         // expressions in head of the loop should actually have variables
         // resolved in the outer scope.
         Scope* body_scope = NewScope(for_scope, BLOCK_SCOPE);
         scope_ = body_scope;
         Block* block =
             factory()->NewBlock(NULL, 1, false, RelocInfo::kNoPosition);
         Statement* body = ParseSubStatement(NULL, CHECK_OK);
         block->statements()->Add(body, zone());
-        InitializeForEachStatement(loop, expression, enumerable, block);
+        InitializeForEachStatement(loop, expression, enumerable, block,
+                                   is_destructuring);
         scope_ = saved_scope;
         body_scope->set_end_position(scanner()->location().end_pos);
         body_scope = body_scope->FinalizeBlockScope();
         if (body_scope != nullptr) {
           block->set_scope(body_scope);
         }
         for_scope->set_end_position(scanner()->location().end_pos);
         for_scope = for_scope->FinalizeBlockScope();
         DCHECK(for_scope == nullptr);
         // Parsed for-in loop.
@@ skipping 2672 matching lines @@
 
 void ParserTraits::QueueDestructuringAssignmentForRewriting(Expression* expr) {
   DCHECK(expr->IsRewritableAssignmentExpression());
   parser_->function_state_->AddDestructuringAssignment(
       Parser::DestructuringAssignment(expr, parser_->scope_));
 }
 
 
 }  // namespace internal
 }  // namespace v8