ES6: Desugaring of instanceof to support @@hasInstance

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-rewriter.h"
 #include "src/ast/ast-expression-visitor.h"
@@ skipping 6270 matching lines @@
     do_block->statements()->Add(get_value, zone);
 
     Variable* dot_result = scope->NewTemporary(avfactory->dot_result_string());
     yield_star = factory->NewDoExpression(do_block, dot_result, nopos);
     Rewriter::Rewrite(parser_, yield_star, avfactory);
   }
 
   return yield_star;
 }
 
+// Desugaring of (lhs) instanceof (rhs)
+// ====================================
+//
+// We desugar instanceof into a load of property @@hasInstance on the rhs.
+// We end up with roughly the following code (O, C):
+//
+//   do {
+//     let O = lhs;
+//     let C = rhs;
+//     if (!IS_RECEIVER(C)) throw MakeTypeError(kNonObjectInInstanceOfCheck);
+//     let handler_result = C[Symbol.hasInstance];
+//     if (handler_result === undefined) {
+//       if (!IS_CALLABLE(C)) {
+//         throw MakeTypeError(kCalledNonCallableInstanceOf);
+//       }
+//       handler_result = %ordinary_has_instance(C, O);
+//     } else {
+//       handler_result = !!(%_Call(handler_result, C, O));
+//     }
+//     handler_result;
+//   }
+//
+Expression* ParserTraits::RewriteInstanceof(Expression* lhs, Expression* rhs,
+                                            int pos) {
+  const int nopos = RelocInfo::kNoPosition;
+
+  auto factory = parser_->factory();
+  auto avfactory = parser_->ast_value_factory();
+  auto scope = parser_->scope_;
+  auto zone = parser_->zone();
+
+  // let O = lhs;
+  Variable* var_O = scope->NewTemporary(avfactory->empty_string());
+  Statement* get_O;
+  {
+    Expression* O_proxy = factory->NewVariableProxy(var_O);
+    Expression* assignment =
+        factory->NewAssignment(Token::ASSIGN, O_proxy, lhs, nopos);
+    get_O = factory->NewExpressionStatement(assignment, nopos);
+  }
+
+  // let C = lhs;
+  Variable* var_C = scope->NewTemporary(avfactory->empty_string());
+  Statement* get_C;
+  {
+    Expression* C_proxy = factory->NewVariableProxy(var_C);
+    Expression* assignment =
+        factory->NewAssignment(Token::ASSIGN, C_proxy, rhs, nopos);
+    get_C = factory->NewExpressionStatement(assignment, nopos);
+  }
+
+  // if (!IS_RECEIVER(C)) throw MakeTypeError(kNonObjectInInstanceOfCheck);
+  Statement* validate_C;
+  {
+    auto args = new (zone) ZoneList<Expression*>(1, zone);
+    args->Add(factory->NewVariableProxy(var_C), zone);
+    Expression* is_receiver_call =
+        factory->NewCallRuntime(Runtime::kInlineIsJSReceiver, args, nopos);
+    Expression* call =
+        NewThrowTypeError(MessageTemplate::kNonObjectInInstanceOfCheck,
+                          avfactory->empty_string(), nopos);
+    Statement* throw_call = factory->NewExpressionStatement(call, nopos);
+
+    validate_C =
+        factory->NewIfStatement(is_receiver_call,
+                                factory->NewEmptyStatement(nopos),
+                                throw_call,
+                                nopos);
+  }
+
+  // let handler_result = C[Symbol.hasInstance];
+  Variable* var_handler_result = scope->NewTemporary(avfactory->empty_string());
+  Statement* initialize_handler;
+  {
+    Expression* hasInstance_symbol_literal =
+        factory->NewSymbolLiteral("hasInstance_symbol", RelocInfo::kNoPosition);
+    Expression* prop = factory->NewProperty(factory->NewVariableProxy(var_C),
+                                            hasInstance_symbol_literal, pos);
+    Expression* handler_proxy = factory->NewVariableProxy(var_handler_result);
+    Expression* assignment =
+        factory->NewAssignment(Token::ASSIGN, handler_proxy, prop, nopos);
+    initialize_handler = factory->NewExpressionStatement(assignment, nopos);
+  }
+
+  // if (handler_result === undefined) {
+  //   if (!IS_CALLABLE(C)) {
+  //     throw MakeTypeError(kCalledNonCallableInstanceOf);
+  //   }
+  //   result = %ordinary_has_instance(C, O);
+  // } else {
+  //   handler_result = !!%_Call(handler_result, C, O);
+  // }
+  Statement* call_handler;
+  {
+    Expression* condition = factory->NewCompareOperation(
+        Token::EQ_STRICT, factory->NewVariableProxy(var_handler_result),
+        factory->NewUndefinedLiteral(nopos), nopos);
+
+    Block* then_side = factory->NewBlock(nullptr, 2, false, nopos);
+    {
+      Expression* throw_expr =
+          NewThrowTypeError(MessageTemplate::kCalledNonCallableInstanceOf,
+                            avfactory->empty_string(), nopos);
+      Statement* validate_C = CheckCallable(var_C, throw_expr);
+      ZoneList<Expression*>* args = new (zone) ZoneList<Expression*>(2, zone);
+      args->Add(factory->NewVariableProxy(var_C), zone);
+      args->Add(factory->NewVariableProxy(var_O), zone);
+      CallRuntime* call = factory->NewCallRuntime(
+          Context::ORDINARY_HAS_INSTANCE_INDEX, args, pos);
+      Expression* result_proxy = factory->NewVariableProxy(var_handler_result);
+      Expression* assignment =
+          factory->NewAssignment(Token::ASSIGN, result_proxy, call, nopos);
+      Statement* assignment_return =
+          factory->NewExpressionStatement(assignment, nopos);
+
+      then_side->statements()->Add(validate_C, zone);
+      then_side->statements()->Add(assignment_return, zone);
+    }
+
+    Statement* else_side;
+    {
+      auto args = new (zone) ZoneList<Expression*>(3, zone);
+      args->Add(factory->NewVariableProxy(var_handler_result), zone);
+      args->Add(factory->NewVariableProxy(var_C), zone);
+      args->Add(factory->NewVariableProxy(var_O), zone);
+      Expression* call =
+          factory->NewCallRuntime(Runtime::kInlineCall, args, nopos);
+      Expression* inner_not =
+          factory->NewUnaryOperation(Token::NOT, call, nopos);
+      Expression* outer_not =
+          factory->NewUnaryOperation(Token::NOT, inner_not, nopos);
+      Expression* result_proxy = factory->NewVariableProxy(var_handler_result);
+      Expression* assignment =
+          factory->NewAssignment(Token::ASSIGN, result_proxy, outer_not, nopos);
+
+      else_side = factory->NewExpressionStatement(assignment, nopos);
+    }
+    call_handler =
+        factory->NewIfStatement(condition, then_side, else_side, nopos);
+  }
+
+  // do { ... }
+  DoExpression* instanceof;
+  {
+    Block* block = factory->NewBlock(nullptr, 5, true, nopos);
+    block->statements()->Add(get_O, zone);
+    block->statements()->Add(get_C, zone);
+    block->statements()->Add(validate_C, zone);
+    block->statements()->Add(initialize_handler, zone);
+    block->statements()->Add(call_handler, zone);
+
+    // Here is the desugared instanceof.
+    instanceof = factory->NewDoExpression(block, var_handler_result, nopos);
+    Rewriter::Rewrite(parser_, instanceof, avfactory);
+  }
+
+  return instanceof;
+}
+
+Statement* ParserTraits::CheckCallable(Variable* var, Expression* error) {

[rossberg, 2016/02/19 12:19:00]

Given that my CL has landed, can you now change FinalizeForOfStatement to invoke
this function?

[mvstanton, 2016/02/19 18:15:59]

Done.

+  auto factory = parser_->factory();
+  auto avfactory = parser_->ast_value_factory();
+  const int nopos = RelocInfo::kNoPosition;
+  Statement* validate_var;
+  {
+    Expression* type_of = factory->NewUnaryOperation(
+        Token::TYPEOF, factory->NewVariableProxy(var), nopos);
+    Expression* function_literal =
+        factory->NewStringLiteral(avfactory->function_string(), nopos);
+    Expression* condition = factory->NewCompareOperation(
+        Token::EQ_STRICT, type_of, function_literal, nopos);
+
+    Statement* throw_call = factory->NewExpressionStatement(error, nopos);
+
+    validate_var = factory->NewIfStatement(
+        condition, factory->NewEmptyStatement(nopos), throw_call, nopos);
+  }
+  return validate_var;
+}
 
 void ParserTraits::BuildIteratorClose(ZoneList<Statement*>* statements,
                                       Variable* iterator,
                                       Expression* input,
                                       Variable* var_output) {
   //
   // This function adds four statements to [statements], corresponding to the
   // following code:
   //
   //   let iteratorReturn = iterator.return;
@@ skipping 426 matching lines @@
   new_body->statements()->Add(loop->body(), zone);
   new_body->statements()->Add(set_completion_normal, zone);
 
   loop->set_body(new_body);
   return final_loop;
 }
 
 
 }  // namespace internal
 }  // namespace v8