[async-iteration] add support for for-await-of loops in Async Functions

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 <memory>
 
 #include "src/api.h"
 #include "src/ast/ast-expression-rewriter.h"
@@ skipping 535 matching lines @@
                 info->extension() == nullptr && can_compile_lazily;
   set_allow_natives(FLAG_allow_natives_syntax || info->is_native());
   set_allow_tailcalls(FLAG_harmony_tailcalls && !info->is_native() &&
                       info->isolate()->is_tail_call_elimination_enabled());
   set_allow_harmony_do_expressions(FLAG_harmony_do_expressions);
   set_allow_harmony_function_sent(FLAG_harmony_function_sent);
   set_allow_harmony_restrictive_generators(FLAG_harmony_restrictive_generators);
   set_allow_harmony_trailing_commas(FLAG_harmony_trailing_commas);
   set_allow_harmony_class_fields(FLAG_harmony_class_fields);
   set_allow_harmony_object_rest_spread(FLAG_harmony_object_rest_spread);
+  set_allow_harmony_async_iteration(FLAG_harmony_async_iteration);
   for (int feature = 0; feature < v8::Isolate::kUseCounterFeatureCount;
        ++feature) {
     use_counts_[feature] = 0;
   }
   if (info->ast_value_factory() == NULL) {
     // info takes ownership of AstValueFactory.
     info->set_ast_value_factory(new AstValueFactory(
         zone(), info->isolate()->ast_string_constants(), info->hash_seed()));
     info->set_ast_value_factory_owned();
     ast_value_factory_ = info->ast_value_factory();
@@ skipping 1245 matching lines @@
       statement = factory()->NewExpressionStatement(
           factory()->NewAssignment(Token::INIT, fproxy,
                                    factory()->NewThisFunction(pos),
                                    kNoSourcePosition),
           kNoSourcePosition);
     }
     result->Set(index, statement);
   }
 }
 
-// !%_IsJSReceiver(result = iterator.next()) &&
-//     %ThrowIteratorResultNotAnObject(result)
+// [if (IteratorType == kNormal)]
+//     !%_IsJSReceiver(result = iterator.next()) &&
+//         %ThrowIteratorResultNotAnObject(result)
+// [else if (IteratorType == kAsync)]
+//     !%_IsJSReceiver(result = Await(iterator.next())) &&
+//         %ThrowIteratorResultNotAnObject(result)
+// [endif]
 Expression* Parser::BuildIteratorNextResult(Expression* iterator,
-                                            Variable* result, int pos) {
+                                            Variable* result, IteratorType type,
+                                            int pos) {
   Expression* next_literal = factory()->NewStringLiteral(
       ast_value_factory()->next_string(), kNoSourcePosition);
   Expression* next_property =
       factory()->NewProperty(iterator, next_literal, kNoSourcePosition);
   ZoneList<Expression*>* next_arguments =
       new (zone()) ZoneList<Expression*>(0, zone());
   Expression* next_call =
       factory()->NewCall(next_property, next_arguments, pos);
+  if (type == IteratorType::kAsync) {
+    next_call = RewriteAwaitExpression(next_call, pos);
+  }
   Expression* result_proxy = factory()->NewVariableProxy(result);
   Expression* left =
       factory()->NewAssignment(Token::ASSIGN, result_proxy, next_call, pos);
 
   // %_IsJSReceiver(...)
   ZoneList<Expression*>* is_spec_object_args =
       new (zone()) ZoneList<Expression*>(1, zone());
   is_spec_object_args->Add(left, zone());
   Expression* is_spec_object_call = factory()->NewCallRuntime(
       Runtime::kInlineIsJSReceiver, is_spec_object_args, pos);
@@ skipping 14 matching lines @@
 
 Statement* Parser::InitializeForEachStatement(ForEachStatement* stmt,
                                               Expression* each,
                                               Expression* subject,
                                               Statement* body,
                                               int each_keyword_pos) {
   ForOfStatement* for_of = stmt->AsForOfStatement();
   if (for_of != NULL) {
     const bool finalize = true;
     return InitializeForOfStatement(for_of, each, subject, body, finalize,
-                                    each_keyword_pos);
+                                    IteratorType::kNormal, each_keyword_pos);
   } else {
     if (each->IsArrayLiteral() || each->IsObjectLiteral()) {
       Variable* temp = NewTemporary(ast_value_factory()->empty_string());
       VariableProxy* temp_proxy = factory()->NewVariableProxy(temp);
       Expression* assign_each = PatternRewriter::RewriteDestructuringAssignment(
           this, factory()->NewAssignment(Token::ASSIGN, each, temp_proxy,
                                          kNoSourcePosition),
           scope());
       auto block = factory()->NewBlock(nullptr, 2, false, kNoSourcePosition);
       block->statements()->Add(
@@ skipping 133 matching lines @@
       // INTERNAL variable that's invisible to the debugger
       // but visible to everything else.
       Declaration* tdz_decl = DeclareVariable(for_info.bound_names[i], LET,
                                               kNoSourcePosition, CHECK_OK);
       tdz_decl->proxy()->var()->set_initializer_position(position());
     }
   }
   return init_block;
 }
 
-Statement* Parser::InitializeForOfStatement(ForOfStatement* for_of,
-                                            Expression* each,
-                                            Expression* iterable,
-                                            Statement* body, bool finalize,
-                                            int next_result_pos) {
+Statement* Parser::InitializeForOfStatement(
+    ForEachStatement* for_each, Expression* each, Expression* iterable,
+    Statement* body, bool finalize, IteratorType type, int next_result_pos) {
   // Create the auxiliary expressions needed for iterating over the iterable,
   // and initialize the given ForOfStatement with them.
   // If finalize is true, also instrument the loop with code that performs the
   // proper ES6 iterator finalization.  In that case, the result is not
   // immediately a ForOfStatement.
+  DCHECK(for_each->IsForOfStatement());
+  ForOfStatement* for_of = for_each->AsForOfStatement();
 
   const int nopos = kNoSourcePosition;
   auto avfactory = ast_value_factory();
 
   Variable* iterator = NewTemporary(avfactory->dot_iterator_string());
   Variable* result = NewTemporary(avfactory->dot_result_string());
   Variable* completion = NewTemporary(avfactory->empty_string());
 
-  // iterator = GetIterator(iterable)
+  // iterator = GetIterator(iterable, type)
   Expression* assign_iterator;
   {
     assign_iterator = factory()->NewAssignment(
         Token::ASSIGN, factory()->NewVariableProxy(iterator),
-        factory()->NewGetIterator(iterable, iterable->position()),
+        factory()->NewGetIterator(iterable, type, iterable->position()),
         iterable->position());
   }
 
-  // !%_IsJSReceiver(result = iterator.next()) &&
-  //     %ThrowIteratorResultNotAnObject(result)
+  // [if (IteratorType == kNormal)]
+  //     !%_IsJSReceiver(result = iterator.next()) &&
+  //         %ThrowIteratorResultNotAnObject(result)
+  // [else if (IteratorType == kAsync)]
+  //     !%_IsJSReceiver(result = Await(iterator.next())) &&
+  //         %ThrowIteratorResultNotAnObject(result)
+  // [endif]
   Expression* next_result;
   {
     Expression* iterator_proxy = factory()->NewVariableProxy(iterator);
     next_result =
-        BuildIteratorNextResult(iterator_proxy, result, next_result_pos);
+        BuildIteratorNextResult(iterator_proxy, result, type, next_result_pos);
   }
 
   // result.done
   Expression* result_done;
   {
     Expression* done_literal = factory()->NewStringLiteral(
         ast_value_factory()->done_string(), kNoSourcePosition);
     Expression* result_proxy = factory()->NewVariableProxy(result);
     result_done =
         factory()->NewProperty(result_proxy, done_literal, kNoSourcePosition);
@@ skipping 67 matching lines @@
   // Statement* body (gets overwritten)
   if (finalize) {
     Block* block = factory()->NewBlock(nullptr, 2, false, nopos);
     block->statements()->Add(body, zone());
     block->statements()->Add(set_completion_normal, zone());
     body = block;
   }
 
   for_of->Initialize(body, iterator, assign_iterator, next_result, result_done,
                      assign_each);
-  return finalize ? FinalizeForOfStatement(for_of, completion, nopos) : for_of;
+  return finalize ? FinalizeForOfStatement(for_of, completion, type, nopos)
+                  : for_of;
 }
 
 Statement* Parser::DesugarLexicalBindingsInForStatement(
     ForStatement* loop, Statement* init, Expression* cond, Statement* next,
     Statement* body, Scope* inner_scope, const ForInfo& for_info, bool* ok) {
   // ES6 13.7.4.8 specifies that on each loop iteration the let variables are
   // copied into a new environment.  Moreover, the "next" statement must be
   // evaluated not in the environment of the just completed iteration but in
   // that of the upcoming one.  We achieve this with the following desugaring.
   // Extra care is needed to preserve the completion value of the original loop.
@@ skipping 644 matching lines @@
     reusable_preparser_ = new PreParser(
         zone(), &scanner_, stack_limit_, ast_value_factory(),
         &pending_error_handler_, runtime_call_stats_, parsing_on_main_thread_);
 #define SET_ALLOW(name) reusable_preparser_->set_allow_##name(allow_##name());
     SET_ALLOW(natives);
     SET_ALLOW(harmony_do_expressions);
     SET_ALLOW(harmony_function_sent);
     SET_ALLOW(harmony_trailing_commas);
     SET_ALLOW(harmony_class_fields);
     SET_ALLOW(harmony_object_rest_spread);
+    SET_ALLOW(harmony_async_iteration);
 #undef SET_ALLOW
   }
   // Aborting inner function preparsing would leave scopes in an inconsistent
   // state; we don't parse inner functions in the abortable mode anyway.
   DCHECK(!is_inner_function || !may_abort);
 
   PreParser::PreParseResult result = reusable_preparser_->PreParseFunction(
       kind, function_scope, parsing_module_, is_inner_function, may_abort,
       use_counts_);
 
@@ skipping 1238 matching lines @@
             factory()->NewCallRuntime(Runtime::kAppendElement,
                                       append_element_args, kNoSourcePosition),
             kNoSourcePosition);
       }
       // for (each of spread) %AppendElement($R, each)
       ForEachStatement* loop = factory()->NewForEachStatement(
           ForEachStatement::ITERATE, nullptr, kNoSourcePosition);
       const bool finalize = false;
       InitializeForOfStatement(loop->AsForOfStatement(),
                                factory()->NewVariableProxy(each), subject,
-                               append_body, finalize);
+                               append_body, finalize, IteratorType::kNormal);
       do_block->statements()->Add(loop, zone());
     }
   }
   // Now, rewind the original array literal to truncate everything from the
   // first spread (included) until the end. This fixes $R's initialization.
   lit->RewindSpreads();
   return factory()->NewDoExpression(do_block, result, lit->position());
 }
 
 void Parser::QueueDestructuringAssignmentForRewriting(Expression* expr) {
@@ skipping 171 matching lines @@
     Expression* assignment =
         factory()->NewAssignment(Token::ASSIGN, output_proxy,
                                  factory()->NewUndefinedLiteral(nopos), nopos);
     initialize_output = factory()->NewExpressionStatement(assignment, nopos);
   }
 
   // let iterator = GetIterator(iterable);
   Variable* var_iterator = NewTemporary(ast_value_factory()->empty_string());
   Statement* get_iterator;
   {
-    Expression* iterator = factory()->NewGetIterator(iterable, nopos);
+    Expression* iterator =
+        factory()->NewGetIterator(iterable, GetIterator::Hint::kNormal, nopos);
     Expression* iterator_proxy = factory()->NewVariableProxy(var_iterator);
     Expression* assignment = factory()->NewAssignment(
         Token::ASSIGN, iterator_proxy, iterator, nopos);
     get_iterator = factory()->NewExpressionStatement(assignment, nopos);
   }
 
   // output = iterator.next(input);
   Statement* call_next;
   {
     Expression* iterator_proxy = factory()->NewVariableProxy(var_iterator);
@@ skipping 61 matching lines @@
         Token::EQ, factory()->NewVariableProxy(var_throw),
         factory()->NewNullLiteral(nopos), nopos);
     Expression* call =
         NewThrowTypeError(MessageTemplate::kThrowMethodMissing,
                           ast_value_factory()->empty_string(), nopos);
     Statement* throw_call = factory()->NewExpressionStatement(call, nopos);
 
     Block* then = factory()->NewBlock(nullptr, 4 + 1, false, nopos);
     BuildIteratorCloseForCompletion(
         scope(), then->statements(), var_iterator,
-        factory()->NewSmiLiteral(Parser::kNormalCompletion, nopos));
+        factory()->NewSmiLiteral(Parser::kNormalCompletion, nopos),
+        IteratorType::kNormal);
     then->statements()->Add(throw_call, zone());
     check_throw = factory()->NewIfStatement(
         condition, then, factory()->NewEmptyStatement(nopos), nopos);
   }
 
   // output = %_Call(iteratorThrow, iterator, input);
   Statement* call_throw;
   {
     auto args = new (zone()) ZoneList<Expression*>(3, zone());
     args->Add(factory()->NewVariableProxy(var_throw), zone());
@@ skipping 258 matching lines @@
                                 Variable* iterator, Variable* input,
                                 Variable* var_output) {
   //
   // This function adds four statements to [statements], corresponding to the
   // following code:
   //
   //   let iteratorReturn = iterator.return;
   //   if (IS_NULL_OR_UNDEFINED(iteratorReturn) {
   //     return {value: input, done: true};
   //   }
-  //   output = %_Call(iteratorReturn, iterator, input);
+  //
+  //   [if (IteratorType == kAsync)]
+  //     output = Await(%_Call(iteratorReturn, iterator, input));
+  //   [else]
+  //     output = %_Call(iteratorReturn, iterator, input);
+  //   [endif]
+  //
   //   if (!IS_RECEIVER(output)) %ThrowIterResultNotAnObject(output);
   //
 
   const int nopos = kNoSourcePosition;
 
   // let iteratorReturn = iterator.return;
   Variable* var_return = var_output;  // Reusing the output variable.
   Statement* get_return;
   {
     Expression* iterator_proxy = factory()->NewVariableProxy(iterator);
@@ skipping 67 matching lines @@
   }
 
   statements->Add(get_return, zone());
   statements->Add(check_return, zone());
   statements->Add(call_return, zone());
   statements->Add(validate_output, zone());
 }
 
 void Parser::FinalizeIteratorUse(Scope* use_scope, Variable* completion,
                                  Expression* condition, Variable* iter,
-                                 Block* iterator_use, Block* target) {
+                                 Block* iterator_use, Block* target,
+                                 IteratorType type) {
   //
   // This function adds two statements to [target], corresponding to the
   // following code:
   //
   //   completion = kNormalCompletion;
   //   try {
   //     try {
   //       iterator_use
   //     } catch(e) {
   //       if (completion === kAbruptCompletion) completion = kThrowCompletion;
@@ skipping 35 matching lines @@
         condition, statement, factory()->NewEmptyStatement(nopos), nopos);
   }
 
   // if (condition) {
   //   #BuildIteratorCloseForCompletion(iter, completion)
   // }
   Block* maybe_close;
   {
     Block* block = factory()->NewBlock(nullptr, 2, true, nopos);
     Expression* proxy = factory()->NewVariableProxy(completion);
-    BuildIteratorCloseForCompletion(use_scope, block->statements(), iter,
-                                    proxy);
+    BuildIteratorCloseForCompletion(use_scope, block->statements(), iter, proxy,
+                                    type);
     DCHECK(block->statements()->length() == 2);
 
     maybe_close = factory()->NewBlock(nullptr, 1, true, nopos);
     maybe_close->statements()->Add(
         factory()->NewIfStatement(condition, block,
                                   factory()->NewEmptyStatement(nopos), nopos),
         zone());
   }
 
   // try { #try_block }
@@ skipping 38 matching lines @@
         factory()->NewTryFinallyStatement(try_block, maybe_close, nopos);
   }
 
   target->statements()->Add(initialize_completion, zone());
   target->statements()->Add(try_finally, zone());
 }
 
 void Parser::BuildIteratorCloseForCompletion(Scope* scope,
                                              ZoneList<Statement*>* statements,
                                              Variable* iterator,
-                                             Expression* completion) {
+                                             Expression* completion,
+                                             IteratorType type) {
   //
   // This function adds two statements to [statements], corresponding to the
   // following code:
   //
   //   let iteratorReturn = iterator.return;
   //   if (!IS_NULL_OR_UNDEFINED(iteratorReturn)) {
   //     if (completion === kThrowCompletion) {
   //       if (!IS_CALLABLE(iteratorReturn)) {
   //         throw MakeTypeError(kReturnMethodNotCallable);
   //       }
@@ skipping 37 matching lines @@
   // try { %_Call(iteratorReturn, iterator) } catch (_) { }
   Statement* try_call_return;
   {
     auto args = new (zone()) ZoneList<Expression*>(2, zone());
     args->Add(factory()->NewVariableProxy(var_return), zone());
     args->Add(factory()->NewVariableProxy(iterator), zone());
 
     Expression* call =
         factory()->NewCallRuntime(Runtime::kInlineCall, args, nopos);
 
+    if (type == IteratorType::kAsync) {
+      call = RewriteAwaitExpression(call, nopos);
+    }
+
     Block* try_block = factory()->NewBlock(nullptr, 1, false, nopos);
     try_block->statements()->Add(factory()->NewExpressionStatement(call, nopos),
                                  zone());
 
     Block* catch_block = factory()->NewBlock(nullptr, 0, false, nopos);
 
     Scope* catch_scope = NewScopeWithParent(scope, CATCH_SCOPE);
     Variable* catch_variable =
         catch_scope->DeclareLocal(ast_value_factory()->dot_catch_string(), VAR);
     catch_scope->set_is_hidden();
@@ skipping 79 matching lines @@
     maybe_call_return = factory()->NewIfStatement(
         condition, factory()->NewEmptyStatement(nopos), call_return_carefully,
         nopos);
   }
 
   statements->Add(get_return, zone());
   statements->Add(maybe_call_return, zone());
 }
 
 Statement* Parser::FinalizeForOfStatement(ForOfStatement* loop,
-                                          Variable* var_completion, int pos) {
+                                          Variable* var_completion,
+                                          IteratorType type, int pos) {
   //
   // This function replaces the loop with the following wrapping:
   //
   //   completion = kNormalCompletion;
   //   try {
   //     try {
   //       #loop;
   //     } catch(e) {
   //       if (completion === kAbruptCompletion) completion = kThrowCompletion;
   //       %ReThrow(e);
@@ skipping 23 matching lines @@
   {
     Block* try_block = factory()->NewBlock(nullptr, 1, false, nopos);
     try_block->statements()->Add(loop, zone());
 
     // The scope in which the parser creates this loop.
     Scope* loop_scope = scope()->outer_scope();
     DCHECK_EQ(loop_scope->scope_type(), BLOCK_SCOPE);
     DCHECK_EQ(scope()->scope_type(), BLOCK_SCOPE);
 
     FinalizeIteratorUse(loop_scope, var_completion, closing_condition,
-                        loop->iterator(), try_block, final_loop);
+                        loop->iterator(), try_block, final_loop, type);
   }
 
   return final_loop;
 }
 
 #undef CHECK_OK
 #undef CHECK_OK_VOID
 #undef CHECK_FAILED
 
 }  // namespace internal
 }  // namespace v8