[esnext] prototype runtime implementation for 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 "src/api.h"
 #include "src/ast/ast.h"
 #include "src/ast/ast-expression-rewriter.h"
 #include "src/ast/ast-expression-visitor.h"
@@ skipping 2702 matching lines @@
         // ES6 14.6.1 Static Semantics: IsInTailPosition
         Scanner::Location loc(pos, pos + 1);
         function_state_->AddExpressionInTailPosition(return_value, loc);
       }
     }
   }
   ExpectSemicolon(CHECK_OK);
 
   if (is_generator()) {
     return_value = BuildIteratorResult(return_value, true);
+  } else if (is_async_function()) {
+    return_value = EmitPromiseResolve(return_value, return_value->position());
   }
 
   result = factory()->NewReturnStatement(return_value, loc.beg_pos);
 
   Scope* decl_scope = scope_->DeclarationScope();
   if (decl_scope->is_script_scope() || decl_scope->is_eval_scope()) {
     ReportMessageAt(loc, MessageTemplate::kIllegalReturn);
     *ok = false;
     return NULL;
   }
@@ skipping 1220 matching lines @@
     expr = assignment->target();
 
     // TODO(adamk): Only call this if necessary.
     RewriteParameterInitializerScope(parser_->stack_limit(), initializer,
                                      parser_->scope_, parameters->scope);
   }
 
   AddFormalParameter(parameters, expr, initializer, end_pos, is_rest);
 }
 
+void ParserTraits::ParseAsyncArrowSingleExpressionBody(
+    ZoneList<Statement*>* body, bool accept_IN,
+    Type::ExpressionClassifier* classifier, int pos, bool* ok) {
+  parser_->DesugarAsyncFunctionBody(
+      parser_->ast_value_factory()->empty_string(), parser_->scope_, body,
+      classifier, kAsyncArrowFunction, FunctionBody::ArrowConcise, accept_IN,
+      pos, ok);
+}
+
+void Parser::DesugarAsyncFunctionBody(const AstRawString* function_name,
+                                      Scope* scope, ZoneList<Statement*>* body,
+                                      ExpressionClassifier* classifier,
+                                      FunctionKind kind, FunctionBody body_type,
+                                      bool accept_IN, int pos, bool* ok) {
+  scope->ForceContextAllocation();
+  // Calling a generator returns a generator object.  That object is
+  // stored
+  // in a temporary variable, a definition that is used by "yield"
+  // expressions. This also marks the FunctionState as a generator.
+  Variable* temp =
+      scope_->NewTemporary(ast_value_factory()->dot_generator_object_string());
+  function_state_->set_generator_object_variable(temp);
+
+  // Create generator, but do not yield.
+  Expression* allocation = EmitCreateJSGeneratorObject(pos);
+  Expression* assign_yield =
+      factory()->NewAssignment(Token::INIT, factory()->NewVariableProxy(temp),
+                               allocation, RelocInfo::kNoPosition);
+
+  body->Add(
+      factory()->NewExpressionStatement(assign_yield, RelocInfo::kNoPosition),
+      zone());
+
+  Block* try_block = factory()->NewBlock(NULL, 8, true, RelocInfo::kNoPosition);
+
+  ZoneList<Statement*>* inner_body = try_block->statements();
+
+  Expression* return_value = nullptr;
+  if (body_type == FunctionBody::Normal) {
+    ParseStatementList(inner_body, Token::RBRACE, ok);
+    if (!*ok) return;
+    return_value = factory()->NewUndefinedLiteral(RelocInfo::kNoPosition);
+  } else {
+    return_value = ParseAssignmentExpression(accept_IN, classifier, ok);
+    if (!*ok) return;
+    ParserTraits::RewriteNonPattern(classifier, ok);
+    if (!*ok) return;
+  }
+
+  return_value = EmitPromiseResolve(return_value, return_value->position());
+  inner_body->Add(
+      factory()->NewReturnStatement(return_value, return_value->position()),
+      zone());
+
+  Block* catch_block = BuildRejectPromiseOnException(try_block);
+
+  body->Add(catch_block, zone());
+
+  scope->set_end_position(scanner()->location().end_pos);
+}
 
 DoExpression* Parser::ParseDoExpression(bool* ok) {
   // AssignmentExpression ::
   //     do '{' StatementList '}'
   int pos = peek_position();
 
   Expect(Token::DO, CHECK_OK);
   Variable* result =
       scope_->NewTemporary(ast_value_factory()->dot_result_string());
   Block* block = ParseBlock(nullptr, false, CHECK_OK);
@@ skipping 107 matching lines @@
     if (is_generator) {
       // For generators, allocating variables in contexts is currently a win
       // because it minimizes the work needed to suspend and resume an
       // activation.  The machine code produced for generators (by full-codegen)
       // relies on this forced context allocation, but not in an essential way.
       scope_->ForceContextAllocation();
 
       // Calling a generator returns a generator object.  That object is stored
       // in a temporary variable, a definition that is used by "yield"
       // expressions. This also marks the FunctionState as a generator.
-      Variable* temp = scope_->NewTemporary(
-          ast_value_factory()->dot_generator_object_string());
-      function_state.set_generator_object_variable(temp);
+      if (is_generator) {
+        Variable* temp = scope_->NewTemporary(
+            ast_value_factory()->dot_generator_object_string());
+        function_state.set_generator_object_variable(temp);

[Dan Ehrenberg, 2016/05/04 22:52:36]

This conditional is redundant--you just checked is_generator above.

Looks like all of this logic applies to DesugarAsyncFunctionBody as well. Is
there any way you could let this code execute for that case as well, so it
doesn't have to be in two places?

[caitp (gmail), 2016/05/06 18:45:26]

It complicates things to do that --- because for AsyncArrowFunctions with
concise bodies, this never gets called, I think

+      }
     }
 
     Expect(Token::LPAREN, CHECK_OK);
     int start_position = scanner()->location().beg_pos;
     scope_->set_start_position(start_position);
     ParserFormalParameters formals(scope);
     ParseFormalParameterList(&formals, &formals_classifier, CHECK_OK);
     arity = formals.Arity();
     Expect(Token::RPAREN, CHECK_OK);
     int formals_end_position = scanner()->location().end_pos;
@@ skipping 398 matching lines @@
       param_scope = param_scope->FinalizeBlockScope();
       if (param_scope != nullptr) {
         CheckConflictingVarDeclarations(param_scope, CHECK_OK);
       }
       init_block->statements()->Add(param_block, zone());
     }
   }
   return init_block;
 }
 
+Block* Parser::BuildRejectPromiseOnException(Block* block) {
+  // try { <block> } catch (error) { return Promise.reject(error); }
+  Block* try_block = block;
+  Scope* catch_scope = NewScope(scope_, CATCH_SCOPE);
+  catch_scope->set_is_hidden();
+  Variable* catch_variable =
+      catch_scope->DeclareLocal(ast_value_factory()->dot_catch_string(), VAR,
+                                kCreatedInitialized, Variable::NORMAL);
+  Block* catch_block =
+      factory()->NewBlock(nullptr, 1, true, RelocInfo::kNoPosition);
+
+  Expression* promise_reject = EmitPromiseReject(
+      factory()->NewVariableProxy(catch_variable), RelocInfo::kNoPosition);
+
+  ReturnStatement* return_promise_reject =
+      factory()->NewReturnStatement(promise_reject, RelocInfo::kNoPosition);
+  catch_block->statements()->Add(return_promise_reject, zone());
+  TryStatement* try_catch_statement =
+      factory()->NewTryCatchStatement(try_block, catch_scope, catch_variable,
+                                      catch_block, RelocInfo::kNoPosition);
+
+  block = factory()->NewBlock(nullptr, 1, true, RelocInfo::kNoPosition);
+  block->statements()->Add(try_catch_statement, zone());
+  return block;
+}
+
+Expression* Parser::EmitCreateJSGeneratorObject(int pos) {
+  DCHECK_NOT_NULL(function_state_->generator_object_variable());
+  ZoneList<Expression*>* args = new (zone()) ZoneList<Expression*>(2, zone());
+  args->Add(factory()->NewThisFunction(pos), zone());
+  args->Add(ThisExpression(scope_, factory(), RelocInfo::kNoPosition), zone());
+  return factory()->NewCallRuntime(Runtime::kCreateJSGeneratorObject, args,
+                                   pos);
+}
+
+Expression* Parser::EmitPromiseResolve(Expression* value, int pos) {
+  ZoneList<Expression*>* args = new (zone()) ZoneList<Expression*>(1, zone());
+  args->Add(value, zone());
+  return factory()->NewCallRuntime(Context::PROMISE_CREATE_RESOLVED_INDEX, args,
+                                   pos);
+}
+
+Expression* Parser::EmitPromiseReject(Expression* value, int pos) {
+  ZoneList<Expression*>* args = new (zone()) ZoneList<Expression*>(1, zone());
+  args->Add(value, zone());
+  return factory()->NewCallRuntime(Context::PROMISE_CREATE_REJECTED_INDEX, args,
+                                   pos);
+}
 
 ZoneList<Statement*>* Parser::ParseEagerFunctionBody(
     const AstRawString* function_name, int pos,
     const ParserFormalParameters& parameters, FunctionKind kind,
     FunctionLiteral::FunctionType function_type, bool* ok) {
   // Everything inside an eagerly parsed function will be parsed eagerly
   // (see comment above).
   ParsingModeScope parsing_mode(this, PARSE_EAGERLY);
   ZoneList<Statement*>* result = new(zone()) ZoneList<Statement*>(8, zone());
 
@@ skipping 33 matching lines @@
       // - InitialYield yields the actual generator object.
       // - Any return statement inside the body will have its argument wrapped
       //   in a "done" iterator result object.
       // - If the generator terminates for whatever reason, we must close it.
       //   Hence the finally clause.
 
       Block* try_block =
           factory()->NewBlock(nullptr, 3, false, RelocInfo::kNoPosition);
 
       {
-        ZoneList<Expression*>* arguments =
-            new (zone()) ZoneList<Expression*>(2, zone());
-        arguments->Add(factory()->NewThisFunction(pos), zone());
-        arguments->Add(
-            ThisExpression(scope_, factory(), RelocInfo::kNoPosition), zone());
-        CallRuntime* allocation = factory()->NewCallRuntime(
-            Runtime::kCreateJSGeneratorObject, arguments, pos);
-
+        Expression* allocation = EmitCreateJSGeneratorObject(pos);
         VariableProxy* init_proxy = factory()->NewVariableProxy(
             function_state_->generator_object_variable());
         Assignment* assignment = factory()->NewAssignment(
             Token::INIT, init_proxy, allocation, RelocInfo::kNoPosition);
         VariableProxy* get_proxy = factory()->NewVariableProxy(
             function_state_->generator_object_variable());
         Yield* yield =
             factory()->NewYield(get_proxy, assignment, RelocInfo::kNoPosition);
+

[Dan Ehrenberg, 2016/05/04 22:52:36]

No need for the extra newline

         try_block->statements()->Add(
             factory()->NewExpressionStatement(yield, RelocInfo::kNoPosition),
             zone());
       }
 
       ParseStatementList(try_block->statements(), Token::RBRACE, CHECK_OK);
 
       Statement* final_return = factory()->NewReturnStatement(
           BuildIteratorResult(nullptr, true), RelocInfo::kNoPosition);
       try_block->statements()->Add(final_return, zone());
 
       Block* finally_block =
           factory()->NewBlock(nullptr, 1, false, RelocInfo::kNoPosition);
       ZoneList<Expression*>* args =
           new (zone()) ZoneList<Expression*>(1, zone());
       VariableProxy* call_proxy = factory()->NewVariableProxy(
           function_state_->generator_object_variable());
       args->Add(call_proxy, zone());
       Expression* call = factory()->NewCallRuntime(
           Runtime::kGeneratorClose, args, RelocInfo::kNoPosition);
       finally_block->statements()->Add(
           factory()->NewExpressionStatement(call, RelocInfo::kNoPosition),
           zone());
 
       body->Add(factory()->NewTryFinallyStatement(try_block, finally_block,
                                                   RelocInfo::kNoPosition),
                 zone());
+    } else if (IsAsyncFunction(kind)) {
+      const bool accept_IN = true;
+      DesugarAsyncFunctionBody(function_name, inner_scope, body, nullptr, kind,
+                               FunctionBody::Normal, accept_IN, pos, CHECK_OK);

[Dan Ehrenberg, 2016/05/04 22:52:36]

I like how you factored out DesugarAsyncFunctionBody. Think you could do the
same for desugaring the generator body (just because this function is getting
larger and larger, and you identified an analogous separable part)?

[caitp (gmail), 2016/05/06 18:45:26]

Sure --- but lets do that in a separate CL

     } else {
       ParseStatementList(body, Token::RBRACE, CHECK_OK);
     }
 
     if (IsSubclassConstructor(kind)) {
       body->Add(
           factory()->NewReturnStatement(
               this->ThisExpression(scope_, factory(), RelocInfo::kNoPosition),
               RelocInfo::kNoPosition),
               zone());
     }
   }
 
   Expect(Token::RBRACE, CHECK_OK);
   scope_->set_end_position(scanner()->location().end_pos);
 
   if (!parameters.is_simple) {
     DCHECK_NOT_NULL(inner_scope);
     DCHECK_EQ(body, inner_block->statements());
     SetLanguageMode(scope_, inner_scope->language_mode());
     Block* init_block = BuildParameterInitializationBlock(parameters, CHECK_OK);
+
+    if (IsAsyncFunction(kind)) {
+      init_block = BuildRejectPromiseOnException(init_block);

[Dan Ehrenberg, 2016/05/04 22:52:36]

Rather than adding a second call to BuildRejectPromiseOnException, would it be
possible to make another call to AddParameterInitializationBlock here to avoid
this extra case of special-casing async functions?

[caitp (gmail), 2016/05/06 18:45:26]

You mean like

```
if (IsAsyncFunction(kind)) {
  init_block =
BuildRejectPromiseOnException(BuildParameterInitializationBlock(parameters,
CHECK_OK));
} else {
  init_block = BuildParameterInitializationBlock(parameters, CHECK_OK);
}
```

? I'm not sure I see much value in that, but maybe I'm misunderstanding what
you're getting at

+    }
+
     DCHECK_NOT_NULL(init_block);
 
     inner_scope->set_end_position(scanner()->location().end_pos);
     inner_scope = inner_scope->FinalizeBlockScope();
     if (inner_scope != nullptr) {
       CheckConflictingVarDeclarations(inner_scope, CHECK_OK);
       InsertShadowingVarBindingInitializers(inner_block);
     }
 
     result->Add(init_block, zone());
@@ skipping 781 matching lines @@
                                                       int pos) {
   return parser_->RewriteAssignExponentiation(left, right, pos);
 }
 
 void ParserTraits::RewriteNonPattern(Type::ExpressionClassifier* classifier,
                                      bool* ok) {
   parser_->RewriteNonPattern(classifier, ok);
 }
 
 Expression* ParserTraits::RewriteAwaitExpression(Expression* value, int pos) {
-  // TODO(caitp): Implement AsyncFunctionAwait()
-  // per tc39.github.io/ecmascript-asyncawait/#abstract-ops-async-function-await
-  return value;
+  Expression* generator_object = parser_->factory()->NewVariableProxy(
+      parser_->function_state_->generator_object_variable());
+
+  ZoneList<Expression*>* async_function_await_args =
+      new (zone()) ZoneList<Expression*>(2, zone());
+  async_function_await_args->Add(generator_object, zone());
+  async_function_await_args->Add(value, zone());
+  Expression* async_function_await = parser_->factory()->NewCallRuntime(
+      Context::ASYNC_FUNCTION_AWAIT_INDEX, async_function_await_args,
+      RelocInfo::kNoPosition);
+
+  generator_object = parser_->factory()->NewVariableProxy(
+      parser_->function_state_->generator_object_variable());
+  return parser_->factory()->NewYield(generator_object, async_function_await,
+                                      pos);
 }
 
 Zone* ParserTraits::zone() const {
   return parser_->function_state_->scope()->zone();
 }
 
 
 ZoneList<Expression*>* ParserTraits::GetNonPatternList() const {
   return parser_->function_state_->non_patterns_to_rewrite();
 }
@@ skipping 1473 matching lines @@
                         try_block, target);
     final_loop = target;
   }
 
   return final_loop;
 }
 
 
 }  // namespace internal
 }  // namespace v8