[vm] Adjust return value of async/async*/sync* after the language spec change

Calculation of element type for the value returned from
async/async*/sync* functions was recently adjusted
in the spec to address soundness issue
(https://github.com/dart-lang/language/pull/3218).

This change adjusts Dart VM to conform to the new spec.

TEST=language/async/regression_54311_test
TEST=co19/Language/Functions/element_type_*

Fixes https://github.com/dart-lang/sdk/issues/54316
Issue https://github.com/dart-lang/sdk/issues/54311
Issue https://github.com/dart-lang/sdk/issues/54159

Change-Id: I4c51e7cba704d034350519375210bdb2086c5432
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/342082
Reviewed-by: Alexander Aprelev <aam@google.com>
Reviewed-by: Erik Ernst <eernst@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>

runtime/vm/compiler/frontend/kernel_binary_flowgraph.cc

@@ -559,33 +559,25 @@ Fragment StreamingFlowGraphBuilder::SetupCapturedParameters(
 }
 
 Fragment StreamingFlowGraphBuilder::InitSuspendableFunction(
-    const Function& dart_function) {
+    const Function& dart_function,
+    const AbstractType* emitted_value_type) {
   Fragment body;
   if (dart_function.IsAsyncFunction()) {
-    const auto& result_type =
-        AbstractType::Handle(Z, dart_function.result_type());
-    auto& type_args = TypeArguments::ZoneHandle(Z);
-    if (result_type.IsType() &&
-        (Class::Handle(Z, result_type.type_class()).IsFutureClass() ||
-         result_type.IsFutureOrType())) {
-      ASSERT(result_type.IsFinalized());
-      type_args = Type::Cast(result_type).GetInstanceTypeArguments(H.thread());
-    }
-
+    ASSERT(emitted_value_type != nullptr);
+    auto& type_args = TypeArguments::ZoneHandle(Z, TypeArguments::New(1));
+    type_args.SetTypeAt(0, *emitted_value_type);
+    type_args = Class::Handle(Z, IG->object_store()->future_class())
+                    .GetInstanceTypeArguments(H.thread(), type_args);
     body += TranslateInstantiatedTypeArguments(type_args);
     body += B->Call1ArgStub(TokenPosition::kNoSource,
                             Call1ArgStubInstr::StubId::kInitAsync);
     body += Drop();
   } else if (dart_function.IsAsyncGenerator()) {
-    const auto& result_type =
-        AbstractType::Handle(Z, dart_function.result_type());
-    auto& type_args = TypeArguments::ZoneHandle(Z);
-    if (result_type.IsType() &&
-        (result_type.type_class() == IG->object_store()->stream_class())) {
-      ASSERT(result_type.IsFinalized());
-      type_args = Type::Cast(result_type).GetInstanceTypeArguments(H.thread());
-    }
-
+    ASSERT(emitted_value_type != nullptr);
+    auto& type_args = TypeArguments::ZoneHandle(Z, TypeArguments::New(1));
+    type_args.SetTypeAt(0, *emitted_value_type);
+    type_args = Class::Handle(Z, IG->object_store()->stream_class())
+                    .GetInstanceTypeArguments(H.thread(), type_args);
     body += TranslateInstantiatedTypeArguments(type_args);
     body += B->Call1ArgStub(TokenPosition::kNoSource,
                             Call1ArgStubInstr::StubId::kInitAsyncStar);
@@ -595,15 +587,11 @@ Fragment StreamingFlowGraphBuilder::InitSuspendableFunction(
                        SuspendInstr::StubId::kYieldAsyncStar);
     body += Drop();
   } else if (dart_function.IsSyncGenerator()) {
-    const auto& result_type =
-        AbstractType::Handle(Z, dart_function.result_type());
-    auto& type_args = TypeArguments::ZoneHandle(Z);
-    if (result_type.IsType() &&
-        (result_type.type_class() == IG->object_store()->iterable_class())) {
-      ASSERT(result_type.IsFinalized());
-      type_args = Type::Cast(result_type).GetInstanceTypeArguments(H.thread());
-    }
-
+    ASSERT(emitted_value_type != nullptr);
+    auto& type_args = TypeArguments::ZoneHandle(Z, TypeArguments::New(1));
+    type_args.SetTypeAt(0, *emitted_value_type);
+    type_args = Class::Handle(Z, IG->object_store()->iterable_class())
+                    .GetInstanceTypeArguments(H.thread(), type_args);
     body += TranslateInstantiatedTypeArguments(type_args);
     body += B->Call1ArgStub(TokenPosition::kNoSource,
                             Call1ArgStubInstr::StubId::kInitSyncStar);
@@ -618,6 +606,8 @@ Fragment StreamingFlowGraphBuilder::InitSuspendableFunction(
     if (scope->num_context_variables() > 0) {
       body += CloneContext(scope->context_slots());
     }
+  } else {
+    ASSERT(emitted_value_type == nullptr);
   }
   return body;
 }
@@ -784,17 +774,30 @@ FlowGraph* StreamingFlowGraphBuilder::BuildGraphOfFunction(
 
   LocalVariable* first_parameter = nullptr;
   TokenPosition token_position = TokenPosition::kNoSource;
+  const AbstractType* emitted_value_type = nullptr;
   {
     AlternativeReadingScope alt(&reader_);
     FunctionNodeHelper function_node_helper(this);
     function_node_helper.ReadUntilExcluding(
         FunctionNodeHelper::kPositionalParameters);
-    intptr_t list_length = ReadListLength();  // read number of positionals.
-    if (list_length > 0) {
-      intptr_t first_parameter_offset = ReaderOffset() + data_program_offset_;
-      first_parameter = LookupVariable(first_parameter_offset);
+    {
+      AlternativeReadingScope alt2(&reader_);
+      intptr_t list_length = ReadListLength();  // read number of positionals.
+      if (list_length > 0) {
+        intptr_t first_parameter_offset = ReaderOffset() + data_program_offset_;
+        first_parameter = LookupVariable(first_parameter_offset);
+      }
     }
     token_position = function_node_helper.position_;
+    if (dart_function.IsSuspendableFunction()) {
+      function_node_helper.ReadUntilExcluding(
+          FunctionNodeHelper::kEmittedValueType);
+      if (ReadTag() == kSomething) {
+        emitted_value_type = &T.BuildType();  // read emitted value type.
+      } else {
+        UNREACHABLE();
+      }
+    }
   }
 
   auto graph_entry = flow_graph_builder_->graph_entry_ =
@@ -833,7 +836,7 @@ FlowGraph* StreamingFlowGraphBuilder::BuildGraphOfFunction(
   // objects than necessary during GC.
   const Fragment body =
       ClearRawParameters(dart_function) + B->BuildNullAssertions() +
-      InitSuspendableFunction(dart_function) +
+      InitSuspendableFunction(dart_function, emitted_value_type) +
       BuildFunctionBody(dart_function, first_parameter, is_constructor);
 
   auto extra_entry_point_style =

runtime/vm/compiler/frontend/kernel_binary_flowgraph.h

@@ -85,7 +85,8 @@ class StreamingFlowGraphBuilder : public KernelReaderHelper {
                                     TokenPosition position);
   Fragment CheckStackOverflowInPrologue(const Function& dart_function);
   Fragment SetupCapturedParameters(const Function& dart_function);
-  Fragment InitSuspendableFunction(const Function& dart_function);
+  Fragment InitSuspendableFunction(const Function& dart_function,
+                                   const AbstractType* emitted_value_type);
   Fragment ShortcutForUserDefinedEquals(const Function& dart_function,
                                         LocalVariable* first_parameter);
   Fragment TypeArgumentsHandling(const Function& dart_function);

runtime/vm/compiler/frontend/scope_builder.cc

@@ -243,6 +243,11 @@ ScopeBuildingResult* ScopeBuilder::BuildScopes() {
         // async/async*/sync* function. It may reference receiver or type
         // arguments of the enclosing function which need to be captured.
         VisitDartType();
+
+        // Visit optional future value type.
+        if (helper_.ReadTag() == kSomething) {
+          VisitDartType();
+        }
       }
 
       // We generate a synthetic body for implicit closure functions - which

tests/language/async/regression_54311_test.dart

@@ -0,0 +1,29 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Verifies that futureValueType(FutureOr<Object>) = Object.
+//
+// This is a special case because NORM(FutureOr<Object>) = Object,
+// and futureValueType(Object) = Object?, so futureValueType cannot be
+// applied to a normalized type.
+//
+// Regression test for https://github.com/dart-lang/sdk/issues/54311.
+
+import 'dart:async';
+
+import "package:expect/expect.dart";
+
+FutureOr<Object> fn1() async {
+  return Future<Object>.value(42);
+}
+
+FutureOr<Object> fn2() async => 42;
+
+void main() async {
+  final value1 = await fn1();
+  Expect.equals(42, value1);
+
+  final value2 = await fn2();
+  Expect.equals(42, value2);
+}