[cfe] Refactor FunctionNode.futureValueType into emitted value type

Previously we would encode the type of the value returned in `async`
functions as the field `futureValueType` on `FunctionNode`. For all
other kinds of functions, such as `sync`, `sync*`, and `async*`, that
field would be null. This CL renames `futureValueType` into
`emittedVAlueType`, and for functions of kinds `async`, `sync*`, and
`async*` that is expected to be the type of values emitted via
`return` or `yield` statements. For `sync` functions that field is
supposed to contain `null`.

In response to #54159

TEST=existing

Change-Id: I1efdbcc4e75d150f5618c7ca50cfe49a0e54fce6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/341662
Reviewed-by: Alexander Markov <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>
Reviewed-by: Ömer Ağacan <[email protected]>
Commit-Queue: Chloe Stefantsova <[email protected]>
Reviewed-by: Mayank Patke <[email protected]>

Author: chloestefantsova

pkg/compiler/lib/src/ir/impact_data.dart

@@ -202,7 +202,7 @@ class ImpactBuilder extends StaticTypeVisitor implements ImpactRegistry {
         break;
 
       case ir.AsyncMarker.Async:
-        registerAsync(function.futureValueType!);
+        registerAsync(function.emittedValueType!);
         break;
 
       case ir.AsyncMarker.AsyncStar:

pkg/compiler/lib/src/js_model/element_map_impl.dart

@@ -2254,7 +2254,7 @@ class JsElementEnvironment extends ElementEnvironment
         return _getSyncStarElementType(returnType);
       case AsyncMarker.ASYNC:
         return elementMap.getDartType(
-            getFunctionNode(elementMap, function)!.futureValueType!);
+            getFunctionNode(elementMap, function)!.emittedValueType!);
       case AsyncMarker.ASYNC_STAR:
         return _getAsyncStarElementType(returnType);
     }

pkg/compiler/lib/src/kernel/transformations/modular/async_lowering.dart

@@ -36,7 +36,7 @@ class AsyncLowering {
 
   bool _shouldTryAsyncLowering(FunctionNode node) =>
       node.asyncMarker == AsyncMarker.Async &&
-      node.futureValueType != null &&
+      node.emittedValueType != null &&
       _functions.last.shouldLower;
 
   void enterFunction(FunctionNode node) {
@@ -54,7 +54,7 @@ class AsyncLowering {
 
   void _wrapBodySync(FunctionNode node) {
     node.asyncMarker = AsyncMarker.Sync;
-    final futureValueType = node.futureValueType!;
+    final futureValueType = node.emittedValueType!;
     _updateFunctionBody(
         node,
         ReturnStatement(StaticInvocation(
@@ -69,7 +69,7 @@ class AsyncLowering {
   }
 
   void _wrapReturns(_FunctionData functionData, FunctionNode node) {
-    final futureValueType = node.futureValueType!;
+    final futureValueType = node.emittedValueType!;
     for (final returnStatement in functionData.returnStatements) {
       final expression = returnStatement.expression;
       // Ensure the returned future has a runtime type (T) matching the

pkg/dart2wasm/lib/transformers.dart

@@ -464,7 +464,7 @@ class _WasmTransformer extends Transformer {
               _addCompleterToController(controller, completer, fileOffset)),
           tryFinally,
         ]),
-        futureValueType: const VoidType(),
+        emittedValueType: const VoidType(),
         returnType: InterfaceType(
             coreTypes.futureClass, Nullability.nonNullable, [const VoidType()]),
         asyncMarker: AsyncMarker.Async,
@@ -544,7 +544,7 @@ class _WasmTransformer extends Transformer {
           coreTypes.objectNullableRawType, Nullability.nonNullable),
       asyncMarker: AsyncMarker.Async,
       dartAsyncMarker: AsyncMarker.Async,
-      futureValueType: coreTypes.objectNullableRawType,
+      emittedValueType: coreTypes.objectNullableRawType,
     ));
 
     // Call `asyncMap`.

pkg/dev_compiler/lib/src/kernel/compiler.dart

@@ -4192,7 +4192,7 @@ class ProgramCompiler extends ComputeOnceConstantVisitor<js_ast.Expression>
     // In the body of an `async`, `await` is generated simply as `yield`.
     var gen = emitGeneratorFn((_) => []);
     var returnType = _currentLibrary!.isNonNullableByDefault
-        ? function.futureValueType!
+        ? function.emittedValueType!
         // Otherwise flatten the return type because futureValueType(T) is not
         // defined for legacy libraries.
         : _types.flatten(function

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -1305,11 +1305,9 @@ class BodyBuilder extends StackListenerImpl
           asyncModifier,
           body);
       body = inferredFunctionBody.body;
-      function.futureValueType = inferredFunctionBody.futureValueType;
-      assert(
-          !(function.asyncMarker == AsyncMarker.Async &&
-              function.futureValueType == null),
-          "No future value type computed.");
+      function.emittedValueType = inferredFunctionBody.emittedValueType;
+      assert(function.asyncMarker == AsyncMarker.Sync ||
+          function.emittedValueType != null);
     }
 
     if (_context.returnType is! OmittedTypeBuilder) {

pkg/front_end/lib/src/fasta/type_inference/closure_context.dart

@@ -40,7 +40,7 @@ abstract class ClosureContext {
   /// the unknown type.
   DartType get yieldContext;
 
-  DartType? get futureValueType;
+  DartType? get emittedValueType;
 
   factory ClosureContext(InferenceVisitorBase inferrer, AsyncMarker asyncMarker,
       DartType returnContext, bool needToInferReturnType) {
@@ -142,6 +142,9 @@ class _SyncClosureContext implements ClosureContext {
   @override
   DartType get yieldContext => const UnknownType();
 
+  @override
+  DartType? get emittedValueType => null;
+
   final DartType _declaredReturnType;
 
   final bool _needToInferReturnType;
@@ -161,9 +164,6 @@ class _SyncClosureContext implements ClosureContext {
   /// being inferred.
   List<DartType>? _returnExpressionTypes;
 
-  @override
-  DartType? get futureValueType => null;
-
   _SyncClosureContext(this.inferrer, this._returnContext,
       this._declaredReturnType, this._needToInferReturnType) {
     if (_needToInferReturnType) {
@@ -493,6 +493,9 @@ class _AsyncClosureContext implements ClosureContext {
   @override
   DartType get yieldContext => const UnknownType();
 
+  @override
+  DartType? emittedValueType;
+
   final DartType _declaredReturnType;
 
   final bool _needToInferReturnType;
@@ -512,15 +515,12 @@ class _AsyncClosureContext implements ClosureContext {
   /// being inferred.
   List<DartType>? _returnExpressionTypes;
 
-  @override
-  DartType? futureValueType;
-
   _AsyncClosureContext(
       this.inferrer,
       this._returnContext,
       this._declaredReturnType,
       this._needToInferReturnType,
-      this.futureValueType) {
+      this.emittedValueType) {
     if (_needToInferReturnType) {
       _returnStatements = [];
       _returnExpressionTypes = [];
@@ -531,14 +531,14 @@ class _AsyncClosureContext implements ClosureContext {
       DartType returnType, ReturnStatement statement, DartType expressionType) {
     if (inferrer.isNonNullableByDefault) {
       assert(
-          futureValueType != null, "Future value type has not been computed.");
+          emittedValueType != null, "Future value type has not been computed.");
 
       if (statement.expression == null) {
         // It is a compile-time error if s is `return;`, unless T_v is void,
         // dynamic, or Null.
-        if (futureValueType is VoidType ||
-            futureValueType is DynamicType ||
-            futureValueType is NullType) {
+        if (emittedValueType is VoidType ||
+            emittedValueType is DynamicType ||
+            emittedValueType is NullType) {
           // Valid return;
         } else {
           statement.expression = inferrer.helper.wrapInProblem(
@@ -560,7 +560,7 @@ class _AsyncClosureContext implements ClosureContext {
 
         DartType flattenedExpressionType =
             inferrer.typeSchemaEnvironment.flatten(expressionType);
-        if (futureValueType is VoidType &&
+        if (emittedValueType is VoidType &&
             !(flattenedExpressionType is VoidType ||
                 flattenedExpressionType is DynamicType ||
                 flattenedExpressionType is NullType)) {
@@ -573,8 +573,8 @@ class _AsyncClosureContext implements ClosureContext {
               statement.expression!.fileOffset,
               noLength)
             ..parent = statement;
-        } else if (!(futureValueType is VoidType ||
-                futureValueType is DynamicType) &&
+        } else if (!(emittedValueType is VoidType ||
+                emittedValueType is DynamicType) &&
             flattenedExpressionType is VoidType) {
           // It is a compile-time error if s is `return e;`, T_v is neither void
           // nor dynamic, and flatten(S) is void.
@@ -588,13 +588,13 @@ class _AsyncClosureContext implements ClosureContext {
         } else if (flattenedExpressionType is! VoidType &&
             !inferrer.typeSchemaEnvironment
                 .performNullabilityAwareSubtypeCheck(
-                    flattenedExpressionType, futureValueType!)
+                    flattenedExpressionType, emittedValueType!)
                 .isSubtypeWhenUsingNullabilities()) {
           // It is a compile-time error if s is `return e;`, flatten(S) is not
           // void, S is not assignable to T_v, and flatten(S) is not a subtype
           // of T_v.
           statement.expression = inferrer.ensureAssignable(
-              futureValueType!, expressionType, statement.expression!,
+              emittedValueType!, expressionType, statement.expression!,
               fileOffset: statement.expression!.fileOffset,
               runtimeCheckedType:
                   inferrer.computeGreatestClosure2(_returnContext),
@@ -831,10 +831,10 @@ class _AsyncClosureContext implements ClosureContext {
     }
 
     if (inferrer.isNonNullableByDefault) {
-      futureValueType =
+      emittedValueType =
           computeFutureValueType(inferrer.coreTypes, inferredType);
     } else {
-      futureValueType = inferrer.typeSchemaEnvironment.flatten(inferredType);
+      emittedValueType = inferrer.typeSchemaEnvironment.flatten(inferredType);
     }
 
     for (int i = 0; i < _returnStatements!.length; ++i) {
@@ -915,21 +915,25 @@ class _SyncStarClosureContext implements ClosureContext {
   @override
   DartType get yieldContext => _yieldElementContext;
 
+  @override
+  DartType? get emittedValueType => _emittedValueType;
+
   final DartType _declaredReturnType;
 
+  DartType? _emittedValueType;
+
   final bool _needToInferReturnType;
 
   /// A list of return expression types in functions whose return type is
   /// being inferred.
   List<DartType>? _yieldElementTypes;
 
-  @override
-  DartType? get futureValueType => null;
-
   _SyncStarClosureContext(this.inferrer, this._yieldElementContext,
       this._declaredReturnType, this._needToInferReturnType) {
     if (_needToInferReturnType) {
       _yieldElementTypes = [];
+    } else {
+      _emittedValueType = inferrer.computeGreatestClosure(_yieldElementContext);
     }
   }
 
@@ -1009,8 +1013,13 @@ class _SyncStarClosureContext implements ClosureContext {
       inferredType = inferrer.computeGreatestClosure2(_declaredReturnType);
     }
 
-    return demoteTypeInLibrary(inferredType,
+    DartType demotedType = demoteTypeInLibrary(inferredType,
         isNonNullableByDefault: inferrer.isNonNullableByDefault);
+    _emittedValueType = inferrer.getTypeArgumentOf(
+        inferrer.typeSchemaEnvironment.getUnionFreeType(demotedType,
+            isNonNullableByDefault: inferrer.isNonNullableByDefault),
+        inferrer.coreTypes.iterableClass);
+    return demotedType;
   }
 
   @override
@@ -1050,21 +1059,25 @@ class _AsyncStarClosureContext implements ClosureContext {
   @override
   DartType get yieldContext => _yieldElementContext;
 
+  @override
+  DartType? get emittedValueType => _emittedValueType;
+
   final DartType _declaredReturnType;
 
+  DartType? _emittedValueType;
+
   final bool _needToInferReturnType;
 
   /// A list of return expression types in functions whose return type is
   /// being inferred.
   List<DartType>? _yieldElementTypes;
 
-  @override
-  DartType? get futureValueType => null;
-
   _AsyncStarClosureContext(this.inferrer, this._yieldElementContext,
       this._declaredReturnType, this._needToInferReturnType) {
     if (_needToInferReturnType) {
       _yieldElementTypes = [];
+    } else {
+      _emittedValueType = inferrer.computeGreatestClosure(_yieldElementContext);
     }
   }
 
@@ -1142,8 +1155,13 @@ class _AsyncStarClosureContext implements ClosureContext {
       inferredType = inferrer.computeGreatestClosure2(_declaredReturnType);
     }
 
-    return demoteTypeInLibrary(inferredType,
+    DartType demotedType = demoteTypeInLibrary(inferredType,
         isNonNullableByDefault: inferrer.isNonNullableByDefault);
+    _emittedValueType = inferrer.getTypeArgumentOf(
+        inferrer.typeSchemaEnvironment.getUnionFreeType(demotedType,
+            isNonNullableByDefault: inferrer.isNonNullableByDefault),
+        inferrer.coreTypes.streamClass);
+    return demotedType;
   }
 
   @override

pkg/front_end/lib/src/fasta/type_inference/inference_visitor_base.dart

@@ -2326,11 +2326,7 @@ abstract class InferenceVisitorBase implements InferenceVisitor {
     }
     bodyResult = closureContext.handleImplicitReturn(
         this, function.body!, bodyResult, fileOffset);
-    function.futureValueType = closureContext.futureValueType;
-    assert(
-        !(function.asyncMarker == AsyncMarker.Async &&
-            function.futureValueType == null),
-        "No future value type computed.");
+    function.emittedValueType = closureContext.emittedValueType;
 
     if (bodyResult.hasChanged) {
       function.body = bodyResult.statement..parent = function;
@@ -3778,7 +3774,7 @@ abstract class InferenceVisitorBase implements InferenceVisitor {
 
   /// Computes the `futureValueTypeSchema` for the type schema [type].
   ///
-  /// This is the same as the [futureValueType] except that this handles
+  /// This is the same as the [emittedValueType] except that this handles
   /// the unknown type.
   DartType computeFutureValueTypeSchema(DartType type) {
     return type.accept1(new FutureValueTypeVisitor(unhandledTypeHandler:

pkg/front_end/lib/src/fasta/type_inference/type_inferrer.dart

@@ -206,12 +206,11 @@ class TypeInferrerImpl implements TypeInferrer {
     result =
         closureContext.handleImplicitReturn(visitor, body, result, fileOffset);
     visitor.checkCleanState();
-    DartType? futureValueType = closureContext.futureValueType;
-    assert(!(asyncMarker == AsyncMarker.Async && futureValueType == null),
-        "No future value type computed.");
+    DartType? emittedValueType = closureContext.emittedValueType;
+    assert(asyncMarker == AsyncMarker.Sync || emittedValueType != null);
     flowAnalysis.finish();
     return new InferredFunctionBody(
-        result.hasChanged ? result.statement : body, futureValueType);
+        result.hasChanged ? result.statement : body, emittedValueType);
   }
 
   @override
@@ -432,7 +431,7 @@ class TypeInferrerImplBenchmarked implements TypeInferrer {
 
 class InferredFunctionBody {
   final Statement body;
-  final DartType? futureValueType;
+  final DartType? emittedValueType;
 
-  InferredFunctionBody(this.body, this.futureValueType);
+  InferredFunctionBody(this.body, this.emittedValueType);
 }

pkg/front_end/test/macros/incremental/data/tests/user_macro/main.0.dart.expect

@@ -36,7 +36,7 @@ macro class MethodMacro extends core::Object implements api::ClassDeclarationsMa
     : super core::Object::•()
     ;
   @#C2
-  method buildDeclarationsForClass(api::ClassDeclaration clazz, api::MemberDeclarationBuilder builder) → FutureOr<void> async /* futureValueType= void */ {}
+  method buildDeclarationsForClass(api::ClassDeclaration clazz, api::MemberDeclarationBuilder builder) → FutureOr<void> async /* emittedValueType= void */ {}
 }
 
 library;

pkg/front_end/test/macros/incremental/data/tests/user_macro/main.1.dart.expect

@@ -33,7 +33,7 @@ macro class MethodMacro extends core::Object implements api::ClassDeclarationsMa
     : super core::Object::•()
     ;
   @#C2
-  method buildDeclarationsForClass(api::ClassDeclaration clazz, api::MemberDeclarationBuilder builder) → FutureOr<void> async /* futureValueType= void */ {
+  method buildDeclarationsForClass(api::ClassDeclaration clazz, api::MemberDeclarationBuilder builder) → FutureOr<void> async /* emittedValueType= void */ {
     builder.{api::MemberDeclarationBuilder::declareInType}(new api::DeclarationCode::fromString(mac2::generateBody())){(api::DeclarationCode) → void};
   }
 }

pkg/front_end/test/macros/incremental/data/tests/user_macro/main.2.dart.expect

@@ -35,7 +35,7 @@ macro class MethodMacro extends core::Object implements api::ClassDeclarationsMa
     : super core::Object::•()
     ;
   @#C2
-  method buildDeclarationsForClass(api::ClassDeclaration clazz, api::MemberDeclarationBuilder builder) → FutureOr<void> async /* futureValueType= void */ {
+  method buildDeclarationsForClass(api::ClassDeclaration clazz, api::MemberDeclarationBuilder builder) → FutureOr<void> async /* emittedValueType= void */ {
     builder.{api::MemberDeclarationBuilder::declareInType}(new api::DeclarationCode::fromString(mac2::generateBody())){(api::DeclarationCode) → void};
   }
 }