[anlyzer][cfe] Use bounds to restrict choices during inference

Closes dart-lang/language#1194

Change-Id: I6866b6ab6f29cddbb293122e09588f705aaea1c1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/387020
Reviewed-by: Paul Berry <[email protected]>
Commit-Queue: Chloe Stefantsova <[email protected]>

Author: chloestefantsova

pkg/_fe_analyzer_shared/lib/src/type_inference/type_analyzer_operations.dart

@@ -658,6 +658,15 @@ abstract interface class TypeAnalyzerOperations<
       SharedTypeSchemaView<TypeStructure> typeSchema1,
       SharedTypeSchemaView<TypeStructure> typeSchema2);
 
+  /// Computes the greatest closure of a type.
+  ///
+  /// Computing the greatest closure of a type is described here:
+  /// https://github.com/dart-lang/language/blob/main/resources/type-system/inference.md#type-variable-elimination-least-and-greatest-closure-of-a-type
+  TypeStructure greatestClosureOfTypeInternal(
+      TypeStructure type,
+      List<SharedTypeParameterStructure<TypeStructure>>
+          typeParametersToEliminate);
+
   /// Converts a type into a corresponding type schema.
   SharedTypeSchemaView<TypeStructure> typeToSchema(
       SharedTypeView<TypeStructure> type);
@@ -888,10 +897,15 @@ abstract class TypeConstraintGenerator<
   /// https://github.com/dart-lang/sdk/issues/51156#issuecomment-2158825417.
   bool get enableDiscrepantObliviousnessOfNullabilitySuffixOfFutureOr;
 
+  /// True if the language feature inference-using-bounds is enabled.
+  final bool inferenceUsingBoundsIsEnabled;
+
   /// Abstract type operations to be used in the matching methods.
   TypeAnalyzerOperations<TypeStructure, Variable, TypeParameterStructure,
       TypeDeclarationType, TypeDeclaration> get typeAnalyzerOperations;
 
+  TypeConstraintGenerator({required this.inferenceUsingBoundsIsEnabled});
+
   /// Returns the type arguments of the supertype of [type] that is an
   /// instantiation of [typeDeclaration]. If none of the supertypes of [type]
   /// are instantiations of [typeDeclaration], returns null.

pkg/_fe_analyzer_shared/test/mini_ast.dart

@@ -3271,6 +3271,13 @@ class MiniAstOperations
       SharedTypeView<Type> type, NullabilitySuffix modifier) {
     return SharedTypeView(type.unwrapTypeView().withNullability(modifier));
   }
+
+  @override
+  Type greatestClosureOfTypeInternal(Type type,
+      List<SharedTypeParameterStructure<Type>> typeParametersToEliminate) {
+    // TODO(paulberry): Implement greatest closure of types in mini ast.
+    throw UnimplementedError();
+  }
 }
 
 /// Representation of an expression or statement in the pseudo-Dart language

pkg/_fe_analyzer_shared/test/type_inference/type_constraint_gatherer_test.dart

@@ -544,8 +544,8 @@ class _TypeConstraintGatherer extends TypeConstraintGenerator<Type,
   final _constraints = <String>[];
 
   _TypeConstraintGatherer(Set<String> typeVariablesBeingConstrained,
-      {this.enableDiscrepantObliviousnessOfNullabilitySuffixOfFutureOr =
-          false}) {
+      {this.enableDiscrepantObliviousnessOfNullabilitySuffixOfFutureOr = false})
+      : super(inferenceUsingBoundsIsEnabled: false) {
     for (var typeVariableName in typeVariablesBeingConstrained) {
       _typeVariablesBeingConstrained
           .add(TypeRegistry.addTypeParameter(typeVariableName));

pkg/analyzer/lib/src/dart/element/generic_inferrer.dart

@@ -772,6 +772,7 @@ class GenericInferrer {
         typeSystem: _typeSystem,
         typeSystemOperations: _typeSystemOperations,
         typeParameters: _typeFormals,
+        inferenceUsingBoundsIsEnabled: inferenceUsingBoundsIsEnabled,
         dataForTesting: null);
     typeConstraintGatherer.trySubtypeMatch(
         lower, typeParameterToInferBound, /* leftSchema */ true,
@@ -889,6 +890,7 @@ class GenericInferrer {
         typeSystem: _typeSystem,
         typeParameters: _typeParameters,
         typeSystemOperations: _typeSystemOperations,
+        inferenceUsingBoundsIsEnabled: inferenceUsingBoundsIsEnabled,
         dataForTesting: dataForTesting);
     var success = gatherer.trySubtypeMatch(t1, t2, !covariant,
         nodeForTesting: nodeForTesting);

pkg/analyzer/lib/src/dart/element/type_constraint_gatherer.dart

@@ -51,6 +51,7 @@ class TypeConstraintGatherer extends shared.TypeConstraintGenerator<
     required TypeSystemImpl typeSystem,
     required Iterable<TypeParameterElement> typeParameters,
     required TypeSystemOperations typeSystemOperations,
+    required super.inferenceUsingBoundsIsEnabled,
     required this.dataForTesting,
   })  : _typeSystem = typeSystem,
         _typeSystemOperations = typeSystemOperations {
@@ -157,7 +158,13 @@ class TypeConstraintGatherer extends shared.TypeConstraintGenerator<
     if (_typeSystemOperations.matchInferableParameter(SharedTypeView(Q))
         case var Q_element?
         when Q_nullability == NullabilitySuffix.none &&
-            _typeParameters.contains(Q_element)) {
+            _typeParameters.contains(Q_element) &&
+            (!inferenceUsingBoundsIsEnabled ||
+                (Q_element.bound == null ||
+                    _typeSystemOperations.isSubtypeOfInternal(
+                        P,
+                        _typeSystemOperations.greatestClosureOfTypeInternal(
+                            Q_element.bound!, [..._typeParameters]))))) {
       _addLower(Q_element, P, nodeForTesting: nodeForTesting);
       return true;
     }
@@ -315,7 +322,9 @@ class TypeConstraintGatherer extends shared.TypeConstraintGenerator<
     }
 
     if (P is FunctionType && Q is FunctionType) {
-      return _functionType(P, Q, leftSchema, nodeForTesting: nodeForTesting);
+      return _functionType(P, Q, leftSchema,
+          nodeForTesting: nodeForTesting,
+          inferenceUsingBoundsIsEnabled: inferenceUsingBoundsIsEnabled);
     }
 
     // A type `P` is a subtype match for `Record` with respect to `L` under no
@@ -330,6 +339,7 @@ class TypeConstraintGatherer extends shared.TypeConstraintGenerator<
     if (P is SharedRecordTypeStructure<DartType> &&
         Q is SharedRecordTypeStructure<DartType>) {
       return _recordType(P as RecordTypeImpl, Q as RecordTypeImpl, leftSchema,
+          inferenceUsingBoundsIsEnabled: inferenceUsingBoundsIsEnabled,
           nodeForTesting: nodeForTesting);
     }
 
@@ -371,7 +381,8 @@ class TypeConstraintGatherer extends shared.TypeConstraintGenerator<
   /// returned. Otherwise, [_constraints] is left unchanged (or rolled back),
   /// and `false` is returned.
   bool _functionType(FunctionType P, FunctionType Q, bool leftSchema,
-      {required AstNode? nodeForTesting}) {
+      {required bool inferenceUsingBoundsIsEnabled,
+      required AstNode? nodeForTesting}) {
     if (P.nullabilitySuffix != NullabilitySuffix.none) {
       return false;
     }
@@ -461,7 +472,8 @@ class TypeConstraintGatherer extends shared.TypeConstraintGenerator<
   /// returned. Otherwise, [_constraints] is left unchanged (or rolled back),
   /// and `false` is returned.
   bool _recordType(RecordTypeImpl P, RecordTypeImpl Q, bool leftSchema,
-      {required AstNode? nodeForTesting}) {
+      {required bool inferenceUsingBoundsIsEnabled,
+      required AstNode? nodeForTesting}) {
     // If `P` is `(M0, ..., Mk)` and `Q` is `(N0, ..., Nk)`, then the match
     // holds under constraints `C0 + ... + Ck`:
     //   If `Mi` is a subtype match for `Ni` with respect to L under

pkg/analyzer/lib/src/dart/resolver/flow_analysis_visitor.dart

@@ -517,6 +517,14 @@ class TypeSystemOperations
         typeSystem.greatestClosureOfSchema(schema.unwrapTypeSchemaView()));
   }
 
+  @override
+  DartType greatestClosureOfTypeInternal(DartType type,
+      List<SharedTypeParameterStructure<DartType>> typeParametersToEliminate) {
+    typeParametersToEliminate.first;
+    return typeSystem.greatestClosure(
+        type, typeParametersToEliminate.cast<TypeParameterElement>());
+  }
+
   @override
   bool isAlwaysExhaustiveType(SharedTypeView<DartType> type) {
     return typeSystem.isAlwaysExhaustive(type.unwrapTypeView());

pkg/analyzer/test/src/dart/element/generic_inferrer_test.dart

@@ -189,7 +189,9 @@ class GenericFunctionInferenceTest extends AbstractTypeSystemTest {
     // Something invalid...
     _assertTypes(
       _inferCall(clone, [stringNone, numNone], expectError: true),
-      [objectNone],
+      [
+        interfaceTypeNone(A, typeArguments: [objectQuestion]),
+      ],
     );
   }
 

pkg/analyzer/test/src/dart/element/type_constraint_gatherer_test.dart

@@ -1271,6 +1271,7 @@ class TypeConstraintGathererTest extends AbstractTypeSystemTest {
       typeParameters: typeParameters,
       typeSystemOperations:
           TypeSystemOperations(typeSystem, strictCasts: false),
+      inferenceUsingBoundsIsEnabled: false,
       dataForTesting: null,
     );
 
@@ -1299,6 +1300,7 @@ class TypeConstraintGathererTest extends AbstractTypeSystemTest {
       typeParameters: typeParameters,
       typeSystemOperations:
           TypeSystemOperations(typeSystem, strictCasts: false),
+      inferenceUsingBoundsIsEnabled: false,
       dataForTesting: null,
     );
 

pkg/front_end/lib/src/source/source_library_builder.dart

@@ -1725,6 +1725,7 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
             }
           } else {
             if (issueInferred) {
+              // Coverage-ignore-block(suite): Not run.
               message = templateIncorrectTypeArgumentInstantiationInferred
                   .withArguments(argument, typeParameter.bound,
                       typeParameter.name!, targetReceiver);

pkg/front_end/lib/src/type_inference/inference_visitor.dart

@@ -2864,6 +2864,8 @@ class InferenceVisitorImpl extends InferenceVisitorBase
       gatherer = typeSchemaEnvironment.setupGenericTypeInference(
           listType, typeParametersToInfer, typeContext,
           isConst: node.isConst,
+          inferenceUsingBoundsIsEnabled:
+              libraryFeatures.inferenceUsingBounds.isEnabled,
           typeOperations: operations,
           inferenceResultForTesting: dataForTesting
               // Coverage-ignore(suite): Not run.
@@ -5294,6 +5296,8 @@ class InferenceVisitorImpl extends InferenceVisitorBase
       gatherer = typeSchemaEnvironment.setupGenericTypeInference(
           mapType, typeParametersToInfer, typeContext,
           isConst: node.isConst,
+          inferenceUsingBoundsIsEnabled:
+              libraryFeatures.inferenceUsingBounds.isEnabled,
           typeOperations: operations,
           inferenceResultForTesting: dataForTesting
               // Coverage-ignore(suite): Not run.
@@ -5376,6 +5380,8 @@ class InferenceVisitorImpl extends InferenceVisitorBase
             typeSchemaEnvironment.setupGenericTypeInference(
                 setType, typeParametersToInfer, typeContext,
                 isConst: node.isConst,
+                inferenceUsingBoundsIsEnabled:
+                    libraryFeatures.inferenceUsingBounds.isEnabled,
                 typeOperations: operations,
                 inferenceResultForTesting: dataForTesting
                     // Coverage-ignore(suite): Not run.
@@ -8670,6 +8676,8 @@ class InferenceVisitorImpl extends InferenceVisitorBase
       gatherer = typeSchemaEnvironment.setupGenericTypeInference(
           setType, typeParametersToInfer, typeContext,
           isConst: node.isConst,
+          inferenceUsingBoundsIsEnabled:
+              libraryFeatures.inferenceUsingBounds.isEnabled,
           typeOperations: operations,
           inferenceResultForTesting: dataForTesting
               // Coverage-ignore(suite): Not run.
@@ -11796,6 +11804,8 @@ class InferenceVisitorImpl extends InferenceVisitorBase
     TypeConstraintGatherer gatherer =
         typeSchemaEnvironment.setupGenericTypeInference(
             declaredType, typeParametersToInfer, contextType,
+            inferenceUsingBoundsIsEnabled:
+                libraryFeatures.inferenceUsingBounds.isEnabled,
             typeOperations: operations,
             inferenceResultForTesting: dataForTesting
                 // Coverage-ignore(suite): Not run.