pkg/analyzer/lib/src/task/strong_mode.dart - sdk.git - Git at Google

 // Copyright (c) 2015, 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.

 import 'dart:collection';

 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/inheritance_manager3.dart';
 import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/type_algebra.dart';
 import 'package:analyzer/src/dart/element/type_system.dart';
 import 'package:analyzer/src/task/inference_error.dart';
 import 'package:collection/collection.dart';

 /// An object used to infer the type of instance fields and the return types of
 /// instance methods within a single compilation unit.
 class InstanceMemberInferrer {
   final InheritanceManager3 inheritance;
   final Set<ClassElement> elementsBeingInferred = HashSet<ClassElement>();

   late TypeSystemImpl typeSystem;
   late bool isNonNullableByDefault;
   late ClassElement currentClassElement;

   /// Initialize a newly create inferrer.
   InstanceMemberInferrer(this.inheritance);

   DartType get _dynamicType => DynamicTypeImpl.instance;

   /// Infer type information for all of the instance members in the given
   /// compilation [unit].
   void inferCompilationUnit(CompilationUnitElement unit) {
     typeSystem = unit.library.typeSystem as TypeSystemImpl;
     isNonNullableByDefault = typeSystem.isNonNullableByDefault;
     _inferClasses(unit.classes);
     _inferClasses(unit.mixins);
   }

   /// Return `true` if the elements corresponding to the [elements] have the
   /// same kind as the [element].
   bool _allSameElementKind(
       ExecutableElement element, List<ExecutableElement> elements) {
     var elementKind = element.kind;
     for (int i = 0; i < elements.length; i++) {
       if (elements[i].kind != elementKind) {
         return false;
       }
     }
     return true;
   }

   /// Given a method, return the parameter in the method that corresponds to the
   /// given [parameter]. If the parameter is positional, then it appears at the
   /// given [index] in its enclosing element's list of parameters.
   ParameterElement? _getCorrespondingParameter(ParameterElement parameter,
       int index, List<ParameterElement> methodParameters) {
     //
     // Find the corresponding parameter.
     //
     if (parameter.isNamed) {
       //
       // If we're looking for a named parameter, only a named parameter with
       // the same name will be matched.
       //
       return methodParameters.lastWhereOrNull(
           (ParameterElement methodParameter) =>
               methodParameter.isNamed &&
               methodParameter.name == parameter.name);
     }
     //
     // If we're looking for a positional parameter we ignore the difference
     // between required and optional parameters.
     //
     if (index < methodParameters.length) {
       var matchingParameter = methodParameters[index];
       if (!matchingParameter.isNamed) {
         return matchingParameter;
       }
     }
     return null;
   }

   /// If the given [accessor] represents a non-synthetic instance property
   /// accessor for which no type was provided, infer its types.
   ///
   /// If the given [field] represents a non-synthetic instance field for
   /// which no type was provided, infer the type of the field.
   void _inferAccessorOrField({
     PropertyAccessorElementImpl? accessor,
     FieldElementImpl? field,
   }) {
     Uri elementLibraryUri;
     String elementName;

     if (accessor != null) {
       if (accessor.isSynthetic || accessor.isStatic) {
         return;
       }
       elementLibraryUri = accessor.library.source.uri;
       elementName = accessor.displayName;
     } else if (field != null) {
       if (field.isSynthetic || field.isStatic) {
         return;
       }
       elementLibraryUri = field.library.source.uri;
       elementName = field.name;
     } else {
       throw UnimplementedError();
     }

     var getterName = Name(elementLibraryUri, elementName);
     var overriddenGetters = inheritance.getOverridden2(
       currentClassElement,
       getterName,
     );
     if (overriddenGetters != null) {
       overriddenGetters = overriddenGetters.where((e) {
         return e is PropertyAccessorElement && e.isGetter;
       }).toList();
     } else {
       overriddenGetters = const [];
     }

     var setterName = Name(elementLibraryUri, '$elementName=');
     var overriddenSetters = inheritance.getOverridden2(
       currentClassElement,
       setterName,
     );
     overriddenSetters ??= const [];

     DartType combinedGetterType() {
       var combinedGetter = inheritance.combineSignatures(
         targetClass: currentClassElement,
         candidates: overriddenGetters!,
         doTopMerge: true,
         name: getterName,
       );
       if (combinedGetter != null) {
         var returnType = combinedGetter.returnType;
         return typeSystem.nonNullifyLegacy(returnType);
       }
       return DynamicTypeImpl.instance;
     }

     DartType combinedSetterType() {
       var combinedSetter = inheritance.combineSignatures(
         targetClass: currentClassElement,
         candidates: overriddenSetters!,
         doTopMerge: true,
         name: setterName,
       );
       if (combinedSetter != null) {
         var parameters = combinedSetter.parameters;
         if (parameters.isNotEmpty) {
           var type = parameters[0].type;
           return typeSystem.nonNullifyLegacy(type);
         }
       }
       return DynamicTypeImpl.instance;
     }

     if (accessor != null && accessor.isGetter) {
       if (!accessor.hasImplicitReturnType) {
         return;
       }

       // The return type of a getter, parameter type of a setter or type of a
       // field which overrides/implements only one or more getters is inferred
       // to be the return type of the combined member signature of said getter
       // in the direct superinterfaces.
       //
       // The return type of a getter which overrides/implements both a setter
       // and a getter is inferred to be the return type of the combined member
       // signature of said getter in the direct superinterfaces.
       if (overriddenGetters.isNotEmpty) {
         accessor.returnType = combinedGetterType();
         return;
       }

       // The return type of a getter, parameter type of a setter or type of
       // field which overrides/implements only one or more setters is inferred
       // to be the parameter type of the combined member signature of said
       // setter in the direct superinterfaces.
       if (overriddenGetters.isEmpty && overriddenSetters.isNotEmpty) {
         accessor.returnType = combinedSetterType();
         return;
       }

       return;
     }

     if (accessor != null && accessor.isSetter) {
       var parameters = accessor.parameters;
       if (parameters.isEmpty) {
         return;
       }
       var parameter = parameters[0] as ParameterElementImpl;

       if (overriddenSetters.any(_isCovariantSetter)) {
         parameter.inheritsCovariant = true;
       }

       if (!parameter.hasImplicitType) {
         return;
       }

       // The return type of a getter, parameter type of a setter or type of a
       // field which overrides/implements only one or more getters is inferred
       // to be the return type of the combined member signature of said getter
       // in the direct superinterfaces.
       if (overriddenGetters.isNotEmpty && overriddenSetters.isEmpty) {
         parameter.type = combinedGetterType();
         return;
       }

       // The return type of a getter, parameter type of a setter or type of
       // field which overrides/implements only one or more setters is inferred
       // to be the parameter type of the combined member signature of said
       // setter in the direct superinterfaces.
       //
       // The parameter type of a setter which overrides/implements both a
       // setter and a getter is inferred to be the parameter type of the
       // combined member signature of said setter in the direct superinterfaces.
       if (overriddenSetters.isNotEmpty) {
         parameter.type = combinedSetterType();
         return;
       }

       return;
     }

     if (field != null) {
       if (field.setter != null) {
         if (overriddenSetters.any(_isCovariantSetter)) {
           var parameter = field.setter!.parameters[0] as ParameterElementImpl;
           parameter.inheritsCovariant = true;
         }
       }

       if (!field.hasImplicitType) {
         return;
       }

       // The return type of a getter, parameter type of a setter or type of a
       // field which overrides/implements only one or more getters is inferred
       // to be the return type of the combined member signature of said getter
       // in the direct superinterfaces.
       if (overriddenGetters.isNotEmpty && overriddenSetters.isEmpty) {
         field.type = combinedGetterType();
         field.hasTypeInferred = true;
         return;
       }

       // The return type of a getter, parameter type of a setter or type of
       // field which overrides/implements only one or more setters is inferred
       // to be the parameter type of the combined member signature of said
       // setter in the direct superinterfaces.
       if (overriddenGetters.isEmpty && overriddenSetters.isNotEmpty) {
         var type = combinedSetterType();
         _setFieldType(field, type);
         return;
       }

       if (overriddenGetters.isNotEmpty && overriddenSetters.isNotEmpty) {
         // The type of a final field which overrides/implements both a setter
         // and a getter is inferred to be the return type of the combined
         // member signature of said getter in the direct superinterfaces.
         if (field.isFinal) {
           var type = combinedGetterType();
           _setFieldType(field, type);
           return;
         }

         // The type of a non-final field which overrides/implements both a
         // setter and a getter is inferred to be the parameter type of the
         // combined member signature of said setter in the direct
         // superinterfaces, if this type is the same as the return type of the
         // combined member signature of said getter in the direct
         // superinterfaces. If the types are not the same then inference
         // fails with an error.
         if (!field.isFinal) {
           var getterType = combinedGetterType();
           var setterType = combinedSetterType();

           if (getterType == setterType) {
             var type = getterType;
             type = typeSystem.nonNullifyLegacy(type);
             _setFieldType(field, type);
           } else {
             field.typeInferenceError = TopLevelInferenceError(
               kind: TopLevelInferenceErrorKind.overrideConflictFieldType,
               arguments: const <String>[],
             );
           }
           return;
         }
       }

       // Otherwise, declarations of static variables and fields that omit a
       // type will be inferred from their initializer if present.
       field.typeInference?.perform();

       return;
     }
   }

   /// Infer type information for all of the instance members in the given
   /// [classElement].
   void _inferClass(ClassElement classElement) {
     if (classElement is ClassElementImpl) {
       if (classElement.hasBeenInferred) {
         return;
       }
       if (!elementsBeingInferred.add(classElement)) {
         // We have found a circularity in the class hierarchy. For now we just
         // stop trying to infer any type information for any classes that
         // inherit from any class in the cycle. We could potentially limit the
         // algorithm to only not inferring types in the classes in the cycle,
         // but it isn't clear that the results would be significantly better.
         throw _CycleException();
       }
       try {
         //
         // Ensure that all of instance members in the supertypes have had types
         // inferred for them.
         //
         _inferType(classElement.supertype);
         classElement.mixins.forEach(_inferType);
         classElement.interfaces.forEach(_inferType);
         classElement.superclassConstraints.forEach(_inferType);
         //
         // Then infer the types for the members.
         //
         currentClassElement = classElement;
         for (var field in classElement.fields) {
           _inferAccessorOrField(
             field: field as FieldElementImpl,
           );
         }
         for (var accessor in classElement.accessors) {
           _inferAccessorOrField(
             accessor: accessor as PropertyAccessorElementImpl,
           );
         }
         for (var method in classElement.methods) {
           _inferExecutable(method as MethodElementImpl);
         }
         //
         // Infer initializing formal parameter types. This must happen after
         // field types are inferred.
         //
         classElement.constructors.forEach(_inferConstructorFieldFormals);
         classElement.hasBeenInferred = true;
       } finally {
         elementsBeingInferred.remove(classElement);
       }
     }
   }

   void _inferClasses(List<ClassElement> elements) {
     for (ClassElement element in elements) {
       try {
         _inferClass(element);
       } on _CycleException {
         // This is a short circuit return to prevent types that inherit from
         // types containing a circular reference from being inferred.
       }
     }
   }

   void _inferConstructorFieldFormals(ConstructorElement constructor) {
     for (ParameterElement parameter in constructor.parameters) {
       if (parameter.hasImplicitType &&
           parameter is FieldFormalParameterElementImpl) {
         var field = parameter.field;
         if (field != null) {
           parameter.type = field.type;
         }
       }
     }
   }

   /// If the given [element] represents a non-synthetic instance method,
   /// getter or setter, infer the return type and any parameter type(s) where
   /// they were not provided.
   void _inferExecutable(MethodElementImpl element) {
     if (element.isSynthetic || element.isStatic) {
       return;
     }

     var name = Name(element.library.source.uri, element.name);
     var overriddenElements = inheritance.getOverridden2(
       currentClassElement,
       name,
     );
     if (overriddenElements == null ||
         !_allSameElementKind(element, overriddenElements)) {
       return;
     }

     FunctionType? combinedSignatureType;
     var hasImplicitType = element.hasImplicitReturnType ||
         element.parameters.any((e) => e.hasImplicitType);
     if (hasImplicitType) {
       var conflicts = <Conflict>[];
       var combinedSignature = inheritance.combineSignatures(
         targetClass: currentClassElement,
         candidates: overriddenElements,
         doTopMerge: true,
         name: name,
         conflicts: conflicts,
       );
       if (combinedSignature != null) {
         combinedSignatureType = _toOverriddenFunctionType(
           element,
           combinedSignature,
         );
         if (combinedSignatureType != null) {}
       } else {
         var conflictExplanation = '<unknown>';
         if (conflicts.length == 1) {
           var conflict = conflicts.single;
           if (conflict is CandidatesConflict) {
             conflictExplanation = conflict.candidates.map((candidate) {
               var className = candidate.enclosingElement.name;
               var typeStr = candidate.type.getDisplayString(
                 withNullability: typeSystem.isNonNullableByDefault,
               );
               return '$className.${name.name} ($typeStr)';
             }).join(', ');
           }
         }

         element.typeInferenceError = TopLevelInferenceError(
           kind: TopLevelInferenceErrorKind.overrideNoCombinedSuperSignature,
           arguments: [conflictExplanation],
         );
       }
     }

     //
     // Infer the return type.
     //
     if (element.hasImplicitReturnType && element.displayName != '[]=') {
       if (combinedSignatureType != null) {
         var returnType = combinedSignatureType.returnType;
         returnType = typeSystem.nonNullifyLegacy(returnType);
         element.returnType = returnType;
       } else {
         element.returnType = DynamicTypeImpl.instance;
       }
     }

     //
     // Infer the parameter types.
     //
     List<ParameterElement> parameters = element.parameters;
     for (var index = 0; index < parameters.length; index++) {
       ParameterElement parameter = parameters[index];
       if (parameter is ParameterElementImpl) {
         _inferParameterCovariance(parameter, index, overriddenElements);

         if (parameter.hasImplicitType) {
           _inferParameterType(parameter, index, combinedSignatureType);
         }
       }
     }

     _resetOperatorEqualParameterTypeToDynamic(element, overriddenElements);
   }

   /// If a parameter is covariant, any parameters that override it are too.
   void _inferParameterCovariance(ParameterElementImpl parameter, int index,
       Iterable<ExecutableElement> overridden) {
     parameter.inheritsCovariant = overridden.any((f) {
       var param = _getCorrespondingParameter(parameter, index, f.parameters);
       return param != null && param.isCovariant;
     });
   }

   /// Set the type for the [parameter] at the given [index] from the given
   /// [combinedSignatureType], which might be `null` if there is no valid
   /// combined signature for signatures from direct superinterfaces.
   void _inferParameterType(ParameterElementImpl parameter, int index,
       FunctionType? combinedSignatureType) {
     if (combinedSignatureType != null) {
       var matchingParameter = _getCorrespondingParameter(
         parameter,
         index,
         combinedSignatureType.parameters,
       );
       if (matchingParameter != null) {
         var type = matchingParameter.type;
         type = typeSystem.nonNullifyLegacy(type);
         parameter.type = type;
       } else {
         parameter.type = DynamicTypeImpl.instance;
       }
     } else {
       parameter.type = DynamicTypeImpl.instance;
     }
   }

   /// Infer type information for all of the instance members in the given
   /// interface [type].
   void _inferType(InterfaceType? type) {
     if (type != null) {
       _inferClass(type.element);
     }
   }

   /// In legacy mode, an override of `operator==` with no explicit parameter
   /// type inherits the parameter type of the overridden method if any override
   /// of `operator==` between the overriding method and `Object.==` has an
   /// explicit parameter type.  Otherwise, the parameter type of the
   /// overriding method is `dynamic`.
   ///
   /// https://github.com/dart-lang/language/issues/569
   void _resetOperatorEqualParameterTypeToDynamic(
     MethodElementImpl element,
     List<ExecutableElement> overriddenElements,
   ) {
     if (element.name != '==') return;

     var parameters = element.parameters;
     if (parameters.length != 1) {
       element.isOperatorEqualWithParameterTypeFromObject = false;
       return;
     }

     var parameter = parameters[0] as ParameterElementImpl;
     if (!parameter.hasImplicitType) {
       element.isOperatorEqualWithParameterTypeFromObject = false;
       return;
     }

     for (var overridden in overriddenElements) {
       overridden = overridden.declaration;

       // Skip Object itself.
       var enclosingElement = overridden.enclosingElement;
       if (enclosingElement is ClassElement &&
           enclosingElement.isDartCoreObject) {
         continue;
       }

       // Keep the type if it is not directly from Object.
       if (overridden is MethodElementImpl &&
           !overridden.isOperatorEqualWithParameterTypeFromObject) {
         element.isOperatorEqualWithParameterTypeFromObject = false;
         return;
       }
     }

     // Reset the type.
     if (!isNonNullableByDefault) {
       parameter.type = _dynamicType;
     }
     element.isOperatorEqualWithParameterTypeFromObject = true;
   }

   /// Return the [FunctionType] of the [overriddenElement] that [element]
   /// overrides. Return `null`, in case of type parameters inconsistency.
   ///
   /// The overridden element must have the same number of generic type
   /// parameters as the target element, or none.
   ///
   /// If we do have generic type parameters on the element we're inferring,
   /// we must express its parameter and return types in terms of its own
   /// parameters. For example, given `m<T>(t)` overriding `m<S>(S s)` we
   /// should infer this as `m<T>(T t)`.
   FunctionType? _toOverriddenFunctionType(
       ExecutableElement element, ExecutableElement overriddenElement) {
     var elementTypeParameters = element.typeParameters;
     var overriddenTypeParameters = overriddenElement.typeParameters;

     if (elementTypeParameters.length != overriddenTypeParameters.length) {
       return null;
     }

     var overriddenType = overriddenElement.type as FunctionTypeImpl;
     if (elementTypeParameters.isEmpty) {
       return overriddenType;
     }

     return replaceTypeParameters(overriddenType, elementTypeParameters);
   }

   static bool _isCovariantSetter(ExecutableElement element) {
     if (element is PropertyAccessorElement) {
       var parameters = element.parameters;
       return parameters.isNotEmpty && parameters[0].isCovariant;
     }
     return false;
   }

   static void _setFieldType(FieldElementImpl field, DartType type) {
     field.type = type;
     field.hasTypeInferred = true;
   }
 }

 /// A class of exception that is not used anywhere else.
 class _CycleException implements Exception {}
	// Copyright (c) 2015, 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.

	import 'dart:collection';

	import 'package:analyzer/dart/element/element.dart';
	import 'package:analyzer/dart/element/type.dart';
	import 'package:analyzer/src/dart/element/element.dart';
	import 'package:analyzer/src/dart/element/inheritance_manager3.dart';
	import 'package:analyzer/src/dart/element/type.dart';
	import 'package:analyzer/src/dart/element/type_algebra.dart';
	import 'package:analyzer/src/dart/element/type_system.dart';
	import 'package:analyzer/src/task/inference_error.dart';
	import 'package:collection/collection.dart';

	/// An object used to infer the type of instance fields and the return types of
	/// instance methods within a single compilation unit.
	class InstanceMemberInferrer {
	final InheritanceManager3 inheritance;
	final Set<ClassElement> elementsBeingInferred = HashSet<ClassElement>();

	late TypeSystemImpl typeSystem;
	late bool isNonNullableByDefault;
	late ClassElement currentClassElement;

	/// Initialize a newly create inferrer.
	InstanceMemberInferrer(this.inheritance);

	DartType get _dynamicType => DynamicTypeImpl.instance;

	/// Infer type information for all of the instance members in the given
	/// compilation [unit].
	void inferCompilationUnit(CompilationUnitElement unit) {
	typeSystem = unit.library.typeSystem as TypeSystemImpl;
	isNonNullableByDefault = typeSystem.isNonNullableByDefault;
	_inferClasses(unit.classes);
	_inferClasses(unit.mixins);
	}

	/// Return `true` if the elements corresponding to the [elements] have the
	/// same kind as the [element].
	bool _allSameElementKind(
	ExecutableElement element, List<ExecutableElement> elements) {
	var elementKind = element.kind;
	for (int i = 0; i < elements.length; i++) {
	if (elements[i].kind != elementKind) {
	return false;
	}
	}
	return true;
	}

	/// Given a method, return the parameter in the method that corresponds to the
	/// given [parameter]. If the parameter is positional, then it appears at the
	/// given [index] in its enclosing element's list of parameters.
	ParameterElement? _getCorrespondingParameter(ParameterElement parameter,
	int index, List<ParameterElement> methodParameters) {
	//
	// Find the corresponding parameter.
	//
	if (parameter.isNamed) {
	//
	// If we're looking for a named parameter, only a named parameter with
	// the same name will be matched.
	//
	return methodParameters.lastWhereOrNull(
	(ParameterElement methodParameter) =>
	methodParameter.isNamed &&
	methodParameter.name == parameter.name);
	}
	//
	// If we're looking for a positional parameter we ignore the difference
	// between required and optional parameters.
	//
	if (index < methodParameters.length) {
	var matchingParameter = methodParameters[index];
	if (!matchingParameter.isNamed) {
	return matchingParameter;
	}
	}
	return null;
	}

	/// If the given [accessor] represents a non-synthetic instance property
	/// accessor for which no type was provided, infer its types.
	///
	/// If the given [field] represents a non-synthetic instance field for
	/// which no type was provided, infer the type of the field.
	void _inferAccessorOrField({
	PropertyAccessorElementImpl? accessor,
	FieldElementImpl? field,
	}) {
	Uri elementLibraryUri;
	String elementName;

	if (accessor != null) {
	if (accessor.isSynthetic \|\| accessor.isStatic) {
	return;
	}
	elementLibraryUri = accessor.library.source.uri;
	elementName = accessor.displayName;
	} else if (field != null) {
	if (field.isSynthetic \|\| field.isStatic) {
	return;
	}
	elementLibraryUri = field.library.source.uri;
	elementName = field.name;
	} else {
	throw UnimplementedError();
	}

	var getterName = Name(elementLibraryUri, elementName);
	var overriddenGetters = inheritance.getOverridden2(
	currentClassElement,
	getterName,
	);
	if (overriddenGetters != null) {
	overriddenGetters = overriddenGetters.where((e) {
	return e is PropertyAccessorElement && e.isGetter;
	}).toList();
	} else {
	overriddenGetters = const [];
	}

	var setterName = Name(elementLibraryUri, '$elementName=');
	var overriddenSetters = inheritance.getOverridden2(
	currentClassElement,
	setterName,
	);
	overriddenSetters ??= const [];

	DartType combinedGetterType() {
	var combinedGetter = inheritance.combineSignatures(
	targetClass: currentClassElement,
	candidates: overriddenGetters!,
	doTopMerge: true,
	name: getterName,
	);
	if (combinedGetter != null) {
	var returnType = combinedGetter.returnType;
	return typeSystem.nonNullifyLegacy(returnType);
	}
	return DynamicTypeImpl.instance;
	}

	DartType combinedSetterType() {
	var combinedSetter = inheritance.combineSignatures(
	targetClass: currentClassElement,
	candidates: overriddenSetters!,
	doTopMerge: true,
	name: setterName,
	);
	if (combinedSetter != null) {
	var parameters = combinedSetter.parameters;
	if (parameters.isNotEmpty) {
	var type = parameters[0].type;
	return typeSystem.nonNullifyLegacy(type);
	}
	}
	return DynamicTypeImpl.instance;
	}

	if (accessor != null && accessor.isGetter) {
	if (!accessor.hasImplicitReturnType) {
	return;
	}

	// The return type of a getter, parameter type of a setter or type of a
	// field which overrides/implements only one or more getters is inferred
	// to be the return type of the combined member signature of said getter
	// in the direct superinterfaces.
	//
	// The return type of a getter which overrides/implements both a setter
	// and a getter is inferred to be the return type of the combined member
	// signature of said getter in the direct superinterfaces.
	if (overriddenGetters.isNotEmpty) {
	accessor.returnType = combinedGetterType();
	return;
	}

	// The return type of a getter, parameter type of a setter or type of
	// field which overrides/implements only one or more setters is inferred
	// to be the parameter type of the combined member signature of said
	// setter in the direct superinterfaces.
	if (overriddenGetters.isEmpty && overriddenSetters.isNotEmpty) {
	accessor.returnType = combinedSetterType();
	return;
	}

	return;
	}

	if (accessor != null && accessor.isSetter) {
	var parameters = accessor.parameters;
	if (parameters.isEmpty) {
	return;
	}
	var parameter = parameters[0] as ParameterElementImpl;

	if (overriddenSetters.any(_isCovariantSetter)) {
	parameter.inheritsCovariant = true;
	}

	if (!parameter.hasImplicitType) {
	return;
	}

	// The return type of a getter, parameter type of a setter or type of a
	// field which overrides/implements only one or more getters is inferred
	// to be the return type of the combined member signature of said getter
	// in the direct superinterfaces.
	if (overriddenGetters.isNotEmpty && overriddenSetters.isEmpty) {
	parameter.type = combinedGetterType();
	return;
	}

	// The return type of a getter, parameter type of a setter or type of
	// field which overrides/implements only one or more setters is inferred
	// to be the parameter type of the combined member signature of said
	// setter in the direct superinterfaces.
	//
	// The parameter type of a setter which overrides/implements both a
	// setter and a getter is inferred to be the parameter type of the
	// combined member signature of said setter in the direct superinterfaces.
	if (overriddenSetters.isNotEmpty) {
	parameter.type = combinedSetterType();
	return;
	}

	return;
	}

	if (field != null) {
	if (field.setter != null) {
	if (overriddenSetters.any(_isCovariantSetter)) {
	var parameter = field.setter!.parameters[0] as ParameterElementImpl;
	parameter.inheritsCovariant = true;
	}
	}

	if (!field.hasImplicitType) {
	return;
	}

	// The return type of a getter, parameter type of a setter or type of a
	// field which overrides/implements only one or more getters is inferred
	// to be the return type of the combined member signature of said getter
	// in the direct superinterfaces.
	if (overriddenGetters.isNotEmpty && overriddenSetters.isEmpty) {
	field.type = combinedGetterType();
	field.hasTypeInferred = true;
	return;
	}

	// The return type of a getter, parameter type of a setter or type of
	// field which overrides/implements only one or more setters is inferred
	// to be the parameter type of the combined member signature of said
	// setter in the direct superinterfaces.
	if (overriddenGetters.isEmpty && overriddenSetters.isNotEmpty) {
	var type = combinedSetterType();
	_setFieldType(field, type);
	return;
	}

	if (overriddenGetters.isNotEmpty && overriddenSetters.isNotEmpty) {
	// The type of a final field which overrides/implements both a setter
	// and a getter is inferred to be the return type of the combined
	// member signature of said getter in the direct superinterfaces.
	if (field.isFinal) {
	var type = combinedGetterType();
	_setFieldType(field, type);
	return;
	}

	// The type of a non-final field which overrides/implements both a
	// setter and a getter is inferred to be the parameter type of the
	// combined member signature of said setter in the direct
	// superinterfaces, if this type is the same as the return type of the
	// combined member signature of said getter in the direct
	// superinterfaces. If the types are not the same then inference
	// fails with an error.
	if (!field.isFinal) {
	var getterType = combinedGetterType();
	var setterType = combinedSetterType();

	if (getterType == setterType) {
	var type = getterType;
	type = typeSystem.nonNullifyLegacy(type);
	_setFieldType(field, type);
	} else {
	field.typeInferenceError = TopLevelInferenceError(
	kind: TopLevelInferenceErrorKind.overrideConflictFieldType,
	arguments: const <String>[],
	);
	}
	return;
	}
	}

	// Otherwise, declarations of static variables and fields that omit a
	// type will be inferred from their initializer if present.
	field.typeInference?.perform();

	return;
	}
	}

	/// Infer type information for all of the instance members in the given
	/// [classElement].
	void _inferClass(ClassElement classElement) {
	if (classElement is ClassElementImpl) {
	if (classElement.hasBeenInferred) {
	return;
	}
	if (!elementsBeingInferred.add(classElement)) {
	// We have found a circularity in the class hierarchy. For now we just
	// stop trying to infer any type information for any classes that
	// inherit from any class in the cycle. We could potentially limit the
	// algorithm to only not inferring types in the classes in the cycle,
	// but it isn't clear that the results would be significantly better.
	throw _CycleException();
	}
	try {
	//
	// Ensure that all of instance members in the supertypes have had types
	// inferred for them.
	//
	_inferType(classElement.supertype);
	classElement.mixins.forEach(_inferType);
	classElement.interfaces.forEach(_inferType);
	classElement.superclassConstraints.forEach(_inferType);
	//
	// Then infer the types for the members.
	//
	currentClassElement = classElement;
	for (var field in classElement.fields) {
	_inferAccessorOrField(
	field: field as FieldElementImpl,
	);
	}
	for (var accessor in classElement.accessors) {
	_inferAccessorOrField(
	accessor: accessor as PropertyAccessorElementImpl,
	);
	}
	for (var method in classElement.methods) {
	_inferExecutable(method as MethodElementImpl);
	}
	//
	// Infer initializing formal parameter types. This must happen after
	// field types are inferred.
	//
	classElement.constructors.forEach(_inferConstructorFieldFormals);
	classElement.hasBeenInferred = true;
	} finally {
	elementsBeingInferred.remove(classElement);
	}
	}
	}

	void _inferClasses(List<ClassElement> elements) {
	for (ClassElement element in elements) {
	try {
	_inferClass(element);
	} on _CycleException {
	// This is a short circuit return to prevent types that inherit from
	// types containing a circular reference from being inferred.
	}
	}
	}

	void _inferConstructorFieldFormals(ConstructorElement constructor) {
	for (ParameterElement parameter in constructor.parameters) {
	if (parameter.hasImplicitType &&
	parameter is FieldFormalParameterElementImpl) {
	var field = parameter.field;
	if (field != null) {
	parameter.type = field.type;
	}
	}
	}
	}

	/// If the given [element] represents a non-synthetic instance method,
	/// getter or setter, infer the return type and any parameter type(s) where
	/// they were not provided.
	void _inferExecutable(MethodElementImpl element) {
	if (element.isSynthetic \|\| element.isStatic) {
	return;
	}

	var name = Name(element.library.source.uri, element.name);
	var overriddenElements = inheritance.getOverridden2(
	currentClassElement,
	name,
	);
	if (overriddenElements == null \|\|
	!_allSameElementKind(element, overriddenElements)) {
	return;
	}

	FunctionType? combinedSignatureType;
	var hasImplicitType = element.hasImplicitReturnType \|\|
	element.parameters.any((e) => e.hasImplicitType);
	if (hasImplicitType) {
	var conflicts = <Conflict>[];
	var combinedSignature = inheritance.combineSignatures(
	targetClass: currentClassElement,
	candidates: overriddenElements,
	doTopMerge: true,
	name: name,
	conflicts: conflicts,
	);
	if (combinedSignature != null) {
	combinedSignatureType = _toOverriddenFunctionType(
	element,
	combinedSignature,
	);
	if (combinedSignatureType != null) {}
	} else {
	var conflictExplanation = '<unknown>';
	if (conflicts.length == 1) {
	var conflict = conflicts.single;
	if (conflict is CandidatesConflict) {
	conflictExplanation = conflict.candidates.map((candidate) {
	var className = candidate.enclosingElement.name;
	var typeStr = candidate.type.getDisplayString(
	withNullability: typeSystem.isNonNullableByDefault,
	);
	return '$className.${name.name} ($typeStr)';
	}).join(', ');
	}
	}

	element.typeInferenceError = TopLevelInferenceError(
	kind: TopLevelInferenceErrorKind.overrideNoCombinedSuperSignature,
	arguments: [conflictExplanation],
	);
	}
	}

	//
	// Infer the return type.
	//
	if (element.hasImplicitReturnType && element.displayName != '[]=') {
	if (combinedSignatureType != null) {
	var returnType = combinedSignatureType.returnType;
	returnType = typeSystem.nonNullifyLegacy(returnType);
	element.returnType = returnType;
	} else {
	element.returnType = DynamicTypeImpl.instance;
	}
	}

	//
	// Infer the parameter types.
	//
	List<ParameterElement> parameters = element.parameters;
	for (var index = 0; index < parameters.length; index++) {
	ParameterElement parameter = parameters[index];
	if (parameter is ParameterElementImpl) {
	_inferParameterCovariance(parameter, index, overriddenElements);

	if (parameter.hasImplicitType) {
	_inferParameterType(parameter, index, combinedSignatureType);
	}
	}
	}

	_resetOperatorEqualParameterTypeToDynamic(element, overriddenElements);
	}

	/// If a parameter is covariant, any parameters that override it are too.
	void _inferParameterCovariance(ParameterElementImpl parameter, int index,
	Iterable<ExecutableElement> overridden) {
	parameter.inheritsCovariant = overridden.any((f) {
	var param = _getCorrespondingParameter(parameter, index, f.parameters);
	return param != null && param.isCovariant;
	});
	}

	/// Set the type for the [parameter] at the given [index] from the given
	/// [combinedSignatureType], which might be `null` if there is no valid
	/// combined signature for signatures from direct superinterfaces.
	void _inferParameterType(ParameterElementImpl parameter, int index,
	FunctionType? combinedSignatureType) {
	if (combinedSignatureType != null) {
	var matchingParameter = _getCorrespondingParameter(
	parameter,
	index,
	combinedSignatureType.parameters,
	);
	if (matchingParameter != null) {
	var type = matchingParameter.type;
	type = typeSystem.nonNullifyLegacy(type);
	parameter.type = type;
	} else {
	parameter.type = DynamicTypeImpl.instance;
	}
	} else {
	parameter.type = DynamicTypeImpl.instance;
	}
	}

	/// Infer type information for all of the instance members in the given
	/// interface [type].
	void _inferType(InterfaceType? type) {
	if (type != null) {
	_inferClass(type.element);
	}
	}

	/// In legacy mode, an override of `operator==` with no explicit parameter
	/// type inherits the parameter type of the overridden method if any override
	/// of `operator==` between the overriding method and `Object.==` has an
	/// explicit parameter type. Otherwise, the parameter type of the
	/// overriding method is `dynamic`.
	///
	/// https://github.com/dart-lang/language/issues/569
	void _resetOperatorEqualParameterTypeToDynamic(
	MethodElementImpl element,
	List<ExecutableElement> overriddenElements,
	) {
	if (element.name != '==') return;

	var parameters = element.parameters;
	if (parameters.length != 1) {
	element.isOperatorEqualWithParameterTypeFromObject = false;
	return;
	}

	var parameter = parameters[0] as ParameterElementImpl;
	if (!parameter.hasImplicitType) {
	element.isOperatorEqualWithParameterTypeFromObject = false;
	return;
	}

	for (var overridden in overriddenElements) {
	overridden = overridden.declaration;

	// Skip Object itself.
	var enclosingElement = overridden.enclosingElement;
	if (enclosingElement is ClassElement &&
	enclosingElement.isDartCoreObject) {
	continue;
	}

	// Keep the type if it is not directly from Object.
	if (overridden is MethodElementImpl &&
	!overridden.isOperatorEqualWithParameterTypeFromObject) {
	element.isOperatorEqualWithParameterTypeFromObject = false;
	return;
	}
	}

	// Reset the type.
	if (!isNonNullableByDefault) {
	parameter.type = _dynamicType;
	}
	element.isOperatorEqualWithParameterTypeFromObject = true;
	}

	/// Return the [FunctionType] of the [overriddenElement] that [element]
	/// overrides. Return `null`, in case of type parameters inconsistency.
	///
	/// The overridden element must have the same number of generic type
	/// parameters as the target element, or none.
	///
	/// If we do have generic type parameters on the element we're inferring,
	/// we must express its parameter and return types in terms of its own
	/// parameters. For example, given `m<T>(t)` overriding `m<S>(S s)` we
	/// should infer this as `m<T>(T t)`.
	FunctionType? _toOverriddenFunctionType(
	ExecutableElement element, ExecutableElement overriddenElement) {
	var elementTypeParameters = element.typeParameters;
	var overriddenTypeParameters = overriddenElement.typeParameters;

	if (elementTypeParameters.length != overriddenTypeParameters.length) {
	return null;
	}

	var overriddenType = overriddenElement.type as FunctionTypeImpl;
	if (elementTypeParameters.isEmpty) {
	return overriddenType;
	}

	return replaceTypeParameters(overriddenType, elementTypeParameters);
	}

	static bool _isCovariantSetter(ExecutableElement element) {
	if (element is PropertyAccessorElement) {
	var parameters = element.parameters;
	return parameters.isNotEmpty && parameters[0].isCovariant;
	}
	return false;
	}

	static void _setFieldType(FieldElementImpl field, DartType type) {
	field.type = type;
	field.hasTypeInferred = true;
	}
	}

	/// A class of exception that is not used anywhere else.
	class _CycleException implements Exception {}