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// 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 'dart:math' as math;
import 'package:analyzer/dart/analysis/features.dart';
import 'package:analyzer/dart/ast/ast.dart' show AstNode, ConstructorName;
import 'package:analyzer/dart/ast/token.dart' show Keyword, TokenType;
import 'package:analyzer/dart/element/element.dart';
import 'package:analyzer/dart/element/nullability_suffix.dart';
import 'package:analyzer/dart/element/type.dart';
import 'package:analyzer/dart/element/type_system.dart' as public;
import 'package:analyzer/error/listener.dart' show ErrorReporter;
import 'package:analyzer/src/dart/element/element.dart';
import 'package:analyzer/src/dart/element/member.dart' show TypeParameterMember;
import 'package:analyzer/src/dart/element/type.dart';
import 'package:analyzer/src/dart/element/type_algebra.dart';
import 'package:analyzer/src/error/codes.dart' show HintCode, StrongModeCode;
import 'package:analyzer/src/generated/engine.dart'
show AnalysisContext, AnalysisOptionsImpl;
import 'package:analyzer/src/generated/resolver.dart' show TypeProvider;
import 'package:analyzer/src/generated/utilities_dart.dart' show ParameterKind;
import 'package:meta/meta.dart';
/**
* `void`, `dynamic`, and `Object` are all equivalent. However, this makes
* LUB/GLB indeterministic. Therefore, for the cases of LUB/GLB, we have some
* types which are more top than others.
*
* So, `void` < `Object` < `dynamic` for the purposes of LUB and GLB.
*
* This is expressed by their topiness (higher = more toppy).
*/
int _getTopiness(DartType t) {
// TODO(mfairhurst): switch legacy Top checks to true Top checks
assert(_isLegacyTop(t, orTrueTop: true), 'only Top types have a topiness');
// Highest top
if (t.isVoid) return 3;
if (t.isDynamic) return 2;
if (t.isObject) return 1;
if (t.isDartAsyncFutureOr)
return -3 + _getTopiness((t as InterfaceType).typeArguments[0]);
// Lowest top
assert(false, 'a Top type without a defined topiness');
// Try to ensure that if this happens, its less toppy than an actual Top type.
return -100000;
}
bool _isBottom(DartType t) {
return (t.isBottom &&
(t as TypeImpl).nullabilitySuffix != NullabilitySuffix.question) ||
identical(t, UnknownInferredType.instance);
}
/// Is [t] the bottom of the legacy type hierarchy.
bool _isLegacyBottom(DartType t, {@required bool orTrueBottom}) {
return (t.isBottom &&
(t as TypeImpl).nullabilitySuffix == NullabilitySuffix.question) ||
t.isDartCoreNull ||
(orTrueBottom ? _isBottom(t) : false);
}
/// Is [t] the top of the legacy type hierarch.
bool _isLegacyTop(DartType t, {@required bool orTrueTop}) {
if (t.isDartAsyncFutureOr) {
return _isLegacyTop((t as InterfaceType).typeArguments[0],
orTrueTop: orTrueTop);
}
if (t.isObject &&
(t as TypeImpl).nullabilitySuffix == NullabilitySuffix.none) {
return true;
}
return orTrueTop ? _isTop(t) : false;
}
bool _isTop(DartType t) {
if (t.isDartAsyncFutureOr) {
return _isTop((t as InterfaceType).typeArguments[0]);
}
return t.isDynamic ||
(t.isObject &&
(t as TypeImpl).nullabilitySuffix != NullabilitySuffix.none) ||
t.isVoid ||
identical(t, UnknownInferredType.instance);
}
/**
* A type system that implements the type semantics for Dart 2.0.
*/
class Dart2TypeSystem extends TypeSystem {
/// Track types currently being compared via type parameter bounds so that we
/// can detect recursion.
static Set<TypeComparison> _typeParameterBoundsComparisons =
new HashSet<TypeComparison>();
/**
* False if implicit casts should always be disallowed, otherwise the
* [FeatureSet] will be used.
*
* This affects the behavior of [isAssignableTo].
*/
final bool implicitCasts;
/// A flag indicating whether inference failures are allowed, off by default.
///
/// This option is experimental and subject to change.
final bool strictInference;
final TypeProvider typeProvider;
Dart2TypeSystem(this.typeProvider,
{this.implicitCasts: true, this.strictInference: false});
/// Returns true iff the type [t] accepts function types, and requires an
/// implicit coercion if interface types with a `call` method are passed in.
///
/// This is true for:
/// - all function types
/// - the special type `Function` that is a supertype of all function types
/// - `FutureOr<T>` where T is one of the two cases above.
///
/// Note that this returns false if [t] is a top type such as Object.
bool acceptsFunctionType(DartType t) {
if (t == null) return false;
if (t.isDartAsyncFutureOr) {
return acceptsFunctionType((t as InterfaceType).typeArguments[0]);
}
return t is FunctionType || t.isDartCoreFunction;
}
bool anyParameterType(FunctionType ft, bool predicate(DartType t)) {
return ft.parameters.any((p) => predicate(p.type));
}
/// Given a type t, if t is an interface type with a call method
/// defined, return the function type for the call method, otherwise
/// return null.
FunctionType getCallMethodType(DartType t) {
if (t is InterfaceType) {
return t.lookUpInheritedMethod("call")?.type;
}
return null;
}
/// Computes the greatest lower bound of [type1] and [type2].
DartType getGreatestLowerBound(DartType type1, DartType type2) {
// The greatest lower bound relation is reflexive.
if (identical(type1, type2)) {
return type1;
}
// For any type T, GLB(?, T) == T.
if (identical(type1, UnknownInferredType.instance)) {
return type2;
}
if (identical(type2, UnknownInferredType.instance)) {
return type1;
}
// For the purpose of GLB, we say some Tops are subtypes (less toppy) than
// the others. Return the least toppy.
// TODO(mfairhurst): switch legacy Top checks to true Top checks
if (_isLegacyTop(type1, orTrueTop: true) &&
_isLegacyTop(type2, orTrueTop: true)) {
return _getTopiness(type1) < _getTopiness(type2) ? type1 : type2;
}
// The GLB of top and any type is just that type.
// Also GLB of bottom and any type is bottom.
// TODO(mfairhurst): switch legacy Top checks to true Top checks
// TODO(mfairhurst): switch legacy Bottom checks to true Bottom checks.
if (_isLegacyTop(type1, orTrueTop: true) ||
_isLegacyBottom(type2, orTrueBottom: true)) {
return type2;
}
// TODO(mfairhurst): switch legacy Bottom checks to true Bottom checks
if (_isLegacyTop(type2, orTrueTop: true) ||
_isLegacyBottom(type1, orTrueBottom: true)) {
return type1;
}
// Function types have structural GLB.
if (type1 is FunctionType && type2 is FunctionType) {
return _functionGreatestLowerBound(type1, type2);
}
// Otherwise, the GLB of two types is one of them it if it is a subtype of
// the other.
if (isSubtypeOf(type1, type2)) {
return type1;
}
if (isSubtypeOf(type2, type1)) {
return type2;
}
// No subtype relation, so no known GLB.
// TODO(mfairhurst): implement fully NNBD GLB, and return Never (non-legacy)
return BottomTypeImpl.instanceLegacy;
}
/**
* Given a generic function type `F<T0, T1, ... Tn>` and a context type C,
* infer an instantiation of F, such that `F<S0, S1, ..., Sn>` <: C.
*
* This is similar to [inferGenericFunctionOrType], but the return type is
* also considered as part of the solution.
*
* If this function is called with a [contextType] that is also
* uninstantiated, or a [fnType] that is already instantiated, it will have
* no effect and return `null`.
*/
List<DartType> inferFunctionTypeInstantiation(
FunctionType contextType, FunctionType fnType,
{ErrorReporter errorReporter, AstNode errorNode}) {
if (contextType.typeFormals.isNotEmpty || fnType.typeFormals.isEmpty) {
return const <DartType>[];
}
// Create a TypeSystem that will allow certain type parameters to be
// inferred. It will optimistically assume these type parameters can be
// subtypes (or supertypes) as necessary, and track the constraints that
// are implied by this.
var inferrer = new GenericInferrer(typeProvider, this, fnType.typeFormals);
inferrer.constrainGenericFunctionInContext(fnType, contextType);
// Infer and instantiate the resulting type.
return inferrer.infer(
fnType.typeFormals,
errorReporter: errorReporter,
errorNode: errorNode,
);
}
/// Infers type arguments for a generic type, function, method, or
/// list/map literal, using the downward context type as well as the
/// argument types if available.
///
/// For example, given a function type with generic type parameters, this
/// infers the type parameters from the actual argument types, and returns the
/// instantiated function type.
///
/// Concretely, given a function type with parameter types P0, P1, ... Pn,
/// result type R, and generic type parameters T0, T1, ... Tm, use the
/// argument types A0, A1, ... An to solve for the type parameters.
///
/// For each parameter Pi, we want to ensure that Ai <: Pi. We can do this by
/// running the subtype algorithm, and when we reach a type parameter Tj,
/// recording the lower or upper bound it must satisfy. At the end, all
/// constraints can be combined to determine the type.
///
/// All constraints on each type parameter Tj are tracked, as well as where
/// they originated, so we can issue an error message tracing back to the
/// argument values, type parameter "extends" clause, or the return type
/// context.
List<DartType> inferGenericFunctionOrType({
ClassElement genericClass,
@required List<TypeParameterElement> typeParameters,
@required List<ParameterElement> parameters,
@required DartType declaredReturnType,
@required List<DartType> argumentTypes,
@required DartType contextReturnType,
ErrorReporter errorReporter,
AstNode errorNode,
bool downwards: false,
bool isConst: false,
}) {
if (typeParameters.isEmpty) {
return null;
}
// Create a TypeSystem that will allow certain type parameters to be
// inferred. It will optimistically assume these type parameters can be
// subtypes (or supertypes) as necessary, and track the constraints that
// are implied by this.
var inferrer = new GenericInferrer(typeProvider, this, typeParameters);
if (contextReturnType != null) {
if (isConst) {
contextReturnType = _eliminateTypeVariables(contextReturnType);
}
inferrer.constrainReturnType(declaredReturnType, contextReturnType);
}
for (int i = 0; i < argumentTypes.length; i++) {
// Try to pass each argument to each parameter, recording any type
// parameter bounds that were implied by this assignment.
inferrer.constrainArgument(
argumentTypes[i],
parameters[i].type,
parameters[i].name,
genericClass: genericClass,
);
}
return inferrer.infer(
typeParameters,
errorReporter: errorReporter,
errorNode: errorNode,
downwardsInferPhase: downwards,
);
}
/**
* Given a [DartType] [type], if [type] is an uninstantiated
* parameterized type then instantiate the parameters to their
* bounds. See the issue for the algorithm description.
*
* https://github.com/dart-lang/sdk/issues/27526#issuecomment-260021397
*
* TODO(scheglov) Move this method to elements for classes, typedefs,
* and generic functions; compute lazily and cache.
*/
DartType instantiateToBounds(DartType type,
{List<bool> hasError, Map<TypeParameterElement, DartType> knownTypes}) {
List<TypeParameterElement> typeFormals = typeFormalsAsElements(type);
List<DartType> arguments = instantiateTypeFormalsToBounds(typeFormals,
hasError: hasError, knownTypes: knownTypes);
if (arguments == null) {
return type;
}
return instantiateType(type, arguments);
}
/**
* Given uninstantiated [typeFormals], instantiate them to their bounds.
* See the issue for the algorithm description.
*
* https://github.com/dart-lang/sdk/issues/27526#issuecomment-260021397
*/
List<DartType> instantiateTypeFormalsToBounds(
List<TypeParameterElement> typeFormals,
{List<bool> hasError,
Map<TypeParameterElement, DartType> knownTypes}) {
int count = typeFormals.length;
if (count == 0) {
return const <DartType>[];
}
Set<TypeParameterElement> all = new Set<TypeParameterElement>();
// all ground
Map<TypeParameterElement, DartType> defaults = knownTypes ?? {};
// not ground
Map<TypeParameterElement, DartType> partials = {};
for (TypeParameterElement typeParameter in typeFormals) {
all.add(typeParameter);
if (!defaults.containsKey(typeParameter)) {
if (typeParameter.bound == null) {
defaults[typeParameter] = DynamicTypeImpl.instance;
} else {
partials[typeParameter] = typeParameter.bound;
}
}
}
List<TypeParameterElement> getFreeParameters(DartType rootType) {
List<TypeParameterElement> parameters;
Set<DartType> visitedTypes = new HashSet<DartType>();
void appendParameters(DartType type) {
if (type == null) {
return;
}
if (visitedTypes.contains(type)) {
return;
}
visitedTypes.add(type);
if (type is TypeParameterType) {
var element = type.element;
if (all.contains(element)) {
parameters ??= <TypeParameterElement>[];
parameters.add(element);
}
} else {
if (type is FunctionType) {
appendParameters(type.returnType);
type.parameters.map((p) => p.type).forEach(appendParameters);
} else if (type is InterfaceType) {
type.typeArguments.forEach(appendParameters);
}
}
}
appendParameters(rootType);
return parameters;
}
bool hasProgress = true;
while (hasProgress) {
hasProgress = false;
for (TypeParameterElement parameter in partials.keys) {
DartType value = partials[parameter];
List<TypeParameterElement> freeParameters = getFreeParameters(value);
if (freeParameters == null) {
defaults[parameter] = value;
partials.remove(parameter);
hasProgress = true;
break;
} else if (freeParameters.every(defaults.containsKey)) {
defaults[parameter] =
Substitution.fromMap(defaults).substituteType(value);
partials.remove(parameter);
hasProgress = true;
break;
}
}
}
// If we stopped making progress, and not all types are ground,
// then the whole type is malbounded and an error should be reported
// if errors are requested, and a partially completed type should
// be returned.
if (partials.isNotEmpty) {
if (hasError != null) {
hasError[0] = true;
}
var domain = defaults.keys.toList();
var range = defaults.values.toList();
// Build a substitution Phi mapping each uncompleted type variable to
// dynamic, and each completed type variable to its default.
for (TypeParameterElement parameter in partials.keys) {
domain.add(parameter);
range.add(DynamicTypeImpl.instance);
}
// Set the default for an uncompleted type variable (T extends B)
// to be Phi(B)
for (TypeParameterElement parameter in partials.keys) {
defaults[parameter] = Substitution.fromPairs(domain, range)
.substituteType(partials[parameter]);
}
}
List<DartType> orderedArguments =
typeFormals.map((p) => defaults[p]).toList();
return orderedArguments;
}
/// Given the type defining [element], instantiate its type formals to
/// their bounds.
List<DartType> instantiateTypeFormalsToBounds2(Element element) {
List<TypeParameterElement> typeParameters;
if (element is ClassElement) {
typeParameters = element.typeParameters;
} else if (element is GenericTypeAliasElement) {
typeParameters = element.typeParameters;
} else {
throw StateError('Unexpected: $element');
}
if (typeParameters.isEmpty) {
return const <DartType>[];
}
return typeParameters
.map((p) => (p as TypeParameterElementImpl).defaultType)
.toList();
}
@override
bool isAssignableTo(DartType fromType, DartType toType,
{FeatureSet featureSet}) {
// An actual subtype
if (isSubtypeOf(fromType, toType)) {
return true;
}
// A call method tearoff
if (fromType is InterfaceType && acceptsFunctionType(toType)) {
var callMethodType = getCallMethodType(fromType);
if (callMethodType != null &&
isAssignableTo(callMethodType, toType, featureSet: featureSet)) {
return true;
}
}
// First make sure --no-implicit-casts disables all downcasts, including
// dynamic casts.
if (!implicitCasts) {
return false;
}
// Now handle NNBD default behavior, where we disable non-dynamic downcasts.
if (featureSet != null && featureSet.isEnabled(Feature.non_nullable)) {
return fromType.isDynamic;
}
// Don't allow implicit downcasts between function types
// and call method objects, as these will almost always fail.
if (fromType is FunctionType && getCallMethodType(toType) != null) {
return false;
}
// Don't allow a non-generic function where a generic one is expected. The
// former wouldn't know how to handle type arguments being passed to it.
// TODO(rnystrom): This same check also exists in FunctionTypeImpl.relate()
// but we don't always reliably go through that code path. This should be
// cleaned up to avoid the redundancy.
if (fromType is FunctionType &&
toType is FunctionType &&
fromType.typeFormals.isEmpty &&
toType.typeFormals.isNotEmpty) {
return false;
}
// If the subtype relation goes the other way, allow the implicit downcast.
if (isSubtypeOf(toType, fromType)) {
// TODO(leafp,jmesserly): we emit warnings/hints for these in
// src/task/strong/checker.dart, which is a bit inconsistent. That
// code should be handled into places that use isAssignableTo, such as
// ErrorVerifier.
return true;
}
return false;
}
bool isGroundType(DartType t) {
// TODO(leafp): Revisit this.
if (t is TypeParameterType) {
return false;
}
// TODO(mfairhurst): switch legacy Top checks to true Top checks
if (_isLegacyTop(t, orTrueTop: true)) {
return true;
}
if (t is FunctionType) {
// TODO(mfairhurst): switch legacy Top checks to true Top checks
// TODO(mfairhurst): switch legacy Bottom checks to true Bottom checks
if (!_isLegacyTop(t.returnType, orTrueTop: true) ||
anyParameterType(
t, (pt) => !_isLegacyBottom(pt, orTrueBottom: true))) {
return false;
} else {
return true;
}
}
if (t is InterfaceType) {
List<DartType> typeArguments = t.typeArguments;
for (DartType typeArgument in typeArguments) {
// TODO(mfairhurst): switch legacy Top checks to true Top checks
if (!_isLegacyTop(typeArgument, orTrueTop: true)) return false;
}
return true;
}
// We should not see any other type aside from malformed code.
return false;
}
@override
bool isMoreSpecificThan(DartType t1, DartType t2) => isSubtypeOf(t1, t2);
@override
bool isOverrideSubtypeOf(FunctionType f1, FunctionType f2) {
return FunctionTypeImpl.relate(f1, f2, isSubtypeOf,
parameterRelation: isOverrideSubtypeOfParameter,
// Type parameter bounds are invariant.
boundsRelation: (t1, t2, p1, p2) =>
isSubtypeOf(t1, t2) && isSubtypeOf(t2, t1));
}
/// Check that parameter [p2] is a subtype of [p1], given that we are
/// checking `f1 <: f2` where `p1` is a parameter of `f1` and `p2` is a
/// parameter of `f2`.
///
/// Parameters are contravariant, so we must check `p2 <: p1` to
/// determine if `f1 <: f2`. This is used by [isOverrideSubtypeOf].
bool isOverrideSubtypeOfParameter(ParameterElement p1, ParameterElement p2) {
return isSubtypeOf(p2.type, p1.type) ||
p1.isCovariant && isSubtypeOf(p1.type, p2.type);
}
/// Check if [_t1] is a subtype of [_t2].
///
/// Partially updated to reflect
/// https://github.com/dart-lang/language/blob/da5adf7eb5f2d479069d8660ed7ca7b230098510/resources/type-system/subtyping.md
///
/// However, it does not correlate 1:1 and does not specialize Null vs Never
/// cases. It also is not guaranteed to be exactly accurate vs the "spec"
/// because it has slightly different order of operations. These should be
/// brought in line or proven equivalent.
@override
bool isSubtypeOf(DartType _t1, DartType _t2) {
var t1 = _t1 as TypeImpl;
var t2 = _t2 as TypeImpl;
// Convert Null to Never? so that NullabilitySuffix can handle more cases.
if (t1.isDartCoreNull) {
t1 = BottomTypeImpl.instanceNullable;
}
if (t2.isDartCoreNull) {
t2 = BottomTypeImpl.instanceNullable;
}
if (identical(t1, t2)) {
return true;
}
// The types are void, dynamic, bottom, interface types, function types,
// FutureOr<T> and type parameters.
//
// We proceed by eliminating these different classes from consideration.
// `?` is treated as a top and a bottom type during inference.
if (identical(t1, UnknownInferredType.instance) ||
identical(t2, UnknownInferredType.instance)) {
return true;
}
// Trivial top case.
if (_isTop(t2)) {
return true;
}
// Legacy top case. Must be done now to find Object* <: Object.
// TODO: handle false positives like FutureOr<Object?>* and T* extends int?.
if (t1.nullabilitySuffix == NullabilitySuffix.star &&
_isLegacyTop(t2, orTrueTop: false)) {
return true;
}
// Having excluded RHS top, this now must be false.
if (_isTop(t1)) {
return false;
}
// Handle T1? <: T2
if (t1.nullabilitySuffix == NullabilitySuffix.question) {
if (t2.nullabilitySuffix == NullabilitySuffix.none) {
// If T2 is not FutureOr<S2>, then subtype is false.
if (!t2.isDartAsyncFutureOr) {
return false;
}
// T1? <: FutureOr<S2> is true if S2 is nullable.
final s2 = (t2 as InterfaceType).typeArguments[0];
if (!isNullable(s2)) {
return false;
}
}
}
// Legacy bottom cases
if (_isLegacyBottom(t1, orTrueBottom: true)) {
return true;
}
if (_isLegacyBottom(t2, orTrueBottom: true)) {
return false;
}
// Handle FutureOr<T> union type.
if (t1 is InterfaceTypeImpl && t1.isDartAsyncFutureOr) {
var t1TypeArg = t1.typeArguments[0];
if (t2 is InterfaceTypeImpl && t2.isDartAsyncFutureOr) {
var t2TypeArg = t2.typeArguments[0];
// FutureOr<A> <: FutureOr<B> iff A <: B
return isSubtypeOf(t1TypeArg, t2TypeArg);
}
// given t1 is Future<A> | A, then:
// (Future<A> | A) <: t2 iff Future<A> <: t2 and A <: t2.
var t1Future = typeProvider.futureType2(t1TypeArg);
return isSubtypeOf(t1Future, t2) && isSubtypeOf(t1TypeArg, t2);
}
if (t2 is InterfaceTypeImpl && t2.isDartAsyncFutureOr) {
// given t2 is Future<A> | A, then:
// t1 <: (Future<A> | A) iff t1 <: Future<A> or t1 <: A
var t2TypeArg = t2.typeArguments[0];
var t2Future = typeProvider.futureType2(t2TypeArg);
return isSubtypeOf(t1, t2Future) || isSubtypeOf(t1, t2TypeArg);
}
// S <: T where S is a type variable
// T is not dynamic or object (handled above)
// True if T == S
// Or true if bound of S is S' and S' <: T
if (t1 is TypeParameterTypeImpl) {
if (t2 is TypeParameterTypeImpl &&
t1.definition == t2.definition &&
_typeParameterBoundsSubtype(t1.bound, t2.bound, true)) {
return true;
}
DartType bound = t1.element.bound;
return bound == null
? false
: _typeParameterBoundsSubtype(bound, t2, false);
}
if (t2 is TypeParameterType) {
return false;
}
// We've eliminated void, dynamic, bottom, type parameters, FutureOr,
// nullable, and legacy nullable types. The only cases are the combinations
// of interface type and function type.
// A function type can only subtype an interface type if
// the interface type is Function
if (t1 is FunctionType && t2 is InterfaceType) {
return t2.isDartCoreFunction;
}
if (t1 is InterfaceType && t2 is FunctionType) return false;
// Two interface types
if (t1 is InterfaceTypeImpl && t2 is InterfaceTypeImpl) {
return _isInterfaceSubtypeOf(t1, t2, null);
}
return _isFunctionSubtypeOf(t1 as FunctionType, t2 as FunctionType);
}
/// Given a [type] T that may have an unknown type `?`, returns a type
/// R such that R <: T for any type substituted for `?`.
///
/// In practice this will always replace `?` with either bottom or top
/// (dynamic), depending on the position of `?`.
///
/// This implements the operation the spec calls "least closure", or
/// sometimes "least closure with respect to `?`".
DartType lowerBoundForType(DartType type) {
return _substituteForUnknownType(type, lowerBound: true);
}
@override
DartType refineBinaryExpressionType(DartType leftType, TokenType operator,
DartType rightType, DartType currentType, FeatureSet featureSet) {
if (leftType is TypeParameterType && leftType.bound.isDartCoreNum) {
if (rightType == leftType || rightType.isDartCoreInt) {
if (operator == TokenType.PLUS ||
operator == TokenType.MINUS ||
operator == TokenType.STAR ||
operator == TokenType.PLUS_EQ ||
operator == TokenType.MINUS_EQ ||
operator == TokenType.STAR_EQ) {
if (featureSet.isEnabled(Feature.non_nullable)) {
return promoteToNonNull(leftType as TypeImpl);
}
return leftType;
}
}
if (rightType.isDartCoreDouble) {
if (operator == TokenType.PLUS ||
operator == TokenType.MINUS ||
operator == TokenType.STAR ||
operator == TokenType.SLASH) {
InterfaceTypeImpl doubleType = typeProvider.doubleType;
if (featureSet.isEnabled(Feature.non_nullable)) {
return promoteToNonNull(doubleType);
}
return doubleType;
}
}
return currentType;
}
return super.refineBinaryExpressionType(
leftType, operator, rightType, currentType, featureSet);
}
@override
DartType tryPromoteToType(DartType to, DartType from) {
// Allow promoting to a subtype, for example:
//
// f(Base b) {
// if (b is SubTypeOfBase) {
// // promote `b` to SubTypeOfBase for this block
// }
// }
//
// This allows the variable to be used wherever the supertype (here `Base`)
// is expected, while gaining a more precise type.
if (isSubtypeOf(to, from)) {
return to;
}
// For a type parameter `T extends U`, allow promoting the upper bound
// `U` to `S` where `S <: U`, yielding a type parameter `T extends S`.
if (from is TypeParameterTypeImpl) {
if (isSubtypeOf(to, from.bound ?? DynamicTypeImpl.instance)) {
var newElement = TypeParameterMember(from.element, null, to);
return newElement.instantiate(
nullabilitySuffix: from.nullabilitySuffix,
);
}
}
return null;
}
/// Given a [type] T that may have an unknown type `?`, returns a type
/// R such that T <: R for any type substituted for `?`.
///
/// In practice this will always replace `?` with either bottom or top
/// (dynamic), depending on the position of `?`.
///
/// This implements the operation the spec calls "greatest closure", or
/// sometimes "greatest closure with respect to `?`".
DartType upperBoundForType(DartType type) {
return _substituteForUnknownType(type);
}
/**
* Eliminates type variables from the context [type], replacing them with
* `Null` or `Object` as appropriate.
*
* For example in `List<T> list = const []`, the context type for inferring
* the list should be changed from `List<T>` to `List<Null>` so the constant
* doesn't depend on the type variables `T` (because it can't be canonicalized
* at compile time, as `T` is unknown).
*
* Conceptually this is similar to the "least closure", except instead of
* eliminating `?` ([UnknownInferredType]) it eliminates all type variables
* ([TypeParameterType]).
*
* The equivalent CFE code can be found in the `TypeVariableEliminator` class.
*/
DartType _eliminateTypeVariables(DartType type) {
return _substituteType(type, true, (type, lowerBound) {
if (type is TypeParameterType) {
return lowerBound ? typeProvider.nullType : typeProvider.objectType;
}
return type;
});
}
/**
* Compute the greatest lower bound of function types [f] and [g].
*
* The spec rules for GLB on function types, informally, are pretty simple:
*
* - If a parameter is required in both, it stays required.
*
* - If a positional parameter is optional or missing in one, it becomes
* optional.
*
* - Named parameters are unioned together.
*
* - For any parameter that exists in both functions, use the LUB of them as
* the resulting parameter type.
*
* - Use the GLB of their return types.
*/
DartType _functionGreatestLowerBound(FunctionType f, FunctionType g) {
// Calculate the LUB of each corresponding pair of parameters.
List<ParameterElement> parameters = [];
bool hasPositional = false;
bool hasNamed = false;
addParameter(
String name, DartType fType, DartType gType, ParameterKind kind) {
DartType paramType;
if (fType != null && gType != null) {
// If both functions have this parameter, include both of their types.
paramType = getLeastUpperBound(fType, gType);
} else {
paramType = fType ?? gType;
}
parameters.add(new ParameterElementImpl.synthetic(name, paramType, kind));
}
// TODO(rnystrom): Right now, this assumes f and g do not have any type
// parameters. Revisit that in the presence of generic methods.
List<DartType> fRequired = f.normalParameterTypes;
List<DartType> gRequired = g.normalParameterTypes;
// We need some parameter names for in the synthesized function type.
List<String> fRequiredNames = f.normalParameterNames;
List<String> gRequiredNames = g.normalParameterNames;
// Parameters that are required in both functions are required in the
// result.
int requiredCount = math.min(fRequired.length, gRequired.length);
for (int i = 0; i < requiredCount; i++) {
addParameter(fRequiredNames[i], fRequired[i], gRequired[i],
ParameterKind.REQUIRED);
}
// Parameters that are optional or missing in either end up optional.
List<DartType> fPositional = f.optionalParameterTypes;
List<DartType> gPositional = g.optionalParameterTypes;
List<String> fPositionalNames = f.optionalParameterNames;
List<String> gPositionalNames = g.optionalParameterNames;
int totalPositional = math.max(fRequired.length + fPositional.length,
gRequired.length + gPositional.length);
for (int i = requiredCount; i < totalPositional; i++) {
// Find the corresponding positional parameters (required or optional) at
// this index, if there is one.
DartType fType;
String fName;
if (i < fRequired.length) {
fType = fRequired[i];
fName = fRequiredNames[i];
} else if (i < fRequired.length + fPositional.length) {
fType = fPositional[i - fRequired.length];
fName = fPositionalNames[i - fRequired.length];
}
DartType gType;
String gName;
if (i < gRequired.length) {
gType = gRequired[i];
gName = gRequiredNames[i];
} else if (i < gRequired.length + gPositional.length) {
gType = gPositional[i - gRequired.length];
gName = gPositionalNames[i - gRequired.length];
}
// The loop should not let us go past both f and g's positional params.
assert(fType != null || gType != null);
addParameter(fName ?? gName, fType, gType, ParameterKind.POSITIONAL);
hasPositional = true;
}
// Union the named parameters together.
// TODO(brianwilkerson) Handle the fact that named parameters can now be
// required.
Map<String, DartType> fNamed = f.namedParameterTypes;
Map<String, DartType> gNamed = g.namedParameterTypes;
for (String name in fNamed.keys.toSet()..addAll(gNamed.keys)) {
addParameter(name, fNamed[name], gNamed[name], ParameterKind.NAMED);
hasNamed = true;
}
// Edge case. Dart does not support functions with both optional positional
// and named parameters. If we would synthesize that, give up.
if (hasPositional && hasNamed) return typeProvider.bottomType;
// Calculate the GLB of the return type.
DartType returnType = getGreatestLowerBound(f.returnType, g.returnType);
return new FunctionElementImpl.synthetic(parameters, returnType).type;
}
@override
DartType _functionParameterBound(DartType f, DartType g) =>
getGreatestLowerBound(f, g);
@override
DartType _interfaceLeastUpperBound(InterfaceType type1, InterfaceType type2) {
var helper = InterfaceLeastUpperBoundHelper(this);
return helper.compute(type1, type2);
}
/// Check that [f1] is a subtype of [f2].
bool _isFunctionSubtypeOf(FunctionType f1, FunctionType f2) {
return FunctionTypeImpl.relate(f1, f2, isSubtypeOf,
parameterRelation: (p1, p2) => isSubtypeOf(p2.type, p1.type),
// Type parameter bounds are invariant.
boundsRelation: (t1, t2, p1, p2) =>
isSubtypeOf(t1, t2) && isSubtypeOf(t2, t1));
}
bool _isInterfaceSubtypeOf(
InterfaceType i1, InterfaceType i2, Set<ClassElement> visitedTypes) {
// Note: we should never reach `_isInterfaceSubtypeOf` with `i2 == Object`,
// because top types are eliminated before `isSubtypeOf` calls this.
if (identical(i1, i2) || i2.isObject) {
return true;
}
// Object cannot subtype anything but itself (handled above).
if (i1.isObject) {
return false;
}
ClassElement i1Element = i1.element;
if (i1Element == i2.element) {
List<DartType> tArgs1 = i1.typeArguments;
List<DartType> tArgs2 = i2.typeArguments;
assert(tArgs1.length == tArgs2.length);
for (int i = 0; i < tArgs1.length; i++) {
DartType t1 = tArgs1[i];
DartType t2 = tArgs2[i];
if (!isSubtypeOf(t1, t2)) {
return false;
}
}
return true;
}
// Classes types cannot subtype `Function` or vice versa.
if (i1.isDartCoreFunction || i2.isDartCoreFunction) {
return false;
}
// Guard against loops in the class hierarchy.
//
// Dart 2 does not allow multiple implementations of the same generic type
// with different type arguments. So we can track just the class element
// to find cycles, rather than tracking the full interface type.
visitedTypes ??= new HashSet<ClassElement>();
if (!visitedTypes.add(i1Element)) return false;
InterfaceType superclass = i1.superclass;
if (superclass != null &&
_isInterfaceSubtypeOf(superclass, i2, visitedTypes)) {
return true;
}
for (final parent in i1.interfaces) {
if (_isInterfaceSubtypeOf(parent, i2, visitedTypes)) {
return true;
}
}
for (final parent in i1.mixins) {
if (_isInterfaceSubtypeOf(parent, i2, visitedTypes)) {
return true;
}
}
if (i1Element.isMixin) {
for (final parent in i1.superclassConstraints) {
if (_isInterfaceSubtypeOf(parent, i2, visitedTypes)) {
return true;
}
}
}
return false;
}
/**
* Returns the greatest or least closure of [type], which replaces `?`
* ([UnknownInferredType]) with `dynamic` or `Null` as appropriate.
*
* If [lowerBound] is true, this will return the "least closure", otherwise
* it returns the "greatest closure".
*/
DartType _substituteForUnknownType(DartType type, {bool lowerBound: false}) {
return _substituteType(type, lowerBound, (type, lowerBound) {
if (identical(type, UnknownInferredType.instance)) {
return lowerBound ? typeProvider.nullType : typeProvider.dynamicType;
}
return type;
});
}
/**
* Apply the [visitType] substitution to [type], using the result value if
* different, otherwise recursively apply the substitution.
*
* This method is used for substituting `?` ([UnknownInferredType]) with its
* greatest/least closure, and for eliminating type parameters for inference
* of `const` objects.
*
* See also [_eliminateTypeVariables] and [_substituteForUnknownType].
*/
DartType _substituteType(DartType type, bool lowerBound,
DartType Function(DartType, bool) visitType) {
// Apply the substitution to this type, and return the result if different.
var newType = visitType(type, lowerBound);
if (!identical(newType, type)) {
return newType;
}
if (type is InterfaceTypeImpl) {
// Generic types are covariant, so keep the constraint direction.
var newTypeArgs = _transformList(
type.typeArguments, (t) => _substituteType(t, lowerBound, visitType));
if (identical(type.typeArguments, newTypeArgs)) return type;
return new InterfaceTypeImpl(type.element,
prunedTypedefs: type.prunedTypedefs,
nullabilitySuffix: type.nullabilitySuffix)
..typeArguments = newTypeArgs;
}
if (type is FunctionType) {
var parameters = type.parameters;
var returnType = type.returnType;
var newParameters = _transformList(parameters, (ParameterElement p) {
// Parameters are contravariant, so flip the constraint direction.
var newType = _substituteType(p.type, !lowerBound, visitType);
return new ParameterElementImpl.synthetic(
p.name,
newType,
// ignore: deprecated_member_use_from_same_package
p.parameterKind);
});
// Return type is covariant.
var newReturnType = _substituteType(returnType, lowerBound, visitType);
if (identical(parameters, newParameters) &&
identical(returnType, newReturnType)) {
return type;
}
return new FunctionTypeImpl.synthetic(
newReturnType,
type.typeFormals,
newParameters,
nullabilitySuffix: (type as TypeImpl).nullabilitySuffix,
);
}
return type;
}
bool _typeParameterBoundsSubtype(
DartType t1, DartType t2, bool recursionValue) {
TypeComparison comparison = TypeComparison(t1, t2);
if (_typeParameterBoundsComparisons.contains(comparison)) {
return recursionValue;
}
_typeParameterBoundsComparisons.add(comparison);
try {
return isSubtypeOf(t1, t2);
} finally {
_typeParameterBoundsComparisons.remove(comparison);
}
}
/**
* This currently just implements a simple least upper bound to
* handle some common cases. It also avoids some termination issues
* with the naive spec algorithm. The least upper bound of two types
* (at least one of which is a type parameter) is computed here as:
* 1. If either type is a supertype of the other, return it.
* 2. If the first type is a type parameter, replace it with its bound,
* with recursive occurrences of itself replaced with Object.
* The second part of this should ensure termination. Informally,
* each type variable instantiation in one of the arguments to the
* least upper bound algorithm now strictly reduces the number
* of bound variables in scope in that argument position.
* 3. If the second type is a type parameter, do the symmetric operation
* to #2.
*
* It's not immediately obvious why this is symmetric in the case that both
* of them are type parameters. For #1, symmetry holds since subtype
* is antisymmetric. For #2, it's clearly not symmetric if upper bounds of
* bottom are allowed. Ignoring this (for various reasons, not least
* of which that there's no way to write it), there's an informal
* argument (that might even be right) that you will always either
* end up expanding both of them or else returning the same result no matter
* which order you expand them in. A key observation is that
* identical(expand(type1), type2) => subtype(type1, type2)
* and hence the contra-positive.
*
* TODO(leafp): Think this through and figure out what's the right
* definition. Be careful about termination.
*
* I suspect in general a reasonable algorithm is to expand the innermost
* type variable first. Alternatively, you could probably choose to treat
* it as just an instance of the interface type upper bound problem, with
* the "inheritance" chain extended by the bounds placed on the variables.
*/
@override
DartType _typeParameterLeastUpperBound(DartType type1, DartType type2) {
if (isSubtypeOf(type1, type2)) {
return type2;
}
if (isSubtypeOf(type2, type1)) {
return type1;
}
if (type1 is TypeParameterType) {
type1 = type1
.resolveToBound(typeProvider.objectType)
.substitute2([typeProvider.objectType], [type1]);
return getLeastUpperBound(type1, type2);
}
// We should only be called when at least one of the types is a
// TypeParameterType
type2 = type2
.resolveToBound(typeProvider.objectType)
.substitute2([typeProvider.objectType], [type2]);
return getLeastUpperBound(type1, type2);
}
static List<T> _transformList<T>(List<T> list, T f(T t)) {
List<T> newList;
for (var i = 0; i < list.length; i++) {
var item = list[i];
var newItem = f(item);
if (!identical(item, newItem)) {
newList ??= new List.from(list);
newList[i] = newItem;
}
}
return newList ?? list;
}
}
/// Tracks upper and lower type bounds for a set of type parameters.
///
/// This class is used by calling [isSubtypeOf]. When it encounters one of
/// the type parameters it is inferring, it will record the constraint, and
/// optimistically assume the constraint will be satisfied.
///
/// For example if we are inferring type parameter A, and we ask if
/// `A <: num`, this will record that A must be a subytpe of `num`. It also
/// handles cases when A appears as part of the structure of another type, for
/// example `Iterable<A> <: Iterable<num>` would infer the same constraint
/// (due to covariant generic types) as would `() -> A <: () -> num`. In
/// contrast `(A) -> void <: (num) -> void`.
///
/// Once the lower/upper bounds are determined, [infer] should be called to
/// finish the inference. It will instantiate a generic function type with the
/// inferred types for each type parameter.
///
/// It can also optionally compute a partial solution, in case some of the type
/// parameters could not be inferred (because the constraints cannot be
/// satisfied), or bail on the inference when this happens.
///
/// As currently designed, an instance of this class should only be used to
/// infer a single call and discarded immediately afterwards.
class GenericInferrer {
final Dart2TypeSystem _typeSystem;
final TypeProvider typeProvider;
final Map<TypeParameterElement, List<_TypeConstraint>> constraints = {};
/// Buffer recording constraints recorded while performing a recursive call to
/// [_matchSubtypeOf] that might fail, so that any constraints recorded during
/// the failed match can be rewound.
final _undoBuffer = <_TypeConstraint>[];
GenericInferrer(this.typeProvider, this._typeSystem,
Iterable<TypeParameterElement> typeFormals) {
for (var formal in typeFormals) {
constraints[formal] = [];
}
}
/// Apply an argument constraint, which asserts that the [argument] staticType
/// is a subtype of the [parameterType].
void constrainArgument(
DartType argumentType, DartType parameterType, String parameterName,
{ClassElement genericClass}) {
var origin = new _TypeConstraintFromArgument(
argumentType, parameterType, parameterName,
genericClass: genericClass);
tryMatchSubtypeOf(argumentType, parameterType, origin, covariant: false);
}
/// Constrain a universal function type [fnType] used in a context
/// [contextType].
void constrainGenericFunctionInContext(
FunctionType fnType, DartType contextType) {
var origin = new _TypeConstraintFromFunctionContext(fnType, contextType);
// Since we're trying to infer the instantiation, we want to ignore type
// formals as we check the parameters and return type.
var inferFnType =
fnType.instantiate(TypeParameterTypeImpl.getTypes(fnType.typeFormals));
tryMatchSubtypeOf(inferFnType, contextType, origin, covariant: true);
}
/// Apply a return type constraint, which asserts that the [declaredType]
/// is a subtype of the [contextType].
void constrainReturnType(DartType declaredType, DartType contextType) {
var origin = new _TypeConstraintFromReturnType(declaredType, contextType);
tryMatchSubtypeOf(declaredType, contextType, origin, covariant: true);
}
/// Given the constraints that were given by calling [constrainArgument] and
/// [constrainReturnType], find the type arguments for the [typeFormals] that
/// satisfies these constraints.
///
/// If [downwardsInferPhase] is set, we are in the first pass of inference,
/// pushing context types down. At that point we are allowed to push down
/// `?` to precisely represent an unknown type. If [downwardsInferPhase] is
/// false, we are on our final inference pass, have all available information
/// including argument types, and must not conclude `?` for any type formal.
List<DartType> infer(List<TypeParameterElement> typeFormals,
{bool considerExtendsClause: true,
ErrorReporter errorReporter,
AstNode errorNode,
bool failAtError: false,
bool downwardsInferPhase: false}) {
// Initialize the inferred type array.
//
// In the downwards phase, they all start as `?` to offer reasonable
// degradation for f-bounded type parameters.
var inferredTypes = new List<DartType>.filled(
typeFormals.length, UnknownInferredType.instance);
var _inferTypeParameter = downwardsInferPhase
? _inferTypeParameterFromContext
: _inferTypeParameterFromAll;
for (int i = 0; i < typeFormals.length; i++) {
TypeParameterElement typeParam = typeFormals[i];
_TypeConstraint extendsClause;
if (considerExtendsClause && typeParam.bound != null) {
extendsClause = new _TypeConstraint.fromExtends(
typeParam,
Substitution.fromPairs(typeFormals, inferredTypes)
.substituteType(typeParam.bound));
}
inferredTypes[i] =
_inferTypeParameter(constraints[typeParam], extendsClause);
}
// If the downwards infer phase has failed, we'll catch this in the upwards
// phase later on.
if (downwardsInferPhase) {
return inferredTypes;
}
// Check the inferred types against all of the constraints.
var knownTypes = <TypeParameterElement, DartType>{};
for (int i = 0; i < typeFormals.length; i++) {
TypeParameterElement typeParam = typeFormals[i];
var constraints = this.constraints[typeParam];
var typeParamBound = typeParam.bound != null
? Substitution.fromPairs(typeFormals, inferredTypes)
.substituteType(typeParam.bound)
: typeProvider.dynamicType;
var inferred = inferredTypes[i];
bool success =
constraints.every((c) => c.isSatisifedBy(_typeSystem, inferred));
if (success && !typeParamBound.isDynamic) {
// If everything else succeeded, check the `extends` constraint.
var extendsConstraint =
new _TypeConstraint.fromExtends(typeParam, typeParamBound);
constraints.add(extendsConstraint);
success = extendsConstraint.isSatisifedBy(_typeSystem, inferred);
}
if (!success) {
if (failAtError) return null;
errorReporter?.reportErrorForNode(
StrongModeCode.COULD_NOT_INFER,
errorNode,
[typeParam.name, _formatError(typeParam, inferred, constraints)]);
// Heuristic: even if we failed, keep the erroneous type.
// It should satisfy at least some of the constraints (e.g. the return
// context). If we fall back to instantiateToBounds, we'll typically get
// more errors (e.g. because `dynamic` is the most common bound).
}
if (inferred is FunctionType && inferred.typeFormals.isNotEmpty) {
if (failAtError) return null;
errorReporter
?.reportErrorForNode(StrongModeCode.COULD_NOT_INFER, errorNode, [
typeParam.name,
' Inferred candidate type $inferred has type parameters'
' ${(inferred as FunctionType).typeFormals}, but a function with'
' type parameters cannot be used as a type argument.'
]);
// Heuristic: Using a generic function type as a bound makes subtyping
// undecidable. Therefore, we cannot keep [inferred] unless we wish to
// generate bogus subtyping errors. Instead generate plain [Function],
// which is the most general function type.
inferred = typeProvider.functionType;
}
if (UnknownInferredType.isKnown(inferred)) {
knownTypes[typeParam] = inferred;
} else if (_typeSystem.strictInference) {
// [typeParam] could not be inferred. A result will still be returned
// by [infer], with [typeParam] filled in as its bounds. This is
// considered a failure of inference, under the "strict-inference"
// mode.
if (errorNode is ConstructorName) {
String constructorName = '${errorNode.type}.${errorNode.name}';
errorReporter?.reportTypeErrorForNode(
HintCode.INFERENCE_FAILURE_ON_INSTANCE_CREATION,
errorNode,
[constructorName]);
}
// TODO(srawlins): More inference failure cases, like functions, and
// function expressions.
}
}
// Use instantiate to bounds to finish things off.
var hasError = new List<bool>.filled(typeFormals.length, false);
var result = _typeSystem.instantiateTypeFormalsToBounds(typeFormals,
hasError: hasError, knownTypes: knownTypes);
// Report any errors from instantiateToBounds.
for (int i = 0; i < hasError.length; i++) {
if (hasError[i]) {
if (failAtError) return null;
TypeParameterElement typeParam = typeFormals[i];
var typeParamBound = Substitution.fromPairs(typeFormals, inferredTypes)
.substituteType(typeParam.bound ?? typeProvider.objectType);
// TODO(jmesserly): improve this error message.
errorReporter
?.reportErrorForNode(StrongModeCode.COULD_NOT_INFER, errorNode, [
typeParam.name,
"\nRecursive bound cannot be instantiated: '$typeParamBound'."
"\nConsider passing explicit type argument(s) "
"to the generic.\n\n'"
]);
}
}
return result;
}
/// Tries to make [i1] a subtype of [i2] and accumulate constraints as needed.
///
/// The return value indicates whether the match was successful. If it was
/// unsuccessful, any constraints that were accumulated during the match
/// attempt have been rewound (see [_rewindConstraints]).
bool tryMatchSubtypeOf(DartType t1, DartType t2, _TypeConstraintOrigin origin,
{bool covariant}) {
int previousRewindBufferLength = _undoBuffer.length;
bool success = _matchSubtypeOf(t1, t2, null, origin, covariant: covariant);
if (!success) {
_rewindConstraints(previousRewindBufferLength);
}
return success;
}
/// Choose the bound that was implied by the return type, if any.
///
/// Which bound this is depends on what positions the type parameter
/// appears in. If the type only appears only in a contravariant position,
/// we will choose the lower bound instead.
///
/// For example given:
///
/// Func1<T, bool> makeComparer<T>(T x) => (T y) => x() == y;
///
/// main() {
/// Func1<num, bool> t = makeComparer/* infer <num> */(42);
/// print(t(42.0)); /// false, no error.
/// }
///
/// The constraints we collect are:
///
/// * `num <: T`
/// * `int <: T`
///
/// ... and no upper bound. Therefore the lower bound is the best choice.
DartType _chooseTypeFromConstraints(Iterable<_TypeConstraint> constraints,
{bool toKnownType: false}) {
DartType lower = UnknownInferredType.instance;
DartType upper = UnknownInferredType.instance;
for (var constraint in constraints) {
// Given constraints:
//
// L1 <: T <: U1
// L2 <: T <: U2
//
// These can be combined to produce:
//
// LUB(L1, L2) <: T <: GLB(U1, U2).
//
// This can then be done for all constraints in sequence.
//
// This resulting constraint may be unsatisfiable; in that case inference
// will fail.
upper = _getGreatestLowerBound(upper, constraint.upperBound);
lower = _typeSystem.getLeastUpperBound(lower, constraint.lowerBound);
}
// Prefer the known bound, if any.
// Otherwise take whatever bound has partial information, e.g. `Iterable<?>`
//
// For both of those, prefer the lower bound (arbitrary heuristic).
if (UnknownInferredType.isKnown(lower)) {
return lower;
}
if (UnknownInferredType.isKnown(upper)) {
return upper;
}
if (!identical(UnknownInferredType.instance, lower)) {
return toKnownType ? _typeSystem.lowerBoundForType(lower) : lower;
}
if (!identical(UnknownInferredType.instance, upper)) {
return toKnownType ? _typeSystem.upperBoundForType(upper) : upper;
}
return lower;
}
String _formatError(TypeParameterElement typeParam, DartType inferred,
Iterable<_TypeConstraint> constraints) {
var intro = "Tried to infer '$inferred' for '${typeParam.name}'"
" which doesn't work:";
var constraintsByOrigin = <_TypeConstraintOrigin, List<_TypeConstraint>>{};
for (var c in constraints) {
constraintsByOrigin.putIfAbsent(c.origin, () => []).add(c);
}
// Only report unique constraint origins.
Iterable<_TypeConstraint> isSatisified(bool expected) => constraintsByOrigin
.values
.where((l) =>
l.every((c) => c.isSatisifedBy(_typeSystem, inferred)) == expected)
.expand((i) => i);
String unsatisified = _formatConstraints(isSatisified(false));
String satisified = _formatConstraints(isSatisified(true));
assert(unsatisified.isNotEmpty);
if (satisified.isNotEmpty) {
satisified = "\nThe type '$inferred' was inferred from:\n$satisified";
}
return '\n\n$intro\n$unsatisified$satisified\n\n'
'Consider passing explicit type argument(s) to the generic.\n\n';
}
/// This is first calls strong mode's GLB, but if it fails to find anything
/// (i.e. returns the bottom type), we kick in a few additional rules:
///
/// - `GLB(FutureOr<A>, B)` is defined as:
/// - `GLB(FutureOr<A>, FutureOr<B>) == FutureOr<GLB(A, B)>`
/// - `GLB(FutureOr<A>, Future<B>) == Future<GLB(A, B)>`
/// - else `GLB(FutureOr<A>, B) == GLB(A, B)`
/// - `GLB(A, FutureOr<B>) == GLB(FutureOr<B>, A)` (defined above),
/// - else `GLB(A, B) == Null`
DartType _getGreatestLowerBound(DartType t1, DartType t2) {
var result = _typeSystem.getGreatestLowerBound(t1, t2);
if (result.isBottom) {
// See if we can do better by considering FutureOr rules.
if (t1 is InterfaceType && t1.isDartAsyncFutureOr) {
var t1TypeArg = t1.typeArguments[0];
if (t2 is InterfaceType) {
// GLB(FutureOr<A>, FutureOr<B>) == FutureOr<GLB(A, B)>
if (t2.isDartAsyncFutureOr) {
var t2TypeArg = t2.typeArguments[0];
return typeProvider
.futureOrType2(_getGreatestLowerBound(t1TypeArg, t2TypeArg));
}
// GLB(FutureOr<A>, Future<B>) == Future<GLB(A, B)>
if (t2.isDartAsyncFuture) {
var t2TypeArg = t2.typeArguments[0];
return typeProvider
.futureType2(_getGreatestLowerBound(t1TypeArg, t2TypeArg));
}
}
// GLB(FutureOr<A>, B) == GLB(A, B)
return _getGreatestLowerBound(t1TypeArg, t2);
}
if (t2 is InterfaceType && t2.isDartAsyncFutureOr) {
// GLB(A, FutureOr<B>) == GLB(FutureOr<B>, A)
return _getGreatestLowerBound(t2, t1);
}
return typeProvider.nullType;
}
return result;
}
DartType _inferTypeParameterFromAll(
List<_TypeConstraint> constraints, _TypeConstraint extendsClause) {
// See if we already fixed this type from downwards inference.
// If so, then we aren't allowed to change it based on argument types.
DartType t = _inferTypeParameterFromContext(
constraints.where((c) => c.isDownwards), extendsClause);
if (UnknownInferredType.isKnown(t)) {
// Remove constraints that aren't downward ones; we'll ignore these for
// error reporting, because inference already succeeded.
constraints.removeWhere((c) => !c.isDownwards);
return t;
}
if (extendsClause != null) {
constraints = constraints.toList()..add(extendsClause);
}
var choice = _chooseTypeFromConstraints(constraints, toKnownType: true);
return choice;
}
DartType _inferTypeParameterFromContext(
Iterable<_TypeConstraint> constraints, _TypeConstraint extendsClause) {
DartType t = _chooseTypeFromConstraints(constraints);
if (UnknownInferredType.isUnknown(t)) {
return t;
}
// If we're about to make our final choice, apply the extends clause.
// This gives us a chance to refine the choice, in case it would violate
// the `extends` clause. For example:
//
// Object obj = math.min/*<infer Object, error>*/(1, 2);
//
// If we consider the `T extends num` we conclude `<num>`, which works.
if (extendsClause != null) {
constraints = constraints.toList()..add(extendsClause);
return _chooseTypeFromConstraints(constraints);
}
return t;
}
/// Tries to make [i1] a subtype of [i2] and accumulate constraints as needed.
///
/// The return value indicates whether the match was successful. If it was
/// unsuccessful, the caller is responsible for ignoring any constraints that
/// were accumulated (see [_rewindConstraints]).
bool _matchInterfaceSubtypeOf(InterfaceType i1, InterfaceType i2,
Set<Element> visited, _TypeConstraintOrigin origin,
{bool covariant}) {
if (identical(i1, i2)) {
return true;
}
if (i1.element == i2.element) {
List<DartType> tArgs1 = i1.typeArguments;
List<DartType> tArgs2 = i2.typeArguments;
assert(tArgs1.length == tArgs2.length);
for (int i = 0; i < tArgs1.length; i++) {
if (!_matchSubtypeOf(
tArgs1[i], tArgs2[i], new HashSet<Element>(), origin,
covariant: covariant)) {
return false;
}
}
return true;
}
if (i1.isObject) {
return false;
}
// Guard against loops in the class hierarchy
bool guardedInterfaceSubtype(InterfaceType t1) {
visited ??= new HashSet<Element>();
if (visited.add(t1.element)) {
bool matched = _matchInterfaceSubtypeOf(t1, i2, visited, origin,
covariant: covariant);
visited.remove(t1.element);
return matched;
} else {
// In the case of a recursive type parameter, consider the subtype
// match to have failed.
return false;
}
}
// We don't need to search the entire class hierarchy, since a given
// subclass can't appear multiple times with different generic parameters.
// So shortcut to the first match found.
//
// We don't need undo logic here because if the classes don't match, nothing
// is added to the constraint set.
var superclass = i1.superclass;
if (superclass != null && guardedInterfaceSubtype(superclass)) return true;
for (final parent in i1.interfaces) {
if (guardedInterfaceSubtype(parent)) return true;
}
for (final parent in i1.mixins) {
if (guardedInterfaceSubtype(parent)) return true;
}
for (final parent in i1.superclassConstraints) {
if (guardedInterfaceSubtype(parent)) return true;
}
return false;
}
/// Assert that [t1] will be a subtype of [t2], and returns if the constraint
/// can be satisfied.
///
/// [covariant] must be true if [t1] is a declared type of the generic
/// function and [t2] is the context type, or false if the reverse. For
/// example [covariant] is used when [t1] is the declared return type
/// and [t2] is the context type. Contravariant would be used if [t1] is the
/// argument type (i.e. passed in to the generic function) and [t2] is the
/// declared parameter type.
///
/// [origin] indicates where the constraint came from, for example an argument
/// or return type.
bool _matchSubtypeOf(DartType t1, DartType t2, Set<Element> visited,
_TypeConstraintOrigin origin,
{bool covariant}) {
if (covariant && t1 is TypeParameterType) {
var constraints = this.constraints[t1.element];
if (constraints != null) {
if (!identical(t2, UnknownInferredType.instance)) {
var constraint = new _TypeConstraint(origin, t1.element, upper: t2);
constraints.add(constraint);
_undoBuffer.add(constraint);
}
return true;
}
}
if (!covariant && t2 is TypeParameterType) {
var constraints = this.constraints[t2.element];
if (constraints != null) {
if (!identical(t1, UnknownInferredType.instance)) {
var constraint = new _TypeConstraint(origin, t2.element, lower: t1);
constraints.add(constraint);
_undoBuffer.add(constraint);
}
return true;
}
}
if (identical(t1, t2)) {
return true;
}
// TODO(jmesserly): this logic is taken from subtype.
bool matchSubtype(DartType t1, DartType t2) {
return _matchSubtypeOf(t1, t2, null, origin, covariant: covariant);
}
// Handle FutureOr<T> union type.
if (t1 is InterfaceType && t1.isDartAsyncFutureOr) {
var t1TypeArg = t1.typeArguments[0];
if (t2 is InterfaceType && t2.isDartAsyncFutureOr) {
var t2TypeArg = t2.typeArguments[0];
// FutureOr<A> <: FutureOr<B> iff A <: B
return matchSubtype(t1TypeArg, t2TypeArg);
}
// given t1 is Future<A> | A, then:
// (Future<A> | A) <: t2 iff Future<A> <: t2 and A <: t2.
var t1Future = typeProvider.futureType2(t1TypeArg);
return matchSubtype(t1Future, t2) && matchSubtype(t1TypeArg, t2);
}
if (t2 is InterfaceType && t2.isDartAsyncFutureOr) {
// given t2 is Future<A> | A, then:
// t1 <: (Future<A> | A) iff t1 <: Future<A> or t1 <: A
var t2TypeArg = t2.typeArguments[0];
var t2Future = typeProvider.futureType2(t2TypeArg);
// First we try matching `t1 <: Future<A>`. If that succeeds *and*
// records at least one constraint, then we proceed using that constraint.
var previousRewindBufferLength = _undoBuffer.length;
var success =
tryMatchSubtypeOf(t1, t2Future, origin, covariant: covariant);
if (_undoBuffer.length != previousRewindBufferLength) {
// Trying to match `t1 <: Future<A>` succeeded and recorded constraints,
// so those are the constraints we want.
return true;
} else {
// Either `t1 <: Future<A>` failed to match, or it matched trivially
// without recording any constraints (e.g. because t1 is `Null`). We
// want constraints, because they let us do more precise inference, so
// go ahead and try matching `t1 <: A` to see if it records any
// constraints.
if (tryMatchSubtypeOf(t1, t2TypeArg, origin, covariant: covariant)) {
// Trying to match `t1 <: A` succeeded. If it recorded constraints,
// those are the constraints we want. If it didn't, then there's no
// way we're going to get any constraints. So either way, we want to
// return `true` since the match suceeded and the constraints we want
// (if any) have been recorded.
return true;
} else {
// Trying to match `t1 <: A` failed. So there's no way we are going
// to get any constraints. Just return `success` to indicate whether
// the match succeeded.
return success;
}
}
}
// S <: T where S is a type variable
// T is not dynamic or object (handled above)
// True if T == S
// Or true if bound of S is S' and S' <: T
if (t1 is TypeParameterType) {
// Guard against recursive type parameters
//
// TODO(jmesserly): this function isn't guarding against anything (it's
// not passsing down `visitedSet`, so adding the element has no effect).
bool guardedSubtype(DartType t1, DartType t2) {
var visitedSet = visited ?? new HashSet<Element>();
if (visitedSet.add(t1.element)) {
bool matched = matchSubtype(t1, t2);
visitedSet.remove(t1.element);
return matched;
} else {
// In the case of a recursive type parameter, consider the subtype
// match to have failed.
return false;
}
}
if (t2 is TypeParameterType && t1.definition == t2.definition) {
return guardedSubtype(t1.bound, t2.bound);
}
return guardedSubtype(t1.bound, t2);
}
if (t2 is TypeParameterType) {
return false;
}
// TODO(mfairhurst): switch legacy Bottom checks to true Bottom checks
// TODO(mfairhurst): switch legacy Top checks to true Top checks
if (_isLegacyBottom(t1, orTrueBottom: true) ||
_isLegacyTop(t2, orTrueTop: true)) return true;
if (t1 is InterfaceType && t2 is InterfaceType) {
return _matchInterfaceSubtypeOf(t1, t2, visited, origin,
covariant: covariant);
}
if (t1 is FunctionType && t2 is FunctionType) {
return FunctionTypeImpl.relate(t1, t2, matchSubtype,
parameterRelation: (p1, p2) {
return _matchSubtypeOf(p2.type, p1.type, null, origin,
covariant: !covariant);
},
// Type parameter bounds are invariant.
boundsRelation: (t1, t2, p1, p2) =>
matchSubtype(t1, t2) && matchSubtype(t2, t1));
}
if (t1 is FunctionType && t2 == typeProvider.functionType) {
return true;
}
return false;
}
/// Un-does constraints that were gathered by a failed match attempt, until
/// [_undoBuffer] has length [previousRewindBufferLength].
///
/// The intended usage is that the caller should record the length of
/// [_undoBuffer] before attempting to make a match. Then, if the match
/// fails, pass the recorded length to this method to erase any constraints
/// that were recorded during the failed match.
void _rewindConstraints(int previousRewindBufferLength) {
while (_undoBuffer.length > previousRewindBufferLength) {
var constraint = _undoBuffer.removeLast();
var element = constraint.typeParameter;
assert(identical(constraints[element].last, constraint));
constraints[element].removeLast();
}
}
static String _formatConstraints(Iterable<_TypeConstraint> constraints) {
List<List<String>> lineParts =
new Set<_TypeConstraintOrigin>.from(constraints.map((c) => c.origin))
.map((o) => o.formatError())
.toList();
int prefixMax = lineParts.map((p) => p[0].length).fold(0, math.max);
// Use a set to prevent identical message lines.
// (It's not uncommon for the same constraint to show up in a few places.)
var messageLines = new Set<String>.from(lineParts.map((parts) {
var prefix = parts[0];
var middle = parts[1];
var prefixPad = ' ' * (prefixMax - prefix.length);
var middlePad = ' ' * (prefixMax);
var end = "";
if (parts.length > 2) {
end = '\n $middlePad ${parts[2]}';
}
return ' $prefix$prefixPad $middle$end';
}));
return messageLines.join('\n');
}
}
/// The instantiation of a [ClassElement] with type arguments.
///
/// It is not a [DartType] itself, because it does not have nullability.
/// But it should be used where nullability does not make sense - to specify
/// superclasses, mixins, and implemented interfaces.
class InstantiatedClass {
final ClassElement element;
final List<DartType> arguments;
final Substitution _substitution;
InstantiatedClass(this.element, this.arguments)
: _substitution = Substitution.fromPairs(
element.typeParameters,
arguments,
);
/// Return the [InstantiatedClass] that corresponds to the [type] - with the
/// same element and type arguments, ignoring its nullability suffix.
factory InstantiatedClass.of(InterfaceType type) {
return InstantiatedClass(type.element, type.typeArguments);
}
@override
int get hashCode {
var hash = 0x3fffffff & element.hashCode;
for (var i = 0; i < arguments.length; i++) {
hash = 0x3fffffff & (hash * 31 + (hash ^ arguments[i].hashCode));
}
return hash;
}
/// Return the interfaces that are directly implemented by this class.
List<InstantiatedClass> get interfaces {
var interfaces = element.interfaces;
var result = List<InstantiatedClass>(interfaces.length);
for (var i = 0; i < interfaces.length; i++) {
var interface = interfaces[i];
var substituted = _substitution.substituteType(interface);
result[i] = InstantiatedClass.of(substituted);
}
return result;
}
/// Return `true` if this type represents the type 'Function' defined in the
/// dart:core library.
bool get isDartCoreFunction {
return element.name == 'Function' && element.library.isDartCore;
}
/// Return the superclass of this type, or `null` if this type represents
/// the class 'Object'.
InstantiatedClass get superclass {
var supertype = element.supertype;
if (supertype == null) return null;
supertype = _substitution.substituteType(supertype);
return InstantiatedClass.of(supertype);
}
/// Return a list containing all of the superclass constraints defined for
/// this class. The list will be empty if this class does not represent a
/// mixin declaration. If this class _does_ represent a mixin declaration but
/// the declaration does not have an `on` clause, then the list will contain
/// the type for the class `Object`.
List<InstantiatedClass> get superclassConstraints {
var constraints = element.superclassConstraints;
var result = List<InstantiatedClass>(constraints.length);
for (var i = 0; i < constraints.length; i++) {
var constraint = constraints[i];
var substituted = _substitution.substituteType(constraint);
result[i] = InstantiatedClass.of(substituted);
}
return result;
}
@visibleForTesting
InterfaceType get withNullabilitySuffixNone {
return withNullability(NullabilitySuffix.none);
}
@override
bool operator ==(Object other) {
if (identical(this, other)) return true;
if (other is InstantiatedClass) {
if (element != other.element) return false;
if (arguments.length != other.arguments.length) return false;
for (var i = 0; i < arguments.length; i++) {
if (arguments[i] != other.arguments[i]) return false;
}
return true;
}
return false;
}
@override
String toString() {
var buffer = StringBuffer();
buffer.write(element.name);
if (arguments.isNotEmpty) {
buffer.write('<');
buffer.write(arguments.join(', '));
buffer.write('>');
}
return buffer.toString();
}
InterfaceType withNullability(NullabilitySuffix nullability) {
return InterfaceTypeImpl.explicit(
element,
arguments,
nullabilitySuffix: nullability,
);
}
}
class InterfaceLeastUpperBoundHelper {
final TypeSystem typeSystem;
InterfaceLeastUpperBoundHelper(this.typeSystem);
/// This currently does not implement a very complete least upper bound
/// algorithm, but handles a couple of the very common cases that are
/// causing pain in real code. The current algorithm is:
/// 1. If either of the types is a supertype of the other, return it.
/// This is in fact the best result in this case.
/// 2. If the two types have the same class element, then take the
/// pointwise least upper bound of the type arguments. This is again
/// the best result, except that the recursive calls may not return
/// the true least upper bounds. The result is guaranteed to be a
/// well-formed type under the assumption that the input types were
/// well-formed (and assuming that the recursive calls return
/// well-formed types).
/// 3. Otherwise return the spec-defined least upper bound. This will
/// be an upper bound, might (or might not) be least, and might
/// (or might not) be a well-formed type.
///
/// TODO(leafp): Use matchTypes or something similar here to handle the
/// case where one of the types is a superclass (but not supertype) of
/// the other, e.g. LUB(Iterable<double>, List<int>) = Iterable<num>
/// TODO(leafp): Figure out the right final algorithm and implement it.
InterfaceTypeImpl compute(InterfaceTypeImpl type1, InterfaceTypeImpl type2) {
var nullability = _chooseNullability(type1, type2);
// Strip off nullability.
type1 = type1.withNullability(NullabilitySuffix.none);
type2 = type2.withNullability(NullabilitySuffix.none);
if (typeSystem.isSubtypeOf(type1, type2)) {
return type2.withNullability(nullability);
}
if (typeSystem.isSubtypeOf(type2, type1)) {
return type1.withNullability(nullability);
}
if (type1.element == type2.element) {
var args1 = type1.typeArguments;
var args2 = type2.typeArguments;
assert(args1.length == args2.length);
var args = List<DartType>(args1.length);
for (int i = 0; i < args1.length; i++) {
args[i] = typeSystem.getLeastUpperBound(args1[i], args2[i]);
}
return new InterfaceTypeImpl.explicit(
type1.element,
args,
nullabilitySuffix: nullability,
);
}
var result = _computeLeastUpperBound(
InstantiatedClass.of(type1),
InstantiatedClass.of(type2),
);
return result.withNullability(nullability);
}
/// Compute the least upper bound of types [i] and [j], both of which are
/// known to be interface types.
///
/// In the event that the algorithm fails (which might occur due to a bug in
/// the analyzer), `null` is returned.
InstantiatedClass _computeLeastUpperBound(
InstantiatedClass i,
InstantiatedClass j,
) {
// compute set of supertypes
var si = computeSuperinterfaceSet(i);
var sj = computeSuperinterfaceSet(j);
// union si with i and sj with j
si.add(i);
sj.add(j);
// compute intersection, reference as set 's'
var s = _intersection(si, sj);
return _computeTypeAtMaxUniqueDepth(s);
}
/**
* Return the length of the longest inheritance path from the [element] to
* Object.
*/
@visibleForTesting
static int computeLongestInheritancePathToObject(ClassElement element) {
return _computeLongestInheritancePathToObject(
element,
0,
Set<ClassElement>(),
);
}
/// Return all of the superinterfaces of the given [type].
@visibleForTesting
static Set<InstantiatedClass> computeSuperinterfaceSet(
InstantiatedClass type) {
var result = Set<InstantiatedClass>();
_addSuperinterfaces(result, type);
return result;
}
/// Add all of the superinterfaces of the given [type] to the given [set].
static void _addSuperinterfaces(
Set<InstantiatedClass> set, InstantiatedClass type) {
for (var interface in type.interfaces) {
if (!interface.isDartCoreFunction) {
if (set.add(interface)) {
_addSuperinterfaces(set, interface);
}
}
}
for (var constraint in type.superclassConstraints) {
if (!constraint.isDartCoreFunction) {
if (set.add(constraint)) {
_addSuperinterfaces(set, constraint);
}
}
}
var supertype = type.superclass;
if (supertype != null && !supertype.isDartCoreFunction) {
if (set.add(supertype)) {
_addSuperinterfaces(set, supertype);
}
}
}
static NullabilitySuffix _chooseNullability(
InterfaceTypeImpl type1,
InterfaceTypeImpl type2,
) {
var nullability1 = type1.nullabilitySuffix;
var nullability2 = type2.nullabilitySuffix;
if (nullability1 == NullabilitySuffix.question ||
nullability2 == NullabilitySuffix.question) {
return NullabilitySuffix.question;
} else if (nullability1 == NullabilitySuffix.star ||
nullability2 == NullabilitySuffix.star) {
return NullabilitySuffix.star;
}
return NullabilitySuffix.none;
}
/// Return the length of the longest inheritance path from a subtype of the
/// given [element] to Object, where the given [depth] is the length of the
/// longest path from the subtype to this type. The set of [visitedElements]
/// is used to prevent infinite recursion in the case of a cyclic type
/// structure.
static int _computeLongestInheritancePathToObject(
ClassElement element, int depth, Set<ClassElement> visitedElements) {
// Object case
if (element.isDartCoreObject || visitedElements.contains(element)) {
return depth;
}
int longestPath = 1;
try {
visitedElements.add(element);
int pathLength;
// loop through each of the superinterfaces recursively calling this
// method and keeping track of the longest path to return
for (InterfaceType interface in element.superclassConstraints) {
pathLength = _computeLongestInheritancePathToObject(
interface.element, depth + 1, visitedElements);
if (pathLength > longestPath) {
longestPath = pathLength;
}
}
// loop through each of the superinterfaces recursively calling this
// method and keeping track of the longest path to return
for (InterfaceType interface in element.interfaces) {
pathLength = _computeLongestInheritancePathToObject(
interface.element, depth + 1, visitedElements);
if (pathLength > longestPath) {
longestPath = pathLength;
}
}
// finally, perform this same check on the super type
// TODO(brianwilkerson) Does this also need to add in the number of mixin
// classes?
InterfaceType supertype = element.supertype;
if (supertype != null) {
pathLength = _computeLongestInheritancePathToObject(
supertype.element, depth + 1, visitedElements);
if (pathLength > longestPath) {
longestPath = pathLength;
}
}
} finally {
visitedElements.remove(element);
}
return longestPath;
}
/// Return the type from the [types] list that has the longest inheritance
/// path to Object of unique length.
static InstantiatedClass _computeTypeAtMaxUniqueDepth(
List<InstantiatedClass> types,
) {
// for each element in Set s, compute the largest inheritance path to Object
List<int> depths = new List<int>.filled(types.length, 0);
int maxDepth = 0;
for (int i = 0; i < types.length; i++) {
depths[i] = computeLongestInheritancePathToObject(types[i].element);
if (depths[i] > maxDepth) {
maxDepth = depths[i];
}
}
// ensure that the currently computed maxDepth is unique,
// otherwise, decrement and test for uniqueness again
for (; maxDepth >= 0; maxDepth--) {
int indexOfLeastUpperBound = -1;
int numberOfTypesAtMaxDepth = 0;
for (int m = 0; m < depths.length; m++) {
if (depths[m] == maxDepth) {
numberOfTypesAtMaxDepth++;
indexOfLeastUpperBound = m;
}
}
if (numberOfTypesAtMaxDepth == 1) {
return types[indexOfLeastUpperBound];
}
}
// Should be impossible--there should always be exactly one type with the
// maximum depth.
assert(false);
return null;
}
/**
* Return the intersection of the [first] and [second] sets of types, where
* intersection is based on the equality of the types themselves.
*/
static List<InstantiatedClass> _intersection(
Set<InstantiatedClass> first,
Set<InstantiatedClass> second,
) {
var result = first.toSet();
result.retainAll(second);
return result.toList();
}
}
/// Used to check for infinite loops, if we repeat the same type comparison.
class TypeComparison {
final DartType lhs;
final DartType rhs;
TypeComparison(this.lhs, this.rhs);
@override
int get hashCode => lhs.hashCode * 11 + rhs.hashCode;
@override
bool operator ==(Object other) {
if (other is TypeComparison) {
return lhs == other.lhs && rhs == other.rhs;
}
return false;
}
@override
String toString() => "$lhs vs $rhs";
}
/**
* The interface `TypeSystem` defines the behavior of an object representing
* the type system. This provides a common location to put methods that act on
* types but may need access to more global data structures, and it paves the
* way for a possible future where we may wish to make the type system
* pluggable.
*/
// TODO(brianwilkerson) Rename this class to TypeSystemImpl.
abstract class TypeSystem implements public.TypeSystem {
/**
* The provider of types for the system
*/
TypeProvider get typeProvider;
@override
DartType flatten(DartType type) {
if (type is InterfaceType) {
// Implement the cases:
// - "If T = FutureOr<S> then flatten(T) = S."
// - "If T = Future<S> then flatten(T) = S."
if (type.isDartAsyncFutureOr || type.isDartAsyncFuture) {
return type.typeArguments.isNotEmpty
? type.typeArguments[0]
: DynamicTypeImpl.instance;
}
// Implement the case: "Otherwise if T <: Future then let S be a type
// such that T << Future<S> and for all R, if T << Future<R> then S << R.
// Then flatten(T) = S."
//
// In other words, given the set of all types R such that T << Future<R>,
// let S be the most specific of those types, if any such S exists.
//
// Since we only care about the most specific type, it is sufficient to
// look at the types appearing as a parameter to Future in the type
// hierarchy of T. We don't need to consider the supertypes of those
// types, since they are by definition less specific.
List<DartType> candidateTypes =
_searchTypeHierarchyForFutureTypeParameters(type);
DartType flattenResult =
InterfaceTypeImpl.findMostSpecificType(candidateTypes, this);
if (flattenResult != null) {
return flattenResult;
}
}
// Implement the case: "In any other circumstance, flatten(T) = T."
return type;
}
List<InterfaceType> gatherMixinSupertypeConstraintsForInference(
ClassElement mixinElement) {
List<InterfaceType> candidates;
if (mixinElement.isMixin) {
candidates = mixinElement.superclassConstraints;
} else {
candidates = [mixinElement.supertype];
candidates.addAll(mixinElement.mixins);
if (mixinElement.isMixinApplication) {
candidates.removeLast();
}
}
return candidates
.where((type) => type.element.typeParameters.isNotEmpty)
.toList();
}
/**
* Compute the least upper bound of two types.
*/
DartType getLeastUpperBound(DartType type1, DartType type2) {
// The least upper bound relation is reflexive.
if (identical(type1, type2)) {
return type1;
}
// For any type T, LUB(?, T) == T.
if (identical(type1, UnknownInferredType.instance)) {
return type2;
}
if (identical(type2, UnknownInferredType.instance)) {
return type1;
}
// For the purpose of LUB, we say some Tops are subtypes (less toppy) than
// the others. Return the most toppy.
// TODO(mfairhurst): switch legacy Top checks to true Top checks
if (_isLegacyTop(type1, orTrueTop: true) &&
_isLegacyTop(type2, orTrueTop: true)) {
return _getTopiness(type1) > _getTopiness(type2) ? type1 : type2;
}
// The least upper bound of top and any type T is top.
// The least upper bound of bottom and any type T is T.
// TODO(mfairhurst): switch legacy Top checks to true Top checks
// TODO(mfairhurst): switch legacy Bottom checks to true Bottom checks
if (_isLegacyTop(type1, orTrueTop: true) ||
_isLegacyBottom(type2, orTrueBottom: true)) {
return type1;
}
// TODO(mfairhurst): switch legacy Top checks to true Top checks
// TODO(mfairhurst): switch legacy Bottom checks to true Bottom checks
if (_isLegacyTop(type2, orTrueTop: true) ||
_isLegacyBottom(type1, orTrueBottom: true)) {
return type2;
}
if (type1 is TypeParameterType || type2 is TypeParameterType) {
return _typeParameterLeastUpperBound(type1, type2);
}
// In Dart 1, the least upper bound of a function type and an interface type
// T is the least upper bound of Function and T.
//
// In Dart 2, the result is `Function` iff T is `Function`, otherwise the
// result is `Object`.
if (type1 is FunctionType && type2 is InterfaceType) {
return type2.isDartCoreFunction ? type2 : typeProvider.objectType;
}
if (type2 is FunctionType && type1 is InterfaceType) {
return type1.isDartCoreFunction ? type1 : typeProvider.objectType;
}
// At this point type1 and type2 should both either be interface types or
// function types.
if (type1 is InterfaceType && type2 is InterfaceType) {
return _interfaceLeastUpperBound(type1, type2);
}
if (type1 is FunctionType && type2 is FunctionType) {
return _functionLeastUpperBound(type1, type2);
}
// Should never happen. As a defensive measure, return the dynamic type.
assert(false);
return typeProvider.dynamicType;
}
/**
* Given a [DartType] [type], instantiate it with its bounds.
*
* The behavior of this method depends on the type system, for example, in
* classic Dart `dynamic` will be used for all type arguments, whereas
* strong mode prefers the actual bound type if it was specified.
*/
DartType instantiateToBounds(DartType type, {List<bool> hasError});
/**
* Given a [DartType] [type] and a list of types
* [typeArguments], instantiate the type formals with the
* provided actuals. If [type] is not a parameterized type,
* no instantiation is done.
*/
DartType instantiateType(DartType type, List<DartType> typeArguments) {
if (type is ParameterizedType) {
return type.instantiate(typeArguments);
} else {
return type;
}
}
/**
* Given uninstantiated [typeFormals], instantiate them to their bounds.
*/
List<DartType> instantiateTypeFormalsToBounds(
List<TypeParameterElement> typeFormals,
{List<bool> hasError});
/**
* Return `true` if the [leftType] is assignable to the [rightType] (that is,
* if leftType <==> rightType). Accepts a [FeatureSet] to correctly handle
* NNBD implicit downcasts.
*/
bool isAssignableTo(DartType leftType, DartType rightType,
{FeatureSet featureSet});
/**
* Return `true` if the [leftType] is more specific than the [rightType]
* (that is, if leftType << rightType), as defined in the Dart language spec.
*
* In strong mode, this is equivalent to [isSubtypeOf].
*/
@Deprecated('Use isSubtypeOf() instead.')
bool isMoreSpecificThan(DartType leftType, DartType rightType);
@override
bool isNonNullable(DartType type) {
if (type.isDynamic || type.isVoid || type.isDartCoreNull) {
return false;
} else if ((type as TypeImpl).nullabilitySuffix ==
NullabilitySuffix.question) {
return false;
} else if (type.isDartAsyncFutureOr) {
return isNonNullable((type as InterfaceType).typeArguments[0]);
} else if (type is TypeParameterType) {
return isNonNullable(type.bound);
}
return true;
}
@override
bool isNullable(DartType type) {
if (type.isDynamic || type.isVoid || type.isDartCoreNull) {
return true;
} else if ((type as TypeImpl).nullabilitySuffix ==
NullabilitySuffix.question) {
return true;
} else if (type.isDartAsyncFutureOr) {
return isNullable((type as InterfaceType).typeArguments[0]);
}
return false;
}
/// Check that [f1] is a subtype of [f2] for a member override.
///
/// This is different from the normal function subtyping in two ways:
/// - we know the function types are strict arrows,
/// - it allows opt-in covariant parameters.
bool isOverrideSubtypeOf(FunctionType f1, FunctionType f2);
@override
bool isPotentiallyNonNullable(DartType type) => !isNullable(type);
@override
bool isPotentiallyNullable(DartType type) => !isNonNullable(type);
/**
* Return `true` if the [leftType] is a subtype of the [rightType] (that is,
* if leftType <: rightType).
*/
bool isSubtypeOf(DartType leftType, DartType rightType);
@override
DartType leastUpperBound(DartType leftType, DartType rightType) {
return getLeastUpperBound(leftType, rightType);
}
/// Returns a nullable version of [type]. The result would be equivalent to
/// the union `type | Null` (if we supported union types).
DartType makeNullable(TypeImpl type) {
// TODO(paulberry): handle type parameter types
return type.withNullability(NullabilitySuffix.question);
}
/// Attempts to find the appropriate substitution for the [mixinElement]
/// type parameters that can be applied to [srcTypes] to make it equal to
/// [destTypes]. If no such substitution can be found, `null` is returned.
List<DartType> matchSupertypeConstraints(
ClassElement mixinElement,
List<DartType> srcTypes,
List<DartType> destTypes,
) {
var typeParameters = mixinElement.typeParameters;
var inferrer = new GenericInferrer(typeProvider, this, typeParameters);
for (int i = 0; i < srcTypes.length; i++) {
inferrer.constrainReturnType(srcTypes[i], destTypes[i]);
inferrer.constrainReturnType(destTypes[i], srcTypes[i]);
}
var inferredTypes = inferrer.infer(
typeParameters,
considerExtendsClause: false,
);
var substitution = Substitution.fromPairs(typeParameters, inferredTypes);
for (int i = 0; i < srcTypes.length; i++) {
if (substitution.substituteType(srcTypes[i]) != destTypes[i]) {
// Failed to find an appropriate substitution
return null;
}
}
return inferredTypes;
}
/**
* Searches the superinterfaces of [type] for implementations of [genericType]
* and returns the most specific type argument used for that generic type.
*
* For a more general/robust solution, use [InterfaceTypeImpl.asInstanceOf].
*
* For example, given [type] `List<int>` and [genericType] `Iterable<T>`,
* returns [int].
*
* Returns `null` if [type] does not implement [genericType].
*/
DartType mostSpecificTypeArgument(DartType type, DartType genericType) {
if (type is! InterfaceType) return null;
if (genericType is! InterfaceType) return null;
var asInstanceOf = (type as InterfaceTypeImpl)
.asInstanceOf((genericType as InterfaceType).element);
if (asInstanceOf != null) {
return asInstanceOf.typeArguments[0];
}
return null;
}
/// Returns a non-nullable version of [type]. This is equivalent to the
/// operation `NonNull` defined in the spec.
DartType promoteToNonNull(covariant TypeImpl type) {
if (type.isDartCoreNull) return BottomTypeImpl.instance;
if (type is TypeParameterTypeImpl) {
var promotedElement = TypeParameterElementImpl.synthetic(
type.element.name,
);
var bound = type.element.bound ?? typeProvider.objectType;
promotedElement.bound = promoteToNonNull(bound);
return TypeParameterTypeImpl(
promotedElement,
nullabilitySuffix: NullabilitySuffix.none,
);
}
return type.withNullability(NullabilitySuffix.none);
}
/**
* Determine the type of a binary expression with the given [operator] whose
* left operand has the type [leftType] and whose right operand has the type
* [rightType], given that resolution has so far produced the [currentType].
* The [featureSet] is used to determine whether any features that effect the
* computation have been enabled.
*/
DartType refineBinaryExpressionType(DartType leftType, TokenType operator,
DartType rightType, DartType currentType, FeatureSet featureSet) {
// bool
if (operator == TokenType.AMPERSAND_AMPERSAND ||
operator == TokenType.BAR_BAR ||
operator == TokenType.EQ_EQ ||
operator == TokenType.BANG_EQ) {
if (featureSet.isEnabled(Feature.non_nullable)) {
return promoteToNonNull(typeProvider.boolType as TypeImpl);
}
return typeProvider.boolType;
}
if (leftType.isDartCoreInt) {
// int op double
if (operator == TokenType.MINUS ||
operator == TokenType.PERCENT ||
operator == TokenType.PLUS ||
operator == TokenType.STAR ||
operator == TokenType.MINUS_EQ ||
operator == TokenType.PERCENT_EQ ||
operator == TokenType.PLUS_EQ ||
operator == TokenType.STAR_EQ) {
if (rightType.isDartCoreDouble) {
InterfaceTypeImpl doubleType = typeProvider.doubleType;
if (featureSet.isEnabled(Feature.non_nullable)) {
return promoteToNonNull(doubleType);
}
return doubleType;
}
}
// int op int
if (operator == TokenType.MINUS ||
operator == TokenType.PERCENT ||
operator == TokenType.PLUS ||
operator == TokenType.STAR ||
operator == TokenType.TILDE_SLASH ||
operator == TokenType.MINUS_EQ ||
operator == TokenType.PERCENT_EQ ||
operator == TokenType.PLUS_EQ ||
operator == TokenType.STAR_EQ ||
operator == TokenType.TILDE_SLASH_EQ) {
if (rightType.isDartCoreInt) {
InterfaceTypeImpl intType = typeProvider.intType;
if (featureSet.isEnabled(Feature.non_nullable)) {
return promoteToNonNull(intType);
}
return intType;
}
}
}
// default
return currentType;
}
@override
DartType resolveToBound(DartType type) {
if (type is TypeParameterTypeImpl) {
var element = type.element;
var bound = element.bound as TypeImpl;
if (bound == null) {
return typeProvider.objectType;
}
NullabilitySuffix nullabilitySuffix = type.nullabilitySuffix;
NullabilitySuffix newNullabilitySuffix;
if (nullabilitySuffix == NullabilitySuffix.question ||
bound.nullabilitySuffix == NullabilitySuffix.question) {
newNullabilitySuffix = NullabilitySuffix.question;
} else if (nullabilitySuffix == NullabilitySuffix.star ||
bound.nullabilitySuffix == NullabilitySuffix.star) {
newNullabilitySuffix = NullabilitySuffix.star;
} else {
newNullabilitySuffix = NullabilitySuffix.none;
}
var resolved = resolveToBound(bound) as TypeImpl;
return resolved.withNullability(newNullabilitySuffix);
}
return type;
}
/**
* Tries to promote from the first type from the second type, and returns the
* promoted type if it succeeds, otherwise null.
*/
DartType tryPromoteToType(DartType to, DartType from);
/**
* Given a [DartType] type, return the [TypeParameterElement]s corresponding
* to its formal type parameters (if any).
*
* @param type the type whose type arguments are to be returned
* @return the type arguments associated with the given type
*/
List<TypeParameterElement> typeFormalsAsElements(DartType type) {
if (type is FunctionType) {
return type.typeFormals;
} else if (type is InterfaceType) {
return type.typeParameters;
} else {
return const <TypeParameterElement>[];
}
}
/**
* Given a [DartType] type, return the [DartType]s corresponding
* to its formal type parameters (if any).
*
* @param type the type whose type arguments are to be returned
* @return the type arguments associated with the given type
*/
List<DartType> typeFormalsAsTypes(DartType type) =>
TypeParameterTypeImpl.getTypes(typeFormalsAsElements(type));
/**
* Compute the least upper bound of function types [f] and [g].
*
* The spec rules for LUB on function types, informally, are pretty simple
* (though unsound):
*
* - If the functions don't have the same number of required parameters,
* always return `Function`.
*
* - Discard any optional named or positional parameters the two types do not
* have in common.
*
* - Compute the LUB of each corresponding pair of parameter and return types.
* Return a function type with those types.
*/
DartType _functionLeastUpperBound(FunctionType f, FunctionType g) {
var fTypeFormals = f.typeFormals;
var gTypeFormals = g.typeFormals;
// If F and G differ in their number of type parameters, then the
// least upper bound of F and G is Function.
if (fTypeFormals.length != gTypeFormals.length) {
return typeProvider.functionType;
}
// If F and G differ in bounds of their of type parameters, then the
// least upper bound of F and G is Function.
var freshTypeFormalTypes =
FunctionTypeImpl.relateTypeFormals(f, g, (t, s, _, __) => t == s);
if (freshTypeFormalTypes == null) {
return typeProvider.functionType;
}
var typeFormals = freshTypeFormalTypes
.map<TypeParameterElement>((t) => t.element)
.toList();
f = f.instantiate(freshTypeFormalTypes);
g = g.instantiate(freshTypeFormalTypes);
List<DartType> fRequired = f.normalParameterTypes;
List<DartType> gRequired = g.normalParameterTypes;
// We need some parameter names for in the synthesized function type, so
// arbitrarily use f's.
List<String> fRequiredNames = f.normalParameterNames;
List<String> fPositionalNames = f.optionalParameterNames;
// If F and G differ in their number of required parameters, then the
// least upper bound of F and G is Function.
if (fRequired.length != gRequired.length) {
return typeProvider.functionType;
}
// Calculate the LUB of each corresponding pair of parameters.
List<ParameterElement> parameters = [];
for (int i = 0; i < fRequired.length; i++) {
parameters.add(new ParameterElementImpl.synthetic(
fRequiredNames[i],
_functionParameterBound(fRequired[i], gRequired[i]),
ParameterKind.REQUIRED));
}
List<DartType> fPositional = f.optionalParameterTypes;
List<DartType> gPositional = g.optionalParameterTypes;
// Ignore any extra optional positional parameters if one has more than the
// other.
int length = math.min(fPositional.length, gPositional.length);
for (int i = 0; i < length; i++) {
parameters.add(new ParameterElementImpl.synthetic(
fPositionalNames[i],
_functionParameterBound(fPositional[i], gPositional[i]),
ParameterKind.POSITIONAL));
}
// TODO(brianwilkerson) Handle the fact that named parameters can now be
// required.
Map<String, DartType> fNamed = f.namedParameterTypes;
Map<String, DartType> gNamed = g.namedParameterTypes;
for (String name in fNamed.keys.toSet()..retainAll(gNamed.keys)) {
parameters.add(new ParameterElementImpl.synthetic(
name,
_functionParameterBound(fNamed[name], gNamed[name]),
ParameterKind.NAMED));
}
// Calculate the LUB of the return type.
DartType returnType = getLeastUpperBound(f.returnType, g.returnType);
return FunctionTypeImpl.synthetic(returnType, typeFormals, parameters);
}
/**
* Calculates the appropriate upper or lower bound of a pair of parameters
* for two function types whose least upper bound is being calculated.
*
* In spec mode, this uses least upper bound, which... doesn't really make
* much sense. Strong mode overrides this to use greatest lower bound.
*/
DartType _functionParameterBound(DartType f, DartType g) =>
getLeastUpperBound(f, g);
/**
* Given two [InterfaceType]s [type1] and [type2] return their least upper
* bound in a type system specific manner.
*/
DartType _interfaceLeastUpperBound(InterfaceType type1, InterfaceType type2);
/**
* Starting from the given [type], search its class hierarchy for types of the
* form Future<R>, and return a list of the resulting R's.
*/
List<DartType> _searchTypeHierarchyForFutureTypeParameters(DartType type) {
List<DartType> result = <DartType>[];
HashSet<ClassElement> visitedClasses = new HashSet<ClassElement>();
void recurse(InterfaceTypeImpl type) {
if (type.isDartAsyncFuture && type.typeArguments.isNotEmpty) {
result.add(type.typeArguments[0]);
}
if (visitedClasses.add(type.element)) {
if (type.superclass != null) {
recurse(type.superclass);
}
for (InterfaceType interface in type.interfaces) {
recurse(interface);
}
visitedClasses.remove(type.element);
}
}
recurse(type);
return result;
}
/**
* Given two [DartType]s [type1] and [type2] at least one of which is a
* [TypeParameterType], return their least upper bound in a type system
* specific manner.
*/
DartType _typeParameterLeastUpperBound(DartType type1, DartType type2);
/**
* Create either a strong mode or regular type system based on context.
*/
static TypeSystem create(AnalysisContext context) {
var options = context.analysisOptions as AnalysisOptionsImpl;
return new Dart2TypeSystem(context.typeProvider,
implicitCasts: options.implicitCasts,
strictInference: options.strictInference);
}
}
/// A type that is being inferred but is not currently known.
///
/// This type will only appear in a downward inference context for type
/// parameters that we do not know yet. Notationally it is written `?`, for
/// example `List<?>`. This is distinct from `List<dynamic>`. These types will
/// never appear in the final resolved AST.
class UnknownInferredType extends TypeImpl {
static final UnknownInferredType instance = new UnknownInferredType._();
UnknownInferredType._()
: super(UnknownInferredTypeElement.instance, Keyword.DYNAMIC.lexeme);
@override
int get hashCode => 1;
@override
bool get isDynamic => true;
@override
NullabilitySuffix get nullabilitySuffix => NullabilitySuffix.star;
@override
bool operator ==(Object object) => identical(object, this);
@override
void appendTo(StringBuffer buffer, Set<TypeImpl> types,
{bool withNullability = false}) {
buffer.write('?');
}
@override
bool isMoreSpecificThan(DartType type,
[bool withDynamic = false, Set<Element> visitedElements]) {
// T is S
if (identical(this, type)) {
return true;
}
// else
return withDynamic;
}
@override
bool isSubtypeOf(DartType type) => true;
@override
bool isSupertypeOf(DartType type) => true;
@override
TypeImpl pruned(List<FunctionTypeAliasElement> prune) => this;
@override
DartType replaceTopAndBottom(TypeProvider typeProvider,
{bool isCovariant = true}) {
// In theory this should never happen, since we only need to do this
// replacement when checking super-boundedness of explicitly-specified
// types, or types produced by mixin inference or instantiate-to-bounds, and
// the unknown type can't occur in any of those cases.
assert(
false, 'Attempted to check super-boundedness of a type including "?"');
// But just in case it does, behave similar to `dynamic`.
if (isCovariant) {
return typeProvider.nullType;
} else {
return this;
}
}
@override
DartType substitute2(
List<DartType> argumentTypes, List<DartType> parameterTypes,
[List<FunctionTypeAliasElement> prune]) {
int length = parameterTypes.length;
for (int i = 0; i < length; i++) {
if (parameterTypes[i] == this) {
return argumentTypes[i];
}
}
return this;
}
@override
TypeImpl withNullability(NullabilitySuffix nullabilitySuffix) => this;
/// Given a [type] T, return true if it does not have an unknown type `?`.
static bool isKnown(DartType type) => !isUnknown(type);
/// Given a [type] T, return true if it has an unknown type `?`.
static bool isUnknown(DartType type) {
if (identical(type, UnknownInferredType.instance)) {
return true;
}
if (type is InterfaceTypeImpl) {
return type.typeArguments.any(isUnknown);
}
if (type is FunctionType) {
return isUnknown(type.returnType) ||
type.parameters.any((p) => isUnknown(p.type));
}
return false;
}
}
/// The synthetic element for [UnknownInferredType].
class UnknownInferredTypeElement extends ElementImpl
implements TypeDefiningElement {
static final UnknownInferredTypeElement instance =
new UnknownInferredTypeElement._();
UnknownInferredTypeElement._() : super(Keyword.DYNAMIC.lexeme, -1) {
setModifier(Modifier.SYNTHETIC, true);
}
@override
ElementKind get kind => ElementKind.DYNAMIC;
@override
UnknownInferredType get type => UnknownInferredType.instance;
@override
T accept<T>(ElementVisitor visitor) => null;
}
/// A constraint on a type parameter that we're inferring.
class _TypeConstraint extends _TypeRange {
/// The type parameter that is constrained by [lowerBound] or [upperBound].
final TypeParameterElement typeParameter;
/// Where this constraint comes from, used for error messages.
///
/// See [toString].
final _TypeConstraintOrigin origin;
_TypeConstraint(this.origin, this.typeParameter,
{DartType upper, DartType lower})
: super(upper: upper, lower: lower);
_TypeConstraint.fromExtends(
TypeParameterElement element, DartType extendsType)
: this(
new _TypeConstraintFromExtendsClause(element, extendsType), element,
upper: extendsType);
bool get isDownwards => origin is! _TypeConstraintFromArgument;
bool isSatisifedBy(TypeSystem ts, DartType type) =>
ts.isSubtypeOf(lowerBound, type) && ts.isSubtypeOf(type, upperBound);
/// Converts this constraint to a message suitable for a type inference error.
@override
String toString() => !identical(upperBound, UnknownInferredType.instance)
? "'$typeParameter' must extend '$upperBound'"
: "'$lowerBound' must extend '$typeParameter'";
}
class _TypeConstraintFromArgument extends _TypeConstraintOrigin {
final DartType argumentType;
final DartType parameterType;
final String parameterName;
final ClassElement genericClass;
_TypeConstraintFromArgument(
this.argumentType, this.parameterType, this.parameterName,
{this.genericClass});