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//===--- Constraint.h - Constraint in the Type Checker ----------*- C++ -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This file provides the \c Constraint class and its related types,
// which is used by the constraint-based type checker to describe a
// constraint that must be solved.
//
//===----------------------------------------------------------------------===//
#ifndef SWIFT_SEMA_CONSTRAINT_H
#define SWIFT_SEMA_CONSTRAINT_H
#include "swift/AST/FunctionRefKind.h"
#include "swift/AST/Identifier.h"
#include "swift/AST/Type.h"
#include "swift/Basic/Debug.h"
#include "swift/Sema/OverloadChoice.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/ilist.h"
#include "llvm/ADT/ilist_node.h"
#include "llvm/Support/TrailingObjects.h"
namespace llvm {
class raw_ostream;
}
namespace swift {
class ProtocolDecl;
class SourceManager;
class TypeVariableType;
namespace constraints {
class ConstraintFix;
class ConstraintLocator;
class ConstraintSystem;
enum class TrailingClosureMatching;
/// Describes the kind of constraint placed on one or more types.
enum class ConstraintKind : char {
/// The two types must be bound to the same type. This is the only
/// truly symmetric constraint.
Bind,
/// The two types must be bound to the same type, dropping
/// lvalueness when comparing a type variable to a type.
Equal,
/// The first type is the type of a function parameter; the second
/// type is the type of a reference to that parameter from within the
/// function body. Specifically, the left type is an inout type iff the right
/// type is an lvalue type with the same object type. Otherwise, the two
/// types must be the same type.
BindParam,
/// Binds the first type to the element type of the second type.
BindToPointerType,
/// The first type is a subtype of the second type, i.e., a value
/// of the type of the first type can be used wherever a value of the
/// second type is expected.
Subtype,
/// The first type is convertible to the second type.
Conversion,
/// The first type can be bridged to the second type.
BridgingConversion,
/// The first type is the element of an argument tuple that is
/// convertible to the second type (which represents the corresponding
/// parameter type).
ArgumentConversion,
/// The first type is convertible to the second type, including inout.
OperatorArgumentConversion,
/// The first type must conform to the second type (which is a
/// protocol type).
ConformsTo,
/// The first type describes a literal that conforms to the second
/// type, which is one of the known expressible-by-literal protocols.
LiteralConformsTo,
/// A checked cast from the first type to the second.
CheckedCast,
/// The first type can act as the Self type of the second type (which
/// is a protocol).
///
/// This constraint is slightly looser than a conforms-to constraint, because
/// an existential can be used as the Self of any protocol within the
/// existential, even if it doesn't conform to that protocol (e.g., due to
/// the use of associated types).
SelfObjectOfProtocol,
/// Both types are function types. The first function type's
/// input is the value being passed to the function and its output
/// is a type variable that describes the output. The second
/// function type is expected to become a function type. Note, we
/// do not require the function type attributes to match.
ApplicableFunction,
/// The first type is a function type whose input is the value passed
/// to the function and whose output is a type variable describing the output.
/// The second type is either a `@dynamicCallable` nominal type or the
/// function type of a `dynamicallyCall` method defined on a
/// `@dynamicCallable` nominal type.
DynamicCallableApplicableFunction,
/// The first type is the type of the dynamicType member of the
/// second type.
DynamicTypeOf,
/// Binds the left-hand type to a particular overload choice.
BindOverload,
/// The first type has a member with the given name, and the
/// type of that member, when referenced as a value, is the second type.
ValueMember,
/// The first type (which is implicit) has a member with the given
/// name, and the type of that member, when referenced as a value, is the
/// second type.
UnresolvedValueMember,
/// The first type conforms to the protocol in which the member requirement
/// resides. Once the conformance is resolved, the value witness will be
/// determined, and the type of that witness, when referenced as a value,
/// will be bound to the second type.
ValueWitness,
/// The first type can be defaulted to the second (which currently
/// cannot be dependent). This is more like a type property than a
/// relational constraint.
Defaultable,
/// A disjunction constraint that specifies that one or more of the
/// stored constraints must hold.
Disjunction,
/// The first type is an optional type whose object type is the second
/// type, preserving lvalue-ness.
OptionalObject,
/// The first type is the same function type as the second type, but
/// made @escaping.
EscapableFunctionOf,
/// The first type is an opened type from the second type (which is
/// an existential).
OpenedExistentialOf,
/// A relation between three types. The first is the key path type,
/// the second is the root type, and the third is the projected value type.
/// The second and third types can be lvalues depending on the kind of key
/// path.
KeyPathApplication,
/// A relation between three types. The first is the key path type,
/// the second is its root type, and the third is the projected value type.
/// The key path type is chosen based on the selection of overloads for the
/// member references along the path.
KeyPath,
/// The first type is a function type, the second is the function's
/// input type.
FunctionInput,
/// The first type is a function type, the second is the function's
/// result type.
FunctionResult,
/// The first type is a type that's a candidate to be the underlying type of
/// the second opaque archetype.
OpaqueUnderlyingType,
/// The first type will be equal to the second type, but only when the
/// second type has been fully determined (and mapped down to a concrete
/// type). At that point, this constraint will be treated like an `Equal`
/// constraint.
OneWayEqual,
/// The second type is the type of a function parameter, and the first type
/// is the type of a reference to that function parameter within the body.
/// Once the second type has been fully determined (and mapped down to a
/// concrete type), this constraint will be treated like a 'BindParam'
/// constraint.
OneWayBindParam,
/// If there is no contextual info e.g. `_ = { 42 }` default first type
/// to a second type (inferred closure type). This is effectively a
/// `Defaultable` constraint which a couple of differences:
///
/// - References inferred closure type and all of the outer parameters
/// referenced by closure body.
/// - Handled specially by binding inference, specifically contributes
/// to the bindings only if there are no contextual types available.
DefaultClosureType,
};
/// Classification of the different kinds of constraints.
enum class ConstraintClassification : char {
/// A relational constraint, which relates two types.
Relational,
/// A member constraint, which names a member of a type and assigns
/// it a reference type.
Member,
/// A property of a single type, such as whether it is defaultable to
/// a particular type.
TypeProperty,
/// A disjunction constraint.
Disjunction
};
/// Specifies a restriction on the kind of conversion that should be
/// performed between the types in a constraint.
///
/// It's common for there to be multiple potential conversions that can
/// apply between two types, e.g., given class types A and B, there might be
/// a superclass conversion from A to B or there might be a user-defined
/// conversion from A to B. The solver may need to explore both paths.
enum class ConversionRestrictionKind {
/// Deep equality comparison.
DeepEquality,
/// Subclass-to-superclass conversion.
Superclass,
/// Class metatype to AnyObject conversion.
ClassMetatypeToAnyObject,
/// Existential metatype to AnyObject conversion.
ExistentialMetatypeToAnyObject,
/// Protocol value metatype to Protocol class conversion.
ProtocolMetatypeToProtocolClass,
/// Inout-to-pointer conversion.
InoutToPointer,
/// Array-to-pointer conversion.
ArrayToPointer,
/// String-to-pointer conversion.
StringToPointer,
/// Pointer-to-pointer conversion.
PointerToPointer,
/// Value to existential value conversion, or existential erasure.
Existential,
/// Metatype to existential metatype conversion.
MetatypeToExistentialMetatype,
/// Existential metatype to metatype conversion.
ExistentialMetatypeToMetatype,
/// T -> U? value to optional conversion (or to implicitly unwrapped
/// optional).
ValueToOptional,
/// T? -> U? optional to optional conversion (or unchecked to unchecked).
OptionalToOptional,
/// Implicit upcast conversion of array types.
ArrayUpcast,
/// Implicit upcast conversion of dictionary types, which includes
/// bridging.
DictionaryUpcast,
/// Implicit upcast conversion of set types, which includes bridging.
SetUpcast,
/// T:Hashable -> AnyHashable conversion.
HashableToAnyHashable,
/// Implicit conversion from a CF type to its toll-free-bridged Objective-C
/// class type.
CFTollFreeBridgeToObjC,
/// Implicit conversion from an Objective-C class type to its
/// toll-free-bridged CF type.
ObjCTollFreeBridgeToCF,
};
/// Specifies whether a given conversion requires the creation of a temporary
/// value which is only valid for a limited scope. For example, the
/// array-to-pointer conversion produces a pointer that is only valid for the
/// duration of the call that it's passed to. Such ephemeral conversions cannot
/// be passed to non-ephemeral parameters.
enum class ConversionEphemeralness {
/// The conversion requires the creation of a temporary value.
Ephemeral,
/// The conversion does not require the creation of a temporary value.
NonEphemeral,
/// It is not currently known whether the conversion will produce a temporary
/// value or not. This can occur for example with an inout-to-pointer
/// conversion of a member whose base type is an unresolved type variable.
Unresolved,
};
/// Return a string representation of a conversion restriction.
llvm::StringRef getName(ConversionRestrictionKind kind);
/// Should we record which choice was taken in this disjunction for
/// the purposes of applying it later?
enum RememberChoice_t : bool {
ForgetChoice = false,
RememberChoice = true
};
/// A constraint between two type variables.
class Constraint final : public llvm::ilist_node<Constraint>,
private llvm::TrailingObjects<Constraint, TypeVariableType *> {
friend TrailingObjects;
/// The kind of constraint.
ConstraintKind Kind : 8;
/// The kind of restriction placed on this constraint.
ConversionRestrictionKind Restriction : 8;
/// The fix to be applied to the constraint before visiting it.
ConstraintFix *TheFix = nullptr;
/// Whether the \c Restriction field is valid.
unsigned HasRestriction : 1;
/// Whether this constraint is currently active, i.e., stored in the worklist.
unsigned IsActive : 1;
/// Was this constraint was determined to be inconsistent with the
/// constraint graph during constraint propagation?
unsigned IsDisabled : 1;
/// Whether the choice of this disjunction should be recorded in the
/// solver state.
unsigned RememberChoice : 1;
/// Whether or not this constraint is 'favored' in the sense that, if
/// successfully applied, it should be preferred over any other constraints
/// in its disjunction.
unsigned IsFavored : 1;
/// The number of type variables referenced by this constraint.
///
/// The type variables themselves are tail-allocated.
unsigned NumTypeVariables : 11;
/// The kind of function reference, for member references.
unsigned TheFunctionRefKind : 2;
/// The trailing closure matching for an applicable function constraint,
/// if any. 0 = None, 1 = Forward, 2 = Backward.
unsigned trailingClosureMatching : 2;
union {
struct {
/// The first type.
Type First;
/// The second type.
Type Second;
/// The third type, if any.
Type Third;
} Types;
struct {
/// The type of the base.
Type First;
/// The type of the member.
Type Second;
union {
/// If non-null, the name of a member of the first type is that
/// being related to the second type.
///
/// Used for ValueMember an UnresolvedValueMember constraints.
DeclNameRef Name;
/// If non-null, the member being referenced.
///
/// Used for ValueWitness constraints.
ValueDecl *Ref;
} Member;
/// The DC in which the use appears.
DeclContext *UseDC;
} Member;
/// The set of constraints for a disjunction.
ArrayRef<Constraint *> Nested;
struct {
/// The first type
Type First;
/// The overload choice
OverloadChoice Choice;
/// The DC in which the use appears.
DeclContext *UseDC;
} Overload;
};
/// The locator that describes where in the expression this
/// constraint applies.
ConstraintLocator *Locator;
/// Constraints are always allocated within a given constraint
/// system.
void *operator new(size_t) = delete;
Constraint(ConstraintKind kind, ArrayRef<Constraint *> constraints,
ConstraintLocator *locator, ArrayRef<TypeVariableType *> typeVars);
/// Construct a new constraint.
Constraint(ConstraintKind kind, Type first, Type second,
ConstraintLocator *locator,
ArrayRef<TypeVariableType *> typeVars);
/// Construct a new constraint.
Constraint(ConstraintKind kind, Type first, Type second, Type third,
ConstraintLocator *locator,
ArrayRef<TypeVariableType *> typeVars);
/// Construct a new member constraint.
Constraint(ConstraintKind kind, Type first, Type second, DeclNameRef member,
DeclContext *useDC, FunctionRefKind functionRefKind,
ConstraintLocator *locator,
ArrayRef<TypeVariableType *> typeVars);
/// Construct a new value witness constraint.
Constraint(ConstraintKind kind, Type first, Type second,
ValueDecl *requirement, DeclContext *useDC,
FunctionRefKind functionRefKind, ConstraintLocator *locator,
ArrayRef<TypeVariableType *> typeVars);
/// Construct a new overload-binding constraint, which might have a fix.
Constraint(Type type, OverloadChoice choice, DeclContext *useDC,
ConstraintFix *fix, ConstraintLocator *locator,
ArrayRef<TypeVariableType *> typeVars);
/// Construct a restricted constraint.
Constraint(ConstraintKind kind, ConversionRestrictionKind restriction,
Type first, Type second, ConstraintLocator *locator,
ArrayRef<TypeVariableType *> typeVars);
/// Construct a relational constraint with a fix.
Constraint(ConstraintKind kind, ConstraintFix *fix, Type first, Type second,
ConstraintLocator *locator, ArrayRef<TypeVariableType *> typeVars);
/// Retrieve the type variables buffer, for internal mutation.
MutableArrayRef<TypeVariableType *> getTypeVariablesBuffer() {
return { getTrailingObjects<TypeVariableType *>(), NumTypeVariables };
}
public:
/// Create a new constraint.
static Constraint *create(ConstraintSystem &cs, ConstraintKind Kind,
Type First, Type Second, ConstraintLocator *locator,
ArrayRef<TypeVariableType *> extraTypeVars = {});
/// Create a new constraint.
static Constraint *create(ConstraintSystem &cs, ConstraintKind Kind,
Type First, Type Second, Type Third,
ConstraintLocator *locator,
ArrayRef<TypeVariableType *> extraTypeVars = { });
/// Create a new member constraint, or a disjunction of that with the outer
/// alternatives.
static Constraint *createMemberOrOuterDisjunction(
ConstraintSystem &cs, ConstraintKind kind, Type first, Type second,
DeclNameRef member, DeclContext *useDC, FunctionRefKind functionRefKind,
ArrayRef<OverloadChoice> outerAlternatives, ConstraintLocator *locator);
/// Create a new member constraint.
static Constraint *createMember(ConstraintSystem &cs, ConstraintKind kind,
Type first, Type second, DeclNameRef member,
DeclContext *useDC,
FunctionRefKind functionRefKind,
ConstraintLocator *locator);
/// Create a new value witness constraint.
static Constraint *createValueWitness(
ConstraintSystem &cs, ConstraintKind kind, Type first, Type second,
ValueDecl *requirement, DeclContext *useDC,
FunctionRefKind functionRefKind, ConstraintLocator *locator);
/// Create an overload-binding constraint.
static Constraint *createBindOverload(ConstraintSystem &cs, Type type,
OverloadChoice choice,
DeclContext *useDC,
ConstraintLocator *locator);
/// Create a restricted relational constraint.
static Constraint *createRestricted(ConstraintSystem &cs, ConstraintKind kind,
ConversionRestrictionKind restriction,
Type first, Type second,
ConstraintLocator *locator);
/// Create a relational constraint with a fix.
static Constraint *createFixed(ConstraintSystem &cs, ConstraintKind kind,
ConstraintFix *fix, Type first, Type second,
ConstraintLocator *locator);
/// Create a bind overload choice with a fix.
/// Note: This constraint is going to be disabled by default.
static Constraint *createFixedChoice(ConstraintSystem &cs, Type type,
OverloadChoice choice,
DeclContext *useDC, ConstraintFix *fix,
ConstraintLocator *locator);
/// Create a new disjunction constraint.
static Constraint *createDisjunction(ConstraintSystem &cs,
ArrayRef<Constraint *> constraints,
ConstraintLocator *locator,
RememberChoice_t shouldRememberChoice
= ForgetChoice);
/// Create a new Applicable Function constraint.
static Constraint *createApplicableFunction(
ConstraintSystem &cs, Type argumentFnType, Type calleeType,
Optional<TrailingClosureMatching> trailingClosureMatching,
ConstraintLocator *locator);
/// Determine the kind of constraint.
ConstraintKind getKind() const { return Kind; }
/// Retrieve the restriction placed on this constraint.
Optional<ConversionRestrictionKind> getRestriction() const {
if (!HasRestriction)
return None;
return Restriction;
}
/// Retrieve the fix associated with this constraint.
ConstraintFix *getFix() const { return TheFix; }
/// Whether this constraint is active, i.e., in the worklist.
bool isActive() const { return IsActive; }
/// Set whether this constraint is active or not.
void setActive(bool active) {
assert(!isDisabled() && "Cannot activate a constraint that is disabled!");
IsActive = active;
}
/// Whether this constraint is active, i.e., in the worklist.
bool isDisabled() const { return IsDisabled; }
/// Set whether this constraint is active or not.
void setDisabled() {
assert(!isActive() && "Cannot disable constraint marked as active!");
IsDisabled = true;
}
void setEnabled() {
assert(isDisabled() && "Can't re-enable already active constraint!");
IsDisabled = false;
}
/// Mark or retrieve whether this constraint should be favored in the system.
void setFavored(bool favored = true) { IsFavored = favored; }
bool isFavored() const { return IsFavored; }
/// Whether the solver should remember which choice was taken for
/// this constraint.
bool shouldRememberChoice() const { return RememberChoice; }
/// Retrieve the set of type variables referenced by this constraint.
ArrayRef<TypeVariableType *> getTypeVariables() const {
return {getTrailingObjects<TypeVariableType*>(), NumTypeVariables};
}
/// Determine the classification of this constraint, providing
/// a broader categorization than \c getKind().
ConstraintClassification getClassification() const {
switch (Kind) {
case ConstraintKind::Bind:
case ConstraintKind::Equal:
case ConstraintKind::BindParam:
case ConstraintKind::BindToPointerType:
case ConstraintKind::Subtype:
case ConstraintKind::Conversion:
case ConstraintKind::BridgingConversion:
case ConstraintKind::ArgumentConversion:
case ConstraintKind::OperatorArgumentConversion:
case ConstraintKind::ConformsTo:
case ConstraintKind::LiteralConformsTo:
case ConstraintKind::CheckedCast:
case ConstraintKind::SelfObjectOfProtocol:
case ConstraintKind::ApplicableFunction:
case ConstraintKind::DynamicCallableApplicableFunction:
case ConstraintKind::BindOverload:
case ConstraintKind::OptionalObject:
case ConstraintKind::OpaqueUnderlyingType:
case ConstraintKind::OneWayEqual:
case ConstraintKind::OneWayBindParam:
case ConstraintKind::DefaultClosureType:
return ConstraintClassification::Relational;
case ConstraintKind::ValueMember:
case ConstraintKind::UnresolvedValueMember:
case ConstraintKind::ValueWitness:
return ConstraintClassification::Member;
case ConstraintKind::DynamicTypeOf:
case ConstraintKind::EscapableFunctionOf:
case ConstraintKind::OpenedExistentialOf:
case ConstraintKind::KeyPath:
case ConstraintKind::KeyPathApplication:
case ConstraintKind::Defaultable:
case ConstraintKind::FunctionInput:
case ConstraintKind::FunctionResult:
return ConstraintClassification::TypeProperty;
case ConstraintKind::Disjunction:
return ConstraintClassification::Disjunction;
}
llvm_unreachable("Unhandled ConstraintKind in switch.");
}
/// Retrieve the first type in the constraint.
Type getFirstType() const {
switch (getKind()) {
case ConstraintKind::Disjunction:
llvm_unreachable("disjunction constraints have no type operands");
case ConstraintKind::BindOverload:
return Overload.First;
case ConstraintKind::ValueMember:
case ConstraintKind::UnresolvedValueMember:
case ConstraintKind::ValueWitness:
return Member.First;
default:
return Types.First;
}
}
/// Retrieve the second type in the constraint.
Type getSecondType() const {
switch (getKind()) {
case ConstraintKind::Disjunction:
case ConstraintKind::BindOverload:
llvm_unreachable("constraint has no second type");
case ConstraintKind::ValueMember:
case ConstraintKind::UnresolvedValueMember:
case ConstraintKind::ValueWitness:
return Member.Second;
default:
return Types.Second;
}
}
/// Retrieve the third type in the constraint.
Type getThirdType() const {
switch (getKind()) {
case ConstraintKind::KeyPath:
case ConstraintKind::KeyPathApplication:
return Types.Third;
default:
llvm_unreachable("no third type");
}
}
/// Retrieve the protocol in a conformance constraint.
ProtocolDecl *getProtocol() const;
/// Retrieve the name of the member for a member constraint.
DeclNameRef getMember() const {
assert(Kind == ConstraintKind::ValueMember ||
Kind == ConstraintKind::UnresolvedValueMember);
return Member.Member.Name;
}
/// Retrieve the requirement being referenced by a value witness constraint.
ValueDecl *getRequirement() const {
assert(Kind == ConstraintKind::ValueWitness);
return Member.Member.Ref;
}
/// Determine the kind of function reference we have for a member reference.
FunctionRefKind getFunctionRefKind() const {
if (Kind == ConstraintKind::ValueMember ||
Kind == ConstraintKind::UnresolvedValueMember ||
Kind == ConstraintKind::ValueWitness)
return static_cast<FunctionRefKind>(TheFunctionRefKind);
// Conservative answer: drop all of the labels.
return FunctionRefKind::Compound;
}
/// Retrieve the set of constraints in a disjunction.
ArrayRef<Constraint *> getNestedConstraints() const {
assert(Kind == ConstraintKind::Disjunction);
return Nested;
}
unsigned countFavoredNestedConstraints() const {
return llvm::count_if(Nested, [](const Constraint *constraint) {
return constraint->isFavored() && !constraint->isDisabled();
});
}
unsigned countActiveNestedConstraints() const {
return llvm::count_if(Nested, [](const Constraint *constraint) {
return !constraint->isDisabled();
});
}
/// Determine if this constraint represents explicit conversion,
/// e.g. coercion constraint "as X" which forms a disjunction.
bool isExplicitConversion() const;
/// Whether this is a one-way constraint.
bool isOneWayConstraint() const {
return Kind == ConstraintKind::OneWayEqual ||
Kind == ConstraintKind::OneWayBindParam;
}
/// Retrieve the overload choice for an overload-binding constraint.
OverloadChoice getOverloadChoice() const {
assert(Kind == ConstraintKind::BindOverload);
return Overload.Choice;
}
/// Retrieve the DC in which the overload was used.
DeclContext *getOverloadUseDC() const {
assert(Kind == ConstraintKind::BindOverload);
return Overload.UseDC;
}
/// Retrieve the DC in which the member was used.
DeclContext *getMemberUseDC() const {
assert(Kind == ConstraintKind::ValueMember ||
Kind == ConstraintKind::UnresolvedValueMember ||
Kind == ConstraintKind::ValueWitness);
return Member.UseDC;
}
/// For an applicable function constraint, retrieve the trailing closure
/// matching rule.
Optional<TrailingClosureMatching> getTrailingClosureMatching() const;
/// Retrieve the locator for this constraint.
ConstraintLocator *getLocator() const { return Locator; }
/// Clone the given constraint.
Constraint *clone(ConstraintSystem &cs) const;
void print(llvm::raw_ostream &Out, SourceManager *sm) const;
SWIFT_DEBUG_DUMPER(dump(SourceManager *SM));
SWIFT_DEBUG_DUMPER(dump(ConstraintSystem *CS));
void *operator new(size_t bytes, ConstraintSystem& cs,
size_t alignment = alignof(Constraint));
inline void operator delete(void *, const ConstraintSystem &cs, size_t) {}
void *operator new(size_t bytes, void *mem) { return mem; }
void operator delete(void *mem) { }
};
} // end namespace constraints
} // end namespace swift
namespace llvm {
/// Specialization of \c ilist_traits for constraints.
template<>
struct ilist_traits<swift::constraints::Constraint>
: public ilist_node_traits<swift::constraints::Constraint> {
using Element = swift::constraints::Constraint;
static Element *createNode(const Element &V) = delete;
static void deleteNode(Element *V) { /* never deleted */ }
};
} // end namespace llvm
#endif // LLVM_SWIFT_SEMA_CONSTRAINT_H