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CSRanking.cpp
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//===--- CSRanking.cpp - Constraint System Ranking ------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2018 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 implements solution ranking heuristics for the
// constraint-based type checker.
//
//===----------------------------------------------------------------------===//
#include "ConstraintSystem.h"
#include "swift/AST/GenericSignature.h"
#include "swift/AST/ParameterList.h"
#include "swift/AST/ProtocolConformance.h"
#include "swift/AST/TypeCheckRequests.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Compiler.h"
using namespace swift;
using namespace constraints;
//===----------------------------------------------------------------------===//
// Statistics
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "Constraint solver overall"
STATISTIC(NumDiscardedSolutions, "Number of solutions discarded");
void ConstraintSystem::increaseScore(ScoreKind kind, unsigned value) {
unsigned index = static_cast<unsigned>(kind);
CurrentScore.Data[index] += value;
if (getASTContext().TypeCheckerOpts.DebugConstraintSolver && value > 0) {
auto &log = getASTContext().TypeCheckerDebug->getStream();
if (solverState)
log.indent(solverState->depth * 2);
log << "(increasing score due to ";
switch (kind) {
case SK_Hole:
log << "hole in the constraint system";
break;
case SK_Unavailable:
log << "use of an unavailable declaration";
break;
case SK_Fix:
log << "attempting to fix the source";
break;
case SK_DisfavoredOverload:
log << "disfavored overload";
break;
case SK_ForceUnchecked:
log << "force of an implicitly unwrapped optional";
break;
case SK_UserConversion:
log << "user conversion";
break;
case SK_FunctionConversion:
log << "function conversion";
break;
case SK_NonDefaultLiteral:
log << "non-default literal";
break;
case SK_CollectionUpcastConversion:
log << "collection upcast conversion";
break;
case SK_ValueToOptional:
log << "value to optional";
break;
case SK_EmptyExistentialConversion:
log << "empty-existential conversion";
break;
case SK_KeyPathSubscript:
log << "key path subscript";
break;
case SK_ValueToPointerConversion:
log << "value-to-pointer conversion";
break;
}
log << ")\n";
}
}
bool ConstraintSystem::worseThanBestSolution() const {
if (getASTContext().TypeCheckerOpts.DisableConstraintSolverPerformanceHacks)
return false;
if (!solverState || !solverState->BestScore ||
CurrentScore <= *solverState->BestScore)
return false;
if (getASTContext().TypeCheckerOpts.DebugConstraintSolver) {
auto &log = getASTContext().TypeCheckerDebug->getStream();
log.indent(solverState->depth * 2)
<< "(solution is worse than the best solution)\n";
}
return true;
}
llvm::raw_ostream &constraints::operator<<(llvm::raw_ostream &out,
const Score &score) {
for (unsigned i = 0; i != NumScoreKinds; ++i) {
if (i) out << ' ';
out << score.Data[i];
}
return out;
}
///\ brief Compare two declarations for equality when they are used.
///
static bool sameDecl(Decl *decl1, Decl *decl2) {
if (decl1 == decl2)
return true;
// All types considered identical.
// FIXME: This is a hack. What we really want is to have substituted the
// base type into the declaration reference, so that we can compare the
// actual types to which two type declarations resolve. If those types are
// equivalent, then it doesn't matter which declaration is chosen.
if (isa<TypeDecl>(decl1) && isa<TypeDecl>(decl2))
return true;
if (decl1->getKind() != decl2->getKind())
return false;
return false;
}
/// Compare two overload choices for equality.
static bool sameOverloadChoice(const OverloadChoice &x,
const OverloadChoice &y) {
if (x.getKind() != y.getKind())
return false;
switch (x.getKind()) {
case OverloadChoiceKind::KeyPathApplication:
// FIXME: Compare base types after substitution?
return true;
case OverloadChoiceKind::Decl:
case OverloadChoiceKind::DeclViaDynamic:
case OverloadChoiceKind::DeclViaBridge:
case OverloadChoiceKind::DeclViaUnwrappedOptional:
case OverloadChoiceKind::DynamicMemberLookup:
case OverloadChoiceKind::KeyPathDynamicMemberLookup:
return sameDecl(x.getDecl(), y.getDecl());
case OverloadChoiceKind::TupleIndex:
return x.getTupleIndex() == y.getTupleIndex();
}
llvm_unreachable("Unhandled OverloadChoiceKind in switch.");
}
namespace {
/// Describes the relationship between the context types for two declarations.
enum class SelfTypeRelationship {
/// The types are unrelated; ignore the bases entirely.
Unrelated,
/// The types are equivalent.
Equivalent,
/// The first type is a subclass of the second.
Subclass,
/// The second type is a subclass of the first.
Superclass,
/// The first type conforms to the second
ConformsTo,
/// The second type conforms to the first.
ConformedToBy
};
} // end anonymous namespace
/// Determines whether the first type is nominally a superclass of the second
/// type, ignore generic arguments.
static bool isNominallySuperclassOf(Type type1, Type type2) {
auto nominal1 = type1->getAnyNominal();
if (!nominal1)
return false;
for (auto super2 = type2; super2; super2 = super2->getSuperclass()) {
if (super2->getAnyNominal() == nominal1)
return true;
}
return false;
}
/// Determine the relationship between the self types of the given declaration
/// contexts..
static std::pair<SelfTypeRelationship, ProtocolConformanceRef>
computeSelfTypeRelationship(DeclContext *dc, ValueDecl *decl1,
ValueDecl *decl2) {
// If both declarations are operators, even through they
// might have Self such types are unrelated.
if (decl1->isOperator() && decl2->isOperator())
return {SelfTypeRelationship::Unrelated, ProtocolConformanceRef()};
auto *dc1 = decl1->getDeclContext();
auto *dc2 = decl2->getDeclContext();
// If at least one of the contexts is a non-type context, the two are
// unrelated.
if (!dc1->isTypeContext() || !dc2->isTypeContext())
return {SelfTypeRelationship::Unrelated, ProtocolConformanceRef()};
Type type1 = dc1->getDeclaredInterfaceType();
Type type2 = dc2->getDeclaredInterfaceType();
// If the types are equal, the answer is simple.
if (type1->isEqual(type2))
return {SelfTypeRelationship::Equivalent, ProtocolConformanceRef()};
// If both types can have superclasses, which whether one is a superclass
// of the other. The subclass is the common base type.
if (type1->mayHaveSuperclass() && type2->mayHaveSuperclass()) {
if (isNominallySuperclassOf(type1, type2))
return {SelfTypeRelationship::Superclass, ProtocolConformanceRef()};
if (isNominallySuperclassOf(type2, type1))
return {SelfTypeRelationship::Subclass, ProtocolConformanceRef()};
return {SelfTypeRelationship::Unrelated, ProtocolConformanceRef()};
}
// If neither or both are protocol types, consider the bases unrelated.
bool isProtocol1 = isa<ProtocolDecl>(dc1);
bool isProtocol2 = isa<ProtocolDecl>(dc2);
if (isProtocol1 == isProtocol2)
return {SelfTypeRelationship::Unrelated, ProtocolConformanceRef()};
// Just one of the two is a protocol. Check whether the other conforms to
// that protocol.
Type protoTy = isProtocol1? type1 : type2;
Type modelTy = isProtocol1? type2 : type1;
auto proto = protoTy->castTo<ProtocolType>()->getDecl();
// If the model type does not conform to the protocol, the bases are
// unrelated.
auto conformance = TypeChecker::conformsToProtocol(
modelTy, proto, dc,
ConformanceCheckFlags::SkipConditionalRequirements);
if (conformance.isInvalid())
return {SelfTypeRelationship::Unrelated, conformance};
if (isProtocol1)
return {SelfTypeRelationship::ConformedToBy, conformance};
return {SelfTypeRelationship::ConformsTo, conformance};
}
/// Given two generic function declarations, signal if the first is more
/// "constrained" than the second by comparing the number of constraints
/// applied to each type parameter.
/// Note that this is not a subtype or conversion check - that takes place
/// in isDeclAsSpecializedAs.
static bool isDeclMoreConstrainedThan(ValueDecl *decl1, ValueDecl *decl2) {
if (decl1->getKind() != decl2->getKind() || isa<TypeDecl>(decl1))
return false;
GenericParamList *gp1 = nullptr, *gp2 = nullptr;
auto func1 = dyn_cast<FuncDecl>(decl1);
auto func2 = dyn_cast<FuncDecl>(decl2);
if (func1 && func2) {
gp1 = func1->getGenericParams();
gp2 = func2->getGenericParams();
}
auto subscript1 = dyn_cast<SubscriptDecl>(decl1);
auto subscript2 = dyn_cast<SubscriptDecl>(decl2);
if (subscript1 && subscript2) {
gp1 = subscript1->getGenericParams();
gp2 = subscript2->getGenericParams();
}
if (gp1 && gp2) {
auto params1 = gp1->getParams();
auto params2 = gp2->getParams();
if (params1.size() == params2.size()) {
for (size_t i = 0; i < params1.size(); i++) {
auto p1 = params1[i];
auto p2 = params2[i];
int np1 = static_cast<int>(p1->getConformingProtocols().size());
int np2 = static_cast<int>(p2->getConformingProtocols().size());
int aDelta = np1 - np2;
if (aDelta)
return aDelta > 0;
}
}
}
return false;
}
/// Determine whether one protocol extension is at least as specialized as
/// another.
static bool isProtocolExtensionAsSpecializedAs(DeclContext *dc1,
DeclContext *dc2) {
assert(dc1->getExtendedProtocolDecl());
assert(dc2->getExtendedProtocolDecl());
// If one of the protocols being extended inherits the other, prefer the
// more specialized protocol.
auto proto1 = dc1->getExtendedProtocolDecl();
auto proto2 = dc2->getExtendedProtocolDecl();
if (proto1 != proto2) {
if (proto1->inheritsFrom(proto2))
return true;
if (proto2->inheritsFrom(proto1))
return false;
}
// If the two generic signatures are identical, neither is as specialized
// as the other.
GenericSignature sig1 = dc1->getGenericSignatureOfContext();
GenericSignature sig2 = dc2->getGenericSignatureOfContext();
if (sig1.getCanonicalSignature() == sig2.getCanonicalSignature())
return false;
// Form a constraint system where we've opened up all of the requirements of
// the second protocol extension.
ConstraintSystem cs(dc1, None);
OpenedTypeMap replacements;
cs.openGeneric(dc2, sig2, ConstraintLocatorBuilder(nullptr), replacements);
// Bind the 'Self' type from the first extension to the type parameter from
// opening 'Self' of the second extension.
Type selfType1 = sig1->getGenericParams()[0];
Type selfType2 = sig2->getGenericParams()[0];
cs.addConstraint(ConstraintKind::Bind,
replacements[cast<GenericTypeParamType>(selfType2->getCanonicalType())],
dc1->mapTypeIntoContext(selfType1),
nullptr);
// Solve the system. If the first extension is at least as specialized as the
// second, we're done.
return cs.solveSingle().hasValue();
}
/// Retrieve the adjusted parameter type for overloading purposes.
static Type getAdjustedParamType(const AnyFunctionType::Param ¶m) {
auto type = param.getOldType();
if (param.isAutoClosure())
return type->castTo<FunctionType>()->getResult();
return type;
}
// Is a particular parameter of a function or subscript declaration
// declared to be an IUO?
static bool paramIsIUO(const ValueDecl *decl, int paramNum) {
return swift::getParameterAt(decl, paramNum)
->isImplicitlyUnwrappedOptional();
}
/// Determine whether the first declaration is as "specialized" as
/// the second declaration.
///
/// "Specialized" is essentially a form of subtyping, defined below.
static bool isDeclAsSpecializedAs(DeclContext *dc, ValueDecl *decl1,
ValueDecl *decl2,
bool isDynamicOverloadComparison = false) {
return evaluateOrDefault(decl1->getASTContext().evaluator,
CompareDeclSpecializationRequest{
dc, decl1, decl2, isDynamicOverloadComparison},
false);
}
bool CompareDeclSpecializationRequest::evaluate(
Evaluator &eval, DeclContext *dc, ValueDecl *decl1, ValueDecl *decl2,
bool isDynamicOverloadComparison) const {
auto &C = decl1->getASTContext();
if (C.TypeCheckerOpts.DebugConstraintSolver) {
auto &log = C.TypeCheckerDebug->getStream();
log << "Comparing declarations\n";
decl1->print(log);
log << "\nand\n";
decl2->print(log);
log << "\n(isDynamicOverloadComparison: ";
log << isDynamicOverloadComparison;
log << ")\n";
}
auto completeResult = [&C](bool result) {
if (C.TypeCheckerOpts.DebugConstraintSolver) {
auto &log = C.TypeCheckerDebug->getStream();
log << "comparison result: " << (result ? "better" : "not better")
<< "\n";
}
return result;
};
auto *innerDC1 = decl1->getInnermostDeclContext();
auto *innerDC2 = decl2->getInnermostDeclContext();
auto *outerDC1 = decl1->getDeclContext();
auto *outerDC2 = decl2->getDeclContext();
// If the kinds are different, there's nothing we can do.
// FIXME: This is wrong for type declarations, which we're skipping
// entirely.
if (decl1->getKind() != decl2->getKind() || isa<TypeDecl>(decl1))
return completeResult(false);
// A non-generic declaration is more specialized than a generic declaration.
if (auto func1 = dyn_cast<AbstractFunctionDecl>(decl1)) {
auto func2 = cast<AbstractFunctionDecl>(decl2);
if (func1->isGeneric() != func2->isGeneric())
return completeResult(func2->isGeneric());
}
if (auto subscript1 = dyn_cast<SubscriptDecl>(decl1)) {
auto subscript2 = cast<SubscriptDecl>(decl2);
if (subscript1->isGeneric() != subscript2->isGeneric())
return completeResult(subscript2->isGeneric());
}
// Members of protocol extensions have special overloading rules.
ProtocolDecl *inProtocolExtension1 = outerDC1->getExtendedProtocolDecl();
ProtocolDecl *inProtocolExtension2 = outerDC2->getExtendedProtocolDecl();
if (inProtocolExtension1 && inProtocolExtension2) {
// Both members are in protocol extensions.
// Determine whether the 'Self' type from the first protocol extension
// satisfies all of the requirements of the second protocol extension.
bool better1 = isProtocolExtensionAsSpecializedAs(outerDC1, outerDC2);
bool better2 = isProtocolExtensionAsSpecializedAs(outerDC2, outerDC1);
if (better1 != better2) {
return completeResult(better1);
}
} else if (inProtocolExtension1 || inProtocolExtension2) {
// One member is in a protocol extension, the other is in a concrete type.
// Prefer the member in the concrete type.
return completeResult(inProtocolExtension2);
}
// A concrete type member is always more specialised than a protocol
// member (bearing in mind that we have already handled the case where
// exactly one member is in a protocol extension). Only apply this rule in
// Swift 5 mode to better maintain source compatibility under Swift 4
// mode.
//
// Don't apply this rule when comparing two overloads found through
// dynamic lookup to ensure we keep cases like this ambiguous:
//
// @objc protocol P {
// var i: String { get }
// }
// class C {
// @objc var i: Int { return 0 }
// }
// func foo(_ x: AnyObject) {
// x.i // ensure ambiguous.
// }
//
if (C.isSwiftVersionAtLeast(5) && !isDynamicOverloadComparison) {
auto inProto1 = isa<ProtocolDecl>(outerDC1);
auto inProto2 = isa<ProtocolDecl>(outerDC2);
if (inProto1 != inProto2)
return completeResult(inProto2);
}
Type type1 = decl1->getInterfaceType();
Type type2 = decl2->getInterfaceType();
// Add curried 'self' types if necessary.
if (!decl1->hasCurriedSelf())
type1 = type1->addCurriedSelfType(outerDC1);
if (!decl2->hasCurriedSelf())
type2 = type2->addCurriedSelfType(outerDC2);
auto openType = [&](ConstraintSystem &cs, DeclContext *innerDC,
DeclContext *outerDC, Type type,
OpenedTypeMap &replacements,
ConstraintLocator *locator) -> Type {
if (auto *funcType = type->getAs<AnyFunctionType>()) {
return cs.openFunctionType(funcType, locator, replacements, outerDC);
}
cs.openGeneric(outerDC, innerDC->getGenericSignatureOfContext(), locator,
replacements);
return cs.openType(type, replacements);
};
// Construct a constraint system to compare the two declarations.
ConstraintSystem cs(dc, ConstraintSystemOptions());
bool knownNonSubtype = false;
auto *locator = cs.getConstraintLocator(nullptr);
// FIXME: Locator when anchored on a declaration.
// Get the type of a reference to the second declaration.
OpenedTypeMap unused, replacements;
auto openedType2 = openType(cs, innerDC1, outerDC2, type2, unused, locator);
auto openedType1 =
openType(cs, innerDC2, outerDC1, type1, replacements, locator);
for (const auto &replacement : replacements) {
if (auto mapped = innerDC1->mapTypeIntoContext(replacement.first)) {
cs.addConstraint(ConstraintKind::Bind, replacement.second, mapped,
locator);
}
}
// Extract the self types from the declarations, if they have them.
auto getSelfType = [](AnyFunctionType *fnType) -> Type {
auto params = fnType->getParams();
assert(params.size() == 1);
return params.front().getPlainType()->getMetatypeInstanceType();
};
Type selfTy1;
Type selfTy2;
if (outerDC1->isTypeContext()) {
auto funcTy1 = openedType1->castTo<FunctionType>();
selfTy1 = getSelfType(funcTy1);
openedType1 = funcTy1->getResult();
}
if (outerDC2->isTypeContext()) {
auto funcTy2 = openedType2->castTo<FunctionType>();
selfTy2 = getSelfType(funcTy2);
openedType2 = funcTy2->getResult();
}
// Determine the relationship between the 'self' types and add the
// appropriate constraints. The constraints themselves never fail, but
// they help deduce type variables that were opened.
auto selfTypeRelationship = computeSelfTypeRelationship(dc, decl1, decl2);
auto relationshipKind = selfTypeRelationship.first;
auto conformance = selfTypeRelationship.second;
(void)conformance;
switch (relationshipKind) {
case SelfTypeRelationship::Unrelated:
// Skip the self types parameter entirely.
break;
case SelfTypeRelationship::Equivalent:
cs.addConstraint(ConstraintKind::Bind, selfTy1, selfTy2, locator);
break;
case SelfTypeRelationship::Subclass:
cs.addConstraint(ConstraintKind::Subtype, selfTy1, selfTy2, locator);
break;
case SelfTypeRelationship::Superclass:
cs.addConstraint(ConstraintKind::Subtype, selfTy2, selfTy1, locator);
break;
case SelfTypeRelationship::ConformsTo:
assert(conformance);
cs.addConstraint(ConstraintKind::ConformsTo, selfTy1,
cast<ProtocolDecl>(outerDC2)->getDeclaredType(), locator);
break;
case SelfTypeRelationship::ConformedToBy:
assert(conformance);
cs.addConstraint(ConstraintKind::ConformsTo, selfTy2,
cast<ProtocolDecl>(outerDC1)->getDeclaredType(), locator);
break;
}
bool fewerEffectiveParameters = false;
if (!decl1->hasParameterList() && !decl2->hasParameterList()) {
// If neither decl has a parameter list, simply check whether the first
// type is a subtype of the second.
cs.addConstraint(ConstraintKind::Subtype, openedType1, openedType2,
locator);
} else if (decl1->hasParameterList() && decl2->hasParameterList()) {
// Otherwise, check whether the first function type's input is a subtype
// of the second type's inputs, i.e., can we forward the arguments?
auto funcTy1 = openedType1->castTo<FunctionType>();
auto funcTy2 = openedType2->castTo<FunctionType>();
auto params1 = funcTy1->getParams();
auto params2 = funcTy2->getParams();
unsigned numParams1 = params1.size();
unsigned numParams2 = params2.size();
if (numParams1 > numParams2)
return completeResult(false);
// If they both have trailing closures, compare those separately.
bool compareTrailingClosureParamsSeparately = false;
if (numParams1 > 0 && numParams2 > 0 &&
params1.back().getOldType()->is<AnyFunctionType>() &&
params2.back().getOldType()->is<AnyFunctionType>()) {
compareTrailingClosureParamsSeparately = true;
}
auto maybeAddSubtypeConstraint =
[&](const AnyFunctionType::Param ¶m1,
const AnyFunctionType::Param ¶m2) -> bool {
// If one parameter is variadic and the other is not...
if (param1.isVariadic() != param2.isVariadic()) {
// If the first parameter is the variadic one, it's not
// more specialized.
if (param1.isVariadic())
return false;
fewerEffectiveParameters = true;
}
Type paramType1 = getAdjustedParamType(param1);
Type paramType2 = getAdjustedParamType(param2);
// Check whether the first parameter is a subtype of the second.
cs.addConstraint(ConstraintKind::Subtype, paramType1, paramType2,
locator);
return true;
};
auto pairMatcher = [&](unsigned idx1, unsigned idx2) -> bool {
// Emulate behavior from when IUO was a type, where IUOs
// were considered subtypes of plain optionals, but not
// vice-versa. This wouldn't normally happen, but there are
// cases where we can rename imported APIs so that we have a
// name collision, and where the parameter type(s) are the
// same except for details of the kind of optional declared.
auto param1IsIUO = paramIsIUO(decl1, idx1);
auto param2IsIUO = paramIsIUO(decl2, idx2);
if (param2IsIUO && !param1IsIUO)
return false;
if (!maybeAddSubtypeConstraint(params1[idx1], params2[idx2]))
return false;
return true;
};
ParameterListInfo paramInfo(params2, decl2, decl2->hasCurriedSelf());
auto params2ForMatching = params2;
if (compareTrailingClosureParamsSeparately) {
--numParams1;
params2ForMatching = params2.drop_back();
}
InputMatcher IM(params2ForMatching, paramInfo);
if (IM.match(numParams1, pairMatcher) != InputMatcher::IM_Succeeded)
return completeResult(false);
fewerEffectiveParameters |= (IM.getNumSkippedParameters() != 0);
if (compareTrailingClosureParamsSeparately)
if (!maybeAddSubtypeConstraint(params1.back(), params2.back()))
knownNonSubtype = true;
}
if (!knownNonSubtype) {
// Solve the system.
auto solution = cs.solveSingle(FreeTypeVariableBinding::Allow);
// Ban value-to-optional conversions.
if (solution && solution->getFixedScore().Data[SK_ValueToOptional] == 0)
return completeResult(true);
}
// If the first function has fewer effective parameters than the
// second, it is more specialized.
if (fewerEffectiveParameters)
return completeResult(true);
return completeResult(false);
}
Comparison TypeChecker::compareDeclarations(DeclContext *dc,
ValueDecl *decl1,
ValueDecl *decl2){
bool decl1Better = isDeclAsSpecializedAs(dc, decl1, decl2);
bool decl2Better = isDeclAsSpecializedAs(dc, decl2, decl1);
if (decl1Better == decl2Better)
return Comparison::Unordered;
return decl1Better ? Comparison::Better : Comparison::Worse;
}
static Type getUnlabeledType(Type type, ASTContext &ctx) {
return type.transform([&](Type type) -> Type {
if (auto *tupleType = dyn_cast<TupleType>(type.getPointer())) {
SmallVector<TupleTypeElt, 8> elts;
for (auto elt : tupleType->getElements()) {
elts.push_back(elt.getWithoutName());
}
return TupleType::get(elts, ctx);
}
return type;
});
}
static void addKeyPathDynamicMemberOverloads(
ArrayRef<Solution> solutions, unsigned idx1, unsigned idx2,
SmallVectorImpl<SolutionDiff::OverloadDiff> &overloadDiff) {
const auto &overloads1 = solutions[idx1].overloadChoices;
const auto &overloads2 = solutions[idx2].overloadChoices;
for (auto &entry : overloads1) {
auto *locator = entry.first;
if (!locator->isForKeyPathDynamicMemberLookup())
continue;
auto overload2 = overloads2.find(locator);
if (overload2 == overloads2.end())
continue;
auto &overloadChoice1 = entry.second.choice;
auto &overloadChoice2 = overload2->second.choice;
SmallVector<OverloadChoice, 4> choices;
choices.resize(solutions.size());
choices[idx1] = overloadChoice1;
choices[idx2] = overloadChoice2;
overloadDiff.push_back(
SolutionDiff::OverloadDiff{locator, std::move(choices)});
}
}
SolutionCompareResult ConstraintSystem::compareSolutions(
ConstraintSystem &cs, ArrayRef<Solution> solutions,
const SolutionDiff &diff, unsigned idx1, unsigned idx2) {
if (cs.getASTContext().TypeCheckerOpts.DebugConstraintSolver) {
auto &log = cs.getASTContext().TypeCheckerDebug->getStream();
log.indent(cs.solverState->depth * 2)
<< "comparing solutions " << idx1 << " and " << idx2 <<"\n";
}
// Whether the solutions are identical.
bool identical = true;
// Compare the fixed scores by themselves.
if (solutions[idx1].getFixedScore() != solutions[idx2].getFixedScore()) {
return solutions[idx1].getFixedScore() < solutions[idx2].getFixedScore()
? SolutionCompareResult::Better
: SolutionCompareResult::Worse;
}
// Compute relative score.
unsigned score1 = 0;
unsigned score2 = 0;
auto foundRefinement1 = false;
auto foundRefinement2 = false;
bool isStdlibOptionalMPlusOperator1 = false;
bool isStdlibOptionalMPlusOperator2 = false;
bool isVarAndNotProtocol1 = false;
bool isVarAndNotProtocol2 = false;
auto getWeight = [&](ConstraintLocator *locator) -> unsigned {
if (auto *anchor = locator->getAnchor()) {
auto weight = cs.getExprDepth(anchor);
if (weight)
return *weight + 1;
}
return 1;
};
SmallVector<SolutionDiff::OverloadDiff, 4> overloadDiff(diff.overloads);
// Single type of keypath dynamic member lookup could refer to different
// member overlaods, we have to do a pair-wise comparison in such cases
// otherwise ranking would miss some viable information e.g.
// `_ = arr[0..<3]` could refer to subscript through writable or read-only
// key path and each of them could also pick overload which returns `Slice<T>`
// or `ArraySlice<T>` (assuming that `arr` is something like `Box<[Int]>`).
addKeyPathDynamicMemberOverloads(solutions, idx1, idx2, overloadDiff);
// Compare overload sets.
for (auto &overload : overloadDiff) {
unsigned weight = getWeight(overload.locator);
auto choice1 = overload.choices[idx1];
auto choice2 = overload.choices[idx2];
// If the systems made the same choice, there's nothing interesting here.
if (sameOverloadChoice(choice1, choice2))
continue;
// If constraint system is underconstrained e.g. because there are
// editor placeholders, it's possible to end up with multiple solutions
// where each ambiguous declaration is going to have its own overload kind:
//
// func foo(_: Int) -> [Int] { ... }
// func foo(_: Double) -> (result: String, count: Int) { ... }
//
// _ = foo(<#arg#>).count
//
// In this case solver would produce 2 solutions: one where `count`
// is a property reference on `[Int]` and another one is tuple access
// for a `count:` element.
if (choice1.isDecl() != choice2.isDecl())
return SolutionCompareResult::Incomparable;
auto decl1 = choice1.getDecl();
auto dc1 = decl1->getDeclContext();
auto decl2 = choice2.getDecl();
auto dc2 = decl2->getDeclContext();
// The two systems are not identical. If the decls in question are distinct
// protocol members, let the checks below determine if the two choices are
// 'identical' or not. This allows us to structurally unify disparate
// protocol members during overload resolution.
// FIXME: Along with the FIXME below, this is a hack to work around
// problems with restating requirements in protocols.
identical = false;
bool decl1InSubprotocol = false;
bool decl2InSubprotocol = false;
if (dc1->getContextKind() == DeclContextKind::GenericTypeDecl &&
dc1->getContextKind() == dc2->getContextKind()) {
auto pd1 = dyn_cast<ProtocolDecl>(dc1);
auto pd2 = dyn_cast<ProtocolDecl>(dc2);
// FIXME: This hack tells us to prefer members of subprotocols over
// those of the protocols they inherit, if all else fails.
// If we were properly handling overrides of protocol members when
// requirements get restated, it would not be necessary.
if (pd1 && pd2 && pd1 != pd2) {
identical = true;
decl1InSubprotocol = pd1->inheritsFrom(pd2);
decl2InSubprotocol = pd2->inheritsFrom(pd1);
}
}
// If the kinds of overload choice don't match...
if (choice1.getKind() != choice2.getKind()) {
identical = false;
// A declaration found directly beats any declaration found via dynamic
// lookup, bridging, or optional unwrapping.
if ((choice1.getKind() == OverloadChoiceKind::Decl) &&
(choice2.getKind() == OverloadChoiceKind::DeclViaDynamic ||
choice2.getKind() == OverloadChoiceKind::DeclViaBridge ||
choice2.getKind() == OverloadChoiceKind::DeclViaUnwrappedOptional)) {
score1 += weight;
continue;
}
if ((choice1.getKind() == OverloadChoiceKind::DeclViaDynamic ||
choice1.getKind() == OverloadChoiceKind::DeclViaBridge ||
choice1.getKind() == OverloadChoiceKind::DeclViaUnwrappedOptional) &&
choice2.getKind() == OverloadChoiceKind::Decl) {
score2 += weight;
continue;
}
if (choice1.getKind() == OverloadChoiceKind::KeyPathDynamicMemberLookup) {
if (choice2.getKind() == OverloadChoiceKind::DynamicMemberLookup)
// Dynamic member lookup through a keypath is better than one using
// string because it carries more type information.
score1 += weight;
else
// Otherwise let's prefer non-dynamic declaration.
score2 += weight;
continue;
}
if (choice2.getKind() == OverloadChoiceKind::KeyPathDynamicMemberLookup) {
if (choice1.getKind() == OverloadChoiceKind::DynamicMemberLookup)
// Dynamic member lookup through a keypath is better than one using
// string because it carries more type information.
score2 += weight;
else
// Otherwise let's prefer non-dynamic declaration.
score1 += weight;
continue;
}
continue;
}
// The kinds of overload choice match, but the contents don't.
switch (choice1.getKind()) {
case OverloadChoiceKind::TupleIndex:
continue;
case OverloadChoiceKind::KeyPathApplication:
llvm_unreachable("Never considered different");
case OverloadChoiceKind::DeclViaDynamic:
case OverloadChoiceKind::Decl:
case OverloadChoiceKind::DeclViaBridge:
case OverloadChoiceKind::DeclViaUnwrappedOptional:
case OverloadChoiceKind::DynamicMemberLookup:
case OverloadChoiceKind::KeyPathDynamicMemberLookup:
break;
}
// We don't apply some ranking rules to overloads found through dynamic
// lookup in order to keep a few potentially ill-formed cases ambiguous.
bool isDynamicOverloadComparison =
choice1.getKind() == OverloadChoiceKind::DeclViaDynamic &&
choice2.getKind() == OverloadChoiceKind::DeclViaDynamic;
// Determine whether one declaration is more specialized than the other.
bool firstAsSpecializedAs = false;
bool secondAsSpecializedAs = false;
if (isDeclAsSpecializedAs(cs.DC, decl1, decl2,
isDynamicOverloadComparison)) {
score1 += weight;
firstAsSpecializedAs = true;
}
if (isDeclAsSpecializedAs(cs.DC, decl2, decl1,
isDynamicOverloadComparison)) {
score2 += weight;
secondAsSpecializedAs = true;
}
// If each is as specialized as the other, and both are constructors,
// check the constructor kind.
if (firstAsSpecializedAs && secondAsSpecializedAs) {
if (auto ctor1 = dyn_cast<ConstructorDecl>(decl1)) {
if (auto ctor2 = dyn_cast<ConstructorDecl>(decl2)) {
if (ctor1->getInitKind() != ctor2->getInitKind()) {
if (ctor1->getInitKind() < ctor2->getInitKind())
score1 += weight;
else
score2 += weight;
} else if (ctor1->getInitKind() ==
CtorInitializerKind::Convenience) {
// If both are convenience initializers, and the instance type of
// one is a subtype of the other's, favor the subtype constructor.
auto resType1 = ctor1->mapTypeIntoContext(
ctor1->getResultInterfaceType());
auto resType2 = ctor2->mapTypeIntoContext(
ctor2->getResultInterfaceType());
if (!resType1->isEqual(resType2)) {
if (TypeChecker::isSubtypeOf(resType1, resType2, cs.DC)) {
score1 += weight;
} else if (TypeChecker::isSubtypeOf(resType2, resType1, cs.DC)) {
score2 += weight;
}
}
}
}
}
}
// If both declarations come from Clang, and one is a type and the other
// is a function, prefer the function.
if (decl1->hasClangNode() &&
decl2->hasClangNode() &&
((isa<TypeDecl>(decl1) &&
isa<AbstractFunctionDecl>(decl2)) ||
(isa<AbstractFunctionDecl>(decl1) &&
isa<TypeDecl>(decl2)))) {
if (isa<TypeDecl>(decl1))
score2 += weight;
else
score1 += weight;
}
// A class member is always better than a curried instance member.
// If the members agree on instance-ness, a property is better than a
// method (because a method is usually immediately invoked).
if (!decl1->isInstanceMember() && decl2->isInstanceMember())
score1 += weight;
else if (!decl2->isInstanceMember() && decl1->isInstanceMember())
score2 += weight;
else if (isa<VarDecl>(decl1) && isa<FuncDecl>(decl2))
score1 += weight;
else if (isa<VarDecl>(decl2) && isa<FuncDecl>(decl1))
score2 += weight;
// If both are class properties with the same name, prefer
// the one attached to the subclass because it could only be
// found if requested directly.
if (!decl1->isInstanceMember() && !decl2->isInstanceMember()) {
if (isa<VarDecl>(decl1) && isa<VarDecl>(decl2)) {
auto *nominal1 = dc1->getSelfNominalTypeDecl();
auto *nominal2 = dc2->getSelfNominalTypeDecl();
if (nominal1 && nominal2 && nominal1 != nominal2) {
auto base1 = nominal1->getDeclaredType();
auto base2 = nominal2->getDeclaredType();