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TypeCheckProtocolInference.cpp
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//===--- TypeCheckProtocolInference.cpp - Associated Type Inference -------===//
//
// 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 implements semantic analysis for protocols, in particular, checking
// whether a given type conforms to a given protocol.
//===----------------------------------------------------------------------===//
#include "TypeCheckProtocol.h"
#include "DerivedConformances.h"
#include "TypeChecker.h"
#include "swift/AST/Decl.h"
#include "swift/AST/GenericSignature.h"
#include "swift/AST/ProtocolConformance.h"
#include "swift/AST/SubstitutionMap.h"
#include "swift/AST/TypeMatcher.h"
#include "swift/AST/Types.h"
#include "swift/Basic/Defer.h"
#include "swift/ClangImporter/ClangModule.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/TinyPtrVector.h"
#define DEBUG_TYPE "Associated type inference"
#include "llvm/Support/Debug.h"
STATISTIC(NumSolutionStates, "# of solution states visited");
STATISTIC(NumSolutionStatesFailedCheck,
"# of solution states that failed constraints check");
STATISTIC(NumConstrainedExtensionChecks,
"# of constrained extension checks");
STATISTIC(NumConstrainedExtensionChecksFailed,
"# of constrained extension checks failed");
STATISTIC(NumDuplicateSolutionStates,
"# of duplicate solution states ");
using namespace swift;
void InferredAssociatedTypesByWitness::dump() const {
dump(llvm::errs(), 0);
}
void InferredAssociatedTypesByWitness::dump(llvm::raw_ostream &out,
unsigned indent) const {
out << "\n";
out.indent(indent) << "(";
if (Witness) {
Witness->dumpRef(out);
}
for (const auto &inferred : Inferred) {
out << "\n";
out.indent(indent + 2);
out << inferred.first->getName() << " := "
<< inferred.second.getString();
}
for (const auto &inferred : NonViable) {
out << "\n";
out.indent(indent + 2);
out << std::get<0>(inferred)->getName() << " := "
<< std::get<1>(inferred).getString();
auto type = std::get<2>(inferred).getRequirement();
out << " [failed constraint " << type.getString() << "]";
}
out << ")";
}
void InferredTypeWitnessesSolution::dump() const {
llvm::errs() << "Type Witnesses:\n";
for (auto &typeWitness : TypeWitnesses) {
llvm::errs() << " " << typeWitness.first->getName() << " := ";
typeWitness.second.first->print(llvm::errs());
llvm::errs() << " value " << typeWitness.second.second << '\n';
}
llvm::errs() << "Value Witnesses:\n";
for (unsigned i : indices(ValueWitnesses)) {
auto &valueWitness = ValueWitnesses[i];
llvm::errs() << i << ": " << (Decl*)valueWitness.first
<< ' ' << valueWitness.first->getBaseName() << '\n';
valueWitness.first->getDeclContext()->dumpContext();
llvm::errs() << " for " << (Decl*)valueWitness.second
<< ' ' << valueWitness.second->getBaseName() << '\n';
valueWitness.second->getDeclContext()->dumpContext();
}
}
namespace {
void dumpInferredAssociatedTypesByWitnesses(
const InferredAssociatedTypesByWitnesses &inferred,
llvm::raw_ostream &out,
unsigned indent) {
for (const auto &value : inferred) {
value.dump(out, indent);
}
}
void dumpInferredAssociatedTypesByWitnesses(
const InferredAssociatedTypesByWitnesses &inferred) LLVM_ATTRIBUTE_USED;
void dumpInferredAssociatedTypesByWitnesses(
const InferredAssociatedTypesByWitnesses &inferred) {
dumpInferredAssociatedTypesByWitnesses(inferred, llvm::errs(), 0);
}
void dumpInferredAssociatedTypes(const InferredAssociatedTypes &inferred,
llvm::raw_ostream &out,
unsigned indent) {
for (const auto &value : inferred) {
out << "\n";
out.indent(indent) << "(";
value.first->dumpRef(out);
dumpInferredAssociatedTypesByWitnesses(value.second, out, indent + 2);
out << ")";
}
out << "\n";
}
void dumpInferredAssociatedTypes(
const InferredAssociatedTypes &inferred) LLVM_ATTRIBUTE_USED;
void dumpInferredAssociatedTypes(const InferredAssociatedTypes &inferred) {
dumpInferredAssociatedTypes(inferred, llvm::errs(), 0);
}
}
AssociatedTypeInference::AssociatedTypeInference(
TypeChecker &tc,
NormalProtocolConformance *conformance)
: tc(tc), conformance(conformance), proto(conformance->getProtocol()),
dc(conformance->getDeclContext()),
adoptee(conformance->getType())
{
}
static bool associatedTypesAreSameEquivalenceClass(AssociatedTypeDecl *a,
AssociatedTypeDecl *b) {
if (a == b)
return true;
// TODO: Do a proper equivalence check here by looking for some relationship
// between a and b's protocols. In practice today, it's unlikely that
// two same-named associated types can currently be independent, since we
// don't have anything like `@implements(P.foo)` to rename witnesses (and
// we still fall back to name lookup for witnesses in more cases than we
// should).
if (a->getName() == b->getName())
return true;
return false;
}
InferredAssociatedTypesByWitnesses
AssociatedTypeInference::inferTypeWitnessesViaValueWitnesses(
ConformanceChecker &checker,
const llvm::SetVector<AssociatedTypeDecl *> &allUnresolved,
ValueDecl *req) {
// Conformances constructed by the ClangImporter should have explicit type
// witnesses already.
if (isa<ClangModuleUnit>(conformance->getDeclContext()->getModuleScopeContext())) {
llvm::errs() << "Cannot infer associated types for imported conformance:\n";
conformance->getType().dump(llvm::errs());
for (auto assocTypeDecl : allUnresolved)
assocTypeDecl->dump(llvm::errs());
abort();
}
InferredAssociatedTypesByWitnesses result;
auto isExtensionUsableForInference = [&](ExtensionDecl *extension) -> bool {
// The extension where the conformance being checked is declared.
auto conformanceExtension = checker.Conformance->
getDeclContext()->getAsDecl();
if (extension == conformanceExtension)
return true;
auto *extendedNominal = extension->getExtendedNominal();
// Invalid case.
if (extendedNominal == nullptr)
return true;
// Assume unconstrained concrete extensions we found witnesses in are
// always viable.
if (!isa<ProtocolDecl>(extendedNominal))
return !extension->isConstrainedExtension();
// Build a generic signature.
tc.validateExtension(extension);
// The extension may not have a generic signature set up yet, as a
// recursion breaker, in which case we can't yet confidently reject its
// witnesses.
if (!extension->getGenericSignature())
return true;
// The condition here is a bit more fickle than
// `isExtensionApplied`. That check would prematurely reject
// extensions like `P where AssocType == T` if we're relying on a
// default implementation inside the extension to infer `AssocType == T`
// in the first place. Only check conformances on the `Self` type,
// because those have to be explicitly declared on the type somewhere
// so won't be affected by whatever answer inference comes up with.
auto selfTy = extension->getSelfInterfaceType();
for (const Requirement &reqt
: extension->getGenericSignature()->getRequirements()) {
switch (reqt.getKind()) {
case RequirementKind::Conformance:
case RequirementKind::Superclass:
// FIXME: This is the wrong check
if (selfTy->isEqual(reqt.getFirstType())
&& !tc.isSubtypeOf(conformance->getType(),reqt.getSecondType(), dc))
return false;
break;
case RequirementKind::Layout:
case RequirementKind::SameType:
break;
}
}
return true;
};
auto typeInContext =
conformance->getDeclContext()->mapTypeIntoContext(conformance->getType());
for (auto witness :
checker.lookupValueWitnesses(req, /*ignoringNames=*/nullptr)) {
LLVM_DEBUG(llvm::dbgs() << "Inferring associated types from decl:\n";
witness->dump(llvm::dbgs()));
// If the potential witness came from an extension, and our `Self`
// type can't use it regardless of what associated types we end up
// inferring, skip the witness.
if (auto extension = dyn_cast<ExtensionDecl>(witness->getDeclContext()))
if (!isExtensionUsableForInference(extension))
continue;
// Try to resolve the type witness via this value witness.
auto witnessResult = inferTypeWitnessesViaValueWitness(req, witness);
// Filter out duplicated inferred types as well as inferred types
// that don't meet the requirements placed on the associated type.
llvm::DenseSet<std::pair<AssociatedTypeDecl *, CanType>> known;
for (unsigned i = 0; i < witnessResult.Inferred.size(); /*nothing*/) {
#define REJECT {\
witnessResult.Inferred.erase(witnessResult.Inferred.begin() + i); \
continue; \
}
auto &result = witnessResult.Inferred[i];
LLVM_DEBUG(llvm::dbgs() << "Considering whether "
<< result.first->getName()
<< " can infer to:\n";
result.second->dump(llvm::dbgs()));
// Filter out errors.
if (result.second->hasError()) {
LLVM_DEBUG(llvm::dbgs() << "-- has error type\n");
REJECT;
}
// Filter out duplicates.
if (!known.insert({result.first, result.second->getCanonicalType()})
.second) {
LLVM_DEBUG(llvm::dbgs() << "-- duplicate\n");
REJECT;
}
// Filter out circular possibilities, e.g. that
// AssocType == S.AssocType or
// AssocType == Foo<S.AssocType>.
bool canInferFromOtherAssociatedType = false;
bool containsTautologicalType =
result.second.findIf([&](Type t) -> bool {
auto dmt = t->getAs<DependentMemberType>();
if (!dmt)
return false;
if (!associatedTypesAreSameEquivalenceClass(dmt->getAssocType(),
result.first))
return false;
if (!dmt->getBase()->isEqual(typeInContext))
return false;
// If this associated type is same-typed to another associated type
// on `Self`, then it may still be an interesting candidate if we find
// an answer for that other type.
auto witnessContext = witness->getDeclContext();
if (witnessContext->getExtendedProtocolDecl()
&& witnessContext->getGenericSignatureOfContext()) {
auto selfTy = witnessContext->getSelfInterfaceType();
auto selfAssocTy = DependentMemberType::get(selfTy,
dmt->getAssocType());
for (auto &reqt : witnessContext->getGenericSignatureOfContext()
->getRequirements()) {
switch (reqt.getKind()) {
case RequirementKind::Conformance:
case RequirementKind::Superclass:
case RequirementKind::Layout:
break;
case RequirementKind::SameType:
Type other;
if (reqt.getFirstType()->isEqual(selfAssocTy)) {
other = reqt.getSecondType();
} else if (reqt.getSecondType()->isEqual(selfAssocTy)) {
other = reqt.getFirstType();
} else {
break;
}
if (auto otherAssoc = other->getAs<DependentMemberType>()) {
if (otherAssoc->getBase()->isEqual(selfTy)) {
auto otherDMT = DependentMemberType::get(dmt->getBase(),
otherAssoc->getAssocType());
// We may be able to infer one associated type from the
// other.
result.second = result.second.transform([&](Type t) -> Type{
if (t->isEqual(dmt))
return otherDMT;
return t;
});
canInferFromOtherAssociatedType = true;
LLVM_DEBUG(llvm::dbgs() << "++ we can same-type to:\n";
result.second->dump(llvm::dbgs()));
return false;
}
}
break;
}
}
}
return true;
});
if (containsTautologicalType) {
LLVM_DEBUG(llvm::dbgs() << "-- tautological\n");
REJECT;
}
// Check that the type witness doesn't contradict an
// explicitly-given type witness. If it does contradict, throw out the
// witness completely.
if (!allUnresolved.count(result.first)) {
auto existingWitness =
conformance->getTypeWitness(result.first);
existingWitness = dc->mapTypeIntoContext(existingWitness);
// If the deduced type contains an irreducible
// DependentMemberType, that indicates a dependency
// on another associated type we haven't deduced,
// so we can't tell whether there's a contradiction
// yet.
auto newWitness = result.second->getCanonicalType();
if (!newWitness->hasTypeParameter() &&
!newWitness->hasDependentMember() &&
!existingWitness->isEqual(newWitness)) {
LLVM_DEBUG(llvm::dbgs() << "** contradicts explicit type witness, "
"rejecting inference from this decl\n");
goto next_witness;
}
}
// If we same-typed to another unresolved associated type, we won't
// be able to check conformances yet.
if (!canInferFromOtherAssociatedType) {
// Check that the type witness meets the
// requirements on the associated type.
if (auto failed = checkTypeWitness(tc, dc, proto, result.first,
result.second)) {
witnessResult.NonViable.push_back(
std::make_tuple(result.first,result.second,failed));
LLVM_DEBUG(llvm::dbgs() << "-- doesn't fulfill requirements\n");
REJECT;
}
}
LLVM_DEBUG(llvm::dbgs() << "++ seems legit\n");
++i;
}
#undef REJECT
// If no inferred types remain, skip this witness.
if (witnessResult.Inferred.empty() && witnessResult.NonViable.empty())
continue;
// If there were any non-viable inferred associated types, don't
// infer anything from this witness.
if (!witnessResult.NonViable.empty())
witnessResult.Inferred.clear();
result.push_back(std::move(witnessResult));
next_witness:;
}
return result;
}
InferredAssociatedTypes
AssociatedTypeInference::inferTypeWitnessesViaValueWitnesses(
ConformanceChecker &checker,
const llvm::SetVector<AssociatedTypeDecl *> &assocTypes)
{
InferredAssociatedTypes result;
for (auto member : proto->getMembers()) {
auto req = dyn_cast<ValueDecl>(member);
if (!req)
continue;
if (!req->isProtocolRequirement())
continue;
// Infer type witnesses for associated types.
if (auto assocType = dyn_cast<AssociatedTypeDecl>(req)) {
// If this is not one of the associated types we are trying to infer,
// just continue.
if (assocTypes.count(assocType) == 0)
continue;
auto reqInferred = inferTypeWitnessesViaAssociatedType(checker,
assocTypes,
assocType);
if (!reqInferred.empty())
result.push_back({req, std::move(reqInferred)});
continue;
}
// Skip operator requirements, because they match globally and
// therefore tend to cause deduction mismatches.
// FIXME: If we had some basic sanity checking of Self, we might be able to
// use these.
if (auto func = dyn_cast<FuncDecl>(req)) {
if (func->isOperator() || isa<AccessorDecl>(func))
continue;
}
// Validate the requirement.
tc.validateDecl(req);
if (req->isInvalid() || !req->hasValidSignature())
continue;
// Check whether any of the associated types we care about are
// referenced in this value requirement.
bool anyAssocTypeMatches = false;
for (auto assocType : checker.getReferencedAssociatedTypes(req)) {
if (assocTypes.count(assocType) > 0) {
anyAssocTypeMatches = true;
break;
}
}
// We cannot deduce anything from the witnesses of this
// requirement; skip it.
if (!anyAssocTypeMatches)
continue;
// Infer associated types from the potential value witnesses for
// this requirement.
auto reqInferred =
inferTypeWitnessesViaValueWitnesses(checker, assocTypes, req);
if (reqInferred.empty())
continue;
result.push_back({req, std::move(reqInferred)});
}
return result;
}
/// Map error types back to their original types.
static Type mapErrorTypeToOriginal(Type type) {
if (auto errorType = type->getAs<ErrorType>()) {
if (auto originalType = errorType->getOriginalType())
return originalType.transform(mapErrorTypeToOriginal);
}
return type;
}
/// Produce the type when matching a witness.
static Type getWitnessTypeForMatching(TypeChecker &tc,
NormalProtocolConformance *conformance,
ValueDecl *witness) {
if (!witness->hasInterfaceType())
tc.validateDecl(witness);
if (witness->isInvalid() || !witness->hasValidSignature())
return Type();
if (!witness->getDeclContext()->isTypeContext()) {
// FIXME: Could we infer from 'Self' to make these work?
return witness->getInterfaceType();
}
// Retrieve the set of substitutions to be applied to the witness.
Type model =
conformance->getDeclContext()->mapTypeIntoContext(conformance->getType());
TypeSubstitutionMap substitutions = model->getMemberSubstitutions(witness);
Type type = witness->getInterfaceType()->getReferenceStorageReferent();
if (substitutions.empty())
return type;
// Strip off the requirements of a generic function type.
// FIXME: This doesn't actually break recursion when substitution
// looks for an inferred type witness, but it makes it far less
// common, because most of the recursion involves the requirements
// of the generic type.
if (auto genericFn = type->getAs<GenericFunctionType>()) {
type = FunctionType::get(genericFn->getParams(),
genericFn->getResult(),
genericFn->getExtInfo());
}
// Remap associated types that reference other protocols into this
// protocol.
auto proto = conformance->getProtocol();
type = type.transformRec([proto](TypeBase *type) -> Optional<Type> {
if (auto depMemTy = dyn_cast<DependentMemberType>(type)) {
if (depMemTy->getAssocType() &&
depMemTy->getAssocType()->getProtocol() != proto) {
for (auto member : proto->lookupDirect(depMemTy->getName())) {
if (auto assocType = dyn_cast<AssociatedTypeDecl>(member)) {
auto origProto = depMemTy->getAssocType()->getProtocol();
if (proto->inheritsFrom(origProto))
return Type(DependentMemberType::get(depMemTy->getBase(),
assocType));
}
}
}
}
return None;
});
ModuleDecl *module = conformance->getDeclContext()->getParentModule();
auto resultType = type.subst(QueryTypeSubstitutionMap{substitutions},
LookUpConformanceInModule(module),
SubstFlags::UseErrorType);
if (!resultType->hasError()) return resultType;
// Map error types with original types *back* to the original, dependent type.
return resultType.transform(mapErrorTypeToOriginal);
}
/// Remove the 'self' type from the given type, if it's a method type.
static Type removeSelfParam(ValueDecl *value, Type type) {
if (auto func = dyn_cast<AbstractFunctionDecl>(value)) {
if (func->getDeclContext()->isTypeContext())
return type->castTo<AnyFunctionType>()->getResult();
}
return type;
}
InferredAssociatedTypesByWitnesses
AssociatedTypeInference::inferTypeWitnessesViaAssociatedType(
ConformanceChecker &checker,
const llvm::SetVector<AssociatedTypeDecl *> &allUnresolved,
AssociatedTypeDecl *assocType) {
auto &tc = checker.TC;
// Form the default name _Default_Foo.
Identifier defaultName;
{
SmallString<32> defaultNameStr;
{
llvm::raw_svector_ostream out(defaultNameStr);
out << "_Default_";
out << assocType->getName().str();
}
defaultName = tc.Context.getIdentifier(defaultNameStr);
}
// Look for types with the given default name that have appropriate
// @_implements attributes.
InferredAssociatedTypesByWitnesses result;
auto lookupOptions = defaultMemberTypeLookupOptions;
lookupOptions -= NameLookupFlags::PerformConformanceCheck;
for (auto candidate : tc.lookupMember(dc, adoptee, defaultName,
lookupOptions)) {
// We want type declarations.
auto typeDecl = dyn_cast<TypeDecl>(candidate.getValueDecl());
if (!typeDecl || isa<AssociatedTypeDecl>(typeDecl))
continue;
// We only find these within a protocol extension.
auto defaultProto = typeDecl->getDeclContext()->getSelfProtocolDecl();
if (!defaultProto)
continue;
// Determine the witness type.
Type witnessType = getWitnessTypeForMatching(tc, conformance, typeDecl);
if (!witnessType) continue;
if (auto witnessMetaType = witnessType->getAs<AnyMetatypeType>())
witnessType = witnessMetaType->getInstanceType();
else
continue;
// Add this result.
InferredAssociatedTypesByWitness inferred;
inferred.Witness = typeDecl;
inferred.Inferred.push_back({assocType, witnessType});
result.push_back(std::move(inferred));
}
return result;
}
Type swift::adjustInferredAssociatedType(Type type, bool &noescapeToEscaping) {
// If we have an optional type, adjust its wrapped type.
if (auto optionalObjectType = type->getOptionalObjectType()) {
auto newOptionalObjectType =
adjustInferredAssociatedType(optionalObjectType, noescapeToEscaping);
if (newOptionalObjectType.getPointer() == optionalObjectType.getPointer())
return type;
return OptionalType::get(newOptionalObjectType);
}
// If we have a noescape function type, make it escaping.
if (auto funcType = type->getAs<FunctionType>()) {
if (funcType->isNoEscape()) {
noescapeToEscaping = true;
return FunctionType::get(funcType->getParams(), funcType->getResult(),
funcType->getExtInfo().withNoEscape(false));
}
}
return type;
}
/// Attempt to resolve a type witness via a specific value witness.
InferredAssociatedTypesByWitness
AssociatedTypeInference::inferTypeWitnessesViaValueWitness(ValueDecl *req,
ValueDecl *witness) {
InferredAssociatedTypesByWitness inferred;
inferred.Witness = witness;
// Compute the requirement and witness types we'll use for matching.
Type fullWitnessType = getWitnessTypeForMatching(tc, conformance, witness);
if (!fullWitnessType) {
return inferred;
}
auto setup = [&]() -> std::tuple<Optional<RequirementMatch>, Type, Type> {
fullWitnessType = removeSelfParam(witness, fullWitnessType);
return std::make_tuple(
None,
removeSelfParam(req, req->getInterfaceType()),
fullWitnessType);
};
/// Visits a requirement type to match it to a potential witness for
/// the purpose of deducing associated types.
///
/// The visitor argument is the witness type. If there are any
/// obvious conflicts between the structure of the two types,
/// returns true. The conflict checking is fairly conservative, only
/// considering rough structure.
class MatchVisitor : public TypeMatcher<MatchVisitor> {
NormalProtocolConformance *Conformance;
InferredAssociatedTypesByWitness &Inferred;
public:
MatchVisitor(NormalProtocolConformance *conformance,
InferredAssociatedTypesByWitness &inferred)
: Conformance(conformance), Inferred(inferred) { }
/// Structural mismatches imply that the witness cannot match.
bool mismatch(TypeBase *firstType, TypeBase *secondType,
Type sugaredFirstType) {
// If either type hit an error, don't stop yet.
if (firstType->hasError() || secondType->hasError())
return true;
// FIXME: Check whether one of the types is dependent?
return false;
}
/// Deduce associated types from dependent member types in the witness.
bool mismatch(DependentMemberType *firstDepMember,
TypeBase *secondType, Type sugaredFirstType) {
// If the second type is an error, don't look at it further.
if (secondType->hasError())
return true;
// Adjust the type to a type that can be written explicitly.
bool noescapeToEscaping = false;
Type inferredType =
adjustInferredAssociatedType(secondType, noescapeToEscaping);
if (!inferredType->isMaterializable())
return true;
// If the type contains a type parameter, there is nothing we can infer
// from it.
// FIXME: This is a weird state introduced by associated type inference
// that should not exist.
if (inferredType->hasTypeParameter())
return true;
auto proto = Conformance->getProtocol();
if (auto assocType = getReferencedAssocTypeOfProtocol(firstDepMember,
proto)) {
Inferred.Inferred.push_back({assocType, inferredType});
}
// Always allow mismatches here.
return true;
}
/// FIXME: Recheck the type of Self against the second type?
bool mismatch(GenericTypeParamType *selfParamType,
TypeBase *secondType, Type sugaredFirstType) {
return true;
}
};
// Match a requirement and witness type.
MatchVisitor matchVisitor(conformance, inferred);
auto matchTypes = [&](Type reqType, Type witnessType)
-> Optional<RequirementMatch> {
if (!matchVisitor.match(reqType, witnessType)) {
return RequirementMatch(witness, MatchKind::TypeConflict,
fullWitnessType);
}
return None;
};
// Finalization of the checking is pretty trivial; just bundle up a
// result we can look at.
auto finalize = [&](bool anyRenaming, ArrayRef<OptionalAdjustment>)
-> RequirementMatch {
return RequirementMatch(witness,
anyRenaming ? MatchKind::RenamedMatch
: MatchKind::ExactMatch,
fullWitnessType);
};
// Match the witness. If we don't succeed, throw away the inference
// information.
// FIXME: A renamed match might be useful to retain for the failure case.
if (matchWitness(dc, req, witness, setup, matchTypes, finalize)
.Kind != MatchKind::ExactMatch) {
inferred.Inferred.clear();
}
return inferred;
}
AssociatedTypeDecl *AssociatedTypeInference::findDefaultedAssociatedType(
TypeChecker &tc,
AssociatedTypeDecl *assocType) {
// If this associated type has a default, we're done.
tc.validateDecl(assocType);
if (assocType->hasDefaultDefinitionType())
return assocType;
// Look at overridden associated types.
SmallPtrSet<CanType, 4> canonicalTypes;
SmallVector<AssociatedTypeDecl *, 2> results;
for (auto overridden : assocType->getOverriddenDecls()) {
auto overriddenDefault = findDefaultedAssociatedType(tc, overridden);
if (!overriddenDefault) continue;
Type overriddenType =
overriddenDefault->getDefaultDefinitionType();
assert(overriddenType);
if (!overriddenType) continue;
CanType key = overriddenType->getCanonicalType();
if (canonicalTypes.insert(key).second)
results.push_back(overriddenDefault);
}
// If there was a single result, return it.
// FIXME: We could find *all* of the non-covered, defaulted associated types.
return results.size() == 1 ? results.front() : nullptr;
}
Type AssociatedTypeInference::computeFixedTypeWitness(
AssociatedTypeDecl *assocType) {
// Look at all of the inherited protocols to determine whether they
// require a fixed type for this associated type.
Type dependentType = assocType->getDeclaredInterfaceType();
Type resultType;
for (auto conformedProto : adoptee->getAnyNominal()->getAllProtocols()) {
if (!conformedProto->inheritsFrom(assocType->getProtocol()))
continue;
auto genericSig = conformedProto->getGenericSignature();
if (!genericSig) return Type();
Type concreteType = genericSig->getConcreteType(dependentType);
if (!concreteType) continue;
if (!resultType) {
resultType = concreteType;
continue;
}
// FIXME: Bailing out on ambiguity.
if (!resultType->isEqual(concreteType))
return Type();
}
return resultType;
}
Type AssociatedTypeInference::computeDefaultTypeWitness(
AssociatedTypeDecl *assocType) {
// Go find a default definition.
auto defaultedAssocType = findDefaultedAssociatedType(tc, assocType);
if (!defaultedAssocType) return Type();
// If we don't have a default definition, we're done.
auto selfType = proto->getSelfInterfaceType();
// Create a set of type substitutions for all known associated type.
// FIXME: Base this on dependent types rather than archetypes?
TypeSubstitutionMap substitutions;
substitutions[proto->mapTypeIntoContext(selfType)
->castTo<ArchetypeType>()] = dc->mapTypeIntoContext(adoptee);
for (auto assocType : proto->getAssociatedTypeMembers()) {
auto archetype = proto->mapTypeIntoContext(
assocType->getDeclaredInterfaceType())
->getAs<ArchetypeType>();
if (!archetype)
continue;
if (conformance->hasTypeWitness(assocType)) {
substitutions[archetype] =
dc->mapTypeIntoContext(conformance->getTypeWitness(assocType));
} else {
auto known = typeWitnesses.begin(assocType);
if (known != typeWitnesses.end())
substitutions[archetype] = known->first;
else
substitutions[archetype] = ErrorType::get(archetype);
}
}
Type defaultType = defaultedAssocType->getDefaultDefinitionType();
// FIXME: Circularity
if (!defaultType)
return Type();
// Map it into our protocol's context.
defaultType = proto->mapTypeIntoContext(defaultType);
defaultType = defaultType.subst(
QueryTypeSubstitutionMap{substitutions},
LookUpConformanceInModule(dc->getParentModule()));
if (!defaultType)
return Type();
if (auto failed = checkTypeWitness(tc, dc, proto, assocType, defaultType)) {
// Record the failure, if we haven't seen one already.
if (!failedDefaultedAssocType && !failed.isError()) {
failedDefaultedAssocType = defaultedAssocType;
failedDefaultedWitness = defaultType;
failedDefaultedResult = failed;
}
return Type();
}
return defaultType;
}
Type AssociatedTypeInference::computeDerivedTypeWitness(
AssociatedTypeDecl *assocType) {
if (adoptee->hasError())
return Type();
// Can we derive conformances for this protocol and adoptee?
NominalTypeDecl *derivingTypeDecl = adoptee->getAnyNominal();
if (!DerivedConformance::derivesProtocolConformance(dc, derivingTypeDecl,
proto))
return Type();
// Try to derive the type witness.
Type derivedType = tc.deriveTypeWitness(dc, derivingTypeDecl, assocType);
if (!derivedType)
return Type();
// Make sure that the derived type is sane.
if (checkTypeWitness(tc, dc, proto, assocType, derivedType)) {
/// FIXME: Diagnose based on this.
failedDerivedAssocType = assocType;
failedDerivedWitness = derivedType;
return Type();
}
return derivedType;
}
Type
AssociatedTypeInference::computeAbstractTypeWitness(
AssociatedTypeDecl *assocType,
bool allowDerived) {
// We don't have a type witness for this associated type, so go
// looking for more options.
if (Type concreteType = computeFixedTypeWitness(assocType))
return concreteType;
// If we can form a default type, do so.
if (Type defaultType = computeDefaultTypeWitness(assocType))
return defaultType;
// If we can derive a type witness, do so.
if (allowDerived) {
if (Type derivedType = computeDerivedTypeWitness(assocType))
return derivedType;
}
// If there is a generic parameter of the named type, use that.
if (auto *genericSig = dc->getGenericSignatureOfContext()) {
for (auto gp : genericSig->getInnermostGenericParams()) {
if (gp->getName() == assocType->getName())
return dc->mapTypeIntoContext(gp);
}
}
return Type();
}
Type AssociatedTypeInference::substCurrentTypeWitnesses(Type type) {
// Local function that folds dependent member types with non-dependent
// bases into actual member references.
std::function<Type(Type)> foldDependentMemberTypes;
llvm::DenseSet<AssociatedTypeDecl *> recursionCheck;
foldDependentMemberTypes = [&](Type type) -> Type {
if (auto depMemTy = type->getAs<DependentMemberType>()) {
auto baseTy = depMemTy->getBase().transform(foldDependentMemberTypes);
if (baseTy.isNull() || baseTy->hasTypeParameter())
return nullptr;
auto assocType = depMemTy->getAssocType();
if (!assocType)
return nullptr;
if (!recursionCheck.insert(assocType).second)
return nullptr;
SWIFT_DEFER { recursionCheck.erase(assocType); };
// Try to substitute into the base type.
if (Type result = depMemTy->substBaseType(dc->getParentModule(), baseTy)){
return result;
}
// If that failed, check whether it's because of the conformance we're
// evaluating.
auto localConformance
= TypeChecker::conformsToProtocol(
baseTy, assocType->getProtocol(), dc,
ConformanceCheckFlags::SkipConditionalRequirements);
if (!localConformance || localConformance->isAbstract() ||
(localConformance->getConcrete()->getRootConformance()
!= conformance)) {
return nullptr;
}
// Find the tentative type witness for this associated type.
auto known = typeWitnesses.begin(assocType);
if (known == typeWitnesses.end())
return nullptr;
return known->first.transform(foldDependentMemberTypes);
}
// The presence of a generic type parameter indicates that we
// cannot use this type binding.
if (type->is<GenericTypeParamType>()) {
return nullptr;
}
return type;
};
return type.transform(foldDependentMemberTypes);
}