swift-mirror/lib/AST/ProtocolConformance.cpp

//===--- ProtocolConformance.cpp - AST Protocol Conformance ---------------===//
//
// 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 the protocol conformance data structures.
//
//===----------------------------------------------------------------------===//

#include "ConformanceLookupTable.h"
#include "swift/AST/ASTContext.h"
#include "swift/AST/Availability.h"
#include "swift/AST/Decl.h"
#include "swift/AST/LazyResolver.h"
#include "swift/AST/GenericEnvironment.h"
#include "swift/AST/Module.h"
#include "swift/AST/ProtocolConformance.h"
#include "swift/AST/Types.h"
#include "swift/AST/TypeWalker.h"
#include "swift/Basic/Statistic.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/TinyPtrVector.h"
#include "llvm/Support/PrettyStackTrace.h"
#include "llvm/Support/SaveAndRestore.h"

#define DEBUG_TYPE "AST"

STATISTIC(NumConformanceLookupTables, "# of conformance lookup tables built");

using namespace swift;

Witness::Witness(ValueDecl *decl, SubstitutionMap substitutions,
                 GenericEnvironment *syntheticEnv,
                 SubstitutionMap reqToSynthesizedEnvSubs) {
  if (!syntheticEnv && substitutions.empty() &&
      reqToSynthesizedEnvSubs.empty()) {
    storage = decl;
    return;
  }

  auto &ctx = decl->getASTContext();
  auto declRef = ConcreteDeclRef(decl, substitutions);
  auto storedMem = ctx.Allocate(sizeof(StoredWitness), alignof(StoredWitness));
  auto stored = new (storedMem) StoredWitness{declRef, syntheticEnv,
                                              reqToSynthesizedEnvSubs};

  storage = stored;
}

void Witness::dump() const { dump(llvm::errs()); }

void Witness::dump(llvm::raw_ostream &out) const {
  // FIXME: Implement!
}

ProtocolConformanceRef::ProtocolConformanceRef(ProtocolDecl *protocol,
                                               ProtocolConformance *conf) {
  assert(protocol != nullptr &&
         "cannot construct ProtocolConformanceRef with null protocol");
  if (conf) {
    assert(protocol == conf->getProtocol() && "protocol conformance mismatch");
    Union = conf;
  } else {
    Union = protocol;
  }
}

ProtocolDecl *ProtocolConformanceRef::getRequirement() const {
  assert(!isInvalid());

  if (isConcrete()) {
    return getConcrete()->getProtocol();
  } else {
    return getAbstract();
  }
}

ProtocolConformanceRef
ProtocolConformanceRef::subst(Type origType,
                              SubstitutionMap subMap,
                              SubstOptions options) const {
  return subst(origType,
               QuerySubstitutionMap{subMap},
               LookUpConformanceInSubstitutionMap(subMap),
               options);
}

ProtocolConformanceRef
ProtocolConformanceRef::subst(Type origType,
                              TypeSubstitutionFn subs,
                              LookupConformanceFn conformances,
                              SubstOptions options) const {
  if (isInvalid())
    return *this;

  // If we have a concrete conformance, we need to substitute the
  // conformance to apply to the new type.
  if (isConcrete())
    return ProtocolConformanceRef(getConcrete()->subst(subs, conformances,
                                                       options));
  // If the type is an opaque archetype, the conformance will remain abstract,
  // unless we're specifically substituting opaque types.
  if (auto origArchetype = origType->getAs<ArchetypeType>()) {
    if (!options.contains(SubstFlags::SubstituteOpaqueArchetypes)
        && isa<OpaqueTypeArchetypeType>(origArchetype->getRoot())) {
      return *this;
    }
  }

  // Otherwise, compute the substituted type.
  auto substType = origType.subst(subs, conformances, options);

  // Opened existentials trivially conform and do not need to go through
  // substitution map lookup.
  if (substType->isOpenedExistential())
    return *this;

  auto *proto = getRequirement();

  // If the type is an existential, it must be self-conforming.
  if (substType->isExistentialType()) {
    auto optConformance =
      proto->getModuleContext()->lookupExistentialConformance(substType, proto);
    assert(optConformance && "existential type didn't self-conform");
    return *optConformance;
  }

  // Check the conformance map.
  if (auto result = conformances(origType->getCanonicalType(),
                                 substType, proto)) {
    return *result;
  }

  llvm_unreachable("Invalid conformance substitution");
}

ProtocolConformanceRef ProtocolConformanceRef::mapConformanceOutOfContext() const {
  if (!isConcrete())
    return *this;

  auto *concrete = getConcrete()->subst(
      [](SubstitutableType *type) -> Type {
        if (auto *archetypeType = type->getAs<ArchetypeType>())
          return archetypeType->getInterfaceType();
        return type;
      },
      MakeAbstractConformanceForGenericType());
  return ProtocolConformanceRef(concrete);
}

Type
ProtocolConformanceRef::getTypeWitnessByName(Type type, Identifier name) const {
  assert(!isInvalid());

  // Find the named requirement.
  ProtocolDecl *proto = getRequirement();
  AssociatedTypeDecl *assocType = nullptr;
  auto members = proto->lookupDirect(name,
                      NominalTypeDecl::LookupDirectFlags::IgnoreNewExtensions);
  for (auto member : members) {
    assocType = dyn_cast<AssociatedTypeDecl>(member);
    if (assocType)
      break;
  }

  // FIXME: Shouldn't this be a hard error?
  if (!assocType)
    return ErrorType::get(proto->getASTContext());

  return assocType->getDeclaredInterfaceType().subst(
    SubstitutionMap::getProtocolSubstitutions(proto, type, *this));
}

ConcreteDeclRef
ProtocolConformanceRef::getWitnessByName(Type type, DeclName name) const {
  // Find the named requirement.
  auto *proto = getRequirement();
  auto results =
    proto->lookupDirect(name,
                      NominalTypeDecl::LookupDirectFlags::IgnoreNewExtensions);

  ValueDecl *requirement = nullptr;
  for (auto *result : results) {
    if (isa<ProtocolDecl>(result->getDeclContext()))
      requirement = result;
  }

  if (requirement == nullptr)
    return ConcreteDeclRef();

  // For a type with dependent conformance, just return the requirement from
  // the protocol. There are no protocol conformance tables.
  if (!isConcrete()) {
    auto subs = SubstitutionMap::getProtocolSubstitutions(proto, type, *this);
    return ConcreteDeclRef(requirement, subs);
  }

  return getConcrete()->getWitnessDeclRef(requirement);
}

void *ProtocolConformance::operator new(size_t bytes, ASTContext &context,
                                        AllocationArena arena,
                                        unsigned alignment) {
  return context.Allocate(bytes, alignment, arena);

}

#define CONFORMANCE_SUBCLASS_DISPATCH(Method, Args)                          \
switch (getKind()) {                                                         \
  case ProtocolConformanceKind::Normal:                                      \
    static_assert(&ProtocolConformance::Method !=                            \
                    &NormalProtocolConformance::Method,                      \
                  "Must override NormalProtocolConformance::" #Method);      \
    return cast<NormalProtocolConformance>(this)->Method Args;               \
  case ProtocolConformanceKind::Self:                                        \
    static_assert(&ProtocolConformance::Method !=                            \
                    &SelfProtocolConformance::Method,                        \
                  "Must override SelfProtocolConformance::" #Method);        \
    return cast<SelfProtocolConformance>(this)->Method Args;                 \
  case ProtocolConformanceKind::Specialized:                                 \
    static_assert(&ProtocolConformance::Method !=                            \
                    &SpecializedProtocolConformance::Method,                 \
                  "Must override SpecializedProtocolConformance::" #Method); \
    return cast<SpecializedProtocolConformance>(this)->Method Args;          \
  case ProtocolConformanceKind::Inherited:                                   \
    static_assert(&ProtocolConformance::Method !=                            \
                    &InheritedProtocolConformance::Method,                   \
                  "Must override InheritedProtocolConformance::" #Method);   \
    return cast<InheritedProtocolConformance>(this)->Method Args;            \
}                                                                            \
llvm_unreachable("bad ProtocolConformanceKind");

#define ROOT_CONFORMANCE_SUBCLASS_DISPATCH(Method, Args)                     \
switch (getKind()) {                                                         \
  case ProtocolConformanceKind::Normal:                                      \
    static_assert(&RootProtocolConformance::Method !=                        \
                    &NormalProtocolConformance::Method,                      \
                  "Must override NormalProtocolConformance::" #Method);      \
    return cast<NormalProtocolConformance>(this)->Method Args;               \
  case ProtocolConformanceKind::Self:                                        \
    static_assert(&RootProtocolConformance::Method !=                        \
                    &SelfProtocolConformance::Method,                        \
                  "Must override SelfProtocolConformance::" #Method);        \
    return cast<SelfProtocolConformance>(this)->Method Args;                 \
  case ProtocolConformanceKind::Specialized:                                 \
  case ProtocolConformanceKind::Inherited:                                   \
    llvm_unreachable("not a root conformance");                              \
}                                                                            \
llvm_unreachable("bad ProtocolConformanceKind");

/// Get the protocol being conformed to.
ProtocolDecl *ProtocolConformance::getProtocol() const {
  CONFORMANCE_SUBCLASS_DISPATCH(getProtocol, ())
}

DeclContext *ProtocolConformance::getDeclContext() const {
  CONFORMANCE_SUBCLASS_DISPATCH(getDeclContext, ())
}

/// Retrieve the state of this conformance.
ProtocolConformanceState ProtocolConformance::getState() const {
  CONFORMANCE_SUBCLASS_DISPATCH(getState, ())
}

ConformanceEntryKind ProtocolConformance::getSourceKind() const {
  CONFORMANCE_SUBCLASS_DISPATCH(getSourceKind, ())
}
NormalProtocolConformance *ProtocolConformance::getImplyingConformance() const {
  CONFORMANCE_SUBCLASS_DISPATCH(getImplyingConformance, ())
}

bool
ProtocolConformance::hasTypeWitness(AssociatedTypeDecl *assocType) const {
  CONFORMANCE_SUBCLASS_DISPATCH(hasTypeWitness, (assocType));
}

std::pair<Type, TypeDecl *>
ProtocolConformance::getTypeWitnessAndDecl(AssociatedTypeDecl *assocType,
                                           SubstOptions options) const {
  CONFORMANCE_SUBCLASS_DISPATCH(getTypeWitnessAndDecl,
                                (assocType, options))
}

Type ProtocolConformance::getTypeWitness(AssociatedTypeDecl *assocType,
                                         SubstOptions options) const {
  return getTypeWitnessAndDecl(assocType, options).first;
}

ConcreteDeclRef
ProtocolConformance::getWitnessDeclRef(ValueDecl *requirement) const {
  CONFORMANCE_SUBCLASS_DISPATCH(getWitnessDeclRef, (requirement))
}

ValueDecl *ProtocolConformance::getWitnessDecl(ValueDecl *requirement) const {
  switch (getKind()) {
  case ProtocolConformanceKind::Normal:
    return cast<NormalProtocolConformance>(this)->getWitness(requirement)
      .getDecl();
  case ProtocolConformanceKind::Self:
    return cast<SelfProtocolConformance>(this)->getWitness(requirement)
      .getDecl();
  case ProtocolConformanceKind::Inherited:
    return cast<InheritedProtocolConformance>(this)
      ->getInheritedConformance()->getWitnessDecl(requirement);

  case ProtocolConformanceKind::Specialized:
    return cast<SpecializedProtocolConformance>(this)
      ->getGenericConformance()->getWitnessDecl(requirement);
  }
  llvm_unreachable("unhandled kind");
}

/// Determine whether the witness for the given requirement
/// is either the default definition or was otherwise deduced.
bool ProtocolConformance::
usesDefaultDefinition(AssociatedTypeDecl *requirement) const {
  CONFORMANCE_SUBCLASS_DISPATCH(usesDefaultDefinition, (requirement))
}

GenericEnvironment *ProtocolConformance::getGenericEnvironment() const {
  switch (getKind()) {
  case ProtocolConformanceKind::Inherited:
  case ProtocolConformanceKind::Normal:
  case ProtocolConformanceKind::Self:
    // If we have a normal or inherited protocol conformance, look for its
    // generic parameters.
    return getDeclContext()->getGenericEnvironmentOfContext();

  case ProtocolConformanceKind::Specialized:
    // If we have a specialized protocol conformance, since we do not support
    // currently partial specialization, we know that it cannot have any open
    // type variables.
    //
    // FIXME: We could return a meaningful GenericEnvironment here
    return nullptr;
  }

  llvm_unreachable("Unhandled ProtocolConformanceKind in switch.");
}

GenericSignature *ProtocolConformance::getGenericSignature() const {
  switch (getKind()) {
  case ProtocolConformanceKind::Inherited:
  case ProtocolConformanceKind::Normal:
  case ProtocolConformanceKind::Self:
    // If we have a normal or inherited protocol conformance, look for its
    // generic signature.
    return getDeclContext()->getGenericSignatureOfContext();

  case ProtocolConformanceKind::Specialized:
    // If we have a specialized protocol conformance, since we do not support
    // currently partial specialization, we know that it cannot have any open
    // type variables.
    return nullptr;
  }

  llvm_unreachable("Unhandled ProtocolConformanceKind in switch.");
}

SubstitutionMap ProtocolConformance::getSubstitutions(ModuleDecl *M) const {
  // Walk down to the base NormalProtocolConformance.
  SubstitutionMap subMap;
  const ProtocolConformance *parent = this;
  while (!isa<RootProtocolConformance>(parent)) {
    switch (parent->getKind()) {
    case ProtocolConformanceKind::Normal:
    case ProtocolConformanceKind::Self:
      llvm_unreachable("should have exited the loop?!");
    case ProtocolConformanceKind::Inherited:
      parent =
          cast<InheritedProtocolConformance>(parent)->getInheritedConformance();
      break;
    case ProtocolConformanceKind::Specialized: {
      auto SC = cast<SpecializedProtocolConformance>(parent);
      parent = SC->getGenericConformance();
      assert(subMap.empty() && "multiple conformance specializations?!");
      subMap = SC->getSubstitutionMap();
      break;
    }
    }
  }

  // Found something; we're done!
  if (!subMap.empty())
    return subMap;

  // If the normal conformance is for a generic type, and we didn't hit a
  // specialized conformance, collect the substitutions from the generic type.
  // FIXME: The AST should do this for us.
  const NormalProtocolConformance *normalC =
      dyn_cast<NormalProtocolConformance>(parent);
  if (!normalC)
    return SubstitutionMap();

  if (!normalC->getType()->isSpecialized())
    return SubstitutionMap();

  auto *DC = normalC->getDeclContext();
  return normalC->getType()->getContextSubstitutionMap(M, DC);
}

bool RootProtocolConformance::isInvalid() const {
  ROOT_CONFORMANCE_SUBCLASS_DISPATCH(isInvalid, ())
}

SourceLoc RootProtocolConformance::getLoc() const {
  ROOT_CONFORMANCE_SUBCLASS_DISPATCH(getLoc, ())
}

bool
RootProtocolConformance::isWeakImported(ModuleDecl *fromModule,
                                        AvailabilityContext fromContext) const {
  auto *dc = getDeclContext();
  if (dc->getParentModule() == fromModule)
    return false;

  // If the protocol is weak imported, so are any conformances to it.
  if (getProtocol()->isWeakImported(fromModule, fromContext))
    return true;

  // If the conforming type is weak imported, so are any of its conformances.
  if (auto *nominal = getType()->getAnyNominal())
    if (nominal->isWeakImported(fromModule, fromContext))
      return true;

  // If the conformance is declared in an extension with the @_weakLinked
  // attribute, it is weak imported.
  if (auto *ext = dyn_cast<ExtensionDecl>(dc))
    if (ext->isWeakImported(fromModule, fromContext))
      return true;

  return false;
}

bool RootProtocolConformance::hasWitness(ValueDecl *requirement) const {
  ROOT_CONFORMANCE_SUBCLASS_DISPATCH(hasWitness, (requirement))
}

bool NormalProtocolConformance::isRetroactive() const {
  auto module = getDeclContext()->getParentModule();

  // If the conformance occurs in the same module as the protocol definition,
  // this is not a retroactive conformance.
  auto protocolModule = getProtocol()->getDeclContext()->getParentModule();
  if (module == protocolModule)
    return false;

  // If the conformance occurs in the same module as the conforming type
  // definition, this is not a retroactive conformance.
  if (auto nominal = getType()->getAnyNominal()) {
    auto nominalModule = nominal->getParentModule();

    // Consider the overlay module to be the "home" of a nominal type
    // defined in a Clang module.
    if (auto nominalLoadedModule =
          dyn_cast<LoadedFile>(nominal->getModuleScopeContext())) {
      if (auto overlayModule = nominalLoadedModule->getOverlayModule())
        nominalModule = overlayModule;
    }

    if (module == nominalModule)
      return false;
  }

  // Everything else is retroactive.
  return true;
}

bool NormalProtocolConformance::isSynthesizedNonUnique() const {
  if (auto *file = dyn_cast<FileUnit>(getDeclContext()->getModuleScopeContext()))
    return file->getKind() == FileUnitKind::ClangModule;
  return false;
}

bool NormalProtocolConformance::isResilient() const {
  // If the type is non-resilient or the module we're in is non-resilient, the
  // conformance is non-resilient.
  // FIXME: Looking at the type is not the right long-term solution. We need an
  // explicit mechanism for declaring conformances as 'fragile', or even
  // individual witnesses.
  if (!getType()->getAnyNominal()->isResilient())
    return false;

  return getDeclContext()->getParentModule()->isResilient();
}

Optional<ArrayRef<Requirement>>
ProtocolConformance::getConditionalRequirementsIfAvailable() const {
  CONFORMANCE_SUBCLASS_DISPATCH(getConditionalRequirementsIfAvailable, ());
}

ArrayRef<Requirement> ProtocolConformance::getConditionalRequirements() const {
  CONFORMANCE_SUBCLASS_DISPATCH(getConditionalRequirements, ());
}

Optional<ArrayRef<Requirement>>
ProtocolConformanceRef::getConditionalRequirementsIfAvailable() const {
  if (isConcrete())
    return getConcrete()->getConditionalRequirementsIfAvailable();
  else
    // An abstract conformance is never conditional: any conditionality in the
    // concrete types that will eventually pass through this at runtime is
    // completely pre-checked and packaged up.
    return ArrayRef<Requirement>();
}

ArrayRef<Requirement>
ProtocolConformanceRef::getConditionalRequirements() const {
  if (isConcrete())
    return getConcrete()->getConditionalRequirements();
  else
    // An abstract conformance is never conditional, as above.
    return {};
}

void NormalProtocolConformance::differenceAndStoreConditionalRequirements()
    const {
  switch (CRState) {
  case ConditionalRequirementsState::Complete:
    // already done!
    return;
  case ConditionalRequirementsState::Computing:
    // recursive
    return;
  case ConditionalRequirementsState::Uncomputed:
    // try to compute it!
    break;
  };

  CRState = ConditionalRequirementsState::Computing;
  auto success = [this](ArrayRef<Requirement> reqs) {
    ConditionalRequirements = reqs;
    assert(CRState == ConditionalRequirementsState::Computing);
    CRState = ConditionalRequirementsState::Complete;
  };
  auto failure = [this] {
    assert(CRState == ConditionalRequirementsState::Computing);
    CRState = ConditionalRequirementsState::Uncomputed;
  };

  auto &ctxt = getProtocol()->getASTContext();
  auto DC = getDeclContext();
  // A non-extension conformance won't have conditional requirements.
  if (!isa<ExtensionDecl>(DC)) {
    success({});
    return;
  }

  auto *ext = cast<ExtensionDecl>(DC);
  auto nominal = ext->getExtendedNominal();
  auto typeSig = nominal->getGenericSignature();

  // A non-generic type won't have conditional requirements.
  if (!typeSig) {
    success({});
    return;
  }

  auto extensionSig = ext->getGenericSignature();
  if (!extensionSig) {
    if (auto lazyResolver = ctxt.getLazyResolver()) {
      lazyResolver->resolveExtension(ext);
      extensionSig = ext->getGenericSignature();
    }
  }

  // The type is generic, but the extension doesn't have a signature yet, so
  // we might be in a recursive validation situation.
  if (!extensionSig) {
    // If the extension is invalid, it won't ever get a signature, so we
    // "succeed" with an empty result instead.
    if (ext->isInvalid()) {
      success({});
      return;
    }

    // Otherwise we'll try again later.
    failure();
    return;
  }

  auto canExtensionSig = extensionSig->getCanonicalSignature();
  auto canTypeSig = typeSig->getCanonicalSignature();
  if (canTypeSig == canExtensionSig) {
    success({});
    return;
  }

  // The extension signature should be a superset of the type signature, meaning
  // every thing in the type signature either is included too or is implied by
  // something else. The most important bit is having the same type
  // parameters. (NB. if/when Swift gets parameterized extensions, this needs to
  // change.)
  assert(canTypeSig.getGenericParams() == canExtensionSig.getGenericParams());

  // Find the requirements in the extension that aren't proved by the original
  // type, these are the ones that make the conformance conditional.
  success(ctxt.AllocateCopy(extensionSig->requirementsNotSatisfiedBy(typeSig)));
}

void NormalProtocolConformance::setSignatureConformances(
                               ArrayRef<ProtocolConformanceRef> conformances) {
  if (conformances.empty()) {
    SignatureConformances = { };
    return;
  }

  auto &ctx = getProtocol()->getASTContext();
  SignatureConformances = ctx.AllocateCopy(conformances);

#if !NDEBUG
  unsigned idx = 0;
  for (const auto &req : getProtocol()->getRequirementSignature()) {
    if (req.getKind() == RequirementKind::Conformance) {
      assert(!conformances[idx].isConcrete() ||
             !conformances[idx].getConcrete()->getType()->hasArchetype() &&
             "Should have interface types here");
      assert(idx < conformances.size());
      assert(conformances[idx].isInvalid() ||
             conformances[idx].getRequirement() ==
               req.getSecondType()->castTo<ProtocolType>()->getDecl());
      ++idx;
    }
  }
  assert(idx == conformances.size() && "Too many conformances");
#endif
}

void NormalProtocolConformance::resolveLazyInfo() const {
  assert(Loader);

  auto *loader = Loader;
  auto *mutableThis = const_cast<NormalProtocolConformance *>(this);
  mutableThis->Loader = nullptr;
  loader->finishNormalConformance(mutableThis, LoaderContextData);
}

void NormalProtocolConformance::setLazyLoader(LazyConformanceLoader *loader,
                                              uint64_t contextData) {
  assert(!Loader && "already has a loader");
  Loader = loader;
  LoaderContextData = contextData;
}

namespace {
  class PrettyStackTraceRequirement : public llvm::PrettyStackTraceEntry {
    const char *Action;
    const ProtocolConformance *Conformance;
    ValueDecl *Requirement;
  public:
    PrettyStackTraceRequirement(const char *action,
                                const ProtocolConformance *conformance,
                                ValueDecl *requirement)
      : Action(action), Conformance(conformance), Requirement(requirement) { }

    void print(llvm::raw_ostream &out) const override {
      out << "While " << Action << " requirement ";
      Requirement->dumpRef(out);
      out << " in conformance ";
      Conformance->printName(out);
      out << "\n";
    }
  };
} // end anonymous namespace

bool NormalProtocolConformance::hasTypeWitness(
                                         AssociatedTypeDecl *assocType) const {
  if (Loader)
    resolveLazyInfo();

  auto found = TypeWitnesses.find(assocType);
  if (found != TypeWitnesses.end()) {
    return !found->getSecond().first.isNull();
  }

  return false;
}

using TypeWitnessAndDecl = std::pair<Type, TypeDecl *>;
TypeWitnessAndDecl
NormalProtocolConformance::getTypeWitnessAndDecl(AssociatedTypeDecl *assocType,
                                                 SubstOptions options) const {
  if (Loader)
    resolveLazyInfo();

  // Check whether we already have a type witness.
  auto known = TypeWitnesses.find(assocType);
  if (known != TypeWitnesses.end())
    return known->second;

  // If there is a tentative-type-witness function, use it.
  if (options.getTentativeTypeWitness) {
   if (Type witnessType =
         Type(options.getTentativeTypeWitness(this, assocType)))
     return { witnessType, nullptr };
  }

  // If this conformance is in a state where it is inferring type witnesses but
  // we didn't find anything, fail.
  if (getState() == ProtocolConformanceState::CheckingTypeWitnesses) {
    return { Type(), nullptr };
  }

  // If the conditional requirements aren't known, we can't properly run
  // inference.
  if (!getConditionalRequirementsIfAvailable()) {
    return {Type(), nullptr};
  }

  // Otherwise, resolve the type witness.
  PrettyStackTraceRequirement trace("resolving", this, assocType);
  auto *resolver = assocType->getASTContext().getLazyResolver();
  assert(resolver && "Unable to resolve type witness");

  // Block recursive resolution of this type witness.
  TypeWitnesses[assocType] = { Type(), nullptr };
  resolver->resolveTypeWitness(this, assocType);

  known = TypeWitnesses.find(assocType);
  assert(known != TypeWitnesses.end() && "Didn't resolve witness?");
  return known->second;
}

void NormalProtocolConformance::setTypeWitness(AssociatedTypeDecl *assocType,
                                               Type type,
                                               TypeDecl *typeDecl) const {
  assert(getProtocol() == cast<ProtocolDecl>(assocType->getDeclContext()) &&
         "associated type in wrong protocol");
  assert((TypeWitnesses.count(assocType) == 0 ||
          TypeWitnesses[assocType].first.isNull()) &&
         "Type witness already known");
  assert((!isComplete() || isInvalid()) && "Conformance already complete?");
  assert(!type->hasArchetype() && "type witnesses must be interface types");
  TypeWitnesses[assocType] = std::make_pair(type, typeDecl);
}

Type ProtocolConformance::getAssociatedType(Type assocType) const {
  assert(assocType->isTypeParameter() &&
         "associated type must be a type parameter");

  ProtocolConformanceRef ref(const_cast<ProtocolConformance*>(this));
  return ref.getAssociatedType(getType(), assocType);
}

Type ProtocolConformanceRef::getAssociatedType(Type conformingType,
                                               Type assocType) const {
  assert(!isConcrete() || getConcrete()->getType()->isEqual(conformingType));

  auto type = assocType->getCanonicalType();
  auto proto = getRequirement();

  // Fast path for generic parameters.
  if (isa<GenericTypeParamType>(type)) {
    assert(type->isEqual(proto->getSelfInterfaceType()) &&
           "type parameter in protocol was not Self");
    return conformingType;
  }

  // Fast path for dependent member types on 'Self' of our associated types.
  auto memberType = cast<DependentMemberType>(type);
  if (memberType.getBase()->isEqual(proto->getSelfInterfaceType()) &&
      memberType->getAssocType()->getProtocol() == proto &&
      isConcrete())
    return getConcrete()->getTypeWitness(memberType->getAssocType());

  // General case: consult the substitution map.
  auto substMap =
    SubstitutionMap::getProtocolSubstitutions(proto, conformingType, *this);
  return type.subst(substMap);
}

ProtocolConformanceRef
ProtocolConformanceRef::getAssociatedConformance(Type conformingType,
                                                 Type assocType,
                                                 ProtocolDecl *protocol) const {
  // If this is a concrete conformance, look up the associated conformance.
  if (isConcrete()) {
    auto conformance = getConcrete();
    assert(conformance->getType()->isEqual(conformingType));
    return conformance->getAssociatedConformance(assocType, protocol);
  }

  // Otherwise, apply the substitution {self -> conformingType}
  // to the abstract conformance requirement laid upon the dependent type
  // by the protocol.
  auto subMap =
    SubstitutionMap::getProtocolSubstitutions(getRequirement(),
                                              conformingType, *this);
  auto abstractConf = ProtocolConformanceRef(protocol);
  return abstractConf.subst(assocType, subMap);
}

ProtocolConformanceRef
ProtocolConformance::getAssociatedConformance(Type assocType,
                                               ProtocolDecl *protocol) const {
  CONFORMANCE_SUBCLASS_DISPATCH(getAssociatedConformance,
                                (assocType, protocol))
}

ProtocolConformanceRef
NormalProtocolConformance::getAssociatedConformance(Type assocType,
                                                ProtocolDecl *protocol) const {
  assert(assocType->isTypeParameter() &&
         "associated type must be a type parameter");

  // Fill in the signature conformances, if we haven't done so yet.
  if (getSignatureConformances().empty()) {
    const_cast<NormalProtocolConformance *>(this)->finishSignatureConformances();
  }

  assert(!getSignatureConformances().empty() &&
         "signature conformances not yet computed");

  unsigned conformanceIndex = 0;
  for (const auto &reqt : getProtocol()->getRequirementSignature()) {
    if (reqt.getKind() == RequirementKind::Conformance) {
      // Is this the conformance we're looking for?
      if (reqt.getFirstType()->isEqual(assocType) &&
          reqt.getSecondType()->castTo<ProtocolType>()->getDecl() == protocol)
        return getSignatureConformances()[conformanceIndex];

      ++conformanceIndex;
    }
  }

  llvm_unreachable(
    "requested conformance was not a direct requirement of the protocol");
}


/// A stripped-down version of Type::subst that only works on the protocol
/// Self type wrapped in zero or more DependentMemberTypes.
static Type
recursivelySubstituteBaseType(ModuleDecl *module,
                              NormalProtocolConformance *conformance,
                              DependentMemberType *depMemTy) {
  Type origBase = depMemTy->getBase();

  // Recursive case.
  if (auto *depBase = origBase->getAs<DependentMemberType>()) {
    Type substBase = recursivelySubstituteBaseType(
        module, conformance, depBase);
    return depMemTy->substBaseType(module, substBase);
  }

  // Base case. The associated type's protocol should be either the
  // conformance protocol or an inherited protocol.
  auto *reqProto = depMemTy->getAssocType()->getProtocol();
  assert(origBase->isEqual(reqProto->getSelfInterfaceType()));

  ProtocolConformance *reqConformance = conformance;

  // If we have an inherited protocol just look up the conformance.
  if (reqProto != conformance->getProtocol()) {
    reqConformance = module->lookupConformance(
        conformance->getType(), reqProto)->getConcrete();
  }

  return reqConformance->getTypeWitness(depMemTy->getAssocType());
}

/// Collect conformances for the requirement signature.
void NormalProtocolConformance::finishSignatureConformances() {
  if (!SignatureConformances.empty())
    return;

  auto *proto = getProtocol();
  auto reqSig = proto->getRequirementSignature();
  if (reqSig.empty())
    return;

  SmallVector<ProtocolConformanceRef, 4> reqConformances;
  for (const auto &req : reqSig) {
    if (req.getKind() != RequirementKind::Conformance)
      continue;

    ModuleDecl *module = getDeclContext()->getParentModule();

    Type substTy;
    auto origTy = req.getFirstType();
    if (origTy->isEqual(proto->getSelfInterfaceType())) {
      substTy = getType();
    } else {
      auto *depMemTy = origTy->castTo<DependentMemberType>();
      substTy = recursivelySubstituteBaseType(module, this, depMemTy);
    }
    auto reqProto = req.getSecondType()->castTo<ProtocolType>()->getDecl();

    // Looking up a conformance for a contextual type and mapping the
    // conformance context produces a more accurate result than looking
    // up a conformance from an interface type.
    //
    // This can happen if the conformance has an associated conformance
    // depending on an associated type that is made concrete in a
    // refining protocol.
    //
    // That is, the conformance of an interface type G<T> : P really
    // depends on the generic signature of the current context, because
    // performing the lookup in a "more" constrained extension than the
    // one where the conformance was defined must produce concrete
    // conformances.
    //
    // FIXME: Eliminate this, perhaps by adding a variant of
    // lookupConformance() taking a generic signature.
    if (substTy->hasTypeParameter())
      substTy = getDeclContext()->mapTypeIntoContext(substTy);

    auto reqConformance = module->lookupConformance(substTy, reqProto);
    if (!reqConformance)
      reqConformance = ProtocolConformanceRef::forInvalid();

    reqConformance = reqConformance->mapConformanceOutOfContext();
    reqConformances.push_back(*reqConformance);
  }
  setSignatureConformances(reqConformances);
}

Witness RootProtocolConformance::getWitness(ValueDecl *requirement) const {
  ROOT_CONFORMANCE_SUBCLASS_DISPATCH(getWitness, (requirement))
}

/// Retrieve the value witness corresponding to the given requirement.
Witness NormalProtocolConformance::getWitness(ValueDecl *requirement) const {
  assert(!isa<AssociatedTypeDecl>(requirement) && "Request type witness");
  assert(requirement->isProtocolRequirement() && "Not a requirement");

  if (Loader)
    resolveLazyInfo();

  auto known = Mapping.find(requirement);
  if (known == Mapping.end()) {
    auto *resolver = requirement->getASTContext().getLazyResolver();
    assert(resolver && "Unable to resolve witness without resolver");
    resolver->resolveWitness(this, requirement);
    known = Mapping.find(requirement);
  }
  if (known != Mapping.end()) {
    return known->second;
  } else {
    assert((!isComplete() || isInvalid()) &&
           "Resolver did not resolve requirement");
    return Witness();
  }
}

Witness SelfProtocolConformance::getWitness(ValueDecl *requirement) const {
  return Witness(requirement, SubstitutionMap(), nullptr, SubstitutionMap());
}

ConcreteDeclRef
RootProtocolConformance::getWitnessDeclRef(ValueDecl *requirement) const {
  if (auto witness = getWitness(requirement)) {
    auto *witnessDecl = witness.getDecl();

    // If the witness is generic, you have to call getWitness() and build
    // your own substitutions in terms of the synthetic environment.
    if (auto *witnessDC = dyn_cast<DeclContext>(witnessDecl))
      assert(!witnessDC->isInnermostContextGeneric());

    // If the witness is not generic, use type substitutions from the
    // witness's parent. Don't use witness.getSubstitutions(), which
    // are written in terms of the synthetic environment.
    auto subs =
      getType()->getContextSubstitutionMap(getDeclContext()->getParentModule(),
                                           witnessDecl->getDeclContext());
    return ConcreteDeclRef(witness.getDecl(), subs);
  }

  return ConcreteDeclRef();
}

void NormalProtocolConformance::setWitness(ValueDecl *requirement,
                                           Witness witness) const {
  assert(!isa<AssociatedTypeDecl>(requirement) && "Request type witness");
  assert(getProtocol() == cast<ProtocolDecl>(requirement->getDeclContext()) &&
         "requirement in wrong protocol");
  assert(Mapping.count(requirement) == 0 && "Witness already known");
  assert((!isComplete() || isInvalid() ||
          requirement->getAttrs().hasAttribute<OptionalAttr>() ||
          requirement->getAttrs().isUnavailable(
                                        requirement->getASTContext())) &&
         "Conformance already complete?");
  Mapping[requirement] = witness;
}

SpecializedProtocolConformance::SpecializedProtocolConformance(
    Type conformingType,
    ProtocolConformance *genericConformance,
    SubstitutionMap substitutions)
  : ProtocolConformance(ProtocolConformanceKind::Specialized, conformingType),
    GenericConformance(genericConformance),
    GenericSubstitutions(substitutions)
{
  assert(genericConformance->getKind() != ProtocolConformanceKind::Specialized);
}

void SpecializedProtocolConformance::computeConditionalRequirements() const {
  // already computed?
  if (ConditionalRequirements)
    return;

  auto parentCondReqs =
      GenericConformance->getConditionalRequirementsIfAvailable();
  if (!parentCondReqs)
    return;

  if (!parentCondReqs->empty()) {
    // Substitute the conditional requirements so that they're phrased in
    // terms of the specialized types, not the conformance-declaring decl's
    // types.
    auto nominal = GenericConformance->getType()->getAnyNominal();
    auto module = nominal->getModuleContext();
    auto subMap = getType()->getContextSubstitutionMap(module, nominal);

    SmallVector<Requirement, 4> newReqs;
    for (auto oldReq : *parentCondReqs) {
      if (auto newReq = oldReq.subst(QuerySubstitutionMap{subMap},
                                     LookUpConformanceInModule(module)))
        newReqs.push_back(*newReq);
    }
    auto &ctxt = getProtocol()->getASTContext();
    ConditionalRequirements = ctxt.AllocateCopy(newReqs);
  } else {
    ConditionalRequirements = ArrayRef<Requirement>();
  }
}

bool SpecializedProtocolConformance::hasTypeWitness(
                                         AssociatedTypeDecl *assocType) const {
  return TypeWitnesses.find(assocType) != TypeWitnesses.end() ||
         GenericConformance->hasTypeWitness(assocType);
}

std::pair<Type, TypeDecl *>
SpecializedProtocolConformance::getTypeWitnessAndDecl(
                      AssociatedTypeDecl *assocType, 
                      SubstOptions options) const {
  assert(getProtocol() == cast<ProtocolDecl>(assocType->getDeclContext()) &&
         "associated type in wrong protocol");

  // If we've already created this type witness, return it.
  auto known = TypeWitnesses.find(assocType);
  if (known != TypeWitnesses.end()) {
    return known->second;
  }

  // Otherwise, perform substitutions to create this witness now.

  // Local function to determine whether we will end up referring to a
  // tentative witness that may not be chosen.
  auto root = GenericConformance->getRootConformance();
  auto isTentativeWitness = [&] {
    if (root->getState() != ProtocolConformanceState::CheckingTypeWitnesses)
      return false;

    return !root->hasTypeWitness(assocType);
  };

  auto genericWitnessAndDecl
    = GenericConformance->getTypeWitnessAndDecl(assocType, options);

  auto genericWitness = genericWitnessAndDecl.first;
  if (!genericWitness)
    return { Type(), nullptr };

  auto *typeDecl = genericWitnessAndDecl.second;

  // Form the substitution.
  auto substitutionMap = getSubstitutionMap();
  if (substitutionMap.empty())
    return {Type(), nullptr};

  // Apply the substitution we computed above
  auto specializedType = genericWitness.subst(substitutionMap, options);
  if (specializedType->hasError()) {
    if (isTentativeWitness())
      return { Type(), nullptr };

    specializedType = ErrorType::get(genericWitness);
  }

  // If we aren't in a case where we used the tentative type witness
  // information, cache the result.
  auto specializedWitnessAndDecl = std::make_pair(specializedType, typeDecl);
  if (!isTentativeWitness() && !specializedType->hasError())
    TypeWitnesses[assocType] = specializedWitnessAndDecl;

  return specializedWitnessAndDecl;
}

ProtocolConformanceRef
SpecializedProtocolConformance::getAssociatedConformance(Type assocType,
                                                ProtocolDecl *protocol) const {
  ProtocolConformanceRef conformance =
    GenericConformance->getAssociatedConformance(assocType, protocol);

  auto subMap = getSubstitutionMap();

  Type origType =
    (conformance.isConcrete()
       ? conformance.getConcrete()->getType()
       : GenericConformance->getAssociatedType(assocType));

  return conformance.subst(origType, subMap);
}

ConcreteDeclRef
SpecializedProtocolConformance::getWitnessDeclRef(
                                              ValueDecl *requirement) const {
  auto baseWitness = GenericConformance->getWitnessDeclRef(requirement);
  if (!baseWitness || !baseWitness.isSpecialized())
    return baseWitness;

  auto specializationMap = getSubstitutionMap();

  auto witnessDecl = baseWitness.getDecl();
  auto witnessMap = baseWitness.getSubstitutions();

  auto combinedMap = witnessMap.subst(specializationMap);
  return ConcreteDeclRef(witnessDecl, combinedMap);
}

ProtocolConformanceRef
InheritedProtocolConformance::getAssociatedConformance(Type assocType,
                                                ProtocolDecl *protocol) const {
  auto underlying =
    InheritedConformance->getAssociatedConformance(assocType, protocol);


  // If the conformance is for Self, return an inherited conformance.
  if (underlying.isConcrete() &&
      assocType->isEqual(getProtocol()->getSelfInterfaceType())) {
    auto subclassType = getType();
    ASTContext &ctx = subclassType->getASTContext();
    return ProtocolConformanceRef(
             ctx.getInheritedConformance(subclassType,
                                         underlying.getConcrete()));
  }

  return underlying;
}

ConcreteDeclRef
InheritedProtocolConformance::getWitnessDeclRef(ValueDecl *requirement) const {
  // FIXME: substitutions?
  return InheritedConformance->getWitnessDeclRef(requirement);
}

const NormalProtocolConformance *
ProtocolConformance::getRootNormalConformance() const {
  // This is an unsafe cast; remove this entire method.
  return cast<NormalProtocolConformance>(getRootConformance());
}

const RootProtocolConformance *
ProtocolConformance::getRootConformance() const {
  const ProtocolConformance *C = this;
  while (true) {
    switch (C->getKind()) {
    case ProtocolConformanceKind::Normal:
    case ProtocolConformanceKind::Self:
      return cast<RootProtocolConformance>(C);
    case ProtocolConformanceKind::Inherited:
      C = cast<InheritedProtocolConformance>(C)
          ->getInheritedConformance();
      break;
    case ProtocolConformanceKind::Specialized:
      C = cast<SpecializedProtocolConformance>(C)
        ->getGenericConformance();
      break;
    }
  }
}

bool ProtocolConformance::isVisibleFrom(const DeclContext *dc) const {
  // FIXME: Implement me!
  return true;
}

ProtocolConformance *
ProtocolConformance::subst(SubstitutionMap subMap,
                           SubstOptions options) const {
  return subst(QuerySubstitutionMap{subMap},
               LookUpConformanceInSubstitutionMap(subMap),
               options);
}

ProtocolConformance *
ProtocolConformance::subst(TypeSubstitutionFn subs,
                           LookupConformanceFn conformances,
                           SubstOptions options) const {
  switch (getKind()) {
  case ProtocolConformanceKind::Normal: {
    auto origType = getType();
    if (!origType->hasTypeParameter() &&
        !origType->hasArchetype())
      return const_cast<ProtocolConformance *>(this);

    auto substType = origType.subst(subs, conformances, options);
    if (substType->isEqual(origType))
      return const_cast<ProtocolConformance *>(this);

    auto subMap = SubstitutionMap::get(getGenericSignature(),
                                       subs, conformances);
    return substType->getASTContext()
        .getSpecializedConformance(substType,
                                   const_cast<ProtocolConformance *>(this),
                                   subMap);
  }
  case ProtocolConformanceKind::Self:
    return const_cast<ProtocolConformance*>(this);
  case ProtocolConformanceKind::Inherited: {
    // Substitute the base.
    auto inheritedConformance
      = cast<InheritedProtocolConformance>(this)->getInheritedConformance();

    auto origType = getType();
    if (!origType->hasTypeParameter() &&
        !origType->hasArchetype()) {
      return const_cast<ProtocolConformance *>(this);
    }

    auto origBaseType = inheritedConformance->getType();
    if (origBaseType->hasTypeParameter() ||
        origBaseType->hasArchetype()) {
      // Substitute into the superclass.
      inheritedConformance = inheritedConformance->subst(subs, conformances,
                                                         options);
    }

    auto substType = origType.subst(subs, conformances, options);
    return substType->getASTContext()
      .getInheritedConformance(substType, inheritedConformance);
  }
  case ProtocolConformanceKind::Specialized: {
    // Substitute the substitutions in the specialized conformance.
    auto spec = cast<SpecializedProtocolConformance>(this);
    auto genericConformance = spec->getGenericConformance();
    auto subMap = spec->getSubstitutionMap();

    auto origType = getType();
    auto substType = origType.subst(subs, conformances, options);
    return substType->getASTContext()
      .getSpecializedConformance(substType, genericConformance,
                                 subMap.subst(subs, conformances, options));
  }
  }
  llvm_unreachable("bad ProtocolConformanceKind");
}

ProtocolConformance *
ProtocolConformance::getInheritedConformance(ProtocolDecl *protocol) const {
  auto result =
    getAssociatedConformance(getProtocol()->getSelfInterfaceType(), protocol);
  return result.isConcrete() ? result.getConcrete() : nullptr;
}

#pragma mark Protocol conformance lookup
void NominalTypeDecl::prepareConformanceTable() const {
  if (ConformanceTable)
    return;

  auto mutableThis = const_cast<NominalTypeDecl *>(this);
  ASTContext &ctx = getASTContext();
  ConformanceTable = new (ctx) ConformanceLookupTable(ctx);
  ++NumConformanceLookupTables;

  // If this type declaration was not parsed from source code or introduced
  // via the Clang importer, don't add any synthesized conformances.
  auto *file = cast<FileUnit>(getModuleScopeContext());
  if (file->getKind() != FileUnitKind::Source &&
      file->getKind() != FileUnitKind::ClangModule &&
      file->getKind() != FileUnitKind::DWARFModule) {
    return;
  }

  SmallPtrSet<ProtocolDecl *, 2> protocols;

  auto addSynthesized = [&](KnownProtocolKind kind) {
    if (auto *proto = getASTContext().getProtocol(kind)) {
      if (protocols.count(proto) == 0) {
        ConformanceTable->addSynthesizedConformance(mutableThis, proto);
        protocols.insert(proto);
      }
    }
  };

  // Add protocols for any synthesized protocol attributes.
  for (auto attr : getAttrs().getAttributes<SynthesizedProtocolAttr>()) {
    addSynthesized(attr->getProtocolKind());
  }

  // Add any implicit conformances.
  if (auto theEnum = dyn_cast<EnumDecl>(mutableThis)) {
    if (theEnum->hasCases() && theEnum->hasOnlyCasesWithoutAssociatedValues()) {
      // Simple enumerations conform to Equatable.
      addSynthesized(KnownProtocolKind::Equatable);

      // Simple enumerations conform to Hashable.
      addSynthesized(KnownProtocolKind::Hashable);
    }

    // Enumerations with a raw type conform to RawRepresentable.
    if (theEnum->hasRawType() && !theEnum->getRawType()->hasError()) {
      addSynthesized(KnownProtocolKind::RawRepresentable);
    }
  }
}

bool NominalTypeDecl::lookupConformance(
       ModuleDecl *module, ProtocolDecl *protocol,
       SmallVectorImpl<ProtocolConformance *> &conformances) const {
  prepareConformanceTable();
  return ConformanceTable->lookupConformance(
           module,
           const_cast<NominalTypeDecl *>(this),
           protocol,
           conformances);
}

SmallVector<ProtocolDecl *, 2> NominalTypeDecl::getAllProtocols() const {
  prepareConformanceTable();
  SmallVector<ProtocolDecl *, 2> result;
  ConformanceTable->getAllProtocols(const_cast<NominalTypeDecl *>(this),
                                    result);
  return result;
}

SmallVector<ProtocolConformance *, 2> NominalTypeDecl::getAllConformances(
                                        bool sorted) const
{
  prepareConformanceTable();
  SmallVector<ProtocolConformance *, 2> result;
  ConformanceTable->getAllConformances(const_cast<NominalTypeDecl *>(this),
                                       sorted,
                                       result);
  return result;
}

void NominalTypeDecl::getImplicitProtocols(
       SmallVectorImpl<ProtocolDecl *> &protocols) {
  prepareConformanceTable();
  ConformanceTable->getImplicitProtocols(this, protocols);
}

void NominalTypeDecl::registerProtocolConformance(
       ProtocolConformance *conformance) {
  prepareConformanceTable();
  ConformanceTable->registerProtocolConformance(conformance);
}

ArrayRef<ValueDecl *>
NominalTypeDecl::getSatisfiedProtocolRequirementsForMember(
                                             const ValueDecl *member,
                                             bool sorted) const {
  assert(member->getDeclContext()->getSelfNominalTypeDecl() == this);
  assert(!isa<ProtocolDecl>(this));
  prepareConformanceTable();
  return ConformanceTable->getSatisfiedProtocolRequirementsForMember(member,
                                           const_cast<NominalTypeDecl *>(this),
                                           sorted);
}

SmallVector<ProtocolDecl *, 2>
DeclContext::getLocalProtocols(
  ConformanceLookupKind lookupKind,
  SmallVectorImpl<ConformanceDiagnostic> *diagnostics) const
{
  SmallVector<ProtocolDecl *, 2> result;

  // Dig out the nominal type.
  NominalTypeDecl *nominal = getSelfNominalTypeDecl();
  if (!nominal)
    return result;

  // Update to record all potential conformances.
  nominal->prepareConformanceTable();
  nominal->ConformanceTable->lookupConformances(
    nominal,
    const_cast<DeclContext *>(this),
    lookupKind,
    &result,
    nullptr,
    diagnostics);

  return result;
}

SmallVector<ProtocolConformance *, 2>
DeclContext::getLocalConformances(
  ConformanceLookupKind lookupKind,
  SmallVectorImpl<ConformanceDiagnostic> *diagnostics) const
{
  SmallVector<ProtocolConformance *, 2> result;

  // Dig out the nominal type.
  NominalTypeDecl *nominal = getSelfNominalTypeDecl();
  if (!nominal)
    return result;

  // Protocols only have self-conformances.
  if (auto protocol = dyn_cast<ProtocolDecl>(nominal)) {
    if (protocol->requiresSelfConformanceWitnessTable())
      return { protocol->getASTContext().getSelfConformance(protocol) };
    return { };
  }

  // Update to record all potential conformances.
  nominal->prepareConformanceTable();
  nominal->ConformanceTable->lookupConformances(
    nominal,
    const_cast<DeclContext *>(this),
    lookupKind,
    nullptr,
    &result,
    diagnostics);

  return result;
}

/// Check of all types used by the conformance are canonical.
bool ProtocolConformance::isCanonical() const {
  // Normal conformances are always canonical by construction.
  if (getKind() == ProtocolConformanceKind::Normal)
    return true;

  if (!getType()->isCanonical())
    return false;

  switch (getKind()) {
  case ProtocolConformanceKind::Self:
  case ProtocolConformanceKind::Normal: {
    return true;
  }
  case ProtocolConformanceKind::Inherited: {
    // Substitute the base.
    auto inheritedConformance
      = cast<InheritedProtocolConformance>(this);
    return inheritedConformance->getInheritedConformance()->isCanonical();
  }
  case ProtocolConformanceKind::Specialized: {
    // Substitute the substitutions in the specialized conformance.
    auto spec = cast<SpecializedProtocolConformance>(this);
    auto genericConformance = spec->getGenericConformance();
    if (!genericConformance->isCanonical())
      return false;
    if (!spec->getSubstitutionMap().isCanonical()) return false;
    return true;
  }
  }
  llvm_unreachable("bad ProtocolConformanceKind");
}

/// Check of all types used by the conformance are canonical.
ProtocolConformance *ProtocolConformance::getCanonicalConformance() {
  if (isCanonical())
    return this;

  switch (getKind()) {
  case ProtocolConformanceKind::Self:
  case ProtocolConformanceKind::Normal: {
    // Root conformances are always canonical by construction.
    return this;
  }

  case ProtocolConformanceKind::Inherited: {
    auto &Ctx = getType()->getASTContext();
    auto inheritedConformance = cast<InheritedProtocolConformance>(this);
    return Ctx.getInheritedConformance(
        getType()->getCanonicalType(),
        inheritedConformance->getInheritedConformance()
            ->getCanonicalConformance());
  }

  case ProtocolConformanceKind::Specialized: {
    auto &Ctx = getType()->getASTContext();
    // Substitute the substitutions in the specialized conformance.
    auto spec = cast<SpecializedProtocolConformance>(this);
    auto genericConformance = spec->getGenericConformance();
    return Ctx.getSpecializedConformance(
                                getType()->getCanonicalType(),
                                genericConformance->getCanonicalConformance(),
                                spec->getSubstitutionMap().getCanonical());
  }
  }
  llvm_unreachable("bad ProtocolConformanceKind");
}

/// Check of all types used by the conformance are canonical.
bool ProtocolConformanceRef::isCanonical() const {
  if (isAbstract() || isInvalid())
    return true;
  return getConcrete()->isCanonical();
}

ProtocolConformanceRef
ProtocolConformanceRef::getCanonicalConformanceRef() const {
  if (isAbstract() || isInvalid())
    return *this;
  return ProtocolConformanceRef(getConcrete()->getCanonicalConformance());
}

// See swift/Basic/Statistic.h for declaration: this enables tracing
// ProtocolConformances, is defined here to avoid too much layering violation /
// circular linkage dependency.

struct ProtocolConformanceTraceFormatter
    : public UnifiedStatsReporter::TraceFormatter {
  void traceName(const void *Entity, raw_ostream &OS) const {
    if (!Entity)
      return;
    const ProtocolConformance *C =
        static_cast<const ProtocolConformance *>(Entity);
    C->printName(OS);
  }
  void traceLoc(const void *Entity, SourceManager *SM,
                clang::SourceManager *CSM, raw_ostream &OS) const {
    if (!Entity)
      return;
    const ProtocolConformance *C =
        static_cast<const ProtocolConformance *>(Entity);
    if (auto const *NPC = dyn_cast<NormalProtocolConformance>(C)) {
      NPC->getLoc().print(OS, *SM);
    } else if (auto const *DC = C->getDeclContext()) {
      if (auto const *D = DC->getAsDecl())
        D->getLoc().print(OS, *SM);
    }
  }
};

static ProtocolConformanceTraceFormatter TF;

template<>
const UnifiedStatsReporter::TraceFormatter*
FrontendStatsTracer::getTraceFormatter<const ProtocolConformance *>() {
  return &TF;
}