TBDGen.cpp

//===--- TBDGen.cpp - Swift TBD Generation --------------------------------===//
//
// 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 entrypoints into TBD file generation.
//
//===----------------------------------------------------------------------===//

#include "swift/TBDGen/TBDGen.h"

#include "swift/AST/Availability.h"
#include "swift/AST/ASTMangler.h"
#include "swift/AST/ASTVisitor.h"
#include "swift/AST/DiagnosticsFrontend.h"
#include "swift/AST/Module.h"
#include "swift/AST/ParameterList.h"
#include "swift/AST/PropertyWrappers.h"
#include "swift/Basic/LLVM.h"
#include "swift/ClangImporter/ClangImporter.h"
#include "swift/IRGen/IRGenPublic.h"
#include "swift/IRGen/Linking.h"
#include "swift/SIL/FormalLinkage.h"
#include "swift/SIL/SILDeclRef.h"
#include "swift/SIL/SILModule.h"
#include "swift/SIL/SILVTableVisitor.h"
#include "swift/SIL/SILWitnessTable.h"
#include "swift/SIL/SILWitnessVisitor.h"
#include "swift/SIL/TypeLowering.h"
#include "clang/Basic/TargetInfo.h"
#include "llvm/ADT/StringSet.h"
#include "llvm/IR/Mangler.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/Process.h"
#include "llvm/Support/YAMLTraits.h"
#include "llvm/TextAPI/MachO/InterfaceFile.h"
#include "llvm/TextAPI/MachO/TextAPIReader.h"
#include "llvm/TextAPI/MachO/TextAPIWriter.h"

#include "TBDGenVisitor.h"

using namespace swift;
using namespace swift::irgen;
using namespace swift::tbdgen;
using StringSet = llvm::StringSet<>;
using SymbolKind = llvm::MachO::SymbolKind;

static bool isGlobalOrStaticVar(VarDecl *VD) {
  return VD->isStatic() || VD->getDeclContext()->isModuleScopeContext();
}

void TBDGenVisitor::addSymbol(StringRef name, SymbolKind kind) {
  // The linker expects to see mangled symbol names in TBD files, so make sure
  // to mangle before inserting the symbol.
  SmallString<32> mangled;
  llvm::Mangler::getNameWithPrefix(mangled, name, DataLayout);

  Symbols.addSymbol(kind, mangled, Targets);

  if (StringSymbols && kind == SymbolKind::GlobalSymbol) {
    auto isNewValue = StringSymbols->insert(mangled).second;
    (void)isNewValue;
    assert(isNewValue && "symbol appears twice");
  }
}

void TBDGenVisitor::addSymbol(SILDeclRef declRef) {
  auto linkage = effectiveLinkageForClassMember(
    declRef.getLinkage(ForDefinition),
    declRef.getSubclassScope());
  if (linkage == SILLinkage::Public)
    addSymbol(declRef.mangle());
}

void TBDGenVisitor::addSymbol(LinkEntity entity) {
  auto linkage =
      LinkInfo::get(UniversalLinkInfo, SwiftModule, entity, ForDefinition);

  auto externallyVisible =
      llvm::GlobalValue::isExternalLinkage(linkage.getLinkage()) &&
      linkage.getVisibility() != llvm::GlobalValue::HiddenVisibility;

  if (externallyVisible)
    addSymbol(linkage.getName());
}

void TBDGenVisitor::addDispatchThunk(SILDeclRef declRef) {
  auto entity = LinkEntity::forDispatchThunk(declRef);
  addSymbol(entity);
}

void TBDGenVisitor::addMethodDescriptor(SILDeclRef declRef) {
  auto entity = LinkEntity::forMethodDescriptor(declRef);
  addSymbol(entity);
}

void TBDGenVisitor::addProtocolRequirementsBaseDescriptor(ProtocolDecl *proto) {
  auto entity = LinkEntity::forProtocolRequirementsBaseDescriptor(proto);
  addSymbol(entity);
}

void TBDGenVisitor::addAssociatedTypeDescriptor(AssociatedTypeDecl *assocType) {
  auto entity = LinkEntity::forAssociatedTypeDescriptor(assocType);
  addSymbol(entity);
}

void TBDGenVisitor::addAssociatedConformanceDescriptor(
                                           AssociatedConformance conformance) {
  auto entity = LinkEntity::forAssociatedConformanceDescriptor(conformance);
  addSymbol(entity);
}

void TBDGenVisitor::addBaseConformanceDescriptor(
                                           BaseConformance conformance) {
  auto entity = LinkEntity::forBaseConformanceDescriptor(conformance);
  addSymbol(entity);
}

void TBDGenVisitor::addConformances(DeclContext *DC) {
  for (auto conformance : DC->getLocalConformances(
                            ConformanceLookupKind::NonInherited)) {
    auto protocol = conformance->getProtocol();
    auto needsWTable =
        Lowering::TypeConverter::protocolRequiresWitnessTable(protocol);
    if (!needsWTable)
      continue;

    // Only root conformances get symbols; the others get any public symbols
    // from their parent conformances.
    auto rootConformance = dyn_cast<RootProtocolConformance>(conformance);
    if (!rootConformance) {
      continue;
    }

    addSymbol(LinkEntity::forProtocolWitnessTable(rootConformance));
    addSymbol(LinkEntity::forProtocolConformanceDescriptor(rootConformance));

    // FIXME: the logic around visibility in extensions is confusing, and
    // sometimes witness thunks need to be manually made public.

    auto conformanceIsFixed = SILWitnessTable::conformanceIsSerialized(
        rootConformance);
    auto addSymbolIfNecessary = [&](ValueDecl *requirementDecl,
                                    ValueDecl *witnessDecl) {
      auto witnessLinkage = SILDeclRef(witnessDecl).getLinkage(ForDefinition);
      if (conformanceIsFixed &&
          (isa<SelfProtocolConformance>(rootConformance) ||
           fixmeWitnessHasLinkageThatNeedsToBePublic(witnessLinkage))) {
        Mangle::ASTMangler Mangler;
        addSymbol(
            Mangler.mangleWitnessThunk(rootConformance, requirementDecl));
      }
    };

    rootConformance->forEachValueWitness(
        [&](ValueDecl *valueReq, Witness witness) {
          auto witnessDecl = witness.getDecl();
          if (isa<AbstractFunctionDecl>(valueReq)) {
            addSymbolIfNecessary(valueReq, witnessDecl);
          } else if (auto *storage = dyn_cast<AbstractStorageDecl>(valueReq)) {
            auto witnessStorage = cast<AbstractStorageDecl>(witnessDecl);
            storage->visitOpaqueAccessors([&](AccessorDecl *reqtAccessor) {
              auto witnessAccessor =
                witnessStorage->getSynthesizedAccessor(
                  reqtAccessor->getAccessorKind());
              addSymbolIfNecessary(reqtAccessor, witnessAccessor);
            });
          }
        });
  }
}

// SWIFT_ENABLE_TENSORFLOW
void TBDGenVisitor::addAutoDiffLinearMapFunction(AbstractFunctionDecl *original,
                                                 IndexSubset *parameterIndices,
                                                 AutoDiffLinearMapKind kind) {
  auto declRef = SILDeclRef(original);

  // Linear maps are public only when the original function is serialized.
  if (!declRef.isSerialized())
    return;

  // Linear maps are emitted only when forward mode is enabled.
  if (kind == AutoDiffLinearMapKind::Differential &&
      !original->getASTContext()
           .LangOpts.EnableExperimentalForwardModeDifferentiation)
    return;

  auto *loweredParamIndices = autodiff::getLoweredParameterIndices(
      parameterIndices,
      original->getInterfaceType()->castTo<AnyFunctionType>());
  Mangle::ASTMangler mangler;
  std::string linearMapName = mangler.mangleAutoDiffLinearMapHelper(
      declRef.mangle(), kind, SILAutoDiffIndices(0, loweredParamIndices));
  addSymbol(linearMapName);
}

void TBDGenVisitor::addAutoDiffDerivativeFunction(
    AbstractFunctionDecl *original, IndexSubset *parameterIndices,
    AutoDiffDerivativeFunctionKind kind) {
  auto *assocFnId = AutoDiffDerivativeFunctionIdentifier::get(
      kind, parameterIndices, original->getASTContext());
  addSymbol(SILDeclRef(original).asAutoDiffDerivativeFunction(assocFnId));
}

void TBDGenVisitor::addDifferentiabilityWitness(
    AbstractFunctionDecl *original, IndexSubset *parameterIndices,
    IndexSubset *resultIndices, GenericSignature derivativeGenericSignature) {
  if (SILDeclRef(original).getLinkage(ForDefinition) != SILLinkage::Public)
    return;

  auto *loweredParamIndices = autodiff::getLoweredParameterIndices(
      parameterIndices,
      original->getInterfaceType()->castTo<AnyFunctionType>());

  std::string originalMangledName = SILDeclRef(original).mangle();
  AutoDiffConfig config{loweredParamIndices, resultIndices,
                        derivativeGenericSignature};
  SILDifferentiabilityWitnessKey key(originalMangledName, config);

  Mangle::ASTMangler mangle;
  std::string mangledName = mangle.mangleSILDifferentiabilityWitnessKey(key);
  addSymbol(mangledName);
}

void TBDGenVisitor::addDerivativeConfiguration(AbstractFunctionDecl *original,
                                               AutoDiffConfig config) {
  addAutoDiffLinearMapFunction(original, config.parameterIndices,
                               AutoDiffLinearMapKind::Differential);
  addAutoDiffLinearMapFunction(original, config.parameterIndices,
                               AutoDiffLinearMapKind::Pullback);
  addAutoDiffDerivativeFunction(original, config.parameterIndices,
                                AutoDiffDerivativeFunctionKind::JVP);
  addAutoDiffDerivativeFunction(original, config.parameterIndices,
                                AutoDiffDerivativeFunctionKind::VJP);
  addDifferentiabilityWitness(original, config.parameterIndices,
                              config.resultIndices,
                              config.derivativeGenericSignature);
}

/// Determine whether dynamic replacement should be emitted for the allocator or
/// the initializer given a decl.
/// The rule is that structs and convenience init of classes emit a
/// dynamic replacement for the allocator.
/// Designated init of classes emit a dynamic replacement for the intializer.
/// This is because the super class init call is emitted to the initializer and
/// needs to be dynamic.
static bool shouldUseAllocatorMangling(const AbstractFunctionDecl *afd) {
  auto constructor = dyn_cast<ConstructorDecl>(afd);
  if (!constructor)
    return false;
  return constructor->getParent()->getSelfClassDecl() == nullptr ||
         constructor->isConvenienceInit();
}

void TBDGenVisitor::visitDefaultArguments(ValueDecl *VD, ParameterList *PL) {
  auto publicDefaultArgGenerators = SwiftModule->isTestingEnabled() ||
                                    SwiftModule->arePrivateImportsEnabled();
  if (!publicDefaultArgGenerators)
    return;

  // In Swift 3 (or under -enable-testing), default arguments (of public
  // functions) are public symbols, as the default values are computed at the
  // call site.
  auto index = 0;
  for (auto *param : *PL) {
    if (param->isDefaultArgument())
      addSymbol(SILDeclRef::getDefaultArgGenerator(VD, index));
    index++;
  }
}

void TBDGenVisitor::visitAbstractFunctionDecl(AbstractFunctionDecl *AFD) {
  // A @_silgen_name("...") function without a body only exists
  // to forward-declare a symbol from another library.
  if (!AFD->hasBody() && AFD->getAttrs().hasAttribute<SILGenNameAttr>()) {
    return;
  }

  addSymbol(SILDeclRef(AFD));

  // Add the global function pointer for a dynamically replaceable function.
  if (AFD->isNativeDynamic()) {
    bool useAllocator = shouldUseAllocatorMangling(AFD);
    addSymbol(LinkEntity::forDynamicallyReplaceableFunctionVariable(
        AFD, useAllocator));
    addSymbol(
        LinkEntity::forDynamicallyReplaceableFunctionKey(AFD, useAllocator));
  }
  if (AFD->getAttrs().hasAttribute<DynamicReplacementAttr>()) {
    bool useAllocator = shouldUseAllocatorMangling(AFD);
    addSymbol(LinkEntity::forDynamicallyReplaceableFunctionVariable(
        AFD, useAllocator));
    addSymbol(
        LinkEntity::forDynamicallyReplaceableFunctionImpl(AFD, useAllocator));
  }

  if (AFD->getAttrs().hasAttribute<CDeclAttr>()) {
    // A @_cdecl("...") function has an extra symbol, with the name from the
    // attribute.
    addSymbol(SILDeclRef(AFD).asForeign());
  }

  // SWIFT_ENABLE_TENSORFLOW
  for (auto derivativeConfig : AFD->getDerivativeFunctionConfigurations()) {
    addDerivativeConfiguration(AFD, derivativeConfig);
  }

  visitDefaultArguments(AFD, AFD->getParameters());
}

void TBDGenVisitor::visitFuncDecl(FuncDecl *FD) {
  // If there's an opaque return type, its descriptor is exported.
  if (auto opaqueResult = FD->getOpaqueResultTypeDecl()) {
    addSymbol(LinkEntity::forOpaqueTypeDescriptor(opaqueResult));
    assert(opaqueResult->getNamingDecl() == FD);
    if (FD->isNativeDynamic()) {
      addSymbol(LinkEntity::forOpaqueTypeDescriptorAccessor(opaqueResult));
      addSymbol(LinkEntity::forOpaqueTypeDescriptorAccessorImpl(opaqueResult));
      addSymbol(LinkEntity::forOpaqueTypeDescriptorAccessorKey(opaqueResult));
      addSymbol(LinkEntity::forOpaqueTypeDescriptorAccessorVar(opaqueResult));
    }
    if (FD->getAttrs().hasAttribute<DynamicReplacementAttr>()) {
      addSymbol(LinkEntity::forOpaqueTypeDescriptorAccessor(opaqueResult));
      addSymbol(LinkEntity::forOpaqueTypeDescriptorAccessorVar(opaqueResult));
    }
  }
  visitAbstractFunctionDecl(FD);
}

void TBDGenVisitor::visitAccessorDecl(AccessorDecl *AD) {
  llvm_unreachable("should not see an accessor here");
}

void TBDGenVisitor::visitAbstractStorageDecl(AbstractStorageDecl *ASD) {
  // Add the property descriptor if the decl needs it.
  if (ASD->exportsPropertyDescriptor()) {
    addSymbol(LinkEntity::forPropertyDescriptor(ASD));
  }
  
  // ...and the opaque result decl if it has one.
  if (auto opaqueResult = ASD->getOpaqueResultTypeDecl()) {
    addSymbol(LinkEntity::forOpaqueTypeDescriptor(opaqueResult));
    assert(opaqueResult->getNamingDecl() == ASD);
    if (ASD->hasAnyNativeDynamicAccessors()) {
      addSymbol(LinkEntity::forOpaqueTypeDescriptorAccessor(opaqueResult));
      addSymbol(LinkEntity::forOpaqueTypeDescriptorAccessorImpl(opaqueResult));
      addSymbol(LinkEntity::forOpaqueTypeDescriptorAccessorKey(opaqueResult));
      addSymbol(LinkEntity::forOpaqueTypeDescriptorAccessorVar(opaqueResult));
    }
    if (ASD->hasAnyDynamicReplacementAccessors()) {
      addSymbol(LinkEntity::forOpaqueTypeDescriptorAccessor(opaqueResult));
      addSymbol(LinkEntity::forOpaqueTypeDescriptorAccessorVar(opaqueResult));
    }
  }

  // Explicitly look at each accessor here: see visitAccessorDecl.
  ASD->visitEmittedAccessors([&](AccessorDecl *accessor) {
    visitFuncDecl(accessor);
  });
}

void TBDGenVisitor::visitVarDecl(VarDecl *VD) {
  // Variables inside non-resilient modules have some additional symbols.
  if (!VD->isResilient()) {
    // Non-global variables might have an explicit initializer symbol, in
    // non-resilient modules.
    if (VD->getAttrs().hasAttribute<HasInitialValueAttr>() &&
        !isGlobalOrStaticVar(VD)) {
      auto declRef = SILDeclRef(VD, SILDeclRef::Kind::StoredPropertyInitializer);
      // Stored property initializers for public properties are currently
      // public.
      addSymbol(declRef);
    }

    // statically/globally stored variables have some special handling.
    if (VD->hasStorage() &&
        isGlobalOrStaticVar(VD)) {
      if (getDeclLinkage(VD) == FormalLinkage::PublicUnique) {
        // The actual variable has a symbol.
        Mangle::ASTMangler mangler;
        addSymbol(mangler.mangleEntity(VD, false));
      }

      if (VD->isLazilyInitializedGlobal())
        addSymbol(SILDeclRef(VD, SILDeclRef::Kind::GlobalAccessor));
    }

    // Wrapped non-static member properties may have a backing initializer.
    if (auto wrapperInfo = VD->getPropertyWrapperBackingPropertyInfo()) {
      if (wrapperInfo.initializeFromOriginal && !VD->isStatic()) {
        addSymbol(
            SILDeclRef(VD, SILDeclRef::Kind::PropertyWrapperBackingInitializer));
      }
    }
  }

  visitAbstractStorageDecl(VD);
}

void TBDGenVisitor::visitNominalTypeDecl(NominalTypeDecl *NTD) {
  auto declaredType = NTD->getDeclaredType()->getCanonicalType();

  addSymbol(LinkEntity::forNominalTypeDescriptor(NTD));

  // Generic types do not get metadata directly, only through the function.
  if (!NTD->isGenericContext()) {
    addSymbol(LinkEntity::forTypeMetadata(declaredType,
                                          TypeMetadataAddress::AddressPoint));
  }
  addSymbol(LinkEntity::forTypeMetadataAccessFunction(declaredType));

  // There are symbols associated with any protocols this type conforms to.
  addConformances(NTD);

  for (auto member : NTD->getMembers())
    visit(member);
}

void TBDGenVisitor::visitClassDecl(ClassDecl *CD) {
  if (getDeclLinkage(CD) != FormalLinkage::PublicUnique)
    return;

  auto &ctxt = CD->getASTContext();
  auto isGeneric = CD->isGenericContext();
  auto objCCompatible = ctxt.LangOpts.EnableObjCInterop && !isGeneric;
  auto isObjC = objCCompatible && CD->isObjC();

  // Metaclasses and ObjC class (duh) are a ObjC thing, and so are not needed in
  // build artifacts/for classes which can't touch ObjC.
  if (objCCompatible) {
    bool addObjCClass = false;
    if (isObjC) {
      addObjCClass = true;
      addSymbol(LinkEntity::forObjCClass(CD));
    }

    if (CD->getMetaclassKind() == ClassDecl::MetaclassKind::ObjC) {
      addObjCClass = true;
      addSymbol(LinkEntity::forObjCMetaclass(CD));
    } else
      addSymbol(LinkEntity::forSwiftMetaclassStub(CD));

    if (addObjCClass) {
      SmallString<128> buffer;
      addSymbol(CD->getObjCRuntimeName(buffer), SymbolKind::ObjectiveCClass);
    }
  }

  // Some members of classes get extra handling, beyond members of struct/enums,
  // so let's walk over them manually.
  for (auto *var : CD->getStoredProperties())
    addSymbol(LinkEntity::forFieldOffset(var));

  visitNominalTypeDecl(CD);

  bool resilientAncestry = CD->checkAncestry(AncestryFlags::ResilientOther);

  // Types with resilient superclasses have some extra symbols.
  if (resilientAncestry || CD->hasResilientMetadata()) {
    addSymbol(LinkEntity::forClassMetadataBaseOffset(CD));
  }

  auto &Ctx = CD->getASTContext();
  if (Ctx.LangOpts.EnableObjCInterop) {
    if (resilientAncestry) {
      addSymbol(LinkEntity::forObjCResilientClassStub(
          CD, TypeMetadataAddress::AddressPoint));
    }
  }

  // Emit dispatch thunks for every new vtable entry.
  struct VTableVisitor : public SILVTableVisitor<VTableVisitor> {
    TBDGenVisitor &TBD;
    ClassDecl *CD;
    bool FirstTime = true;

  public:
    VTableVisitor(TBDGenVisitor &TBD, ClassDecl *CD)
        : TBD(TBD), CD(CD) {}

    void addMethod(SILDeclRef method) {
      assert(method.getDecl()->getDeclContext() == CD);

      if (CD->hasResilientMetadata()) {
        if (FirstTime) {
          FirstTime = false;

          // If the class is itself resilient and has at least one vtable entry,
          // it has a method lookup function.
          TBD.addSymbol(LinkEntity::forMethodLookupFunction(CD));
        }

        TBD.addDispatchThunk(method);
      }

      TBD.addMethodDescriptor(method);
    }

    void addMethodOverride(SILDeclRef baseRef, SILDeclRef derivedRef) {}

    void addPlaceholder(MissingMemberDecl *) {}

    void doIt() {
      addVTableEntries(CD);
    }
  };

  VTableVisitor(*this, CD).doIt();
}

void TBDGenVisitor::visitConstructorDecl(ConstructorDecl *CD) {
  if (CD->getParent()->getSelfClassDecl()) {
    // Class constructors come in two forms, allocating and non-allocating. The
    // default ValueDecl handling gives the allocating one, so we have to
    // manually include the non-allocating one.
    addSymbol(SILDeclRef(CD, SILDeclRef::Kind::Initializer));
  }
  visitAbstractFunctionDecl(CD);
}

void TBDGenVisitor::visitDestructorDecl(DestructorDecl *DD) {
  // Class destructors come in two forms (deallocating and non-deallocating),
  // like constructors above. This is the deallocating one:
  visitAbstractFunctionDecl(DD);

  auto parentClass = DD->getParent()->getSelfClassDecl();

  // But the non-deallocating one doesn't apply to some @objc classes.
  if (!Lowering::usesObjCAllocator(parentClass)) {
    addSymbol(SILDeclRef(DD, SILDeclRef::Kind::Destroyer));
  }
}

void TBDGenVisitor::visitExtensionDecl(ExtensionDecl *ED) {
  if (!isa<ProtocolDecl>(ED->getExtendedNominal())) {
    addConformances(ED);
  }

  for (auto member : ED->getMembers())
    visit(member);
}

#ifndef NDEBUG
static bool isValidProtocolMemberForTBDGen(const Decl *D) {
  switch (D->getKind()) {
  case DeclKind::TypeAlias:
  case DeclKind::AssociatedType:
  case DeclKind::Var:
  case DeclKind::Subscript:
  case DeclKind::PatternBinding:
  case DeclKind::Func:
  case DeclKind::Accessor:
  case DeclKind::Constructor:
  case DeclKind::Destructor:
  case DeclKind::IfConfig:
  case DeclKind::PoundDiagnostic:
    return true;
  case DeclKind::OpaqueType:
  case DeclKind::Enum:
  case DeclKind::Struct:
  case DeclKind::Class:
  case DeclKind::Protocol:
  case DeclKind::GenericTypeParam:
  case DeclKind::Module:
  case DeclKind::Param:
  case DeclKind::EnumElement:
  case DeclKind::Extension:
  case DeclKind::TopLevelCode:
  case DeclKind::Import:
  case DeclKind::PrecedenceGroup:
  case DeclKind::MissingMember:
  case DeclKind::EnumCase:
  case DeclKind::InfixOperator:
  case DeclKind::PrefixOperator:
  case DeclKind::PostfixOperator:
    return false;
  }
  llvm_unreachable("covered switch");
}
#endif

void TBDGenVisitor::visitProtocolDecl(ProtocolDecl *PD) {
  if (!PD->isObjC()) {
    addSymbol(LinkEntity::forProtocolDescriptor(PD));

    struct WitnessVisitor : public SILWitnessVisitor<WitnessVisitor> {
      TBDGenVisitor &TBD;
      ProtocolDecl *PD;

    public:
      WitnessVisitor(TBDGenVisitor &TBD, ProtocolDecl *PD)
          : TBD(TBD), PD(PD) {}

      void addMethod(SILDeclRef declRef) {
        if (PD->isResilient()) {
          TBD.addDispatchThunk(declRef);
          TBD.addMethodDescriptor(declRef);
        }
      }

      void addAssociatedType(AssociatedType associatedType) {
        TBD.addAssociatedTypeDescriptor(associatedType.getAssociation());
      }

      void addProtocolConformanceDescriptor() {
        TBD.addProtocolRequirementsBaseDescriptor(PD);
      }

      void addOutOfLineBaseProtocol(ProtocolDecl *proto) {
        TBD.addBaseConformanceDescriptor(BaseConformance(PD, proto));
      }

      void addAssociatedConformance(AssociatedConformance associatedConf) {
        TBD.addAssociatedConformanceDescriptor(associatedConf);
      }

      void addPlaceholder(MissingMemberDecl *decl) {}

      void doIt() {
        visitProtocolDecl(PD);
      }
    };

    WitnessVisitor(*this, PD).doIt();

    // Include the self-conformance.
    addConformances(PD);
  }

#ifndef NDEBUG
  // There's no (currently) relevant information about members of a protocol at
  // individual protocols, each conforming type has to handle them individually
  // (NB. anything within an active IfConfigDecls also appears outside). Let's
  // assert this fact:
  for (auto *member : PD->getMembers()) {
    assert(isValidProtocolMemberForTBDGen(member) &&
           "unexpected member of protocol during TBD generation");
  }
#endif
}

void TBDGenVisitor::visitEnumDecl(EnumDecl *ED) {
  visitNominalTypeDecl(ED);

  if (!ED->isResilient())
    return;
}

void TBDGenVisitor::visitEnumElementDecl(EnumElementDecl *EED) {
  addSymbol(LinkEntity::forEnumCase(EED));
  if (auto *PL = EED->getParameterList())
    visitDefaultArguments(EED, PL);
}

void TBDGenVisitor::addFirstFileSymbols() {
  if (!Opts.ModuleLinkName.empty()) {
    SmallString<32> buf;
    addSymbol(irgen::encodeForceLoadSymbolName(buf, Opts.ModuleLinkName));
  }
}

/// The kind of version being parsed, used for diagnostics.
/// Note: Must match the order in DiagnosticsFrontend.def
enum DylibVersionKind_t: unsigned {
  CurrentVersion,
  CompatibilityVersion
};

/// Converts a version string into a packed version, truncating each component
/// if necessary to fit all 3 into a 32-bit packed structure.
///
/// For example, the version '1219.37.11' will be packed as
///
///  Major (1,219)       Minor (37) Patch (11)
/// ┌───────────────────┬──────────┬──────────┐
/// │ 00001100 11000011 │ 00100101 │ 00001011 │
/// └───────────────────┴──────────┴──────────┘
///
/// If an individual component is greater than the highest number that can be
/// represented in its alloted space, it will be truncated to the maximum value
/// that fits in the alloted space, which matches the behavior of the linker.
static Optional<llvm::MachO::PackedVersion>
parsePackedVersion(DylibVersionKind_t kind, StringRef versionString,
                   ASTContext &ctx) {
  if (versionString.empty())
    return None;

  llvm::MachO::PackedVersion version;
  auto result = version.parse64(versionString);
  if (!result.first) {
    ctx.Diags.diagnose(SourceLoc(), diag::tbd_err_invalid_version,
                       (unsigned)kind, versionString);
    return None;
  }
  if (result.second) {
    ctx.Diags.diagnose(SourceLoc(), diag::tbd_warn_truncating_version,
                       (unsigned)kind, versionString);
  }
  return version;
}

static bool isApplicationExtensionSafe(const LangOptions &LangOpts) {
  // Existing linkers respect these flags to determine app extension safety.
  return LangOpts.EnableAppExtensionRestrictions ||
         llvm::sys::Process::GetEnv("LD_NO_ENCRYPT") ||
         llvm::sys::Process::GetEnv("LD_APPLICATION_EXTENSION_SAFE");
}

static void enumeratePublicSymbolsAndWrite(ModuleDecl *M, FileUnit *singleFile,
                                           StringSet *symbols,
                                           llvm::raw_ostream *os,
                                           const TBDGenOptions &opts) {
  auto &ctx = M->getASTContext();
  auto isWholeModule = singleFile == nullptr;
  const auto &triple = ctx.LangOpts.Target;
  UniversalLinkageInfo linkInfo(triple, opts.HasMultipleIGMs, false,
                                isWholeModule);

  llvm::MachO::InterfaceFile file;
  file.setFileType(llvm::MachO::FileType::TBD_V3);
  file.setApplicationExtensionSafe(
    isApplicationExtensionSafe(M->getASTContext().LangOpts));
  file.setInstallName(opts.InstallName);
  file.setTwoLevelNamespace();
  file.setSwiftABIVersion(irgen::getSwiftABIVersion());
  file.setInstallAPI(opts.IsInstallAPI);

  if (auto packed = parsePackedVersion(CurrentVersion,
                                       opts.CurrentVersion, ctx)) {
    file.setCurrentVersion(*packed);
  }

  if (auto packed = parsePackedVersion(CompatibilityVersion,
                                       opts.CompatibilityVersion, ctx)) {
    file.setCompatibilityVersion(*packed);
  }

  llvm::MachO::Target target(triple);
  file.addTarget(target);

  auto *clang = static_cast<ClangImporter *>(ctx.getClangModuleLoader());
  TBDGenVisitor visitor(file, {target}, symbols,
                        clang->getTargetInfo().getDataLayout(),
                        linkInfo, M, opts);

  auto visitFile = [&](FileUnit *file) {
    if (file == M->getFiles()[0]) {
      visitor.addFirstFileSymbols();
    }

    SmallVector<Decl *, 16> decls;
    file->getTopLevelDecls(decls);

    visitor.addMainIfNecessary(file);

    for (auto d : decls)
      visitor.visit(d);
  };

  if (singleFile) {
    assert(M == singleFile->getParentModule() && "mismatched file and module");
    visitFile(singleFile);
  } else {
    for (auto *file : M->getFiles()) {
      visitFile(file);
    }
  }

  if (os) {
    llvm::cantFail(llvm::MachO::TextAPIWriter::writeToStream(*os, file),
                   "YAML writing should be error-free");
  }
}

void swift::enumeratePublicSymbols(FileUnit *file, StringSet &symbols,
                                   const TBDGenOptions &opts) {
  enumeratePublicSymbolsAndWrite(file->getParentModule(), file, &symbols,
                                 nullptr, opts);
}
void swift::enumeratePublicSymbols(ModuleDecl *M, StringSet &symbols,
                                   const TBDGenOptions &opts) {
  enumeratePublicSymbolsAndWrite(M, nullptr, &symbols, nullptr, opts);
}
void swift::writeTBDFile(ModuleDecl *M, llvm::raw_ostream &os,
                         const TBDGenOptions &opts) {
  enumeratePublicSymbolsAndWrite(M, nullptr, nullptr, &os, opts);
}