//===--- ClangImporter.h - Import Clang Modules -----------------*- C++ -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This file implements support for loading Clang modules into Swift.
//
//===----------------------------------------------------------------------===//
#ifndef SWIFT_CLANG_IMPORTER_H
#define SWIFT_CLANG_IMPORTER_H

#include "swift/AST/Attr.h"
#include "swift/AST/AttrKind.h"
#include "swift/AST/ClangModuleLoader.h"
#include "clang/AST/Attr.h"
#include "clang/Basic/Specifiers.h"
#include "llvm/Support/VirtualFileSystem.h"

/// The maximum number of SIMD vector elements we currently try to import.
#define SWIFT_MAX_IMPORTED_SIMD_ELEMENTS 4

namespace llvm {
  class Triple;
  class FileCollectorBase;
  template<typename Fn> class function_ref;
  namespace opt {
    class InputArgList;
  }
  namespace vfs {
    class FileSystem;
    class OutputBackend;
  }
}

namespace clang {
  class ASTContext;
  class CodeGenOptions;
  class Decl;
  class DependencyCollector;
  class DiagnosticConsumer;
  class EnumConstantDecl;
  class EnumDecl;
  class MacroInfo;
  class Module;
  class ModuleMacro;
  class NamedDecl;
  class Sema;
  class TargetInfo;
  class Type;
  class VisibleDeclConsumer;
  class DeclarationName;
  class CompilerInvocation;
  class TargetOptions;
  namespace driver {
    class Driver;
  }
namespace tooling {
namespace dependencies {
  struct ModuleDeps;
  struct TranslationUnitDeps;
  enum class ModuleOutputKind;
  using ModuleDepsGraph = std::vector<ModuleDeps>;
}
}
}

namespace swift {
enum class ResultConvention : uint8_t;
class ASTContext;
class CompilerInvocation;
class ClangImporterOptions;
class ClangInheritanceInfo;
class ClangModuleUnit;
class ClangNode;
class ConcreteDeclRef;
class Decl;
class DeclContext;
class EffectiveClangContext;
class EnumDecl;
class FuncDecl;
class ImportDecl;
class IRGenOptions;
class LangOptions;
class ModuleDecl;
struct ModuleDependencyID;
class NominalTypeDecl;
class SearchPathOptions;
class StructDecl;
class SwiftLookupTable;
class TypeDecl;
class ValueDecl;
class VisibleDeclConsumer;
using ModuleDependencyIDSetVector =
    llvm::SetVector<ModuleDependencyID, std::vector<ModuleDependencyID>,
                    std::set<ModuleDependencyID>>;
enum class SelectorSplitKind;

/// Kinds of optional types.
enum OptionalTypeKind : unsigned {
  /// The type is not an optional type.
  OTK_None = 0,

  /// The type is Optional<T>.
  OTK_Optional,

  /// The type is ImplicitlyUnwrappedOptional<T>.
  OTK_ImplicitlyUnwrappedOptional
};
enum { NumOptionalTypeKinds = 2 };

/// This interface is implemented by LLDB to serve as a fallback when Clang
/// modules can't be imported from source in the debugger.
///
/// During compile time, ClangImporter-imported Clang modules are compiled with
/// -gmodules, which emits a DWARF rendition of all types defined in the module
/// into the .pcm file. On Darwin, these types can be collected by
/// dsymutil. This delegate allows DWARFImporter to ask LLDB to look up a Clang
/// type by name, synthesize a Clang AST from it. DWARFImporter then hands this
/// Clang AST to ClangImporter to import the type into Swift.
class DWARFImporterDelegate {
public:
  virtual ~DWARFImporterDelegate() = default;
  /// Perform a qualified lookup of a Clang type with this name.
  /// \param kind  Only return results with this type kind.
  /// \param inModule only return results from this module.
  virtual void lookupValue(StringRef name, std::optional<ClangTypeKind> kind,
                           StringRef inModule,
                           SmallVectorImpl<clang::Decl *> &results) {}
  /// vtable anchor.
  virtual void anchor();
};

// ⚠️ DANGER ⚠️
// Putting more than four types in this `PointerUnion` will break the build for
// 32-bit hosts. If we need five or more types in the future, we'll need to
// design a proper larger-than-word-sized type.
typedef llvm::PointerUnion<const clang::Decl *, const clang::MacroInfo *,
                           const clang::Type *, const clang::Token *>
    ImportDiagnosticTarget;

/// Class that imports Clang modules into Swift, mapping directly
/// from Clang ASTs over to Swift ASTs.
class ClangImporter final : public ClangModuleLoader {
  friend class ClangModuleUnit;
  friend class SwiftDeclSynthesizer;

  // Make requests in the ClangImporter zone friends so they can access `Impl`.
#define SWIFT_REQUEST(Zone, Name, Sig, Caching, LocOptions)                    \
  friend class Name;
#include "swift/ClangImporter/ClangImporterTypeIDZone.def"
#undef SWIFT_REQUEST

public:
  class Implementation;

private:
  Implementation &Impl;

  bool requiresBuiltinHeadersInSystemModules = false;

  ClangImporter(ASTContext &ctx,
                DependencyTracker *tracker,
                DWARFImporterDelegate *dwarfImporterDelegate);

  /// Creates a clone of Clang importer's compiler instance that has been
  /// configured for operations on precompiled outputs (either emitting a
  /// precompiled header, emitting a precompiled module, or dumping a
  /// precompiled module).
  ///
  /// The caller of this method should set any action-specific invocation
  /// options (like FrontendOptions::ProgramAction, input files, and output
  /// paths), then create the appropriate FrontendAction and execute it.
  std::unique_ptr<clang::CompilerInstance>
  cloneCompilerInstanceForPrecompiling();

public:
  /// Create a new Clang importer that can import a suitable Clang
  /// module into the given ASTContext.
  ///
  /// \param ctx The ASTContext into which the module will be imported.
  /// The ASTContext's SearchPathOptions will be used for the Clang importer.
  ///
  /// \param swiftPCHHash A hash of Swift's various options in a compiler
  /// invocation, used to create a unique Bridging PCH if requested.
  ///
  /// \param tracker The object tracking files this compilation depends on.
  ///
  /// \param dwarfImporterDelegate A helper object that can synthesize
  /// Clang Decls from debug info. Used by LLDB.
  ///
  /// \returns a new Clang module importer, or null (with a diagnostic) if
  /// an error occurred.
  static std::unique_ptr<ClangImporter>
  create(ASTContext &ctx,
         std::string swiftPCHHash = "", DependencyTracker *tracker = nullptr,
         DWARFImporterDelegate *dwarfImporterDelegate = nullptr,
         bool ignoreFileMapping = false);

  std::vector<std::string>
  getClangDriverArguments(ASTContext &ctx, bool ignoreClangTarget = false);

  std::optional<std::vector<std::string>>
  getClangCC1Arguments(ASTContext &ctx,
                       llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
                       bool ignoreClangTarget = false);

  std::vector<std::string>
  getClangDepScanningInvocationArguments(ASTContext &ctx);

  static std::unique_ptr<clang::CompilerInvocation>
  createClangInvocation(ClangImporter *importer,
                        const ClangImporterOptions &importerOpts,
                        llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS,
                        const std::vector<std::string> &CC1Args);

  /// Creates a Clang Driver based on the Swift compiler options.
  ///
  /// \return a pair of the Clang Driver and the diagnostic engine, which needs
  /// to be alive during the use of the Driver.
  static std::pair<clang::driver::Driver,
                   llvm::IntrusiveRefCntPtr<clang::DiagnosticsEngine>>
  createClangDriver(
      const LangOptions &LangOpts,
      const ClangImporterOptions &ClangImporterOpts,
      llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> vfs = nullptr);

  static llvm::opt::InputArgList
  createClangArgs(const ClangImporterOptions &ClangImporterOpts,
                  const SearchPathOptions &SearchPathOpts,
                  clang::driver::Driver &clangDriver);

  ClangImporter(const ClangImporter &) = delete;
  ClangImporter(ClangImporter &&) = delete;
  ClangImporter &operator=(const ClangImporter &) = delete;
  ClangImporter &operator=(ClangImporter &&) = delete;

  ~ClangImporter();

  /// Only to be used by lldb-moduleimport-test.
  void setDWARFImporterDelegate(DWARFImporterDelegate &delegate);

  /// Create a new clang::DependencyCollector customized to
  /// ClangImporter's specific uses.
  static std::shared_ptr<clang::DependencyCollector> createDependencyCollector(
      IntermoduleDepTrackingMode Mode,
      std::shared_ptr<llvm::FileCollectorBase> FileCollector);

  static bool isKnownCFTypeName(llvm::StringRef name);

  /// Append visible module names to \p names. Note that names are possibly
  /// duplicated, and not guaranteed to be ordered in any way.
  void collectVisibleTopLevelModuleNames(
      SmallVectorImpl<Identifier> &names) const override;

  /// Check whether the module with a given name can be imported without
  /// importing it.
  ///
  /// Note that even if this check succeeds, errors may still occur if the
  /// module is loaded in full.
  ///
  /// If a non-null \p versionInfo is provided, the module version will be
  /// parsed and populated.
  virtual bool canImportModule(ImportPath::Module named, SourceLoc loc,
                               ModuleVersionInfo *versionInfo,
                               bool isTestableImport = false) override;

  /// Import a module with the given module path.
  ///
  /// Clang modules will be imported using the Objective-C ARC dialect,
  /// with all warnings disabled.
  ///
  /// \param importLoc The location of the 'import' keyword.
  ///
  /// \param path A sequence of (identifier, location) pairs that denote
  /// the dotted module name to load, e.g., AppKit.NSWindow.
  ///
  /// \param AllowMemoryCache Affects only loading serialized Swift modules,
  /// this parameter has no effect in the ClangImporter.
  ///
  /// \returns the module referenced, if it could be loaded. Otherwise,
  /// emits a diagnostic and returns NULL.
  virtual ModuleDecl *loadModule(
                        SourceLoc importLoc,
                        ImportPath::Module path,
                        bool AllowMemoryCache = true)
                      override;

  /// Determine whether \c overlayDC is within an overlay module for the
  /// imported context enclosing \c importedDC.
  ///
  /// This routine is used for various hacks that are only permitted within
  /// overlays of imported modules, e.g., Objective-C bridging conformances.
  bool isInOverlayModuleForImportedModule(
                                      const DeclContext *overlayDC,
                                      const DeclContext *importedDC) override;

  /// Look for declarations associated with the given name.
  ///
  /// \param name The name we're searching for.
  void lookupValue(DeclName name, VisibleDeclConsumer &consumer) override;

  /// Look up a type declaration by its Clang name.
  ///
  /// Note that this method does no filtering. If it finds the type in a loaded
  /// module, it returns it. This is intended for use in reflection / debugging
  /// contexts where access is not a problem.
  void lookupTypeDecl(StringRef clangName, ClangTypeKind kind,
                      llvm::function_ref<void(TypeDecl *)> receiver) override;

  /// Look up type a declaration synthesized by the Clang importer itself, using
  /// a "related entity kind" to determine which type it should be. For example,
  /// this can be used to find the synthesized error struct for an
  /// NS_ERROR_ENUM.
  ///
  /// Note that this method does no filtering. If it finds the type in a loaded
  /// module, it returns it. This is intended for use in reflection / debugging
  /// contexts where access is not a problem.
  void
  lookupRelatedEntity(StringRef clangName, ClangTypeKind kind,
                      StringRef relatedEntityKind,
                      llvm::function_ref<void(TypeDecl *)> receiver) override;

  StructDecl *
  instantiateCXXClassTemplate(clang::ClassTemplateDecl *decl,
                      ArrayRef<clang::TemplateArgument> arguments) override;

  ConcreteDeclRef getCXXFunctionTemplateSpecialization(
          SubstitutionMap subst, ValueDecl *decl) override;

  FuncDecl *getCXXSynthesizedOperatorFunc(FuncDecl *decl);

  /// Just like Decl::getClangNode() except we look through to the 'Code'
  /// enum of an error wrapper struct.
  ClangNode getEffectiveClangNode(const Decl *decl) const override;

  /// Look for textually included declarations from the bridging header.
  ///
  /// \param filter returns true if the given clang decl/macro should be
  /// imported and fed to the consumer
  /// \param receiver will be fed decls as they are found and imported.
  ///
  /// \c receiver is not a VisibleDeclConsumer so that it is not limited to
  /// accepting ValueDecls only.
  void lookupBridgingHeaderDecls(llvm::function_ref<bool(ClangNode)> filter,
                                llvm::function_ref<void(Decl*)> receiver) const;

  /// Look for declarations from a particular header. The header may be part of
  /// a clang module or included from the bridging header.
  ///
  /// \param filename path to the header
  /// \param filter returns true if the given clang decl/macro should be
  /// imported and fed to the consumer
  /// \param receiver will be fed decls as they are found and imported.
  ///
  /// \c receiver is not a VisibleDeclConsumer so that it is not limited to
  /// accepting ValueDecls only.
  ///
  /// \returns true if there was a problem, e.g. the file does not exist.
  bool lookupDeclsFromHeader(StringRef filename,
                             llvm::function_ref<bool(ClangNode)> filter,
                             llvm::function_ref<void(Decl*)> receiver) const;

  /// Load extensions to the given nominal type.
  ///
  /// \param nominal The nominal type whose extensions should be loaded.
  ///
  /// \param previousGeneration The previous generation number. The AST already
  /// contains extensions loaded from any generation up to and including this
  /// one.
  virtual void loadExtensions(NominalTypeDecl *nominal,
                              unsigned previousGeneration) override;

  virtual void loadObjCMethods(
                 NominalTypeDecl *typeDecl,
                 ObjCSelector selector,
                 bool isInstanceMethod,
                 unsigned previousGeneration,
                 llvm::TinyPtrVector<AbstractFunctionDecl *> &methods) override;

  /// Adds a new search path to the Clang CompilerInstance, as if specified with
  /// -I or -F.
  ///
  /// \returns true if there was an error adding the search path.
  bool addSearchPath(StringRef newSearchPath, bool isFramework,
                     bool isSystem) override;

  /// Imports an Objective-C header file into the shared imported header module.
  ///
  /// \param header A header name or full path, to be used in a \#import
  /// directive.
  /// \param adapter The module that depends on the contents of this header.
  /// \param expectedSize The size of the header when the module was compiled
  ///        against it.
  /// \param expectedModTime The mtime of the header when the module was
  ///        compiled against it.
  /// \param cachedContents A buffer to use if the header has been modified
  ///        since the module was compiled.
  /// \param diagLoc A location to attach any diagnostics to if import fails.
  ///
  /// \returns true if there was an error importing the header.
  ///
  /// \sa getImportedHeaderModule
  bool importHeader(StringRef header, ModuleDecl *adapter, off_t expectedSize,
                    time_t expectedModTime, StringRef cachedContents,
                    SourceLoc diagLoc);

  /// Imports an Objective-C header file into the shared imported header module.
  ///
  /// \param header A header name or full path, to be used in a \#import
  ///        directive.
  /// \param adapter The module that depends on the contents of this header.
  /// \param diagLoc A location to attach any diagnostics to if import fails.
  /// \param trackParsedSymbols If true, tracks decls and macros that were
  ///        parsed from the bridging header.
  /// \param implicitImport If true, indicates that this import was implicit
  ///        from a reference in a module file (deprecated behavior).
  ///
  /// \returns true if there was an error importing the header.
  ///
  /// \sa getImportedHeaderModule
  bool importBridgingHeader(StringRef header, ModuleDecl *adapter,
                            SourceLoc diagLoc = {},
                            bool trackParsedSymbols = false,
                            bool implicitImport = false);

  /// Bind the bridging header content to the module.
  ///
  /// \param adapter The module that depends on the contents of this header.
  /// \param diagLoc A location to attach any diagnostics to if import fails.
  ///
  /// \returns true if there was an error importing the header.
  ///
  /// \sa importBridgingHeader
  bool bindBridgingHeader(ModuleDecl *adapter, SourceLoc diagLoc);

  /// Returns the module that contains imports and declarations from all loaded
  /// Objective-C header files.
  ///
  /// \sa importHeader
  ModuleDecl *getImportedHeaderModule() const override;

  /// Retrieves the Swift wrapper for the given Clang module, creating
  /// it if necessary.
  ModuleDecl *
  getWrapperForModule(const clang::Module *mod,
                      bool returnOverlayIfPossible = false) const override;

  std::string
  getBridgingHeaderContents(StringRef headerPath, off_t &fileSize,
                            time_t &fileModTime,
                            StringRef pchIncludeTree);

  /// Makes a temporary replica of the ClangImporter's CompilerInstance, reads
  /// an Objective-C header file into the replica and emits a PCH file of its
  /// content. Delegates to clang for everything except construction of the
  /// replica.
  ///
  /// \sa clang::GeneratePCHAction
  bool emitBridgingPCH(StringRef headerPath, StringRef outputPCHPath,
                       bool cached);

  /// Returns true if a clang CompilerInstance can successfully read in a PCH,
  /// assuming it exists, with the current options. This can be used to find out
  /// if we need to persist a PCH for later reuse.
  bool canReadPCH(StringRef PCHFilename);

  /// Reads the original source file name from PCH.
  std::string getOriginalSourceFile(StringRef PCHFilename);

  /// Makes a temporary replica of the ClangImporter's CompilerInstance, reads a
  /// module map into the replica and emits a PCM file for one of the modules it
  /// declares. Delegates to clang for everything except construction of the
  /// replica.
  bool emitPrecompiledModule(StringRef moduleMapPath, StringRef moduleName,
                             StringRef outputPath);

  /// Makes a temporary replica of the ClangImporter's CompilerInstance and
  /// dumps information about a PCM file (assumed to be generated by -emit-pcm
  /// or in the Swift module cache). Delegates to clang for everything except
  /// construction of the replica.
  bool dumpPrecompiledModule(StringRef modulePath, StringRef outputPath);

  bool runPreprocessor(StringRef inputPath, StringRef outputPath);
  const clang::Module *getClangOwningModule(ClangNode Node) const;
  bool hasTypedef(const clang::Decl *typeDecl) const;

  void verifyAllModules() override;

  using RemapPathCallback = llvm::function_ref<std::string(StringRef)>;
  using LookupModuleOutputCallback =
      llvm::function_ref<std::string(const clang::tooling::dependencies::ModuleDeps &,
                                     clang::tooling::dependencies::ModuleOutputKind)>;

  static llvm::SmallVector<std::pair<ModuleDependencyID, ModuleDependencyInfo>, 1>
  bridgeClangModuleDependencies(
      const ASTContext &ctx,
      clang::tooling::dependencies::DependencyScanningTool &clangScanningTool,
      clang::tooling::dependencies::ModuleDepsGraph &clangDependencies,
      LookupModuleOutputCallback LookupModuleOutput,
      RemapPathCallback remapPath = nullptr);

  static void getBridgingHeaderOptions(
      const ASTContext &ctx,
      const clang::tooling::dependencies::TranslationUnitDeps &deps,
      std::vector<std::string> &swiftArgs);

  clang::TargetInfo &getModuleAvailabilityTarget() const override;
  clang::ASTContext &getClangASTContext() const override;
  clang::Preprocessor &getClangPreprocessor() const override;
  clang::Sema &getClangSema() const override;
  const clang::CompilerInstance &getClangInstance() const override;

  /// ClangImporter's Clang instance may be configured with a different
  /// (higher) OS version than the compilation target itself in order to be able
  /// to load pre-compiled Clang modules that are aligned with the broader SDK,
  /// and match the SDK deployment target against which Swift modules are also
  /// built.
  ///
  /// In this case, we must use the Swift compiler's OS version triple when
  /// performing codegen, and the importer's Clang instance OS version triple
  /// during module loading.
  ///
  /// `ClangImporter`'s `Implementation` keeps track of a distinct `TargetInfo`
  /// and `CodeGenOpts` containers that are meant to be used by clients in
  /// IRGen. When a separate `-clang-target` is not set, they are defined to be
  /// copies of the `ClangImporter`'s built-in module-loading Clang instance.
  /// When `-clang-target` is set, they are configured with the Swift
  /// compilation's target triple and OS version (but otherwise identical)
  /// instead. To distinguish IRGen clients from module loading clients,
  /// `getModuleAvailabilityTarget` should be used instead by module-loading
  /// clients.
  clang::TargetInfo &getTargetInfo() const;
  clang::CodeGenOptions &getCodeGenOpts() const;

  std::string getClangModuleHash() const;

  /// Get clang import creation cc1 args for swift explicit module build.
  std::vector<std::string> getSwiftExplicitModuleDirectCC1Args() const;

  /// If we already imported a given decl successfully, return the corresponding
  /// Swift decl as an Optional<Decl *>, but if we previously tried and failed
  /// to import said decl then return nullptr.
  /// Otherwise, if we have never encountered this decl previously then return
  /// None.
  std::optional<Decl *> importDeclCached(const clang::NamedDecl *ClangDecl);

  // Returns true if it is expected that the macro is ignored.
  bool shouldIgnoreMacro(StringRef Name, const clang::MacroInfo *Macro);

  /// Returns the name of the given enum element as it would be imported into
  /// Swift.
  ///
  /// The return value may be an empty identifier, in which case the enum would
  /// not be imported.
  ///
  /// This is not used by the importer itself, but is used by the debugger.
  Identifier getEnumConstantName(const clang::EnumConstantDecl *enumConstant);

  /// Writes the mangled name of \p clangDecl to \p os.
  void getMangledName(raw_ostream &os, const clang::NamedDecl *clangDecl) const;

  // Print statistics from the Clang AST reader.
  void printStatistics() const override;

  /// Dump Swift lookup tables.
  void dumpSwiftLookupTables() const override;

  /// Given the path of a Clang module, collect the names of all its submodules.
  /// Calling this function does not load the module.
  void collectSubModuleNames(
      ImportPath::Module path,
      std::vector<std::string> &names) const;

  /// Given a Clang module, decide whether this module is imported already.
  static bool isModuleImported(const clang::Module *M);

  DeclName importName(
      const clang::NamedDecl *D,
      clang::DeclarationName givenName = clang::DeclarationName()) override;

  std::optional<Type>
  importFunctionReturnType(const clang::FunctionDecl *clangDecl,
                           DeclContext *dc) override;

  Type importVarDeclType(const clang::VarDecl *clangDecl,
                         VarDecl *swiftDecl,
                         DeclContext *dc) override;

  std::optional<std::string>
  getOrCreatePCH(const ClangImporterOptions &ImporterOptions,
                 StringRef SwiftPCHHash, bool Cached);
  std::optional<std::string>
  /// \param isExplicit true if the PCH filename was passed directly
  /// with -import-objc-header option.
  getPCHFilename(const ClangImporterOptions &ImporterOptions,
                 StringRef SwiftPCHHash, bool &isExplicit);

  const clang::Type *parseClangFunctionType(StringRef type,
                                            SourceLoc loc) const override;
  void printClangType(const clang::Type *type,
                      llvm::raw_ostream &os) const override;

  StableSerializationPath
  findStableSerializationPath(const clang::Decl *decl) const override;

  const clang::Decl *
  resolveStableSerializationPath(
                            const StableSerializationPath &path) const override;

  bool isSerializable(const clang::Type *type,
                      bool checkCanonical) const override;

  clang::FunctionDecl *
  instantiateCXXFunctionTemplate(ASTContext &ctx,
                                 clang::FunctionTemplateDecl *func,
                                 SubstitutionMap subst) override;

  bool isSynthesizedAndVisibleFromAllModules(const clang::Decl *decl);

  bool isCXXMethodMutating(const clang::CXXMethodDecl *method) override;

  bool isUnsafeCXXMethod(const FuncDecl *func) override;

  FuncDecl *getDefaultArgGenerator(const clang::ParmVarDecl *param) override;

  bool isAnnotatedWith(const clang::CXXMethodDecl *method, StringRef attr);

  /// Find the lookup table that corresponds to the given Clang module.
  ///
  /// \param clangModule The module, or null to indicate that we're talking
  /// about the directly-parsed headers.
  SwiftLookupTable *findLookupTable(const clang::Module *clangModule) override;

  /// Determine the effective Clang context for the given Swift nominal type.
  EffectiveClangContext
  getEffectiveClangContext(const NominalTypeDecl *nominal) override;

  /// Imports a clang decl directly, rather than looking up it's name.
  Decl *importDeclDirectly(const clang::NamedDecl *decl) override;

  ValueDecl *importBaseMemberDecl(ValueDecl *decl, DeclContext *newContext,
                                  ClangInheritanceInfo inheritance) override;

  bool isClonedMemberDecl(ValueDecl *decl) override;

  /// Emits diagnostics for any declarations named name
  /// whose direct declaration context is a TU.
  void diagnoseTopLevelValue(const DeclName &name) override;

  /// Emit diagnostics for declarations named name that are members
  /// of the provided baseType.
  void diagnoseMemberValue(const DeclName &name, const Type &baseType) override;

  const clang::TypedefType *getTypeDefForCXXCFOptionsDefinition(
      const clang::Decl *candidateDecl) override;

  /// Create cache key for embedded bridging header.
  static llvm::Expected<llvm::cas::ObjectRef>
  createEmbeddedBridgingHeaderCacheKey(
      llvm::cas::ObjectStore &CAS, llvm::cas::ObjectRef ChainedPCHIncludeTree);

  SourceLoc importSourceLocation(clang::SourceLocation loc) override;
};

ImportDecl *createImportDecl(ASTContext &Ctx, DeclContext *DC, ClangNode ClangN,
                             ArrayRef<clang::Module *> Exported);

/// Extract the specified-or-defaulted -module-cache-path that winds up in
/// the clang importer, for reuse as the .swiftmodule cache path when
/// building a ModuleInterfaceLoader.
std::string
getModuleCachePathFromClang(const clang::CompilerInstance &Instance);

/// Whether the given parameter name identifies a completion handler.
bool isCompletionHandlerParamName(StringRef paramName);

namespace importer {

/// Returns true if the given module has a 'cplusplus' requirement.
bool requiresCPlusPlus(const clang::Module *module);

/// Returns true if the given module is one of the C++ standard library modules.
/// This could be the top-level std module, or any of the libc++ split modules
/// (std_vector, std_iosfwd, etc).
bool isCxxStdModule(const clang::Module *module);

/// Returns true if the given module is one of the C++ standard library modules.
/// This could be the top-level std module, or any of the libc++ split modules
/// (std_vector, std_iosfwd, etc).
bool isCxxStdModule(StringRef moduleName, bool IsSystem);

/// Returns the pointee type if the given type is a C++ `const`
/// reference type, `None` otherwise.
std::optional<clang::QualType>
getCxxReferencePointeeTypeOrNone(const clang::Type *type);

/// Returns true if the given type is a C++ `const` reference type.
bool isCxxConstReferenceType(const clang::Type *type);

/// Determine whether this typedef is a CF type.
bool isCFTypeDecl(const clang::TypedefNameDecl *Decl);

/// Determine the imported CF type for the given typedef-name, or the empty
/// string if this is not an imported CF type name.
llvm::StringRef getCFTypeName(const clang::TypedefNameDecl *decl);

/// Lookup and return the synthesized conformance operator like '==' '-' or '+='
/// for the given type.
ValueDecl *getImportedMemberOperator(const DeclBaseName &name,
                                     NominalTypeDecl *selfType,
                                     std::optional<Type> parameterType);

/// Map the access specifier of a Clang record member to a Swift access level.
///
/// This mapping is conservative: the resulting Swift access should be at _most_
/// as permissive as the input C++ access.
AccessLevel convertClangAccess(clang::AccessSpecifier access);

/// Read file IDs from 'private_fileid' Swift attributes on a Clang decl.
///
/// May return >1 fileID when a decl is annotated more than once, which should
/// be treated as an error and appropriately diagnosed (using the included
/// SourceLocation).
///
/// The returned fileIDs may not be of a valid format (e.g., missing a '/'),
/// and should be parsed using swift::SourceFile::FileIDStr::parse().
SmallVector<std::pair<StringRef, clang::SourceLocation>, 1>
getPrivateFileIDAttrs(const clang::CXXRecordDecl *decl);

/// Use some heuristics to determine whether the clang::Decl associated with
/// \a decl would not exist without C++ interop.
///
/// For instance, a namespace is C++-only, but a plain struct is valid in both
/// C and C++.
///
/// Returns false if \a decl was not imported by ClangImporter.
bool declIsCxxOnly(const Decl *decl);

/// Is this DeclContext an `enum` that represents a C++ namespace?
bool isClangNamespace(const DeclContext *dc);

/// For some \a templatedClass that inherits from \a base, whether they are
/// derived from the same class template.
///
/// This kind of circular inheritance can happen when a templated class inherits
/// from a specialization of itself, e.g.:
///
///     template <typename T> class C;
///     template <> class C<void> { /* ... */ };
///     template <typename T> class C<T> : C<void> { /* ... */ };
///
/// Checking for this kind of scenario is necessary for avoiding infinite
/// recursion during symbolic imports (importSymbolicCXXDecls), where
/// specialized class templates are instead imported as unspecialized.
bool isSymbolicCircularBase(const clang::CXXRecordDecl *templatedClass,
                            const clang::RecordDecl *base);

/// Match a `[[swift_attr("...")]]` annotation on the given Clang decl.
///
/// \param decl The Clang declaration to inspect.
/// \param patterns List of (attribute name, value) pairs.
/// \returns The value for the first matching attribute, or `std::nullopt`.
template <typename T>
std::optional<T>
matchSwiftAttr(const clang::Decl *decl,
               llvm::ArrayRef<std::pair<llvm::StringRef, T>> patterns) {
  if (!decl || !decl->hasAttrs())
    return std::nullopt;

  for (const auto *attr : decl->getAttrs()) {
    if (const auto *swiftAttr = llvm::dyn_cast<clang::SwiftAttrAttr>(attr)) {
      for (const auto &p : patterns) {
        if (swiftAttr->getAttribute() == p.first)
          return p.second;
      }
    }
  }
  return std::nullopt;
}

/// Like `matchSwiftAttr`, but also searches C++ base classes.
///
/// \param decl The Clang declaration to inspect.
/// \param patterns List of (attribute name, value) pairs.
/// \returns The matched value from this decl or its bases, or `std::nullopt`.
template <typename T>
std::optional<T> matchSwiftAttrConsideringInheritance(
    const clang::Decl *decl,
    llvm::ArrayRef<std::pair<llvm::StringRef, T>> patterns) {
  if (!decl)
    return std::nullopt;

  if (auto match = matchSwiftAttr<T>(decl, patterns))
    return match;

  if (const auto *recordDecl = llvm::dyn_cast<clang::CXXRecordDecl>(decl)) {
    std::optional<T> result;
    recordDecl->forallBases([&](const clang::CXXRecordDecl *base) -> bool {
      if (auto baseMatch = matchSwiftAttr<T>(base, patterns)) {
        result = baseMatch;
        return false;
      }

      return true;
    });

    return result;
  }

  return std::nullopt;
}

/// Matches a `swift_attr("...")` on the record type pointed to by the given
/// Clang type, searching base classes if it's a C++ class.
///
/// \param type A Clang pointer type.
/// \param patterns List of attribute name-value pairs to match.
/// \returns Matched value or std::nullopt.
template <typename T>
std::optional<T> matchSwiftAttrOnRecordPtr(
    const clang::QualType &type,
    llvm::ArrayRef<std::pair<llvm::StringRef, T>> patterns) {
  if (const auto *ptrType = type->getAs<clang::PointerType>()) {
    if (const auto *recordDecl = ptrType->getPointeeType()->getAsRecordDecl()) {
      return matchSwiftAttrConsideringInheritance<T>(recordDecl, patterns);
    }
  }
  return std::nullopt;
}

/// Determines the C++ reference ownership convention for the return value
/// using `SWIFT_RETURNS_(UN)RETAINED` on the API; falls back to
/// `SWIFT_RETURNED_AS_(UN)RETAINED_BY_DEFAULT` on the pointee record type.
///
/// \param decl The Clang function or method declaration to inspect.
/// \returns Matched `ResultConvention`, or `std::nullopt` if none applies.
std::optional<ResultConvention>
getCxxRefConventionWithAttrs(const clang::Decl *decl);
} // namespace importer

struct ClangInvocationFileMapping {
  /// Mapping from a file name to an existing file path.
  SmallVector<std::pair<std::string, std::string>, 2> redirectedFiles;

  /// Mapping from a file name to a string of characters that represents the
  /// contents of the file.
  SmallVector<std::pair<std::string, std::string>, 1> overridenFiles;

  bool requiresBuiltinHeadersInSystemModules;
};

/// On Linux, some platform libraries (glibc, libstdc++) are not modularized.
/// We inject modulemaps for those libraries into their include directories
/// to allow using them from Swift.
///
/// `suppressDiagnostic` prevents us from emitting warning messages when we
/// are unable to find headers.
ClangInvocationFileMapping getClangInvocationFileMapping(
    const ASTContext &ctx,
    llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> vfs = nullptr,
    bool suppressDiagnostic = false);

/// Apply the given file mapping to the specified 'fileSystem', used
/// primarily to inject modulemaps on platforms with non-modularized
/// platform libraries.
ClangInvocationFileMapping applyClangInvocationMapping(
    const ASTContext &ctx,
    llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> baseVFS,
    llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> &fileSystem,
    bool suppressDiagnostics = false);

/// Information used to compute the access level of inherited C++ members.
class ClangInheritanceInfo {
  /// The cumulative inheritance access specifier, that is used to compute the
  /// effective access level of a particular inherited member.
  ///
  /// When constructing ClangInheritanceInfo for nested inheritance, this field
  /// gets clamped to the least permissive level between its current value and
  /// the inheritance access specifier.
  ///
  /// If we encounter \e nested private inheritance in the class hierarchy
  /// (i.e., private inheritance beyond the first level of inheritance), we set
  /// the access level to nullopt to indicate that none of the members from
  /// classes beyond that point in the hierarchy should be accessible. This case
  /// must be treated separately from non-nested private inheritance, where
  /// inherited members are private but accessible from extensions.
  ///
  /// See ClangInheritanceInfo::cumulativeInheritedAccess() for an example.
  std::optional<clang::AccessSpecifier> access;

public:
  /// Default constructor for this class that is used as the base case when
  /// recursively walking up a class inheritance hierarchy.
  ClangInheritanceInfo() : access(clang::AS_none) {}

  /// Inductive case for this class that is used to accumulate inheritance
  /// metadata for cases of (nested) inheritance.
  ClangInheritanceInfo(ClangInheritanceInfo prev, clang::CXXBaseSpecifier base)
      : access(computeAccess(prev, base)) {}

  /// Whether this info represents a case of nested private inheritance.
  bool isNestedPrivate() const { return !access.has_value(); }

  /// Whether this info represents a case of C++ inheritance.
  ///
  /// Returns \c false for the default instance of this class.
  bool isInheriting() const {
    return isNestedPrivate() || *access != clang::AS_none;
  }

  /// Whether this is info represents a case of C++ inheritance.
  operator bool() const { return isInheriting(); }

  /// Compute the (Swift) access level for inherited base member \param decl,
  /// for when its inherited (cloned) member in the derived class.
  ///
  /// This access level is determined by whichever is more restrictive: what the
  /// \param decl was declared with (in its base class), or what it is being
  /// inherited with (ClangInheritanceInfo::access).
  ///
  /// Always returns swift::AccessLevel::Public (i.e., corresponding to
  /// clang::AS_none) if this ClangInheritanceInfo::isInheriting() is \c false.
  AccessLevel accessForBaseDecl(const ValueDecl *baseDecl) const;

  /// Marks \param clonedDecl as unavailable (using \c @available) if it
  /// cannot be accessed from the derived class, either because \param baseDecl
  /// was declared as private in the base class, or because \param clonedDecl
  /// was inherited with private inheritance.
  ///
  /// Does nothing if this ClangInheritanceInfo::isInheriting() is \c false.
  void setUnavailableIfNecessary(const ValueDecl *baseDecl,
                                 ValueDecl *clonedDecl) const;

  friend llvm::hash_code hash_value(const ClangInheritanceInfo &info) {
    return llvm::hash_combine(info.access);
  }

private:
  /// An example of how ClangInheritanceInfo:access is accumulated while
  /// recursively traversing the class hierarchy starting from \c E:
  ///
  /// \code{.cpp}
  /// struct A { ... };               // access = nullopt (nested private)
  /// struct B : private   A { ... }; // access = protected
  /// struct C : public    B { ... }; // access = protected
  /// struct D : protected C { ... }; // access = public
  /// struct E : public    D { ... }; // access = none [base case]
  /// \endcode
  ///
  /// Another example, this time with non-nested private inheritance:
  ///
  /// \code{.cpp}
  /// struct A { ... };               // access = nullopt
  /// struct B : public    A { ... }; // access = nullopt
  /// struct C : private   B { ... }; // access = private
  /// struct D : public    C { ... }; // access = private
  /// struct E : private   D { ... }; // access = none [base case]
  /// \endcode
  static std::optional<clang::AccessSpecifier>
  computeAccess(ClangInheritanceInfo prev, clang::CXXBaseSpecifier base) {
    auto baseAccess = base.getAccessSpecifier();
    assert(baseAccess != clang::AS_none &&
           "this should always be public, protected, or private");

    if (!prev.isInheriting())
      // This is the first level of inheritance, so we just take the access
      // specifier from CXXBaseSpecifier. Note that this is the only scenario
      // where we can have access = private.
      return {baseAccess};

    if (prev.isNestedPrivate() || baseAccess == clang::AS_private)
      // This is a case of nested inheritance, and either we encountered nested
      // private inheritance before, or this is our first time encountering it.
      return std::nullopt;

    static_assert(clang::AS_private > clang::AS_protected &&
                  clang::AS_protected > clang::AS_public &&
                  "using std::max() relies on this ordering");
    return {std::max(*prev.access, baseAccess)};
  }
};

} // end namespace swift

#endif