text: //===- ModuleMap.h - Describe the layout of modules -------------*- C++ -*-===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // This file defines the ModuleMap interface, which describes the layout of a
  // module as it relates to headers.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_CLANG_LEX_MODULEMAP_H
  #define LLVM_CLANG_LEX_MODULEMAP_H
  
  #include "clang/Basic/IdentifierTable.h"
  #include "clang/Basic/LangOptions.h"
  #include "clang/Basic/Module.h"
  #include "clang/Basic/SourceLocation.h"
  #include "llvm/ADT/ArrayRef.h"
  #include "llvm/ADT/DenseMap.h"
  #include "llvm/ADT/PointerIntPair.h"
  #include "llvm/ADT/SmallPtrSet.h"
  #include "llvm/ADT/SmallVector.h"
  #include "llvm/ADT/StringMap.h"
  #include "llvm/ADT/StringRef.h"
  #include "llvm/ADT/StringSet.h"
  #include "llvm/ADT/TinyPtrVector.h"
  #include "llvm/ADT/Twine.h"
  #include <ctime>
  #include <memory>
  #include <string>
  #include <utility>
  
  namespace clang {
  
  class DiagnosticsEngine;
  class DirectoryEntry;
  class FileEntry;
  class FileManager;
  class HeaderSearch;
  class SourceManager;
  
  /// A mechanism to observe the actions of the module map parser as it
  /// reads module map files.
  class ModuleMapCallbacks {
    virtual void anchor();
  
  public:
    virtual ~ModuleMapCallbacks() = default;
  
    /// Called when a module map file has been read.
    ///
    /// \param FileStart A SourceLocation referring to the start of the file's
    /// contents.
    /// \param File The file itself.
    /// \param IsSystem Whether this is a module map from a system include path.
    virtual void moduleMapFileRead(SourceLocation FileStart,
                                   const FileEntry &File, bool IsSystem) {}
  
    /// Called when a module map file matches a module lookup
    ///
    /// \param File The file itself.
    /// \param M The module found that matches this module map.
    /// \param IsSystem Whether this is a module map from a system include path.
    virtual void moduleMapFoundForModule(const FileEntry &File, const Module *M,
                                         bool IsSystem) {}
  
    /// Called when a header is added during module map parsing.
    ///
    /// \param Filename The header file itself.
    virtual void moduleMapAddHeader(StringRef Filename) {}
  
    /// Called when an umbrella header is added during module map parsing.
    ///
    /// \param FileMgr FileManager instance
    /// \param Header The umbrella header to collect.
    virtual void moduleMapAddUmbrellaHeader(FileManager *FileMgr,
                                            const FileEntry *Header) {}
  };
  
  class ModuleMap {
    SourceManager &SourceMgr;
    DiagnosticsEngine &Diags;
    const LangOptions &LangOpts;
    const TargetInfo *Target;
    HeaderSearch &HeaderInfo;
  
    llvm::SmallVector<std::unique_ptr<ModuleMapCallbacks>, 1> Callbacks;
  
    /// The directory used for Clang-supplied, builtin include headers,
    /// such as "stdint.h".
    const DirectoryEntry *BuiltinIncludeDir = nullptr;
  
    /// Language options used to parse the module map itself.
    ///
    /// These are always simple C language options.
    LangOptions MMapLangOpts;
  
    /// The module that the main source file is associated with (the module
    /// named LangOpts::CurrentModule, if we've loaded it).
    Module *SourceModule = nullptr;
  
    /// Submodules of the current module that have not yet been attached to it.
    /// (Ownership is transferred if/when we create an enclosing module.)
    llvm::SmallVector<std::unique_ptr<Module>, 8> PendingSubmodules;
  
    /// The top-level modules that are known.
    llvm::StringMap<Module *> Modules;
  
    /// Module loading cache that includes submodules, indexed by IdentifierInfo.
    /// nullptr is stored for modules that are known to fail to load.
    llvm::DenseMap<const IdentifierInfo *, Module *> CachedModuleLoads;
  
    /// Shadow modules created while building this module map.
    llvm::SmallVector<Module*, 2> ShadowModules;
  
    /// The number of modules we have created in total.
    unsigned NumCreatedModules = 0;
  
    /// In case a module has a export_as entry, it might have a pending link
    /// name to be determined if that module is imported.
    llvm::StringMap<llvm::StringSet<>> PendingLinkAsModule;
  
  public:
    /// Use PendingLinkAsModule information to mark top level link names that
    /// are going to be replaced by export_as aliases.
    void resolveLinkAsDependencies(Module *Mod);
  
    /// Make module to use export_as as the link dependency name if enough
    /// information is available or add it to a pending list otherwise.
    void addLinkAsDependency(Module *Mod);
  
    /// Flags describing the role of a module header.
    enum ModuleHeaderRole {
      /// This header is normally included in the module.
      NormalHeader  = 0x0,
  
      /// This header is included but private.
      PrivateHeader = 0x1,
  
      /// This header is part of the module (for layering purposes) but
      /// should be textually included.
      TextualHeader = 0x2,
  
      // Caution: Adding an enumerator needs other changes.
      // Adjust the number of bits for KnownHeader::Storage.
      // Adjust the bitfield HeaderFileInfo::HeaderRole size.
      // Adjust the HeaderFileInfoTrait::ReadData streaming.
      // Adjust the HeaderFileInfoTrait::EmitData streaming.
      // Adjust ModuleMap::addHeader.
    };
  
    /// Convert a header kind to a role. Requires Kind to not be HK_Excluded.
    static ModuleHeaderRole headerKindToRole(Module::HeaderKind Kind);
  
    /// Convert a header role to a kind.
    static Module::HeaderKind headerRoleToKind(ModuleHeaderRole Role);
  
    /// A header that is known to reside within a given module,
    /// whether it was included or excluded.
    class KnownHeader {
      llvm::PointerIntPair<Module *, 2, ModuleHeaderRole> Storage;
  
    public:
      KnownHeader() : Storage(nullptr, NormalHeader) {}
      KnownHeader(Module *M, ModuleHeaderRole Role) : Storage(M, Role) {}
  
      friend bool operator==(const KnownHeader &A, const KnownHeader &B) {
        return A.Storage == B.Storage;
      }
      friend bool operator!=(const KnownHeader &A, const KnownHeader &B) {
        return A.Storage != B.Storage;
      }
  
      /// Retrieve the module the header is stored in.
      Module *getModule() const { return Storage.getPointer(); }
  
      /// The role of this header within the module.
      ModuleHeaderRole getRole() const { return Storage.getInt(); }
  
      /// Whether this header is available in the module.
      bool isAvailable() const {
        return getModule()->isAvailable();
      }
  
      /// Whether this header is accessible from the specified module.
      bool isAccessibleFrom(Module *M) const {
        return !(getRole() & PrivateHeader) ||
               (M && M->getTopLevelModule() == getModule()->getTopLevelModule());
      }
  
      // Whether this known header is valid (i.e., it has an
      // associated module).
      explicit operator bool() const {
        return Storage.getPointer() != nullptr;
      }
    };
  
    using AdditionalModMapsSet = llvm::SmallPtrSet<const FileEntry *, 1>;
  
  private:
    friend class ModuleMapParser;
  
    using HeadersMap =
        llvm::DenseMap<const FileEntry *, SmallVector<KnownHeader, 1>>;
  
    /// Mapping from each header to the module that owns the contents of
    /// that header.
    HeadersMap Headers;
  
    /// Map from file sizes to modules with lazy header directives of that size.
    mutable llvm::DenseMap<off_t, llvm::TinyPtrVector<Module*>> LazyHeadersBySize;
  
    /// Map from mtimes to modules with lazy header directives with those mtimes.
    mutable llvm::DenseMap<time_t, llvm::TinyPtrVector<Module*>>
                LazyHeadersByModTime;
  
    /// Mapping from directories with umbrella headers to the module
    /// that is generated from the umbrella header.
    ///
    /// This mapping is used to map headers that haven't explicitly been named
    /// in the module map over to the module that includes them via its umbrella
    /// header.
    llvm::DenseMap<const DirectoryEntry *, Module *> UmbrellaDirs;
  
    /// A generation counter that is used to test whether modules of the
    /// same name may shadow or are illegal redefinitions.
    ///
    /// Modules from earlier scopes may shadow modules from later ones.
    /// Modules from the same scope may not have the same name.
    unsigned CurrentModuleScopeID = 0;
  
    llvm::DenseMap<Module *, unsigned> ModuleScopeIDs;
  
    /// The set of attributes that can be attached to a module.
    struct Attributes {
      /// Whether this is a system module.
      unsigned IsSystem : 1;
  
      /// Whether this is an extern "C" module.
      unsigned IsExternC : 1;
  
      /// Whether this is an exhaustive set of configuration macros.
      unsigned IsExhaustive : 1;
  
      /// \brief Whether this is a module who has its swift_names inferred.
      unsigned IsSwiftInferImportAsMember : 1;
  
      /// Whether files in this module can only include non-modular headers
      /// and headers from used modules.
      unsigned NoUndeclaredIncludes : 1;
  
      Attributes()
          : IsSystem(false), IsExternC(false), IsExhaustive(false),
            NoUndeclaredIncludes(false) {}
    };
  
    /// A directory for which framework modules can be inferred.
    struct InferredDirectory {
      /// Whether to infer modules from this directory.
      unsigned InferModules : 1;
  
      /// The attributes to use for inferred modules.
      Attributes Attrs;
  
      /// If \c InferModules is non-zero, the module map file that allowed
      /// inferred modules.  Otherwise, nullptr.
      const FileEntry *ModuleMapFile;
  
      /// The names of modules that cannot be inferred within this
      /// directory.
      SmallVector<std::string, 2> ExcludedModules;
  
      InferredDirectory() : InferModules(false) {}
    };
  
    /// A mapping from directories to information about inferring
    /// framework modules from within those directories.
    llvm::DenseMap<const DirectoryEntry *, InferredDirectory> InferredDirectories;
  
    /// A mapping from an inferred module to the module map that allowed the
    /// inference.
    llvm::DenseMap<const Module *, const FileEntry *> InferredModuleAllowedBy;
  
    llvm::DenseMap<const Module *, AdditionalModMapsSet> AdditionalModMaps;
  
    /// Describes whether we haved parsed a particular file as a module
    /// map.
    llvm::DenseMap<const FileEntry *, bool> ParsedModuleMap;
  
    /// Resolve the given export declaration into an actual export
    /// declaration.
    ///
    /// \param Mod The module in which we're resolving the export declaration.
    ///
    /// \param Unresolved The export declaration to resolve.
    ///
    /// \param Complain Whether this routine should complain about unresolvable
    /// exports.
    ///
    /// \returns The resolved export declaration, which will have a NULL pointer
    /// if the export could not be resolved.
    Module::ExportDecl
    resolveExport(Module *Mod, const Module::UnresolvedExportDecl &Unresolved,
                  bool Complain) const;
  
    /// Resolve the given module id to an actual module.
    ///
    /// \param Id The module-id to resolve.
    ///
    /// \param Mod The module in which we're resolving the module-id.
    ///
    /// \param Complain Whether this routine should complain about unresolvable
    /// module-ids.
    ///
    /// \returns The resolved module, or null if the module-id could not be
    /// resolved.
    Module *resolveModuleId(const ModuleId &Id, Module *Mod, bool Complain) const;
  
    /// Add an unresolved header to a module.
    ///
    /// \param Mod The module in which we're adding the unresolved header
    ///        directive.
    /// \param Header The unresolved header directive.
    /// \param NeedsFramework If Mod is not a framework but a missing header would
    ///        be found in case Mod was, set it to true. False otherwise.
    void addUnresolvedHeader(Module *Mod,
                             Module::UnresolvedHeaderDirective Header,
                             bool &NeedsFramework);
  
    /// Look up the given header directive to find an actual header file.
    ///
    /// \param M The module in which we're resolving the header directive.
    /// \param Header The header directive to resolve.
    /// \param RelativePathName Filled in with the relative path name from the
    ///        module to the resolved header.
    /// \param NeedsFramework If M is not a framework but a missing header would
    ///        be found in case M was, set it to true. False otherwise.
    /// \return The resolved file, if any.
    const FileEntry *findHeader(Module *M,
                                const Module::UnresolvedHeaderDirective &Header,
                                SmallVectorImpl<char> &RelativePathName,
                                bool &NeedsFramework);
  
    /// Resolve the given header directive.
    ///
    /// \param M The module in which we're resolving the header directive.
    /// \param Header The header directive to resolve.
    /// \param NeedsFramework If M is not a framework but a missing header would
    ///        be found in case M was, set it to true. False otherwise.
    void resolveHeader(Module *M, const Module::UnresolvedHeaderDirective &Header,
                       bool &NeedsFramework);
  
    /// Attempt to resolve the specified header directive as naming a builtin
    /// header.
    /// \return \c true if a corresponding builtin header was found.
    bool resolveAsBuiltinHeader(Module *M,
                                const Module::UnresolvedHeaderDirective &Header);
  
    /// Looks up the modules that \p File corresponds to.
    ///
    /// If \p File represents a builtin header within Clang's builtin include
    /// directory, this also loads all of the module maps to see if it will get
    /// associated with a specific module (e.g. in /usr/include).
    HeadersMap::iterator findKnownHeader(const FileEntry *File);
  
    /// Searches for a module whose umbrella directory contains \p File.
    ///
    /// \param File The header to search for.
    ///
    /// \param IntermediateDirs On success, contains the set of directories
    /// searched before finding \p File.
    KnownHeader findHeaderInUmbrellaDirs(const FileEntry *File,
                      SmallVectorImpl<const DirectoryEntry *> &IntermediateDirs);
  
    /// Given that \p File is not in the Headers map, look it up within
    /// umbrella directories and find or create a module for it.
    KnownHeader findOrCreateModuleForHeaderInUmbrellaDir(const FileEntry *File);
  
    /// A convenience method to determine if \p File is (possibly nested)
    /// in an umbrella directory.
    bool isHeaderInUmbrellaDirs(const FileEntry *File) {
      SmallVector<const DirectoryEntry *, 2> IntermediateDirs;
      return static_cast<bool>(findHeaderInUmbrellaDirs(File, IntermediateDirs));
    }
  
    Module *inferFrameworkModule(const DirectoryEntry *FrameworkDir,
                                 Attributes Attrs, Module *Parent);
  
  public:
    /// Construct a new module map.
    ///
    /// \param SourceMgr The source manager used to find module files and headers.
    /// This source manager should be shared with the header-search mechanism,
    /// since they will refer to the same headers.
    ///
    /// \param Diags A diagnostic engine used for diagnostics.
    ///
    /// \param LangOpts Language options for this translation unit.
    ///
    /// \param Target The target for this translation unit.
    ModuleMap(SourceManager &SourceMgr, DiagnosticsEngine &Diags,
              const LangOptions &LangOpts, const TargetInfo *Target,
              HeaderSearch &HeaderInfo);
  
    /// Destroy the module map.
    ~ModuleMap();
  
    /// Set the target information.
    void setTarget(const TargetInfo &Target);
  
    /// Set the directory that contains Clang-supplied include
    /// files, such as our stdarg.h or tgmath.h.
    void setBuiltinIncludeDir(const DirectoryEntry *Dir) {
      BuiltinIncludeDir = Dir;
    }
  
    /// Get the directory that contains Clang-supplied include files.
    const DirectoryEntry *getBuiltinDir() const {
      return BuiltinIncludeDir;
    }
  
    /// Is this a compiler builtin header?
    static bool isBuiltinHeader(StringRef FileName);
  
    /// Add a module map callback.
    void addModuleMapCallbacks(std::unique_ptr<ModuleMapCallbacks> Callback) {
      Callbacks.push_back(std::move(Callback));
    }
  
    /// Retrieve the module that owns the given header file, if any. Note that
    /// this does not implicitly load module maps, except for builtin headers,
    /// and does not consult the external source. (Those checks are the
    /// responsibility of \ref HeaderSearch.)
    ///
    /// \param File The header file that is likely to be included.
    ///
    /// \param AllowTextual If \c true and \p File is a textual header, return
    /// its owning module. Otherwise, no KnownHeader will be returned if the
    /// file is only known as a textual header.
    ///
    /// \returns The module KnownHeader, which provides the module that owns the
    /// given header file.  The KnownHeader is default constructed to indicate
    /// that no module owns this header file.
    KnownHeader findModuleForHeader(const FileEntry *File,
                                    bool AllowTextual = false);
  
    /// Retrieve all the modules that contain the given header file. Note that
    /// this does not implicitly load module maps, except for builtin headers,
    /// and does not consult the external source. (Those checks are the
    /// responsibility of \ref HeaderSearch.)
    ///
    /// Typically, \ref findModuleForHeader should be used instead, as it picks
    /// the preferred module for the header.
    ArrayRef<KnownHeader> findAllModulesForHeader(const FileEntry *File);
  
    /// Like \ref findAllModulesForHeader, but do not attempt to infer module
    /// ownership from umbrella headers if we've not already done so.
    ArrayRef<KnownHeader>
    findResolvedModulesForHeader(const FileEntry *File) const;
  
    /// Resolve all lazy header directives for the specified file.
    ///
    /// This ensures that the HeaderFileInfo on HeaderSearch is up to date. This
    /// is effectively internal, but is exposed so HeaderSearch can call it.
    void resolveHeaderDirectives(const FileEntry *File) const;
  
    /// Resolve all lazy header directives for the specified module.
    void resolveHeaderDirectives(Module *Mod) const;
  
    /// Reports errors if a module must not include a specific file.
    ///
    /// \param RequestingModule The module including a file.
    ///
    /// \param RequestingModuleIsModuleInterface \c true if the inclusion is in
    ///        the interface of RequestingModule, \c false if it's in the
    ///        implementation of RequestingModule. Value is ignored and
    ///        meaningless if RequestingModule is nullptr.
    ///
    /// \param FilenameLoc The location of the inclusion's filename.
    ///
    /// \param Filename The included filename as written.
    ///
    /// \param File The included file.
    void diagnoseHeaderInclusion(Module *RequestingModule,
                                 bool RequestingModuleIsModuleInterface,
                                 SourceLocation FilenameLoc, StringRef Filename,
                                 const FileEntry *File);
  
    /// Determine whether the given header is part of a module
    /// marked 'unavailable'.
    bool isHeaderInUnavailableModule(const FileEntry *Header) const;
  
    /// Determine whether the given header is unavailable as part
    /// of the specified module.
    bool isHeaderUnavailableInModule(const FileEntry *Header,
                                     const Module *RequestingModule) const;
  
    /// Retrieve a module with the given name.
    ///
    /// \param Name The name of the module to look up.
    ///
    /// \returns The named module, if known; otherwise, returns null.
    Module *findModule(StringRef Name) const;
  
    /// Retrieve a module with the given name using lexical name lookup,
    /// starting at the given context.
    ///
    /// \param Name The name of the module to look up.
    ///
    /// \param Context The module context, from which we will perform lexical
    /// name lookup.
    ///
    /// \returns The named module, if known; otherwise, returns null.
    Module *lookupModuleUnqualified(StringRef Name, Module *Context) const;
  
    /// Retrieve a module with the given name within the given context,
    /// using direct (qualified) name lookup.
    ///
    /// \param Name The name of the module to look up.
    ///
    /// \param Context The module for which we will look for a submodule. If
    /// null, we will look for a top-level module.
    ///
    /// \returns The named submodule, if known; otherwose, returns null.
    Module *lookupModuleQualified(StringRef Name, Module *Context) const;
  
    /// Find a new module or submodule, or create it if it does not already
    /// exist.
    ///
    /// \param Name The name of the module to find or create.
    ///
    /// \param Parent The module that will act as the parent of this submodule,
    /// or nullptr to indicate that this is a top-level module.
    ///
    /// \param IsFramework Whether this is a framework module.
    ///
    /// \param IsExplicit Whether this is an explicit submodule.
    ///
    /// \returns The found or newly-created module, along with a boolean value
    /// that will be true if the module is newly-created.
    std::pair<Module *, bool> findOrCreateModule(StringRef Name, Module *Parent,
                                                 bool IsFramework,
                                                 bool IsExplicit);
  
    /// Create a global module fragment for a C++ module unit.
    ///
    /// We model the global module fragment as a submodule of the module
    /// interface unit. Unfortunately, we can't create the module interface
    /// unit's Module until later, because we don't know what it will be called.
    Module *createGlobalModuleFragmentForModuleUnit(SourceLocation Loc);
  
    /// Create a global module fragment for a C++ module interface unit.
    Module *createPrivateModuleFragmentForInterfaceUnit(Module *Parent,
                                                        SourceLocation Loc);
  
    /// Create a new module for a C++ module interface unit.
    /// The module must not already exist, and will be configured for the current
    /// compilation.
    ///
    /// Note that this also sets the current module to the newly-created module.
    ///
    /// \returns The newly-created module.
    Module *createModuleForInterfaceUnit(SourceLocation Loc, StringRef Name,
                                         Module *GlobalModule);
  
    /// Create a header module from the specified list of headers.
    Module *createHeaderModule(StringRef Name, ArrayRef<Module::Header> Headers);
  
    /// Infer the contents of a framework module map from the given
    /// framework directory.
    Module *inferFrameworkModule(const DirectoryEntry *FrameworkDir,
                                 bool IsSystem, Module *Parent);
  
    /// Create a new top-level module that is shadowed by
    /// \p ShadowingModule.
    Module *createShadowedModule(StringRef Name, bool IsFramework,
                                 Module *ShadowingModule);
  
    /// Creates a new declaration scope for module names, allowing
    /// previously defined modules to shadow definitions from the new scope.
    ///
    /// \note Module names from earlier scopes will shadow names from the new
    /// scope, which is the opposite of how shadowing works for variables.
    void finishModuleDeclarationScope() { CurrentModuleScopeID += 1; }
  
    bool mayShadowNewModule(Module *ExistingModule) {
      assert(!ExistingModule->Parent && "expected top-level module");
      assert(ModuleScopeIDs.count(ExistingModule) && "unknown module");
      return ModuleScopeIDs[ExistingModule] < CurrentModuleScopeID;
    }
  
    /// Retrieve the module map file containing the definition of the given
    /// module.
    ///
    /// \param Module The module whose module map file will be returned, if known.
    ///
    /// \returns The file entry for the module map file containing the given
    /// module, or nullptr if the module definition was inferred.
    const FileEntry *getContainingModuleMapFile(const Module *Module) const;
  
    /// Get the module map file that (along with the module name) uniquely
    /// identifies this module.
    ///
    /// The particular module that \c Name refers to may depend on how the module
    /// was found in header search. However, the combination of \c Name and
    /// this module map will be globally unique for top-level modules. In the case
    /// of inferred modules, returns the module map that allowed the inference
    /// (e.g. contained 'module *'). Otherwise, returns
    /// getContainingModuleMapFile().
    const FileEntry *getModuleMapFileForUniquing(const Module *M) const;
  
    void setInferredModuleAllowedBy(Module *M, const FileEntry *ModMap);
  
    /// Get any module map files other than getModuleMapFileForUniquing(M)
    /// that define submodules of a top-level module \p M. This is cheaper than
    /// getting the module map file for each submodule individually, since the
    /// expected number of results is very small.
    AdditionalModMapsSet *getAdditionalModuleMapFiles(const Module *M) {
      auto I = AdditionalModMaps.find(M);
      if (I == AdditionalModMaps.end())
        return nullptr;
      return &I->second;
    }
  
    void addAdditionalModuleMapFile(const Module *M, const FileEntry *ModuleMap);
  
    /// Resolve all of the unresolved exports in the given module.
    ///
    /// \param Mod The module whose exports should be resolved.
    ///
    /// \param Complain Whether to emit diagnostics for failures.
    ///
    /// \returns true if any errors were encountered while resolving exports,
    /// false otherwise.
    bool resolveExports(Module *Mod, bool Complain);
  
    /// Resolve all of the unresolved uses in the given module.
    ///
    /// \param Mod The module whose uses should be resolved.
    ///
    /// \param Complain Whether to emit diagnostics for failures.
    ///
    /// \returns true if any errors were encountered while resolving uses,
    /// false otherwise.
    bool resolveUses(Module *Mod, bool Complain);
  
    /// Resolve all of the unresolved conflicts in the given module.
    ///
    /// \param Mod The module whose conflicts should be resolved.
    ///
    /// \param Complain Whether to emit diagnostics for failures.
    ///
    /// \returns true if any errors were encountered while resolving conflicts,
    /// false otherwise.
    bool resolveConflicts(Module *Mod, bool Complain);
  
    /// Sets the umbrella header of the given module to the given
    /// header.
    void setUmbrellaHeader(Module *Mod, const FileEntry *UmbrellaHeader,
                           Twine NameAsWritten,
                           Twine PathRelativeToRootModuleDirectory);
  
    /// Sets the umbrella directory of the given module to the given
    /// directory.
    void setUmbrellaDir(Module *Mod, const DirectoryEntry *UmbrellaDir,
                        Twine NameAsWritten,
                        Twine PathRelativeToRootModuleDirectory);
  
    /// Adds this header to the given module.
    /// \param Role The role of the header wrt the module.
    void addHeader(Module *Mod, Module::Header Header,
                   ModuleHeaderRole Role, bool Imported = false);
  
    /// Marks this header as being excluded from the given module.
    void excludeHeader(Module *Mod, Module::Header Header);
  
    /// Parse the given module map file, and record any modules we
    /// encounter.
    ///
    /// \param File The file to be parsed.
    ///
    /// \param IsSystem Whether this module map file is in a system header
    /// directory, and therefore should be considered a system module.
    ///
    /// \param HomeDir The directory in which relative paths within this module
    ///        map file will be resolved.
    ///
    /// \param ID The FileID of the file to process, if we've already entered it.
    ///
    /// \param Offset [inout] On input the offset at which to start parsing. On
    ///        output, the offset at which the module map terminated.
    ///
    /// \param ExternModuleLoc The location of the "extern module" declaration
    ///        that caused us to load this module map file, if any.
    ///
    /// \returns true if an error occurred, false otherwise.
    bool parseModuleMapFile(const FileEntry *File, bool IsSystem,
                            const DirectoryEntry *HomeDir,
                            FileID ID = FileID(), unsigned *Offset = nullptr,
                            SourceLocation ExternModuleLoc = SourceLocation());
  
    /// Dump the contents of the module map, for debugging purposes.
    void dump();
  
    using module_iterator = llvm::StringMap<Module *>::const_iterator;
  
    module_iterator module_begin() const { return Modules.begin(); }
    module_iterator module_end()   const { return Modules.end(); }
  
    /// Cache a module load.  M might be nullptr.
    void cacheModuleLoad(const IdentifierInfo &II, Module *M) {
      CachedModuleLoads[&II] = M;
    }
  
    /// Return a cached module load.
    llvm::Optional<Module *> getCachedModuleLoad(const IdentifierInfo &II) {
      auto I = CachedModuleLoads.find(&II);
      if (I == CachedModuleLoads.end())
        return None;
      return I->second;
    }
  };
  
  } // namespace clang
  
  #endif // LLVM_CLANG_LEX_MODULEMAP_H
  