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 //===- HeaderSearch.h - Resolve Header File Locations -----------*- 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 HeaderSearch interface.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_LEX_HEADERSEARCH_H
 #define LLVM_CLANG_LEX_HEADERSEARCH_H
 
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Lex/DirectoryLookup.h"
 #include "clang/Lex/ExternalPreprocessorSource.h"
 #include "clang/Lex/HeaderMap.h"
 #include "clang/Lex/ModuleMap.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/Support/Allocator.h"
 #include <cassert>
 #include <cstddef>
 #include <memory>
 #include <string>
 #include <utility>
 #include <vector>
 
 namespace llvm {
 
 class Triple;
 
 } // namespace llvm
 
 namespace clang {
 
 class DiagnosticsEngine;
 class DirectoryEntry;
 class ExternalPreprocessorSource;
 class FileEntry;
 class FileManager;
 class HeaderSearch;
 class HeaderSearchOptions;
 class IdentifierInfo;
 class LangOptions;
 class Module;
 class Preprocessor;
 class TargetInfo;
 
 /// The preprocessor keeps track of this information for each
 /// file that is \#included.
 struct HeaderFileInfo {
   // TODO: Whether the file was included is not a property of the file itself.
   // It's a preprocessor state, move it there.
   /// True if this file has been included (or imported) **locally**.
   LLVM_PREFERRED_TYPE(bool)
   unsigned IsLocallyIncluded : 1;
 
   // TODO: Whether the file was imported is not a property of the file itself.
   // It's a preprocessor state, move it there.
   /// True if this is a \#import'd file.
   LLVM_PREFERRED_TYPE(bool)
   unsigned isImport : 1;
 
   /// True if this is a \#pragma once file.
   LLVM_PREFERRED_TYPE(bool)
   unsigned isPragmaOnce : 1;
 
   /// Keep track of whether this is a system header, and if so,
   /// whether it is C++ clean or not.  This can be set by the include paths or
   /// by \#pragma gcc system_header.  This is an instance of
   /// SrcMgr::CharacteristicKind.
   LLVM_PREFERRED_TYPE(SrcMgr::CharacteristicKind)
   unsigned DirInfo : 3;
 
   /// Whether this header file info was supplied by an external source,
   /// and has not changed since.
   LLVM_PREFERRED_TYPE(bool)
   unsigned External : 1;
 
   /// Whether this header is part of and built with a module.  i.e. it is listed
   /// in a module map, and is not `excluded` or `textual`. (same meaning as
   /// `ModuleMap::isModular()`).
   LLVM_PREFERRED_TYPE(bool)
   unsigned isModuleHeader : 1;
 
   /// Whether this header is a `textual header` in a module. If a header is
   /// textual in one module and normal in another module, this bit will not be
   /// set, only `isModuleHeader`.
   LLVM_PREFERRED_TYPE(bool)
   unsigned isTextualModuleHeader : 1;
 
   /// Whether this header is part of the module that we are building, even if it
   /// doesn't build with the module. i.e. this will include `excluded` and
   /// `textual` headers as well as normal headers.
   LLVM_PREFERRED_TYPE(bool)
   unsigned isCompilingModuleHeader : 1;
 
   /// Whether this structure is considered to already have been
   /// "resolved", meaning that it was loaded from the external source.
   LLVM_PREFERRED_TYPE(bool)
   unsigned Resolved : 1;
 
   /// Whether this file has been looked up as a header.
   LLVM_PREFERRED_TYPE(bool)
   unsigned IsValid : 1;
 
   /// If this file has a \#ifndef XXX (or equivalent) guard that
   /// protects the entire contents of the file, this is the identifier
   /// for the macro that controls whether or not it has any effect.
   ///
   /// Note: Most clients should use getControllingMacro() to access
   /// the controlling macro of this header, since
   /// getControllingMacro() is able to load a controlling macro from
   /// external storage.
   LazyIdentifierInfoPtr LazyControllingMacro;
 
   HeaderFileInfo()
       : IsLocallyIncluded(false), isImport(false), isPragmaOnce(false),
         DirInfo(SrcMgr::C_User), External(false), isModuleHeader(false),
         isTextualModuleHeader(false), isCompilingModuleHeader(false),
         Resolved(false), IsValid(false) {}
 
   /// Retrieve the controlling macro for this header file, if
   /// any.
   const IdentifierInfo *
   getControllingMacro(ExternalPreprocessorSource *External);
 
   /// Update the module membership bits based on the header role.
   ///
   /// isModuleHeader will potentially be set, but not cleared.
   /// isTextualModuleHeader will be set or cleared based on the role update.
   void mergeModuleMembership(ModuleMap::ModuleHeaderRole Role);
 };
 
 static_assert(sizeof(HeaderFileInfo) <= 16);
 
 /// An external source of header file information, which may supply
 /// information about header files already included.
 class ExternalHeaderFileInfoSource {
 public:
   virtual ~ExternalHeaderFileInfoSource();
 
   /// Retrieve the header file information for the given file entry.
   ///
   /// \returns Header file information for the given file entry, with the
   /// \c External bit set. If the file entry is not known, return a
   /// default-constructed \c HeaderFileInfo.
   virtual HeaderFileInfo GetHeaderFileInfo(FileEntryRef FE) = 0;
 };
 
 /// This structure is used to record entries in our framework cache.
 struct FrameworkCacheEntry {
   /// The directory entry which should be used for the cached framework.
   OptionalDirectoryEntryRef Directory;
 
   /// Whether this framework has been "user-specified" to be treated as if it
   /// were a system framework (even if it was found outside a system framework
   /// directory).
   bool IsUserSpecifiedSystemFramework;
 };
 
 namespace detail {
 template <bool Const, typename T>
 using Qualified = std::conditional_t<Const, const T, T>;
 
 /// Forward iterator over the search directories of \c HeaderSearch.
 template <bool IsConst>
 struct SearchDirIteratorImpl
     : llvm::iterator_facade_base<SearchDirIteratorImpl<IsConst>,
                                  std::forward_iterator_tag,
                                  Qualified<IsConst, DirectoryLookup>> {
   /// Const -> non-const iterator conversion.
   template <typename Enable = std::enable_if<IsConst, bool>>
   SearchDirIteratorImpl(const SearchDirIteratorImpl<false> &Other)
       : HS(Other.HS), Idx(Other.Idx) {}
 
   SearchDirIteratorImpl(const SearchDirIteratorImpl &) = default;
 
   SearchDirIteratorImpl &operator=(const SearchDirIteratorImpl &) = default;
 
   bool operator==(const SearchDirIteratorImpl &RHS) const {
     return HS == RHS.HS && Idx == RHS.Idx;
   }
 
   SearchDirIteratorImpl &operator++() {
     assert(*this && "Invalid iterator.");
     ++Idx;
     return *this;
   }
 
   Qualified<IsConst, DirectoryLookup> &operator*() const {
     assert(*this && "Invalid iterator.");
     return HS->SearchDirs[Idx];
   }
 
   /// Creates an invalid iterator.
   SearchDirIteratorImpl(std::nullptr_t) : HS(nullptr), Idx(0) {}
 
   /// Checks whether the iterator is valid.
   explicit operator bool() const { return HS != nullptr; }
 
 private:
   /// The parent \c HeaderSearch. This is \c nullptr for invalid iterator.
   Qualified<IsConst, HeaderSearch> *HS;
 
   /// The index of the current element.
   size_t Idx;
 
   /// The constructor that creates a valid iterator.
   SearchDirIteratorImpl(Qualified<IsConst, HeaderSearch> &HS, size_t Idx)
       : HS(&HS), Idx(Idx) {}
 
   /// Only HeaderSearch is allowed to instantiate valid iterators.
   friend HeaderSearch;
 
   /// Enables const -> non-const conversion.
   friend SearchDirIteratorImpl<!IsConst>;
 };
 } // namespace detail
 
 using ConstSearchDirIterator = detail::SearchDirIteratorImpl<true>;
 using SearchDirIterator = detail::SearchDirIteratorImpl<false>;
 
 using ConstSearchDirRange = llvm::iterator_range<ConstSearchDirIterator>;
 using SearchDirRange = llvm::iterator_range<SearchDirIterator>;
 
 /// Encapsulates the information needed to find the file referenced
 /// by a \#include or \#include_next, (sub-)framework lookup, etc.
 class HeaderSearch {
   friend class DirectoryLookup;
 
   friend ConstSearchDirIterator;
   friend SearchDirIterator;
 
   /// Header-search options used to initialize this header search.
   std::shared_ptr<HeaderSearchOptions> HSOpts;
 
   /// Mapping from SearchDir to HeaderSearchOptions::UserEntries indices.
   llvm::DenseMap<unsigned, unsigned> SearchDirToHSEntry;
 
   DiagnosticsEngine &Diags;
   FileManager &FileMgr;
 
   /// \#include search path information.  Requests for \#include "x" search the
   /// directory of the \#including file first, then each directory in SearchDirs
   /// consecutively. Requests for <x> search the current dir first, then each
   /// directory in SearchDirs, starting at AngledDirIdx, consecutively.
   std::vector<DirectoryLookup> SearchDirs;
   /// Whether the DirectoryLookup at the corresponding index in SearchDirs has
   /// been successfully used to lookup a file.
   std::vector<bool> SearchDirsUsage;
   unsigned AngledDirIdx = 0;
   unsigned SystemDirIdx = 0;
 
   /// Maps HeaderMap keys to SearchDir indices. When HeaderMaps are used
   /// heavily, SearchDirs can start with thousands of HeaderMaps, so this Index
   /// lets us avoid scanning them all to find a match.
   llvm::StringMap<unsigned, llvm::BumpPtrAllocator> SearchDirHeaderMapIndex;
 
   /// The index of the first SearchDir that isn't a header map.
   unsigned FirstNonHeaderMapSearchDirIdx = 0;
 
   /// \#include prefixes for which the 'system header' property is
   /// overridden.
   ///
   /// For a \#include "x" or \#include \<x> directive, the last string in this
   /// list which is a prefix of 'x' determines whether the file is treated as
   /// a system header.
   std::vector<std::pair<std::string, bool>> SystemHeaderPrefixes;
 
   /// The hash used for module cache paths.
   std::string ModuleHash;
 
   /// The path to the module cache.
   std::string ModuleCachePath;
 
   /// All of the preprocessor-specific data about files that are
   /// included, indexed by the FileEntry's UID.
   mutable std::vector<HeaderFileInfo> FileInfo;
 
   /// Keeps track of each lookup performed by LookupFile.
   struct LookupFileCacheInfo {
     // The requesting module for the lookup we cached.
     const Module *RequestingModule = nullptr;
 
     /// Starting search directory iterator that the cached search was performed
     /// from. If there is a hit and this value doesn't match the current query,
     /// the cache has to be ignored.
     ConstSearchDirIterator StartIt = nullptr;
 
     /// The search directory iterator that satisfied the query.
     ConstSearchDirIterator HitIt = nullptr;
 
     /// This is non-null if the original filename was mapped to a framework
     /// include via a headermap.
     const char *MappedName = nullptr;
 
     /// Default constructor -- Initialize all members with zero.
     LookupFileCacheInfo() = default;
 
     void reset(const Module *NewRequestingModule,
                ConstSearchDirIterator NewStartIt) {
       RequestingModule = NewRequestingModule;
       StartIt = NewStartIt;
       MappedName = nullptr;
     }
   };
   llvm::StringMap<LookupFileCacheInfo, llvm::BumpPtrAllocator> LookupFileCache;
 
   /// Collection mapping a framework or subframework
   /// name like "Carbon" to the Carbon.framework directory.
   llvm::StringMap<FrameworkCacheEntry, llvm::BumpPtrAllocator> FrameworkMap;
 
   /// Maps include file names (including the quotes or
   /// angle brackets) to other include file names.  This is used to support the
   /// include_alias pragma for Microsoft compatibility.
   using IncludeAliasMap =
       llvm::StringMap<std::string, llvm::BumpPtrAllocator>;
   std::unique_ptr<IncludeAliasMap> IncludeAliases;
 
   /// This is a mapping from FileEntry -> HeaderMap, uniquing headermaps.
   std::vector<std::pair<FileEntryRef, std::unique_ptr<HeaderMap>>> HeaderMaps;
 
   /// The mapping between modules and headers.
   mutable ModuleMap ModMap;
 
   /// Describes whether a given directory has a module map in it.
   llvm::DenseMap<const DirectoryEntry *, bool> DirectoryHasModuleMap;
 
   /// Set of module map files we've already loaded, and a flag indicating
   /// whether they were valid or not.
   llvm::DenseMap<const FileEntry *, bool> LoadedModuleMaps;
 
   // A map of discovered headers with their associated include file name.
   llvm::DenseMap<const FileEntry *, llvm::SmallString<64>> IncludeNames;
 
   /// Uniqued set of framework names, which is used to track which
   /// headers were included as framework headers.
   llvm::StringSet<llvm::BumpPtrAllocator> FrameworkNames;
 
   /// Entity used to resolve the identifier IDs of controlling
   /// macros into IdentifierInfo pointers, and keep the identifire up to date,
   /// as needed.
   ExternalPreprocessorSource *ExternalLookup = nullptr;
 
   /// Entity used to look up stored header file information.
   ExternalHeaderFileInfoSource *ExternalSource = nullptr;
 
   /// Scan all of the header maps at the beginning of SearchDirs and
   /// map their keys to the SearchDir index of their header map.
   void indexInitialHeaderMaps();
 
 public:
   HeaderSearch(std::shared_ptr<HeaderSearchOptions> HSOpts,
                SourceManager &SourceMgr, DiagnosticsEngine &Diags,
                const LangOptions &LangOpts, const TargetInfo *Target);
   HeaderSearch(const HeaderSearch &) = delete;
   HeaderSearch &operator=(const HeaderSearch &) = delete;
 
   /// Retrieve the header-search options with which this header search
   /// was initialized.
   HeaderSearchOptions &getHeaderSearchOpts() const { return *HSOpts; }
 
   FileManager &getFileMgr() const { return FileMgr; }
 
   DiagnosticsEngine &getDiags() const { return Diags; }
 
   /// Interface for setting the file search paths.
   void SetSearchPaths(std::vector<DirectoryLookup> dirs, unsigned angledDirIdx,
                       unsigned systemDirIdx,
                       llvm::DenseMap<unsigned, unsigned> searchDirToHSEntry);
 
   /// Add an additional search path.
   void AddSearchPath(const DirectoryLookup &dir, bool isAngled);
 
   /// Add an additional system search path.
   void AddSystemSearchPath(const DirectoryLookup &dir) {
     SearchDirs.push_back(dir);
     SearchDirsUsage.push_back(false);
   }
 
   /// Set the list of system header prefixes.
   void SetSystemHeaderPrefixes(ArrayRef<std::pair<std::string, bool>> P) {
     SystemHeaderPrefixes.assign(P.begin(), P.end());
   }
 
   /// Checks whether the map exists or not.
   bool HasIncludeAliasMap() const { return (bool)IncludeAliases; }
 
   /// Map the source include name to the dest include name.
   ///
   /// The Source should include the angle brackets or quotes, the dest
   /// should not.  This allows for distinction between <> and "" headers.
   void AddIncludeAlias(StringRef Source, StringRef Dest) {
     if (!IncludeAliases)
       IncludeAliases.reset(new IncludeAliasMap);
     (*IncludeAliases)[Source] = std::string(Dest);
   }
 
   /// Maps one header file name to a different header
   /// file name, for use with the include_alias pragma.  Note that the source
   /// file name should include the angle brackets or quotes.  Returns StringRef
   /// as null if the header cannot be mapped.
   StringRef MapHeaderToIncludeAlias(StringRef Source) {
     assert(IncludeAliases && "Trying to map headers when there's no map");
 
     // Do any filename replacements before anything else
     IncludeAliasMap::const_iterator Iter = IncludeAliases->find(Source);
     if (Iter != IncludeAliases->end())
       return Iter->second;
     return {};
   }
 
   /// Set the hash to use for module cache paths.
   void setModuleHash(StringRef Hash) { ModuleHash = std::string(Hash); }
 
   /// Set the path to the module cache.
   void setModuleCachePath(StringRef CachePath) {
     ModuleCachePath = std::string(CachePath);
   }
 
   /// Retrieve the module hash.
   StringRef getModuleHash() const { return ModuleHash; }
 
   /// Retrieve the path to the module cache.
   StringRef getModuleCachePath() const { return ModuleCachePath; }
 
   /// Consider modules when including files from this directory.
   void setDirectoryHasModuleMap(const DirectoryEntry* Dir) {
     DirectoryHasModuleMap[Dir] = true;
   }
 
   /// Forget everything we know about headers so far.
   void ClearFileInfo() {
     FileInfo.clear();
   }
 
   void SetExternalLookup(ExternalPreprocessorSource *EPS) {
     ExternalLookup = EPS;
   }
 
   ExternalPreprocessorSource *getExternalLookup() const {
     return ExternalLookup;
   }
 
   /// Set the external source of header information.
   void SetExternalSource(ExternalHeaderFileInfoSource *ES) {
     ExternalSource = ES;
   }
 
   /// Set the target information for the header search, if not
   /// already known.
   void setTarget(const TargetInfo &Target);
 
   /// Given a "foo" or \<foo> reference, look up the indicated file,
   /// return null on failure.
   ///
   /// \returns If successful, this returns 'UsedDir', the DirectoryLookup member
   /// the file was found in, or null if not applicable.
   ///
   /// \param IncludeLoc Used for diagnostics if valid.
   ///
   /// \param isAngled indicates whether the file reference is a <> reference.
   ///
   /// \param CurDir If non-null, the file was found in the specified directory
   /// search location.  This is used to implement \#include_next.
   ///
   /// \param Includers Indicates where the \#including file(s) are, in case
   /// relative searches are needed. In reverse order of inclusion.
   ///
   /// \param SearchPath If non-null, will be set to the search path relative
   /// to which the file was found. If the include path is absolute, SearchPath
   /// will be set to an empty string.
   ///
   /// \param RelativePath If non-null, will be set to the path relative to
   /// SearchPath at which the file was found. This only differs from the
   /// Filename for framework includes.
   ///
   /// \param SuggestedModule If non-null, and the file found is semantically
   /// part of a known module, this will be set to the module that should
   /// be imported instead of preprocessing/parsing the file found.
   ///
   /// \param IsMapped If non-null, and the search involved header maps, set to
   /// true.
   ///
   /// \param IsFrameworkFound If non-null, will be set to true if a framework is
   /// found in any of searched SearchDirs. Will be set to false if a framework
   /// is found only through header maps. Doesn't guarantee the requested file is
   /// found.
   OptionalFileEntryRef LookupFile(
       StringRef Filename, SourceLocation IncludeLoc, bool isAngled,
       ConstSearchDirIterator FromDir, ConstSearchDirIterator *CurDir,
       ArrayRef<std::pair<OptionalFileEntryRef, DirectoryEntryRef>> Includers,
       SmallVectorImpl<char> *SearchPath, SmallVectorImpl<char> *RelativePath,
       Module *RequestingModule, ModuleMap::KnownHeader *SuggestedModule,
       bool *IsMapped, bool *IsFrameworkFound, bool SkipCache = false,
       bool BuildSystemModule = false, bool OpenFile = true,
       bool CacheFailures = true);
 
   /// Look up a subframework for the specified \#include file.
   ///
   /// For example, if \#include'ing <HIToolbox/HIToolbox.h> from
   /// within ".../Carbon.framework/Headers/Carbon.h", check to see if
   /// HIToolbox is a subframework within Carbon.framework.  If so, return
   /// the FileEntry for the designated file, otherwise return null.
   OptionalFileEntryRef LookupSubframeworkHeader(
       StringRef Filename, FileEntryRef ContextFileEnt,
       SmallVectorImpl<char> *SearchPath, SmallVectorImpl<char> *RelativePath,
       Module *RequestingModule, ModuleMap::KnownHeader *SuggestedModule);
 
   /// Look up the specified framework name in our framework cache.
   /// \returns The DirectoryEntry it is in if we know, null otherwise.
   FrameworkCacheEntry &LookupFrameworkCache(StringRef FWName) {
     return FrameworkMap[FWName];
   }
 
   /// Mark the specified file as a target of a \#include,
   /// \#include_next, or \#import directive.
   ///
   /// \return false if \#including the file will have no effect or true
   /// if we should include it.
   ///
   /// \param M The module to which `File` belongs (this should usually be the
   /// SuggestedModule returned by LookupFile/LookupSubframeworkHeader)
   bool ShouldEnterIncludeFile(Preprocessor &PP, FileEntryRef File,
                               bool isImport, bool ModulesEnabled, Module *M,
                               bool &IsFirstIncludeOfFile);
 
   /// Return whether the specified file is a normal header,
   /// a system header, or a C++ friendly system header.
   SrcMgr::CharacteristicKind getFileDirFlavor(FileEntryRef File) {
     if (const HeaderFileInfo *HFI = getExistingFileInfo(File))
       return (SrcMgr::CharacteristicKind)HFI->DirInfo;
     return (SrcMgr::CharacteristicKind)HeaderFileInfo().DirInfo;
   }
 
   /// Mark the specified file as a "once only" file due to
   /// \#pragma once.
   void MarkFileIncludeOnce(FileEntryRef File) {
     getFileInfo(File).isPragmaOnce = true;
   }
 
   /// Mark the specified file as a system header, e.g. due to
   /// \#pragma GCC system_header.
   void MarkFileSystemHeader(FileEntryRef File) {
     getFileInfo(File).DirInfo = SrcMgr::C_System;
   }
 
   /// Mark the specified file as part of a module.
   void MarkFileModuleHeader(FileEntryRef FE, ModuleMap::ModuleHeaderRole Role,
                             bool isCompilingModuleHeader);
 
   /// Mark the specified file as having a controlling macro.
   ///
   /// This is used by the multiple-include optimization to eliminate
   /// no-op \#includes.
   void SetFileControllingMacro(FileEntryRef File,
                                const IdentifierInfo *ControllingMacro) {
     getFileInfo(File).LazyControllingMacro = ControllingMacro;
   }
 
   /// Determine whether this file is intended to be safe from
   /// multiple inclusions, e.g., it has \#pragma once or a controlling
   /// macro.
   ///
   /// This routine does not consider the effect of \#import
   bool isFileMultipleIncludeGuarded(FileEntryRef File) const;
 
   /// Determine whether the given file is known to have ever been \#imported.
   bool hasFileBeenImported(FileEntryRef File) const {
     const HeaderFileInfo *FI = getExistingFileInfo(File);
     return FI && FI->isImport;
   }
 
   /// Determine which HeaderSearchOptions::UserEntries have been successfully
   /// used so far and mark their index with 'true' in the resulting bit vector.
   /// Note: implicit module maps don't contribute to entry usage.
   std::vector<bool> computeUserEntryUsage() const;
 
   /// Collect which HeaderSearchOptions::VFSOverlayFiles have been meaningfully
   /// used so far and mark their index with 'true' in the resulting bit vector.
   ///
   /// Note: this ignores VFSs that redirect non-affecting files such as unused
   /// modulemaps.
   std::vector<bool> collectVFSUsageAndClear() const;
 
   /// This method returns a HeaderMap for the specified
   /// FileEntry, uniquing them through the 'HeaderMaps' datastructure.
   const HeaderMap *CreateHeaderMap(FileEntryRef FE);
 
   /// Get filenames for all registered header maps.
   void getHeaderMapFileNames(SmallVectorImpl<std::string> &Names) const;
 
   /// Retrieve the name of the cached module file that should be used
   /// to load the given module.
   ///
   /// \param Module The module whose module file name will be returned.
   ///
   /// \returns The name of the module file that corresponds to this module,
   /// or an empty string if this module does not correspond to any module file.
   std::string getCachedModuleFileName(Module *Module);
 
   /// Retrieve the name of the prebuilt module file that should be used
   /// to load a module with the given name.
   ///
   /// \param ModuleName The module whose module file name will be returned.
   ///
   /// \param FileMapOnly If true, then only look in the explicit module name
   //  to file name map and skip the directory search.
   ///
   /// \returns The name of the module file that corresponds to this module,
   /// or an empty string if this module does not correspond to any module file.
   std::string getPrebuiltModuleFileName(StringRef ModuleName,
                                         bool FileMapOnly = false);
 
   /// Retrieve the name of the prebuilt module file that should be used
   /// to load the given module.
   ///
   /// \param Module The module whose module file name will be returned.
   ///
   /// \returns The name of the module file that corresponds to this module,
   /// or an empty string if this module does not correspond to any module file.
   std::string getPrebuiltImplicitModuleFileName(Module *Module);
 
   /// Retrieve the name of the (to-be-)cached module file that should
   /// be used to load a module with the given name.
   ///
   /// \param ModuleName The module whose module file name will be returned.
   ///
   /// \param ModuleMapPath A path that when combined with \c ModuleName
   /// uniquely identifies this module. See Module::ModuleMap.
   ///
   /// \returns The name of the module file that corresponds to this module,
   /// or an empty string if this module does not correspond to any module file.
   std::string getCachedModuleFileName(StringRef ModuleName,
                                       StringRef ModuleMapPath);
 
   /// Lookup a module Search for a module with the given name.
   ///
   /// \param ModuleName The name of the module we're looking for.
   ///
   /// \param ImportLoc Location of the module include/import.
   ///
   /// \param AllowSearch Whether we are allowed to search in the various
   /// search directories to produce a module definition. If not, this lookup
   /// will only return an already-known module.
   ///
   /// \param AllowExtraModuleMapSearch Whether we allow to search modulemaps
   /// in subdirectories.
   ///
   /// \returns The module with the given name.
   Module *lookupModule(StringRef ModuleName,
                        SourceLocation ImportLoc = SourceLocation(),
                        bool AllowSearch = true,
                        bool AllowExtraModuleMapSearch = false);
 
   /// Try to find a module map file in the given directory, returning
   /// \c nullopt if none is found.
   OptionalFileEntryRef lookupModuleMapFile(DirectoryEntryRef Dir,
                                            bool IsFramework);
 
   /// Determine whether there is a module map that may map the header
   /// with the given file name to a (sub)module.
   /// Always returns false if modules are disabled.
   ///
   /// \param Filename The name of the file.
   ///
   /// \param Root The "root" directory, at which we should stop looking for
   /// module maps.
   ///
   /// \param IsSystem Whether the directories we're looking at are system
   /// header directories.
   bool hasModuleMap(StringRef Filename, const DirectoryEntry *Root,
                     bool IsSystem);
 
   /// Retrieve the module that corresponds to the given file, if any.
   ///
   /// \param File The header that we wish to map to a module.
   /// \param AllowTextual Whether we want to find textual headers too.
   ModuleMap::KnownHeader findModuleForHeader(FileEntryRef File,
                                              bool AllowTextual = false,
                                              bool AllowExcluded = false) const;
 
   /// Retrieve all the modules corresponding to the given file.
   ///
   /// \ref findModuleForHeader should typically be used instead of this.
   ArrayRef<ModuleMap::KnownHeader>
   findAllModulesForHeader(FileEntryRef File) const;
 
   /// Like \ref findAllModulesForHeader, but do not attempt to infer module
   /// ownership from umbrella headers if we've not already done so.
   ArrayRef<ModuleMap::KnownHeader>
   findResolvedModulesForHeader(FileEntryRef File) const;
 
   /// Read the contents of the given module map file.
   ///
   /// \param File The module map file.
   /// \param IsSystem Whether this file is in a system header directory.
   /// \param ID If the module map file is already mapped (perhaps as part of
   ///        processing a preprocessed module), the ID of the file.
   /// \param Offset [inout] An offset within ID to start parsing. On exit,
   ///        filled by the end of the parsed contents (either EOF or the
   ///        location of an end-of-module-map pragma).
   /// \param OriginalModuleMapFile The original path to the module map file,
   ///        used to resolve paths within the module (this is required when
   ///        building the module from preprocessed source).
   /// \returns true if an error occurred, false otherwise.
   bool loadModuleMapFile(FileEntryRef File, bool IsSystem, FileID ID = FileID(),
                          unsigned *Offset = nullptr,
                          StringRef OriginalModuleMapFile = StringRef());
 
   /// Collect the set of all known, top-level modules.
   ///
   /// \param Modules Will be filled with the set of known, top-level modules.
   void collectAllModules(SmallVectorImpl<Module *> &Modules);
 
   /// Load all known, top-level system modules.
   void loadTopLevelSystemModules();
 
 private:
   /// Lookup a module with the given module name and search-name.
   ///
   /// \param ModuleName The name of the module we're looking for.
   ///
   /// \param SearchName The "search-name" to derive filesystem paths from
   /// when looking for the module map; this is usually equal to ModuleName,
   /// but for compatibility with some buggy frameworks, additional attempts
   /// may be made to find the module under a related-but-different search-name.
   ///
   /// \param ImportLoc Location of the module include/import.
   ///
   /// \param AllowExtraModuleMapSearch Whether we allow to search modulemaps
   /// in subdirectories.
   ///
   /// \returns The module named ModuleName.
   Module *lookupModule(StringRef ModuleName, StringRef SearchName,
                        SourceLocation ImportLoc,
                        bool AllowExtraModuleMapSearch = false);
 
   /// Retrieve the name of the (to-be-)cached module file that should
   /// be used to load a module with the given name.
   ///
   /// \param ModuleName The module whose module file name will be returned.
   ///
   /// \param ModuleMapPath A path that when combined with \c ModuleName
   /// uniquely identifies this module. See Module::ModuleMap.
   ///
   /// \param CachePath A path to the module cache.
   ///
   /// \returns The name of the module file that corresponds to this module,
   /// or an empty string if this module does not correspond to any module file.
   std::string getCachedModuleFileNameImpl(StringRef ModuleName,
                                           StringRef ModuleMapPath,
                                           StringRef CachePath);
 
   /// Retrieve a module with the given name, which may be part of the
   /// given framework.
   ///
   /// \param Name The name of the module to retrieve.
   ///
   /// \param Dir The framework directory (e.g., ModuleName.framework).
   ///
   /// \param IsSystem Whether the framework directory is part of the system
   /// frameworks.
   ///
   /// \returns The module, if found; otherwise, null.
   Module *loadFrameworkModule(StringRef Name, DirectoryEntryRef Dir,
                               bool IsSystem);
 
   /// Load all of the module maps within the immediate subdirectories
   /// of the given search directory.
   void loadSubdirectoryModuleMaps(DirectoryLookup &SearchDir);
 
   /// Find and suggest a usable module for the given file.
   ///
   /// \return \c true if the file can be used, \c false if we are not permitted to
   ///         find this file due to requirements from \p RequestingModule.
   bool findUsableModuleForHeader(FileEntryRef File, const DirectoryEntry *Root,
                                  Module *RequestingModule,
                                  ModuleMap::KnownHeader *SuggestedModule,
                                  bool IsSystemHeaderDir);
 
   /// Find and suggest a usable module for the given file, which is part of
   /// the specified framework.
   ///
   /// \return \c true if the file can be used, \c false if we are not permitted to
   ///         find this file due to requirements from \p RequestingModule.
   bool findUsableModuleForFrameworkHeader(
       FileEntryRef File, StringRef FrameworkName, Module *RequestingModule,
       ModuleMap::KnownHeader *SuggestedModule, bool IsSystemFramework);
 
   /// Look up the file with the specified name and determine its owning
   /// module.
   OptionalFileEntryRef
   getFileAndSuggestModule(StringRef FileName, SourceLocation IncludeLoc,
                           const DirectoryEntry *Dir, bool IsSystemHeaderDir,
                           Module *RequestingModule,
                           ModuleMap::KnownHeader *SuggestedModule,
                           bool OpenFile = true, bool CacheFailures = true);
 
   /// Cache the result of a successful lookup at the given include location
   /// using the search path at \c HitIt.
   void cacheLookupSuccess(LookupFileCacheInfo &CacheLookup,
                           ConstSearchDirIterator HitIt,
                           SourceLocation IncludeLoc);
 
   /// Note that a lookup at the given include location was successful using the
   /// search path at index `HitIdx`.
   void noteLookupUsage(unsigned HitIdx, SourceLocation IncludeLoc);
 
 public:
   /// Retrieve the module map.
   ModuleMap &getModuleMap() { return ModMap; }
 
   /// Retrieve the module map.
   const ModuleMap &getModuleMap() const { return ModMap; }
 
   unsigned header_file_size() const { return FileInfo.size(); }
 
   /// Return the HeaderFileInfo structure for the specified FileEntry, in
   /// preparation for updating it in some way.
   HeaderFileInfo &getFileInfo(FileEntryRef FE);
 
   /// Return the HeaderFileInfo structure for the specified FileEntry, if it has
   /// ever been filled in (either locally or externally).
   const HeaderFileInfo *getExistingFileInfo(FileEntryRef FE) const;
 
   /// Return the headerFileInfo structure for the specified FileEntry, if it has
   /// ever been filled in locally.
   const HeaderFileInfo *getExistingLocalFileInfo(FileEntryRef FE) const;
 
   SearchDirIterator search_dir_begin() { return {*this, 0}; }
   SearchDirIterator search_dir_end() { return {*this, SearchDirs.size()}; }
   SearchDirRange search_dir_range() {
     return {search_dir_begin(), search_dir_end()};
   }
 
   ConstSearchDirIterator search_dir_begin() const { return quoted_dir_begin(); }
   ConstSearchDirIterator search_dir_nth(size_t n) const {
     assert(n < SearchDirs.size());
     return {*this, n};
   }
   ConstSearchDirIterator search_dir_end() const { return system_dir_end(); }
   ConstSearchDirRange search_dir_range() const {
     return {search_dir_begin(), search_dir_end()};
   }
 
   unsigned search_dir_size() const { return SearchDirs.size(); }
 
   ConstSearchDirIterator quoted_dir_begin() const { return {*this, 0}; }
   ConstSearchDirIterator quoted_dir_end() const { return angled_dir_begin(); }
 
   ConstSearchDirIterator angled_dir_begin() const {
     return {*this, AngledDirIdx};
   }
   ConstSearchDirIterator angled_dir_end() const { return system_dir_begin(); }
 
   ConstSearchDirIterator system_dir_begin() const {
     return {*this, SystemDirIdx};
   }
   ConstSearchDirIterator system_dir_end() const {
     return {*this, SearchDirs.size()};
   }
 
   /// Get the index of the given search directory.
   unsigned searchDirIdx(const DirectoryLookup &DL) const;
 
   /// Retrieve a uniqued framework name.
   StringRef getUniqueFrameworkName(StringRef Framework);
 
   /// Retrieve the include name for the header.
   ///
   /// \param File The entry for a given header.
   /// \returns The name of how the file was included when the header's location
   /// was resolved.
   StringRef getIncludeNameForHeader(const FileEntry *File) const;
 
   /// Suggest a path by which the specified file could be found, for use in
   /// diagnostics to suggest a #include. Returned path will only contain forward
   /// slashes as separators. MainFile is the absolute path of the file that we
   /// are generating the diagnostics for. It will try to shorten the path using
   /// MainFile location, if none of the include search directories were prefix
   /// of File.
   ///
   /// \param IsAngled If non-null, filled in to indicate whether the suggested
   ///        path should be referenced as <Header.h> instead of "Header.h".
   std::string suggestPathToFileForDiagnostics(FileEntryRef File,
                                               llvm::StringRef MainFile,
                                               bool *IsAngled = nullptr) const;
 
   /// Suggest a path by which the specified file could be found, for use in
   /// diagnostics to suggest a #include. Returned path will only contain forward
   /// slashes as separators. MainFile is the absolute path of the file that we
   /// are generating the diagnostics for. It will try to shorten the path using
   /// MainFile location, if none of the include search directories were prefix
   /// of File.
   ///
   /// \param WorkingDir If non-empty, this will be prepended to search directory
   /// paths that are relative.
   std::string suggestPathToFileForDiagnostics(llvm::StringRef File,
                                               llvm::StringRef WorkingDir,
                                               llvm::StringRef MainFile,
                                               bool *IsAngled = nullptr) const;
 
   void PrintStats();
 
   size_t getTotalMemory() const;
 
 private:
   /// Describes what happened when we tried to load a module map file.
   enum LoadModuleMapResult {
     /// The module map file had already been loaded.
     LMM_AlreadyLoaded,
 
     /// The module map file was loaded by this invocation.
     LMM_NewlyLoaded,
 
     /// There is was directory with the given name.
     LMM_NoDirectory,
 
     /// There was either no module map file or the module map file was
     /// invalid.
     LMM_InvalidModuleMap
   };
 
   LoadModuleMapResult loadModuleMapFileImpl(FileEntryRef File, bool IsSystem,
                                             DirectoryEntryRef Dir,
                                             FileID ID = FileID(),
                                             unsigned *Offset = nullptr);
 
   /// Try to load the module map file in the given directory.
   ///
   /// \param DirName The name of the directory where we will look for a module
   /// map file.
   /// \param IsSystem Whether this is a system header directory.
   /// \param IsFramework Whether this is a framework directory.
   ///
   /// \returns The result of attempting to load the module map file from the
   /// named directory.
   LoadModuleMapResult loadModuleMapFile(StringRef DirName, bool IsSystem,
                                         bool IsFramework);
 
   /// Try to load the module map file in the given directory.
   ///
   /// \param Dir The directory where we will look for a module map file.
   /// \param IsSystem Whether this is a system header directory.
   /// \param IsFramework Whether this is a framework directory.
   ///
   /// \returns The result of attempting to load the module map file from the
   /// named directory.
   LoadModuleMapResult loadModuleMapFile(DirectoryEntryRef Dir, bool IsSystem,
                                         bool IsFramework);
 };
 
 /// Apply the header search options to get given HeaderSearch object.
 void ApplyHeaderSearchOptions(HeaderSearch &HS,
                               const HeaderSearchOptions &HSOpts,
                               const LangOptions &Lang,
                               const llvm::Triple &triple);
 
 } // namespace clang
 
 #endif // LLVM_CLANG_LEX_HEADERSEARCH_H

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