--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang/lib/Lex/HeaderSearch.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,1802 @@
+//===- HeaderSearch.cpp - Resolve Header File Locations -------------------===//
+//
+// 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 implements the DirectoryLookup and HeaderSearch interfaces.
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/Lex/HeaderSearch.h"
+#include "clang/Basic/Diagnostic.h"
+#include "clang/Basic/FileManager.h"
+#include "clang/Basic/IdentifierTable.h"
+#include "clang/Basic/Module.h"
+#include "clang/Basic/SourceManager.h"
+#include "clang/Lex/DirectoryLookup.h"
+#include "clang/Lex/ExternalPreprocessorSource.h"
+#include "clang/Lex/HeaderMap.h"
+#include "clang/Lex/HeaderSearchOptions.h"
+#include "clang/Lex/LexDiagnostic.h"
+#include "clang/Lex/ModuleMap.h"
+#include "clang/Lex/Preprocessor.h"
+#include "llvm/ADT/APInt.h"
+#include "llvm/ADT/Hashing.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/Capacity.h"
+#include "llvm/Support/Errc.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/VirtualFileSystem.h"
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <cstdio>
+#include <cstring>
+#include <string>
+#include <system_error>
+#include <utility>
+
+using namespace clang;
+
+#define DEBUG_TYPE "file-search"
+
+ALWAYS_ENABLED_STATISTIC(NumIncluded, "Number of attempted #includes.");
+ALWAYS_ENABLED_STATISTIC(
+    NumMultiIncludeFileOptzn,
+    "Number of #includes skipped due to the multi-include optimization.");
+ALWAYS_ENABLED_STATISTIC(NumFrameworkLookups, "Number of framework lookups.");
+ALWAYS_ENABLED_STATISTIC(NumSubFrameworkLookups,
+                         "Number of subframework lookups.");
+
+const IdentifierInfo *
+HeaderFileInfo::getControllingMacro(ExternalPreprocessorSource *External) {
+  if (ControllingMacro) {
+    if (ControllingMacro->isOutOfDate()) {
+      assert(External && "We must have an external source if we have a "
+                         "controlling macro that is out of date.");
+      External->updateOutOfDateIdentifier(
+          *const_cast<IdentifierInfo *>(ControllingMacro));
+    }
+    return ControllingMacro;
+  }
+
+  if (!ControllingMacroID || !External)
+    return nullptr;
+
+  ControllingMacro = External->GetIdentifier(ControllingMacroID);
+  return ControllingMacro;
+}
+
+ExternalHeaderFileInfoSource::~ExternalHeaderFileInfoSource() = default;
+
+HeaderSearch::HeaderSearch(std::shared_ptr<HeaderSearchOptions> HSOpts,
+                           SourceManager &SourceMgr, DiagnosticsEngine &Diags,
+                           const LangOptions &LangOpts,
+                           const TargetInfo *Target)
+    : HSOpts(std::move(HSOpts)), Diags(Diags),
+      FileMgr(SourceMgr.getFileManager()), FrameworkMap(64),
+      ModMap(SourceMgr, Diags, LangOpts, Target, *this) {}
+
+void HeaderSearch::PrintStats() {
+  llvm::errs() << "\n*** HeaderSearch Stats:\n"
+               << FileInfo.size() << " files tracked.\n";
+  unsigned NumOnceOnlyFiles = 0, MaxNumIncludes = 0, NumSingleIncludedFiles = 0;
+  for (unsigned i = 0, e = FileInfo.size(); i != e; ++i) {
+    NumOnceOnlyFiles += FileInfo[i].isImport;
+    if (MaxNumIncludes < FileInfo[i].NumIncludes)
+      MaxNumIncludes = FileInfo[i].NumIncludes;
+    NumSingleIncludedFiles += FileInfo[i].NumIncludes == 1;
+  }
+  llvm::errs() << "  " << NumOnceOnlyFiles << " #import/#pragma once files.\n"
+               << "  " << NumSingleIncludedFiles << " included exactly once.\n"
+               << "  " << MaxNumIncludes << " max times a file is included.\n";
+
+  llvm::errs() << "  " << NumIncluded << " #include/#include_next/#import.\n"
+               << "    " << NumMultiIncludeFileOptzn
+               << " #includes skipped due to the multi-include optimization.\n";
+
+  llvm::errs() << NumFrameworkLookups << " framework lookups.\n"
+               << NumSubFrameworkLookups << " subframework lookups.\n";
+}
+
+/// CreateHeaderMap - This method returns a HeaderMap for the specified
+/// FileEntry, uniquing them through the 'HeaderMaps' datastructure.
+const HeaderMap *HeaderSearch::CreateHeaderMap(const FileEntry *FE) {
+  // We expect the number of headermaps to be small, and almost always empty.
+  // If it ever grows, use of a linear search should be re-evaluated.
+  if (!HeaderMaps.empty()) {
+    for (unsigned i = 0, e = HeaderMaps.size(); i != e; ++i)
+      // Pointer equality comparison of FileEntries works because they are
+      // already uniqued by inode.
+      if (HeaderMaps[i].first == FE)
+        return HeaderMaps[i].second.get();
+  }
+
+  if (std::unique_ptr<HeaderMap> HM = HeaderMap::Create(FE, FileMgr)) {
+    HeaderMaps.emplace_back(FE, std::move(HM));
+    return HeaderMaps.back().second.get();
+  }
+
+  return nullptr;
+}
+
+/// Get filenames for all registered header maps.
+void HeaderSearch::getHeaderMapFileNames(
+    SmallVectorImpl<std::string> &Names) const {
+  for (auto &HM : HeaderMaps)
+    Names.push_back(std::string(HM.first->getName()));
+}
+
+std::string HeaderSearch::getCachedModuleFileName(Module *Module) {
+  const FileEntry *ModuleMap =
+      getModuleMap().getModuleMapFileForUniquing(Module);
+  return getCachedModuleFileName(Module->Name, ModuleMap->getName());
+}
+
+std::string HeaderSearch::getPrebuiltModuleFileName(StringRef ModuleName,
+                                                    bool FileMapOnly) {
+  // First check the module name to pcm file map.
+  auto i(HSOpts->PrebuiltModuleFiles.find(ModuleName));
+  if (i != HSOpts->PrebuiltModuleFiles.end())
+    return i->second;
+
+  if (FileMapOnly || HSOpts->PrebuiltModulePaths.empty())
+    return {};
+
+  // Then go through each prebuilt module directory and try to find the pcm
+  // file.
+  for (const std::string &Dir : HSOpts->PrebuiltModulePaths) {
+    SmallString<256> Result(Dir);
+    llvm::sys::fs::make_absolute(Result);
+    llvm::sys::path::append(Result, ModuleName + ".pcm");
+    if (getFileMgr().getFile(Result.str()))
+      return std::string(Result);
+  }
+  return {};
+}
+
+std::string HeaderSearch::getCachedModuleFileName(StringRef ModuleName,
+                                                  StringRef ModuleMapPath) {
+  // If we don't have a module cache path or aren't supposed to use one, we
+  // can't do anything.
+  if (getModuleCachePath().empty())
+    return {};
+
+  SmallString<256> Result(getModuleCachePath());
+  llvm::sys::fs::make_absolute(Result);
+
+  if (HSOpts->DisableModuleHash) {
+    llvm::sys::path::append(Result, ModuleName + ".pcm");
+  } else {
+    // Construct the name <ModuleName>-<hash of ModuleMapPath>.pcm which should
+    // ideally be globally unique to this particular module. Name collisions
+    // in the hash are safe (because any translation unit can only import one
+    // module with each name), but result in a loss of caching.
+    //
+    // To avoid false-negatives, we form as canonical a path as we can, and map
+    // to lower-case in case we're on a case-insensitive file system.
+    std::string Parent =
+        std::string(llvm::sys::path::parent_path(ModuleMapPath));
+    if (Parent.empty())
+      Parent = ".";
+    auto Dir = FileMgr.getDirectory(Parent);
+    if (!Dir)
+      return {};
+    auto DirName = FileMgr.getCanonicalName(*Dir);
+    auto FileName = llvm::sys::path::filename(ModuleMapPath);
+
+    llvm::hash_code Hash =
+      llvm::hash_combine(DirName.lower(), FileName.lower());
+
+    SmallString<128> HashStr;
+    llvm::APInt(64, size_t(Hash)).toStringUnsigned(HashStr, /*Radix*/36);
+    llvm::sys::path::append(Result, ModuleName + "-" + HashStr + ".pcm");
+  }
+  return Result.str().str();
+}
+
+Module *HeaderSearch::lookupModule(StringRef ModuleName, bool AllowSearch,
+                                   bool AllowExtraModuleMapSearch) {
+  // Look in the module map to determine if there is a module by this name.
+  Module *Module = ModMap.findModule(ModuleName);
+  if (Module || !AllowSearch || !HSOpts->ImplicitModuleMaps)
+    return Module;
+
+  StringRef SearchName = ModuleName;
+  Module = lookupModule(ModuleName, SearchName, AllowExtraModuleMapSearch);
+
+  // The facility for "private modules" -- adjacent, optional module maps named
+  // module.private.modulemap that are supposed to define private submodules --
+  // may have different flavors of names: FooPrivate, Foo_Private and Foo.Private.
+  //
+  // Foo.Private is now deprecated in favor of Foo_Private. Users of FooPrivate
+  // should also rename to Foo_Private. Representing private as submodules
+  // could force building unwanted dependencies into the parent module and cause
+  // dependency cycles.
+  if (!Module && SearchName.consume_back("_Private"))
+    Module = lookupModule(ModuleName, SearchName, AllowExtraModuleMapSearch);
+  if (!Module && SearchName.consume_back("Private"))
+    Module = lookupModule(ModuleName, SearchName, AllowExtraModuleMapSearch);
+  return Module;
+}
+
+Module *HeaderSearch::lookupModule(StringRef ModuleName, StringRef SearchName,
+                                   bool AllowExtraModuleMapSearch) {
+  Module *Module = nullptr;
+
+  // Look through the various header search paths to load any available module
+  // maps, searching for a module map that describes this module.
+  for (unsigned Idx = 0, N = SearchDirs.size(); Idx != N; ++Idx) {
+    if (SearchDirs[Idx].isFramework()) {
+      // Search for or infer a module map for a framework. Here we use
+      // SearchName rather than ModuleName, to permit finding private modules
+      // named FooPrivate in buggy frameworks named Foo.
+      SmallString<128> FrameworkDirName;
+      FrameworkDirName += SearchDirs[Idx].getFrameworkDir()->getName();
+      llvm::sys::path::append(FrameworkDirName, SearchName + ".framework");
+      if (auto FrameworkDir = FileMgr.getDirectory(FrameworkDirName)) {
+        bool IsSystem
+          = SearchDirs[Idx].getDirCharacteristic() != SrcMgr::C_User;
+        Module = loadFrameworkModule(ModuleName, *FrameworkDir, IsSystem);
+        if (Module)
+          break;
+      }
+    }
+
+    // FIXME: Figure out how header maps and module maps will work together.
+
+    // Only deal with normal search directories.
+    if (!SearchDirs[Idx].isNormalDir())
+      continue;
+
+    bool IsSystem = SearchDirs[Idx].isSystemHeaderDirectory();
+    // Search for a module map file in this directory.
+    if (loadModuleMapFile(SearchDirs[Idx].getDir(), IsSystem,
+                          /*IsFramework*/false) == LMM_NewlyLoaded) {
+      // We just loaded a module map file; check whether the module is
+      // available now.
+      Module = ModMap.findModule(ModuleName);
+      if (Module)
+        break;
+    }
+
+    // Search for a module map in a subdirectory with the same name as the
+    // module.
+    SmallString<128> NestedModuleMapDirName;
+    NestedModuleMapDirName = SearchDirs[Idx].getDir()->getName();
+    llvm::sys::path::append(NestedModuleMapDirName, ModuleName);
+    if (loadModuleMapFile(NestedModuleMapDirName, IsSystem,
+                          /*IsFramework*/false) == LMM_NewlyLoaded){
+      // If we just loaded a module map file, look for the module again.
+      Module = ModMap.findModule(ModuleName);
+      if (Module)
+        break;
+    }
+
+    // If we've already performed the exhaustive search for module maps in this
+    // search directory, don't do it again.
+    if (SearchDirs[Idx].haveSearchedAllModuleMaps())
+      continue;
+
+    // Load all module maps in the immediate subdirectories of this search
+    // directory if ModuleName was from @import.
+    if (AllowExtraModuleMapSearch)
+      loadSubdirectoryModuleMaps(SearchDirs[Idx]);
+
+    // Look again for the module.
+    Module = ModMap.findModule(ModuleName);
+    if (Module)
+      break;
+  }
+
+  return Module;
+}
+
+//===----------------------------------------------------------------------===//
+// File lookup within a DirectoryLookup scope
+//===----------------------------------------------------------------------===//
+
+/// getName - Return the directory or filename corresponding to this lookup
+/// object.
+StringRef DirectoryLookup::getName() const {
+  // FIXME: Use the name from \c DirectoryEntryRef.
+  if (isNormalDir())
+    return getDir()->getName();
+  if (isFramework())
+    return getFrameworkDir()->getName();
+  assert(isHeaderMap() && "Unknown DirectoryLookup");
+  return getHeaderMap()->getFileName();
+}
+
+Optional<FileEntryRef> HeaderSearch::getFileAndSuggestModule(
+    StringRef FileName, SourceLocation IncludeLoc, const DirectoryEntry *Dir,
+    bool IsSystemHeaderDir, Module *RequestingModule,
+    ModuleMap::KnownHeader *SuggestedModule) {
+  // If we have a module map that might map this header, load it and
+  // check whether we'll have a suggestion for a module.
+  auto File = getFileMgr().getFileRef(FileName, /*OpenFile=*/true);
+  if (!File) {
+    // For rare, surprising errors (e.g. "out of file handles"), diag the EC
+    // message.
+    std::error_code EC = llvm::errorToErrorCode(File.takeError());
+    if (EC != llvm::errc::no_such_file_or_directory &&
+        EC != llvm::errc::invalid_argument &&
+        EC != llvm::errc::is_a_directory && EC != llvm::errc::not_a_directory) {
+      Diags.Report(IncludeLoc, diag::err_cannot_open_file)
+          << FileName << EC.message();
+    }
+    return None;
+  }
+
+  // If there is a module that corresponds to this header, suggest it.
+  if (!findUsableModuleForHeader(
+          &File->getFileEntry(), Dir ? Dir : File->getFileEntry().getDir(),
+          RequestingModule, SuggestedModule, IsSystemHeaderDir))
+    return None;
+
+  return *File;
+}
+
+/// LookupFile - Lookup the specified file in this search path, returning it
+/// if it exists or returning null if not.
+Optional<FileEntryRef> DirectoryLookup::LookupFile(
+    StringRef &Filename, HeaderSearch &HS, SourceLocation IncludeLoc,
+    SmallVectorImpl<char> *SearchPath, SmallVectorImpl<char> *RelativePath,
+    Module *RequestingModule, ModuleMap::KnownHeader *SuggestedModule,
+    bool &InUserSpecifiedSystemFramework, bool &IsFrameworkFound,
+    bool &IsInHeaderMap, SmallVectorImpl<char> &MappedName) const {
+  InUserSpecifiedSystemFramework = false;
+  IsInHeaderMap = false;
+  MappedName.clear();
+
+  SmallString<1024> TmpDir;
+  if (isNormalDir()) {
+    // Concatenate the requested file onto the directory.
+    TmpDir = getDir()->getName();
+    llvm::sys::path::append(TmpDir, Filename);
+    if (SearchPath) {
+      StringRef SearchPathRef(getDir()->getName());
+      SearchPath->clear();
+      SearchPath->append(SearchPathRef.begin(), SearchPathRef.end());
+    }
+    if (RelativePath) {
+      RelativePath->clear();
+      RelativePath->append(Filename.begin(), Filename.end());
+    }
+
+    return HS.getFileAndSuggestModule(TmpDir, IncludeLoc, getDir(),
+                                      isSystemHeaderDirectory(),
+                                      RequestingModule, SuggestedModule);
+  }
+
+  if (isFramework())
+    return DoFrameworkLookup(Filename, HS, SearchPath, RelativePath,
+                             RequestingModule, SuggestedModule,
+                             InUserSpecifiedSystemFramework, IsFrameworkFound);
+
+  assert(isHeaderMap() && "Unknown directory lookup");
+  const HeaderMap *HM = getHeaderMap();
+  SmallString<1024> Path;
+  StringRef Dest = HM->lookupFilename(Filename, Path);
+  if (Dest.empty())
+    return None;
+
+  IsInHeaderMap = true;
+
+  auto FixupSearchPath = [&]() {
+    if (SearchPath) {
+      StringRef SearchPathRef(getName());
+      SearchPath->clear();
+      SearchPath->append(SearchPathRef.begin(), SearchPathRef.end());
+    }
+    if (RelativePath) {
+      RelativePath->clear();
+      RelativePath->append(Filename.begin(), Filename.end());
+    }
+  };
+
+  // Check if the headermap maps the filename to a framework include
+  // ("Foo.h" -> "Foo/Foo.h"), in which case continue header lookup using the
+  // framework include.
+  if (llvm::sys::path::is_relative(Dest)) {
+    MappedName.append(Dest.begin(), Dest.end());
+    Filename = StringRef(MappedName.begin(), MappedName.size());
+    Optional<FileEntryRef> Result = HM->LookupFile(Filename, HS.getFileMgr());
+    if (Result) {
+      FixupSearchPath();
+      return *Result;
+    }
+  } else if (auto Res = HS.getFileMgr().getOptionalFileRef(Dest)) {
+    FixupSearchPath();
+    return *Res;
+  }
+
+  return None;
+}
+
+/// Given a framework directory, find the top-most framework directory.
+///
+/// \param FileMgr The file manager to use for directory lookups.
+/// \param DirName The name of the framework directory.
+/// \param SubmodulePath Will be populated with the submodule path from the
+/// returned top-level module to the originally named framework.
+static const DirectoryEntry *
+getTopFrameworkDir(FileManager &FileMgr, StringRef DirName,
+                   SmallVectorImpl<std::string> &SubmodulePath) {
+  assert(llvm::sys::path::extension(DirName) == ".framework" &&
+         "Not a framework directory");
+
+  // Note: as an egregious but useful hack we use the real path here, because
+  // frameworks moving between top-level frameworks to embedded frameworks tend
+  // to be symlinked, and we base the logical structure of modules on the
+  // physical layout. In particular, we need to deal with crazy includes like
+  //
+  //   #include <Foo/Frameworks/Bar.framework/Headers/Wibble.h>
+  //
+  // where 'Bar' used to be embedded in 'Foo', is now a top-level framework
+  // which one should access with, e.g.,
+  //
+  //   #include <Bar/Wibble.h>
+  //
+  // Similar issues occur when a top-level framework has moved into an
+  // embedded framework.
+  const DirectoryEntry *TopFrameworkDir = nullptr;
+  if (auto TopFrameworkDirOrErr = FileMgr.getDirectory(DirName))
+    TopFrameworkDir = *TopFrameworkDirOrErr;
+
+  if (TopFrameworkDir)
+    DirName = FileMgr.getCanonicalName(TopFrameworkDir);
+  do {
+    // Get the parent directory name.
+    DirName = llvm::sys::path::parent_path(DirName);
+    if (DirName.empty())
+      break;
+
+    // Determine whether this directory exists.
+    auto Dir = FileMgr.getDirectory(DirName);
+    if (!Dir)
+      break;
+
+    // If this is a framework directory, then we're a subframework of this
+    // framework.
+    if (llvm::sys::path::extension(DirName) == ".framework") {
+      SubmodulePath.push_back(std::string(llvm::sys::path::stem(DirName)));
+      TopFrameworkDir = *Dir;
+    }
+  } while (true);
+
+  return TopFrameworkDir;
+}
+
+static bool needModuleLookup(Module *RequestingModule,
+                             bool HasSuggestedModule) {
+  return HasSuggestedModule ||
+         (RequestingModule && RequestingModule->NoUndeclaredIncludes);
+}
+
+/// DoFrameworkLookup - Do a lookup of the specified file in the current
+/// DirectoryLookup, which is a framework directory.
+Optional<FileEntryRef> DirectoryLookup::DoFrameworkLookup(
+    StringRef Filename, HeaderSearch &HS, SmallVectorImpl<char> *SearchPath,
+    SmallVectorImpl<char> *RelativePath, Module *RequestingModule,
+    ModuleMap::KnownHeader *SuggestedModule,
+    bool &InUserSpecifiedSystemFramework, bool &IsFrameworkFound) const {
+  FileManager &FileMgr = HS.getFileMgr();
+
+  // Framework names must have a '/' in the filename.
+  size_t SlashPos = Filename.find('/');
+  if (SlashPos == StringRef::npos)
+    return None;
+
+  // Find out if this is the home for the specified framework, by checking
+  // HeaderSearch.  Possible answers are yes/no and unknown.
+  FrameworkCacheEntry &CacheEntry =
+    HS.LookupFrameworkCache(Filename.substr(0, SlashPos));
+
+  // If it is known and in some other directory, fail.
+  if (CacheEntry.Directory && CacheEntry.Directory != getFrameworkDir())
+    return None;
+
+  // Otherwise, construct the path to this framework dir.
+
+  // FrameworkName = "/System/Library/Frameworks/"
+  SmallString<1024> FrameworkName;
+  FrameworkName += getFrameworkDirRef()->getName();
+  if (FrameworkName.empty() || FrameworkName.back() != '/')
+    FrameworkName.push_back('/');
+
+  // FrameworkName = "/System/Library/Frameworks/Cocoa"
+  StringRef ModuleName(Filename.begin(), SlashPos);
+  FrameworkName += ModuleName;
+
+  // FrameworkName = "/System/Library/Frameworks/Cocoa.framework/"
+  FrameworkName += ".framework/";
+
+  // If the cache entry was unresolved, populate it now.
+  if (!CacheEntry.Directory) {
+    ++NumFrameworkLookups;
+
+    // If the framework dir doesn't exist, we fail.
+    auto Dir = FileMgr.getDirectory(FrameworkName);
+    if (!Dir)
+      return None;
+
+    // Otherwise, if it does, remember that this is the right direntry for this
+    // framework.
+    CacheEntry.Directory = getFrameworkDir();
+
+    // If this is a user search directory, check if the framework has been
+    // user-specified as a system framework.
+    if (getDirCharacteristic() == SrcMgr::C_User) {
+      SmallString<1024> SystemFrameworkMarker(FrameworkName);
+      SystemFrameworkMarker += ".system_framework";
+      if (llvm::sys::fs::exists(SystemFrameworkMarker)) {
+        CacheEntry.IsUserSpecifiedSystemFramework = true;
+      }
+    }
+  }
+
+  // Set out flags.
+  InUserSpecifiedSystemFramework = CacheEntry.IsUserSpecifiedSystemFramework;
+  IsFrameworkFound = CacheEntry.Directory;
+
+  if (RelativePath) {
+    RelativePath->clear();
+    RelativePath->append(Filename.begin()+SlashPos+1, Filename.end());
+  }
+
+  // Check "/System/Library/Frameworks/Cocoa.framework/Headers/file.h"
+  unsigned OrigSize = FrameworkName.size();
+
+  FrameworkName += "Headers/";
+
+  if (SearchPath) {
+    SearchPath->clear();
+    // Without trailing '/'.
+    SearchPath->append(FrameworkName.begin(), FrameworkName.end()-1);
+  }
+
+  FrameworkName.append(Filename.begin()+SlashPos+1, Filename.end());
+
+  auto File =
+      FileMgr.getOptionalFileRef(FrameworkName, /*OpenFile=*/!SuggestedModule);
+  if (!File) {
+    // Check "/System/Library/Frameworks/Cocoa.framework/PrivateHeaders/file.h"
+    const char *Private = "Private";
+    FrameworkName.insert(FrameworkName.begin()+OrigSize, Private,
+                         Private+strlen(Private));
+    if (SearchPath)
+      SearchPath->insert(SearchPath->begin()+OrigSize, Private,
+                         Private+strlen(Private));
+
+    File = FileMgr.getOptionalFileRef(FrameworkName,
+                                      /*OpenFile=*/!SuggestedModule);
+  }
+
+  // If we found the header and are allowed to suggest a module, do so now.
+  if (File && needModuleLookup(RequestingModule, SuggestedModule)) {
+    // Find the framework in which this header occurs.
+    StringRef FrameworkPath = File->getFileEntry().getDir()->getName();
+    bool FoundFramework = false;
+    do {
+      // Determine whether this directory exists.
+      auto Dir = FileMgr.getDirectory(FrameworkPath);
+      if (!Dir)
+        break;
+
+      // If this is a framework directory, then we're a subframework of this
+      // framework.
+      if (llvm::sys::path::extension(FrameworkPath) == ".framework") {
+        FoundFramework = true;
+        break;
+      }
+
+      // Get the parent directory name.
+      FrameworkPath = llvm::sys::path::parent_path(FrameworkPath);
+      if (FrameworkPath.empty())
+        break;
+    } while (true);
+
+    bool IsSystem = getDirCharacteristic() != SrcMgr::C_User;
+    if (FoundFramework) {
+      if (!HS.findUsableModuleForFrameworkHeader(
+              &File->getFileEntry(), FrameworkPath, RequestingModule,
+              SuggestedModule, IsSystem))
+        return None;
+    } else {
+      if (!HS.findUsableModuleForHeader(&File->getFileEntry(), getDir(),
+                                        RequestingModule, SuggestedModule,
+                                        IsSystem))
+        return None;
+    }
+  }
+  if (File)
+    return *File;
+  return None;
+}
+
+void HeaderSearch::setTarget(const TargetInfo &Target) {
+  ModMap.setTarget(Target);
+}
+
+//===----------------------------------------------------------------------===//
+// Header File Location.
+//===----------------------------------------------------------------------===//
+
+/// Return true with a diagnostic if the file that MSVC would have found
+/// fails to match the one that Clang would have found with MSVC header search
+/// disabled.
+static bool checkMSVCHeaderSearch(DiagnosticsEngine &Diags,
+                                  const FileEntry *MSFE, const FileEntry *FE,
+                                  SourceLocation IncludeLoc) {
+  if (MSFE && FE != MSFE) {
+    Diags.Report(IncludeLoc, diag::ext_pp_include_search_ms) << MSFE->getName();
+    return true;
+  }
+  return false;
+}
+
+static const char *copyString(StringRef Str, llvm::BumpPtrAllocator &Alloc) {
+  assert(!Str.empty());
+  char *CopyStr = Alloc.Allocate<char>(Str.size()+1);
+  std::copy(Str.begin(), Str.end(), CopyStr);
+  CopyStr[Str.size()] = '\0';
+  return CopyStr;
+}
+
+static bool isFrameworkStylePath(StringRef Path, bool &IsPrivateHeader,
+                                 SmallVectorImpl<char> &FrameworkName) {
+  using namespace llvm::sys;
+  path::const_iterator I = path::begin(Path);
+  path::const_iterator E = path::end(Path);
+  IsPrivateHeader = false;
+
+  // Detect different types of framework style paths:
+  //
+  //   ...Foo.framework/{Headers,PrivateHeaders}
+  //   ...Foo.framework/Versions/{A,Current}/{Headers,PrivateHeaders}
+  //   ...Foo.framework/Frameworks/Nested.framework/{Headers,PrivateHeaders}
+  //   ...<other variations with 'Versions' like in the above path>
+  //
+  // and some other variations among these lines.
+  int FoundComp = 0;
+  while (I != E) {
+    if (*I == "Headers")
+      ++FoundComp;
+    if (I->endswith(".framework")) {
+      FrameworkName.append(I->begin(), I->end());
+      ++FoundComp;
+    }
+    if (*I == "PrivateHeaders") {
+      ++FoundComp;
+      IsPrivateHeader = true;
+    }
+    ++I;
+  }
+
+  return !FrameworkName.empty() && FoundComp >= 2;
+}
+
+static void
+diagnoseFrameworkInclude(DiagnosticsEngine &Diags, SourceLocation IncludeLoc,
+                         StringRef Includer, StringRef IncludeFilename,
+                         const FileEntry *IncludeFE, bool isAngled = false,
+                         bool FoundByHeaderMap = false) {
+  bool IsIncluderPrivateHeader = false;
+  SmallString<128> FromFramework, ToFramework;
+  if (!isFrameworkStylePath(Includer, IsIncluderPrivateHeader, FromFramework))
+    return;
+  bool IsIncludeePrivateHeader = false;
+  bool IsIncludeeInFramework = isFrameworkStylePath(
+      IncludeFE->getName(), IsIncludeePrivateHeader, ToFramework);
+
+  if (!isAngled && !FoundByHeaderMap) {
+    SmallString<128> NewInclude("<");
+    if (IsIncludeeInFramework) {
+      NewInclude += StringRef(ToFramework).drop_back(10); // drop .framework
+      NewInclude += "/";
+    }
+    NewInclude += IncludeFilename;
+    NewInclude += ">";
+    Diags.Report(IncludeLoc, diag::warn_quoted_include_in_framework_header)
+        << IncludeFilename
+        << FixItHint::CreateReplacement(IncludeLoc, NewInclude);
+  }
+
+  // Headers in Foo.framework/Headers should not include headers
+  // from Foo.framework/PrivateHeaders, since this violates public/private
+  // API boundaries and can cause modular dependency cycles.
+  if (!IsIncluderPrivateHeader && IsIncludeeInFramework &&
+      IsIncludeePrivateHeader && FromFramework == ToFramework)
+    Diags.Report(IncludeLoc, diag::warn_framework_include_private_from_public)
+        << IncludeFilename;
+}
+
+/// LookupFile - Given a "foo" or \<foo> reference, look up the indicated file,
+/// return null on failure.  isAngled indicates whether the file reference is
+/// for system \#include's or not (i.e. using <> instead of ""). Includers, if
+/// non-empty, indicates where the \#including file(s) are, in case a relative
+/// search is needed. Microsoft mode will pass all \#including files.
+Optional<FileEntryRef> HeaderSearch::LookupFile(
+    StringRef Filename, SourceLocation IncludeLoc, bool isAngled,
+    const DirectoryLookup *FromDir, const DirectoryLookup *&CurDir,
+    ArrayRef<std::pair<const FileEntry *, const DirectoryEntry *>> Includers,
+    SmallVectorImpl<char> *SearchPath, SmallVectorImpl<char> *RelativePath,
+    Module *RequestingModule, ModuleMap::KnownHeader *SuggestedModule,
+    bool *IsMapped, bool *IsFrameworkFound, bool SkipCache,
+    bool BuildSystemModule) {
+  if (IsMapped)
+    *IsMapped = false;
+
+  if (IsFrameworkFound)
+    *IsFrameworkFound = false;
+
+  if (SuggestedModule)
+    *SuggestedModule = ModuleMap::KnownHeader();
+
+  // If 'Filename' is absolute, check to see if it exists and no searching.
+  if (llvm::sys::path::is_absolute(Filename)) {
+    CurDir = nullptr;
+
+    // If this was an #include_next "/absolute/file", fail.
+    if (FromDir)
+      return None;
+
+    if (SearchPath)
+      SearchPath->clear();
+    if (RelativePath) {
+      RelativePath->clear();
+      RelativePath->append(Filename.begin(), Filename.end());
+    }
+    // Otherwise, just return the file.
+    return getFileAndSuggestModule(Filename, IncludeLoc, nullptr,
+                                   /*IsSystemHeaderDir*/false,
+                                   RequestingModule, SuggestedModule);
+  }
+
+  // This is the header that MSVC's header search would have found.
+  ModuleMap::KnownHeader MSSuggestedModule;
+  const FileEntry *MSFE_FE = nullptr;
+  StringRef MSFE_Name;
+
+  // Unless disabled, check to see if the file is in the #includer's
+  // directory.  This cannot be based on CurDir, because each includer could be
+  // a #include of a subdirectory (#include "foo/bar.h") and a subsequent
+  // include of "baz.h" should resolve to "whatever/foo/baz.h".
+  // This search is not done for <> headers.
+  if (!Includers.empty() && !isAngled && !NoCurDirSearch) {
+    SmallString<1024> TmpDir;
+    bool First = true;
+    for (const auto &IncluderAndDir : Includers) {
+      const FileEntry *Includer = IncluderAndDir.first;
+
+      // Concatenate the requested file onto the directory.
+      // FIXME: Portability.  Filename concatenation should be in sys::Path.
+      TmpDir = IncluderAndDir.second->getName();
+      TmpDir.push_back('/');
+      TmpDir.append(Filename.begin(), Filename.end());
+
+      // FIXME: We don't cache the result of getFileInfo across the call to
+      // getFileAndSuggestModule, because it's a reference to an element of
+      // a container that could be reallocated across this call.
+      //
+      // If we have no includer, that means we're processing a #include
+      // from a module build. We should treat this as a system header if we're
+      // building a [system] module.
+      bool IncluderIsSystemHeader =
+          Includer ? getFileInfo(Includer).DirInfo != SrcMgr::C_User :
+          BuildSystemModule;
+      if (Optional<FileEntryRef> FE = getFileAndSuggestModule(
+              TmpDir, IncludeLoc, IncluderAndDir.second, IncluderIsSystemHeader,
+              RequestingModule, SuggestedModule)) {
+        if (!Includer) {
+          assert(First && "only first includer can have no file");
+          return FE;
+        }
+
+        // Leave CurDir unset.
+        // This file is a system header or C++ unfriendly if the old file is.
+        //
+        // Note that we only use one of FromHFI/ToHFI at once, due to potential
+        // reallocation of the underlying vector potentially making the first
+        // reference binding dangling.
+        HeaderFileInfo &FromHFI = getFileInfo(Includer);
+        unsigned DirInfo = FromHFI.DirInfo;
+        bool IndexHeaderMapHeader = FromHFI.IndexHeaderMapHeader;
+        StringRef Framework = FromHFI.Framework;
+
+        HeaderFileInfo &ToHFI = getFileInfo(&FE->getFileEntry());
+        ToHFI.DirInfo = DirInfo;
+        ToHFI.IndexHeaderMapHeader = IndexHeaderMapHeader;
+        ToHFI.Framework = Framework;
+
+        if (SearchPath) {
+          StringRef SearchPathRef(IncluderAndDir.second->getName());
+          SearchPath->clear();
+          SearchPath->append(SearchPathRef.begin(), SearchPathRef.end());
+        }
+        if (RelativePath) {
+          RelativePath->clear();
+          RelativePath->append(Filename.begin(), Filename.end());
+        }
+        if (First) {
+          diagnoseFrameworkInclude(Diags, IncludeLoc,
+                                   IncluderAndDir.second->getName(), Filename,
+                                   &FE->getFileEntry());
+          return FE;
+        }
+
+        // Otherwise, we found the path via MSVC header search rules.  If
+        // -Wmsvc-include is enabled, we have to keep searching to see if we
+        // would've found this header in -I or -isystem directories.
+        if (Diags.isIgnored(diag::ext_pp_include_search_ms, IncludeLoc)) {
+          return FE;
+        } else {
+          MSFE_FE = &FE->getFileEntry();
+          MSFE_Name = FE->getName();
+          if (SuggestedModule) {
+            MSSuggestedModule = *SuggestedModule;
+            *SuggestedModule = ModuleMap::KnownHeader();
+          }
+          break;
+        }
+      }
+      First = false;
+    }
+  }
+
+  Optional<FileEntryRef> MSFE(MSFE_FE ? FileEntryRef(MSFE_Name, *MSFE_FE)
+                                      : Optional<FileEntryRef>());
+
+  CurDir = nullptr;
+
+  // If this is a system #include, ignore the user #include locs.
+  unsigned i = isAngled ? AngledDirIdx : 0;
+
+  // If this is a #include_next request, start searching after the directory the
+  // file was found in.
+  if (FromDir)
+    i = FromDir-&SearchDirs[0];
+
+  // Cache all of the lookups performed by this method.  Many headers are
+  // multiply included, and the "pragma once" optimization prevents them from
+  // being relex/pp'd, but they would still have to search through a
+  // (potentially huge) series of SearchDirs to find it.
+  LookupFileCacheInfo &CacheLookup = LookupFileCache[Filename];
+
+  // If the entry has been previously looked up, the first value will be
+  // non-zero.  If the value is equal to i (the start point of our search), then
+  // this is a matching hit.
+  if (!SkipCache && CacheLookup.StartIdx == i+1) {
+    // Skip querying potentially lots of directories for this lookup.
+    i = CacheLookup.HitIdx;
+    if (CacheLookup.MappedName) {
+      Filename = CacheLookup.MappedName;
+      if (IsMapped)
+        *IsMapped = true;
+    }
+  } else {
+    // Otherwise, this is the first query, or the previous query didn't match
+    // our search start.  We will fill in our found location below, so prime the
+    // start point value.
+    CacheLookup.reset(/*StartIdx=*/i+1);
+  }
+
+  SmallString<64> MappedName;
+
+  // Check each directory in sequence to see if it contains this file.
+  for (; i != SearchDirs.size(); ++i) {
+    bool InUserSpecifiedSystemFramework = false;
+    bool IsInHeaderMap = false;
+    bool IsFrameworkFoundInDir = false;
+    Optional<FileEntryRef> File = SearchDirs[i].LookupFile(
+        Filename, *this, IncludeLoc, SearchPath, RelativePath, RequestingModule,
+        SuggestedModule, InUserSpecifiedSystemFramework, IsFrameworkFoundInDir,
+        IsInHeaderMap, MappedName);
+    if (!MappedName.empty()) {
+      assert(IsInHeaderMap && "MappedName should come from a header map");
+      CacheLookup.MappedName =
+          copyString(MappedName, LookupFileCache.getAllocator());
+    }
+    if (IsMapped)
+      // A filename is mapped when a header map remapped it to a relative path
+      // used in subsequent header search or to an absolute path pointing to an
+      // existing file.
+      *IsMapped |= (!MappedName.empty() || (IsInHeaderMap && File));
+    if (IsFrameworkFound)
+      // Because we keep a filename remapped for subsequent search directory
+      // lookups, ignore IsFrameworkFoundInDir after the first remapping and not
+      // just for remapping in a current search directory.
+      *IsFrameworkFound |= (IsFrameworkFoundInDir && !CacheLookup.MappedName);
+    if (!File)
+      continue;
+
+    CurDir = &SearchDirs[i];
+
+    // This file is a system header or C++ unfriendly if the dir is.
+    HeaderFileInfo &HFI = getFileInfo(&File->getFileEntry());
+    HFI.DirInfo = CurDir->getDirCharacteristic();
+
+    // If the directory characteristic is User but this framework was
+    // user-specified to be treated as a system framework, promote the
+    // characteristic.
+    if (HFI.DirInfo == SrcMgr::C_User && InUserSpecifiedSystemFramework)
+      HFI.DirInfo = SrcMgr::C_System;
+
+    // If the filename matches a known system header prefix, override
+    // whether the file is a system header.
+    for (unsigned j = SystemHeaderPrefixes.size(); j; --j) {
+      if (Filename.startswith(SystemHeaderPrefixes[j-1].first)) {
+        HFI.DirInfo = SystemHeaderPrefixes[j-1].second ? SrcMgr::C_System
+                                                       : SrcMgr::C_User;
+        break;
+      }
+    }
+
+    // If this file is found in a header map and uses the framework style of
+    // includes, then this header is part of a framework we're building.
+    if (CurDir->isIndexHeaderMap()) {
+      size_t SlashPos = Filename.find('/');
+      if (SlashPos != StringRef::npos) {
+        HFI.IndexHeaderMapHeader = 1;
+        HFI.Framework = getUniqueFrameworkName(StringRef(Filename.begin(),
+                                                         SlashPos));
+      }
+    }
+
+    if (checkMSVCHeaderSearch(Diags, MSFE ? &MSFE->getFileEntry() : nullptr,
+                              &File->getFileEntry(), IncludeLoc)) {
+      if (SuggestedModule)
+        *SuggestedModule = MSSuggestedModule;
+      return MSFE;
+    }
+
+    bool FoundByHeaderMap = !IsMapped ? false : *IsMapped;
+    if (!Includers.empty())
+      diagnoseFrameworkInclude(
+          Diags, IncludeLoc, Includers.front().second->getName(), Filename,
+          &File->getFileEntry(), isAngled, FoundByHeaderMap);
+
+    // Remember this location for the next lookup we do.
+    CacheLookup.HitIdx = i;
+    return File;
+  }
+
+  // If we are including a file with a quoted include "foo.h" from inside
+  // a header in a framework that is currently being built, and we couldn't
+  // resolve "foo.h" any other way, change the include to <Foo/foo.h>, where
+  // "Foo" is the name of the framework in which the including header was found.
+  if (!Includers.empty() && Includers.front().first && !isAngled &&
+      Filename.find('/') == StringRef::npos) {
+    HeaderFileInfo &IncludingHFI = getFileInfo(Includers.front().first);
+    if (IncludingHFI.IndexHeaderMapHeader) {
+      SmallString<128> ScratchFilename;
+      ScratchFilename += IncludingHFI.Framework;
+      ScratchFilename += '/';
+      ScratchFilename += Filename;
+
+      Optional<FileEntryRef> File = LookupFile(
+          ScratchFilename, IncludeLoc, /*isAngled=*/true, FromDir, CurDir,
+          Includers.front(), SearchPath, RelativePath, RequestingModule,
+          SuggestedModule, IsMapped, /*IsFrameworkFound=*/nullptr);
+
+      if (checkMSVCHeaderSearch(Diags, MSFE ? &MSFE->getFileEntry() : nullptr,
+                                File ? &File->getFileEntry() : nullptr,
+                                IncludeLoc)) {
+        if (SuggestedModule)
+          *SuggestedModule = MSSuggestedModule;
+        return MSFE;
+      }
+
+      LookupFileCacheInfo &CacheLookup = LookupFileCache[Filename];
+      CacheLookup.HitIdx = LookupFileCache[ScratchFilename].HitIdx;
+      // FIXME: SuggestedModule.
+      return File;
+    }
+  }
+
+  if (checkMSVCHeaderSearch(Diags, MSFE ? &MSFE->getFileEntry() : nullptr,
+                            nullptr, IncludeLoc)) {
+    if (SuggestedModule)
+      *SuggestedModule = MSSuggestedModule;
+    return MSFE;
+  }
+
+  // Otherwise, didn't find it. Remember we didn't find this.
+  CacheLookup.HitIdx = SearchDirs.size();
+  return None;
+}
+
+/// LookupSubframeworkHeader - 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.
+Optional<FileEntryRef> HeaderSearch::LookupSubframeworkHeader(
+    StringRef Filename, const FileEntry *ContextFileEnt,
+    SmallVectorImpl<char> *SearchPath, SmallVectorImpl<char> *RelativePath,
+    Module *RequestingModule, ModuleMap::KnownHeader *SuggestedModule) {
+  assert(ContextFileEnt && "No context file?");
+
+  // Framework names must have a '/' in the filename.  Find it.
+  // FIXME: Should we permit '\' on Windows?
+  size_t SlashPos = Filename.find('/');
+  if (SlashPos == StringRef::npos)
+    return None;
+
+  // Look up the base framework name of the ContextFileEnt.
+  StringRef ContextName = ContextFileEnt->getName();
+
+  // If the context info wasn't a framework, couldn't be a subframework.
+  const unsigned DotFrameworkLen = 10;
+  auto FrameworkPos = ContextName.find(".framework");
+  if (FrameworkPos == StringRef::npos ||
+      (ContextName[FrameworkPos + DotFrameworkLen] != '/' &&
+       ContextName[FrameworkPos + DotFrameworkLen] != '\\'))
+    return None;
+
+  SmallString<1024> FrameworkName(ContextName.data(), ContextName.data() +
+                                                          FrameworkPos +
+                                                          DotFrameworkLen + 1);
+
+  // Append Frameworks/HIToolbox.framework/
+  FrameworkName += "Frameworks/";
+  FrameworkName.append(Filename.begin(), Filename.begin()+SlashPos);
+  FrameworkName += ".framework/";
+
+  auto &CacheLookup =
+      *FrameworkMap.insert(std::make_pair(Filename.substr(0, SlashPos),
+                                          FrameworkCacheEntry())).first;
+
+  // Some other location?
+  if (CacheLookup.second.Directory &&
+      CacheLookup.first().size() == FrameworkName.size() &&
+      memcmp(CacheLookup.first().data(), &FrameworkName[0],
+             CacheLookup.first().size()) != 0)
+    return None;
+
+  // Cache subframework.
+  if (!CacheLookup.second.Directory) {
+    ++NumSubFrameworkLookups;
+
+    // If the framework dir doesn't exist, we fail.
+    auto Dir = FileMgr.getDirectory(FrameworkName);
+    if (!Dir)
+      return None;
+
+    // Otherwise, if it does, remember that this is the right direntry for this
+    // framework.
+    CacheLookup.second.Directory = *Dir;
+  }
+
+
+  if (RelativePath) {
+    RelativePath->clear();
+    RelativePath->append(Filename.begin()+SlashPos+1, Filename.end());
+  }
+
+  // Check ".../Frameworks/HIToolbox.framework/Headers/HIToolbox.h"
+  SmallString<1024> HeadersFilename(FrameworkName);
+  HeadersFilename += "Headers/";
+  if (SearchPath) {
+    SearchPath->clear();
+    // Without trailing '/'.
+    SearchPath->append(HeadersFilename.begin(), HeadersFilename.end()-1);
+  }
+
+  HeadersFilename.append(Filename.begin()+SlashPos+1, Filename.end());
+  auto File = FileMgr.getOptionalFileRef(HeadersFilename, /*OpenFile=*/true);
+  if (!File) {
+    // Check ".../Frameworks/HIToolbox.framework/PrivateHeaders/HIToolbox.h"
+    HeadersFilename = FrameworkName;
+    HeadersFilename += "PrivateHeaders/";
+    if (SearchPath) {
+      SearchPath->clear();
+      // Without trailing '/'.
+      SearchPath->append(HeadersFilename.begin(), HeadersFilename.end()-1);
+    }
+
+    HeadersFilename.append(Filename.begin()+SlashPos+1, Filename.end());
+    File = FileMgr.getOptionalFileRef(HeadersFilename, /*OpenFile=*/true);
+
+    if (!File)
+      return None;
+  }
+
+  // This file is a system header or C++ unfriendly if the old file is.
+  //
+  // Note that the temporary 'DirInfo' is required here, as either call to
+  // getFileInfo could resize the vector and we don't want to rely on order
+  // of evaluation.
+  unsigned DirInfo = getFileInfo(ContextFileEnt).DirInfo;
+  getFileInfo(&File->getFileEntry()).DirInfo = DirInfo;
+
+  FrameworkName.pop_back(); // remove the trailing '/'
+  if (!findUsableModuleForFrameworkHeader(&File->getFileEntry(), FrameworkName,
+                                          RequestingModule, SuggestedModule,
+                                          /*IsSystem*/ false))
+    return None;
+
+  return *File;
+}
+
+//===----------------------------------------------------------------------===//
+// File Info Management.
+//===----------------------------------------------------------------------===//
+
+/// Merge the header file info provided by \p OtherHFI into the current
+/// header file info (\p HFI)
+static void mergeHeaderFileInfo(HeaderFileInfo &HFI,
+                                const HeaderFileInfo &OtherHFI) {
+  assert(OtherHFI.External && "expected to merge external HFI");
+
+  HFI.isImport |= OtherHFI.isImport;
+  HFI.isPragmaOnce |= OtherHFI.isPragmaOnce;
+  HFI.isModuleHeader |= OtherHFI.isModuleHeader;
+  HFI.NumIncludes += OtherHFI.NumIncludes;
+
+  if (!HFI.ControllingMacro && !HFI.ControllingMacroID) {
+    HFI.ControllingMacro = OtherHFI.ControllingMacro;
+    HFI.ControllingMacroID = OtherHFI.ControllingMacroID;
+  }
+
+  HFI.DirInfo = OtherHFI.DirInfo;
+  HFI.External = (!HFI.IsValid || HFI.External);
+  HFI.IsValid = true;
+  HFI.IndexHeaderMapHeader = OtherHFI.IndexHeaderMapHeader;
+
+  if (HFI.Framework.empty())
+    HFI.Framework = OtherHFI.Framework;
+}
+
+/// getFileInfo - Return the HeaderFileInfo structure for the specified
+/// FileEntry.
+HeaderFileInfo &HeaderSearch::getFileInfo(const FileEntry *FE) {
+  if (FE->getUID() >= FileInfo.size())
+    FileInfo.resize(FE->getUID() + 1);
+
+  HeaderFileInfo *HFI = &FileInfo[FE->getUID()];
+  // FIXME: Use a generation count to check whether this is really up to date.
+  if (ExternalSource && !HFI->Resolved) {
+    HFI->Resolved = true;
+    auto ExternalHFI = ExternalSource->GetHeaderFileInfo(FE);
+
+    HFI = &FileInfo[FE->getUID()];
+    if (ExternalHFI.External)
+      mergeHeaderFileInfo(*HFI, ExternalHFI);
+  }
+
+  HFI->IsValid = true;
+  // We have local information about this header file, so it's no longer
+  // strictly external.
+  HFI->External = false;
+  return *HFI;
+}
+
+const HeaderFileInfo *
+HeaderSearch::getExistingFileInfo(const FileEntry *FE,
+                                  bool WantExternal) const {
+  // If we have an external source, ensure we have the latest information.
+  // FIXME: Use a generation count to check whether this is really up to date.
+  HeaderFileInfo *HFI;
+  if (ExternalSource) {
+    if (FE->getUID() >= FileInfo.size()) {
+      if (!WantExternal)
+        return nullptr;
+      FileInfo.resize(FE->getUID() + 1);
+    }
+
+    HFI = &FileInfo[FE->getUID()];
+    if (!WantExternal && (!HFI->IsValid || HFI->External))
+      return nullptr;
+    if (!HFI->Resolved) {
+      HFI->Resolved = true;
+      auto ExternalHFI = ExternalSource->GetHeaderFileInfo(FE);
+
+      HFI = &FileInfo[FE->getUID()];
+      if (ExternalHFI.External)
+        mergeHeaderFileInfo(*HFI, ExternalHFI);
+    }
+  } else if (FE->getUID() >= FileInfo.size()) {
+    return nullptr;
+  } else {
+    HFI = &FileInfo[FE->getUID()];
+  }
+
+  if (!HFI->IsValid || (HFI->External && !WantExternal))
+    return nullptr;
+
+  return HFI;
+}
+
+bool HeaderSearch::isFileMultipleIncludeGuarded(const FileEntry *File) {
+  // Check if we've ever seen this file as a header.
+  if (auto *HFI = getExistingFileInfo(File))
+    return HFI->isPragmaOnce || HFI->isImport || HFI->ControllingMacro ||
+           HFI->ControllingMacroID;
+  return false;
+}
+
+void HeaderSearch::MarkFileModuleHeader(const FileEntry *FE,
+                                        ModuleMap::ModuleHeaderRole Role,
+                                        bool isCompilingModuleHeader) {
+  bool isModularHeader = !(Role & ModuleMap::TextualHeader);
+
+  // Don't mark the file info as non-external if there's nothing to change.
+  if (!isCompilingModuleHeader) {
+    if (!isModularHeader)
+      return;
+    auto *HFI = getExistingFileInfo(FE);
+    if (HFI && HFI->isModuleHeader)
+      return;
+  }
+
+  auto &HFI = getFileInfo(FE);
+  HFI.isModuleHeader |= isModularHeader;
+  HFI.isCompilingModuleHeader |= isCompilingModuleHeader;
+}
+
+bool HeaderSearch::ShouldEnterIncludeFile(Preprocessor &PP,
+                                          const FileEntry *File, bool isImport,
+                                          bool ModulesEnabled, Module *M) {
+  ++NumIncluded; // Count # of attempted #includes.
+
+  // Get information about this file.
+  HeaderFileInfo &FileInfo = getFileInfo(File);
+
+  // FIXME: this is a workaround for the lack of proper modules-aware support
+  // for #import / #pragma once
+  auto TryEnterImported = [&]() -> bool {
+    if (!ModulesEnabled)
+      return false;
+    // Ensure FileInfo bits are up to date.
+    ModMap.resolveHeaderDirectives(File);
+    // Modules with builtins are special; multiple modules use builtins as
+    // modular headers, example:
+    //
+    //    module stddef { header "stddef.h" export * }
+    //
+    // After module map parsing, this expands to:
+    //
+    //    module stddef {
+    //      header "/path_to_builtin_dirs/stddef.h"
+    //      textual "stddef.h"
+    //    }
+    //
+    // It's common that libc++ and system modules will both define such
+    // submodules. Make sure cached results for a builtin header won't
+    // prevent other builtin modules to potentially enter the builtin header.
+    // Note that builtins are header guarded and the decision to actually
+    // enter them is postponed to the controlling macros logic below.
+    bool TryEnterHdr = false;
+    if (FileInfo.isCompilingModuleHeader && FileInfo.isModuleHeader)
+      TryEnterHdr = File->getDir() == ModMap.getBuiltinDir() &&
+                    ModuleMap::isBuiltinHeader(
+                        llvm::sys::path::filename(File->getName()));
+
+    // Textual headers can be #imported from different modules. Since ObjC
+    // headers find in the wild might rely only on #import and do not contain
+    // controlling macros, be conservative and only try to enter textual headers
+    // if such macro is present.
+    if (!FileInfo.isModuleHeader &&
+        FileInfo.getControllingMacro(ExternalLookup))
+      TryEnterHdr = true;
+    return TryEnterHdr;
+  };
+
+  // If this is a #import directive, check that we have not already imported
+  // this header.
+  if (isImport) {
+    // If this has already been imported, don't import it again.
+    FileInfo.isImport = true;
+
+    // Has this already been #import'ed or #include'd?
+    if (FileInfo.NumIncludes && !TryEnterImported())
+      return false;
+  } else {
+    // Otherwise, if this is a #include of a file that was previously #import'd
+    // or if this is the second #include of a #pragma once file, ignore it.
+    if (FileInfo.isImport && !TryEnterImported())
+      return false;
+  }
+
+  // Next, check to see if the file is wrapped with #ifndef guards.  If so, and
+  // if the macro that guards it is defined, we know the #include has no effect.
+  if (const IdentifierInfo *ControllingMacro
+      = FileInfo.getControllingMacro(ExternalLookup)) {
+    // If the header corresponds to a module, check whether the macro is already
+    // defined in that module rather than checking in the current set of visible
+    // modules.
+    if (M ? PP.isMacroDefinedInLocalModule(ControllingMacro, M)
+          : PP.isMacroDefined(ControllingMacro)) {
+      ++NumMultiIncludeFileOptzn;
+      return false;
+    }
+  }
+
+  // Increment the number of times this file has been included.
+  ++FileInfo.NumIncludes;
+
+  return true;
+}
+
+size_t HeaderSearch::getTotalMemory() const {
+  return SearchDirs.capacity()
+    + llvm::capacity_in_bytes(FileInfo)
+    + llvm::capacity_in_bytes(HeaderMaps)
+    + LookupFileCache.getAllocator().getTotalMemory()
+    + FrameworkMap.getAllocator().getTotalMemory();
+}
+
+StringRef HeaderSearch::getUniqueFrameworkName(StringRef Framework) {
+  return FrameworkNames.insert(Framework).first->first();
+}
+
+bool HeaderSearch::hasModuleMap(StringRef FileName,
+                                const DirectoryEntry *Root,
+                                bool IsSystem) {
+  if (!HSOpts->ImplicitModuleMaps)
+    return false;
+
+  SmallVector<const DirectoryEntry *, 2> FixUpDirectories;
+
+  StringRef DirName = FileName;
+  do {
+    // Get the parent directory name.
+    DirName = llvm::sys::path::parent_path(DirName);
+    if (DirName.empty())
+      return false;
+
+    // Determine whether this directory exists.
+    auto Dir = FileMgr.getDirectory(DirName);
+    if (!Dir)
+      return false;
+
+    // Try to load the module map file in this directory.
+    switch (loadModuleMapFile(*Dir, IsSystem,
+                              llvm::sys::path::extension((*Dir)->getName()) ==
+                                  ".framework")) {
+    case LMM_NewlyLoaded:
+    case LMM_AlreadyLoaded:
+      // Success. All of the directories we stepped through inherit this module
+      // map file.
+      for (unsigned I = 0, N = FixUpDirectories.size(); I != N; ++I)
+        DirectoryHasModuleMap[FixUpDirectories[I]] = true;
+      return true;
+
+    case LMM_NoDirectory:
+    case LMM_InvalidModuleMap:
+      break;
+    }
+
+    // If we hit the top of our search, we're done.
+    if (*Dir == Root)
+      return false;
+
+    // Keep track of all of the directories we checked, so we can mark them as
+    // having module maps if we eventually do find a module map.
+    FixUpDirectories.push_back(*Dir);
+  } while (true);
+}
+
+ModuleMap::KnownHeader
+HeaderSearch::findModuleForHeader(const FileEntry *File,
+                                  bool AllowTextual) const {
+  if (ExternalSource) {
+    // Make sure the external source has handled header info about this file,
+    // which includes whether the file is part of a module.
+    (void)getExistingFileInfo(File);
+  }
+  return ModMap.findModuleForHeader(File, AllowTextual);
+}
+
+static bool suggestModule(HeaderSearch &HS, const FileEntry *File,
+                          Module *RequestingModule,
+                          ModuleMap::KnownHeader *SuggestedModule) {
+  ModuleMap::KnownHeader Module =
+      HS.findModuleForHeader(File, /*AllowTextual*/true);
+  if (SuggestedModule)
+    *SuggestedModule = (Module.getRole() & ModuleMap::TextualHeader)
+                           ? ModuleMap::KnownHeader()
+                           : Module;
+
+  // If this module specifies [no_undeclared_includes], we cannot find any
+  // file that's in a non-dependency module.
+  if (RequestingModule && Module && RequestingModule->NoUndeclaredIncludes) {
+    HS.getModuleMap().resolveUses(RequestingModule, /*Complain*/false);
+    if (!RequestingModule->directlyUses(Module.getModule())) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool HeaderSearch::findUsableModuleForHeader(
+    const FileEntry *File, const DirectoryEntry *Root, Module *RequestingModule,
+    ModuleMap::KnownHeader *SuggestedModule, bool IsSystemHeaderDir) {
+  if (File && needModuleLookup(RequestingModule, SuggestedModule)) {
+    // If there is a module that corresponds to this header, suggest it.
+    hasModuleMap(File->getName(), Root, IsSystemHeaderDir);
+    return suggestModule(*this, File, RequestingModule, SuggestedModule);
+  }
+  return true;
+}
+
+bool HeaderSearch::findUsableModuleForFrameworkHeader(
+    const FileEntry *File, StringRef FrameworkName, Module *RequestingModule,
+    ModuleMap::KnownHeader *SuggestedModule, bool IsSystemFramework) {
+  // If we're supposed to suggest a module, look for one now.
+  if (needModuleLookup(RequestingModule, SuggestedModule)) {
+    // Find the top-level framework based on this framework.
+    SmallVector<std::string, 4> SubmodulePath;
+    const DirectoryEntry *TopFrameworkDir
+      = ::getTopFrameworkDir(FileMgr, FrameworkName, SubmodulePath);
+
+    // Determine the name of the top-level framework.
+    StringRef ModuleName = llvm::sys::path::stem(TopFrameworkDir->getName());
+
+    // Load this framework module. If that succeeds, find the suggested module
+    // for this header, if any.
+    loadFrameworkModule(ModuleName, TopFrameworkDir, IsSystemFramework);
+
+    // FIXME: This can find a module not part of ModuleName, which is
+    // important so that we're consistent about whether this header
+    // corresponds to a module. Possibly we should lock down framework modules
+    // so that this is not possible.
+    return suggestModule(*this, File, RequestingModule, SuggestedModule);
+  }
+  return true;
+}
+
+static const FileEntry *getPrivateModuleMap(const FileEntry *File,
+                                            FileManager &FileMgr) {
+  StringRef Filename = llvm::sys::path::filename(File->getName());
+  SmallString<128>  PrivateFilename(File->getDir()->getName());
+  if (Filename == "module.map")
+    llvm::sys::path::append(PrivateFilename, "module_private.map");
+  else if (Filename == "module.modulemap")
+    llvm::sys::path::append(PrivateFilename, "module.private.modulemap");
+  else
+    return nullptr;
+  if (auto File = FileMgr.getFile(PrivateFilename))
+    return *File;
+  return nullptr;
+}
+
+bool HeaderSearch::loadModuleMapFile(const FileEntry *File, bool IsSystem,
+                                     FileID ID, unsigned *Offset,
+                                     StringRef OriginalModuleMapFile) {
+  // Find the directory for the module. For frameworks, that may require going
+  // up from the 'Modules' directory.
+  const DirectoryEntry *Dir = nullptr;
+  if (getHeaderSearchOpts().ModuleMapFileHomeIsCwd) {
+    if (auto DirOrErr = FileMgr.getDirectory("."))
+      Dir = *DirOrErr;
+  } else {
+    if (!OriginalModuleMapFile.empty()) {
+      // We're building a preprocessed module map. Find or invent the directory
+      // that it originally occupied.
+      auto DirOrErr = FileMgr.getDirectory(
+          llvm::sys::path::parent_path(OriginalModuleMapFile));
+      if (DirOrErr) {
+        Dir = *DirOrErr;
+      } else {
+        auto *FakeFile = FileMgr.getVirtualFile(OriginalModuleMapFile, 0, 0);
+        Dir = FakeFile->getDir();
+      }
+    } else {
+      Dir = File->getDir();
+    }
+
+    StringRef DirName(Dir->getName());
+    if (llvm::sys::path::filename(DirName) == "Modules") {
+      DirName = llvm::sys::path::parent_path(DirName);
+      if (DirName.endswith(".framework"))
+        if (auto DirOrErr = FileMgr.getDirectory(DirName))
+          Dir = *DirOrErr;
+      // FIXME: This assert can fail if there's a race between the above check
+      // and the removal of the directory.
+      assert(Dir && "parent must exist");
+    }
+  }
+
+  switch (loadModuleMapFileImpl(File, IsSystem, Dir, ID, Offset)) {
+  case LMM_AlreadyLoaded:
+  case LMM_NewlyLoaded:
+    return false;
+  case LMM_NoDirectory:
+  case LMM_InvalidModuleMap:
+    return true;
+  }
+  llvm_unreachable("Unknown load module map result");
+}
+
+HeaderSearch::LoadModuleMapResult
+HeaderSearch::loadModuleMapFileImpl(const FileEntry *File, bool IsSystem,
+                                    const DirectoryEntry *Dir, FileID ID,
+                                    unsigned *Offset) {
+  assert(File && "expected FileEntry");
+
+  // Check whether we've already loaded this module map, and mark it as being
+  // loaded in case we recursively try to load it from itself.
+  auto AddResult = LoadedModuleMaps.insert(std::make_pair(File, true));
+  if (!AddResult.second)
+    return AddResult.first->second ? LMM_AlreadyLoaded : LMM_InvalidModuleMap;
+
+  if (ModMap.parseModuleMapFile(File, IsSystem, Dir, ID, Offset)) {
+    LoadedModuleMaps[File] = false;
+    return LMM_InvalidModuleMap;
+  }
+
+  // Try to load a corresponding private module map.
+  if (const FileEntry *PMMFile = getPrivateModuleMap(File, FileMgr)) {
+    if (ModMap.parseModuleMapFile(PMMFile, IsSystem, Dir)) {
+      LoadedModuleMaps[File] = false;
+      return LMM_InvalidModuleMap;
+    }
+  }
+
+  // This directory has a module map.
+  return LMM_NewlyLoaded;
+}
+
+const FileEntry *
+HeaderSearch::lookupModuleMapFile(const DirectoryEntry *Dir, bool IsFramework) {
+  if (!HSOpts->ImplicitModuleMaps)
+    return nullptr;
+  // For frameworks, the preferred spelling is Modules/module.modulemap, but
+  // module.map at the framework root is also accepted.
+  SmallString<128> ModuleMapFileName(Dir->getName());
+  if (IsFramework)
+    llvm::sys::path::append(ModuleMapFileName, "Modules");
+  llvm::sys::path::append(ModuleMapFileName, "module.modulemap");
+  if (auto F = FileMgr.getFile(ModuleMapFileName))
+    return *F;
+
+  // Continue to allow module.map
+  ModuleMapFileName = Dir->getName();
+  llvm::sys::path::append(ModuleMapFileName, "module.map");
+  if (auto F = FileMgr.getFile(ModuleMapFileName))
+    return *F;
+  return nullptr;
+}
+
+Module *HeaderSearch::loadFrameworkModule(StringRef Name,
+                                          const DirectoryEntry *Dir,
+                                          bool IsSystem) {
+  if (Module *Module = ModMap.findModule(Name))
+    return Module;
+
+  // Try to load a module map file.
+  switch (loadModuleMapFile(Dir, IsSystem, /*IsFramework*/true)) {
+  case LMM_InvalidModuleMap:
+    // Try to infer a module map from the framework directory.
+    if (HSOpts->ImplicitModuleMaps)
+      ModMap.inferFrameworkModule(Dir, IsSystem, /*Parent=*/nullptr);
+    break;
+
+  case LMM_AlreadyLoaded:
+  case LMM_NoDirectory:
+    return nullptr;
+
+  case LMM_NewlyLoaded:
+    break;
+  }
+
+  return ModMap.findModule(Name);
+}
+
+HeaderSearch::LoadModuleMapResult
+HeaderSearch::loadModuleMapFile(StringRef DirName, bool IsSystem,
+                                bool IsFramework) {
+  if (auto Dir = FileMgr.getDirectory(DirName))
+    return loadModuleMapFile(*Dir, IsSystem, IsFramework);
+
+  return LMM_NoDirectory;
+}
+
+HeaderSearch::LoadModuleMapResult
+HeaderSearch::loadModuleMapFile(const DirectoryEntry *Dir, bool IsSystem,
+                                bool IsFramework) {
+  auto KnownDir = DirectoryHasModuleMap.find(Dir);
+  if (KnownDir != DirectoryHasModuleMap.end())
+    return KnownDir->second ? LMM_AlreadyLoaded : LMM_InvalidModuleMap;
+
+  if (const FileEntry *ModuleMapFile = lookupModuleMapFile(Dir, IsFramework)) {
+    LoadModuleMapResult Result =
+        loadModuleMapFileImpl(ModuleMapFile, IsSystem, Dir);
+    // Add Dir explicitly in case ModuleMapFile is in a subdirectory.
+    // E.g. Foo.framework/Modules/module.modulemap
+    //      ^Dir                  ^ModuleMapFile
+    if (Result == LMM_NewlyLoaded)
+      DirectoryHasModuleMap[Dir] = true;
+    else if (Result == LMM_InvalidModuleMap)
+      DirectoryHasModuleMap[Dir] = false;
+    return Result;
+  }
+  return LMM_InvalidModuleMap;
+}
+
+void HeaderSearch::collectAllModules(SmallVectorImpl<Module *> &Modules) {
+  Modules.clear();
+
+  if (HSOpts->ImplicitModuleMaps) {
+    // Load module maps for each of the header search directories.
+    for (unsigned Idx = 0, N = SearchDirs.size(); Idx != N; ++Idx) {
+      bool IsSystem = SearchDirs[Idx].isSystemHeaderDirectory();
+      if (SearchDirs[Idx].isFramework()) {
+        std::error_code EC;
+        SmallString<128> DirNative;
+        llvm::sys::path::native(SearchDirs[Idx].getFrameworkDir()->getName(),
+                                DirNative);
+
+        // Search each of the ".framework" directories to load them as modules.
+        llvm::vfs::FileSystem &FS = FileMgr.getVirtualFileSystem();
+        for (llvm::vfs::directory_iterator Dir = FS.dir_begin(DirNative, EC),
+                                           DirEnd;
+             Dir != DirEnd && !EC; Dir.increment(EC)) {
+          if (llvm::sys::path::extension(Dir->path()) != ".framework")
+            continue;
+
+          auto FrameworkDir =
+              FileMgr.getDirectory(Dir->path());
+          if (!FrameworkDir)
+            continue;
+
+          // Load this framework module.
+          loadFrameworkModule(llvm::sys::path::stem(Dir->path()), *FrameworkDir,
+                              IsSystem);
+        }
+        continue;
+      }
+
+      // FIXME: Deal with header maps.
+      if (SearchDirs[Idx].isHeaderMap())
+        continue;
+
+      // Try to load a module map file for the search directory.
+      loadModuleMapFile(SearchDirs[Idx].getDir(), IsSystem,
+                        /*IsFramework*/ false);
+
+      // Try to load module map files for immediate subdirectories of this
+      // search directory.
+      loadSubdirectoryModuleMaps(SearchDirs[Idx]);
+    }
+  }
+
+  // Populate the list of modules.
+  for (ModuleMap::module_iterator M = ModMap.module_begin(),
+                               MEnd = ModMap.module_end();
+       M != MEnd; ++M) {
+    Modules.push_back(M->getValue());
+  }
+}
+
+void HeaderSearch::loadTopLevelSystemModules() {
+  if (!HSOpts->ImplicitModuleMaps)
+    return;
+
+  // Load module maps for each of the header search directories.
+  for (unsigned Idx = 0, N = SearchDirs.size(); Idx != N; ++Idx) {
+    // We only care about normal header directories.
+    if (!SearchDirs[Idx].isNormalDir()) {
+      continue;
+    }
+
+    // Try to load a module map file for the search directory.
+    loadModuleMapFile(SearchDirs[Idx].getDir(),
+                      SearchDirs[Idx].isSystemHeaderDirectory(),
+                      SearchDirs[Idx].isFramework());
+  }
+}
+
+void HeaderSearch::loadSubdirectoryModuleMaps(DirectoryLookup &SearchDir) {
+  assert(HSOpts->ImplicitModuleMaps &&
+         "Should not be loading subdirectory module maps");
+
+  if (SearchDir.haveSearchedAllModuleMaps())
+    return;
+
+  std::error_code EC;
+  SmallString<128> Dir = SearchDir.getDir()->getName();
+  FileMgr.makeAbsolutePath(Dir);
+  SmallString<128> DirNative;
+  llvm::sys::path::native(Dir, DirNative);
+  llvm::vfs::FileSystem &FS = FileMgr.getVirtualFileSystem();
+  for (llvm::vfs::directory_iterator Dir = FS.dir_begin(DirNative, EC), DirEnd;
+       Dir != DirEnd && !EC; Dir.increment(EC)) {
+    bool IsFramework = llvm::sys::path::extension(Dir->path()) == ".framework";
+    if (IsFramework == SearchDir.isFramework())
+      loadModuleMapFile(Dir->path(), SearchDir.isSystemHeaderDirectory(),
+                        SearchDir.isFramework());
+  }
+
+  SearchDir.setSearchedAllModuleMaps(true);
+}
+
+std::string HeaderSearch::suggestPathToFileForDiagnostics(
+    const FileEntry *File, llvm::StringRef MainFile, bool *IsSystem) {
+  // FIXME: We assume that the path name currently cached in the FileEntry is
+  // the most appropriate one for this analysis (and that it's spelled the
+  // same way as the corresponding header search path).
+  return suggestPathToFileForDiagnostics(File->getName(), /*WorkingDir=*/"",
+                                         MainFile, IsSystem);
+}
+
+std::string HeaderSearch::suggestPathToFileForDiagnostics(
+    llvm::StringRef File, llvm::StringRef WorkingDir, llvm::StringRef MainFile,
+    bool *IsSystem) {
+  using namespace llvm::sys;
+
+  unsigned BestPrefixLength = 0;
+  // Checks whether Dir and File shares a common prefix, if they do and that's
+  // the longest prefix we've seen so for it returns true and updates the
+  // BestPrefixLength accordingly.
+  auto CheckDir = [&](llvm::StringRef Dir) -> bool {
+    llvm::SmallString<32> DirPath(Dir.begin(), Dir.end());
+    if (!WorkingDir.empty() && !path::is_absolute(Dir))
+      fs::make_absolute(WorkingDir, DirPath);
+    path::remove_dots(DirPath, /*remove_dot_dot=*/true);
+    Dir = DirPath;
+    for (auto NI = path::begin(File), NE = path::end(File),
+              DI = path::begin(Dir), DE = path::end(Dir);
+         /*termination condition in loop*/; ++NI, ++DI) {
+      // '.' components in File are ignored.
+      while (NI != NE && *NI == ".")
+        ++NI;
+      if (NI == NE)
+        break;
+
+      // '.' components in Dir are ignored.
+      while (DI != DE && *DI == ".")
+        ++DI;
+      if (DI == DE) {
+        // Dir is a prefix of File, up to '.' components and choice of path
+        // separators.
+        unsigned PrefixLength = NI - path::begin(File);
+        if (PrefixLength > BestPrefixLength) {
+          BestPrefixLength = PrefixLength;
+          return true;
+        }
+        break;
+      }
+
+      // Consider all path separators equal.
+      if (NI->size() == 1 && DI->size() == 1 &&
+          path::is_separator(NI->front()) && path::is_separator(DI->front()))
+        continue;
+
+      if (*NI != *DI)
+        break;
+    }
+    return false;
+  };
+
+  for (unsigned I = 0; I != SearchDirs.size(); ++I) {
+    // FIXME: Support this search within frameworks and header maps.
+    if (!SearchDirs[I].isNormalDir())
+      continue;
+
+    StringRef Dir = SearchDirs[I].getDir()->getName();
+    if (CheckDir(Dir) && IsSystem)
+      *IsSystem = BestPrefixLength ? I >= SystemDirIdx : false;
+  }
+
+  // Try to shorten include path using TUs directory, if we couldn't find any
+  // suitable prefix in include search paths.
+  if (!BestPrefixLength && CheckDir(path::parent_path(MainFile)) && IsSystem)
+    *IsSystem = false;
+
+
+  return path::convert_to_slash(File.drop_front(BestPrefixLength));
+}