Lift VFS from clang to llvm (NFC)

This patch moves the virtual file system form clang to llvm so it can be
used by more projects.

Concretely the patch:
 - Moves VirtualFileSystem.{h|cpp} from clang/Basic to llvm/Support.
 - Moves the corresponding unit test from clang to llvm.
 - Moves the vfs namespace from clang::vfs to llvm::vfs.
 - Formats the lines affected by this change, mostly this is the result of
   the added llvm namespace.

RFC on the mailing list:
http://lists.llvm.org/pipermail/llvm-dev/2018-October/126657.html

Differential revision: https://reviews.llvm.org/D52783

llvm-svn: 344140

1 files changed, 0 insertions, 2142 deletions

diff --git a/clang/lib/Basic/VirtualFileSystem.cpp b/clang/lib/Basic/VirtualFileSystem.cpp
deleted file mode 100644
index 6d96f16a..0000000
--- a/clang/lib/Basic/VirtualFileSystem.cpp
+++ /dev/null
@@ -1,2142 +0,0 @@
-//===- VirtualFileSystem.cpp - Virtual File System Layer ------------------===//
-//
-//                     The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This file implements the VirtualFileSystem interface.
-//
-//===----------------------------------------------------------------------===//
-
-#include "clang/Basic/VirtualFileSystem.h"
-#include "clang/Basic/LLVM.h"
-#include "llvm/ADT/ArrayRef.h"
-#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/IntrusiveRefCntPtr.h"
-#include "llvm/ADT/None.h"
-#include "llvm/ADT/Optional.h"
-#include "llvm/ADT/STLExtras.h"
-#include "llvm/ADT/SmallString.h"
-#include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/StringRef.h"
-#include "llvm/ADT/StringSet.h"
-#include "llvm/ADT/Twine.h"
-#include "llvm/ADT/iterator_range.h"
-#include "llvm/Config/llvm-config.h"
-#include "llvm/Support/Casting.h"
-#include "llvm/Support/Chrono.h"
-#include "llvm/Support/Compiler.h"
-#include "llvm/Support/Debug.h"
-#include "llvm/Support/Errc.h"
-#include "llvm/Support/ErrorHandling.h"
-#include "llvm/Support/ErrorOr.h"
-#include "llvm/Support/FileSystem.h"
-#include "llvm/Support/MemoryBuffer.h"
-#include "llvm/Support/Path.h"
-#include "llvm/Support/Process.h"
-#include "llvm/Support/SMLoc.h"
-#include "llvm/Support/SourceMgr.h"
-#include "llvm/Support/YAMLParser.h"
-#include "llvm/Support/raw_ostream.h"
-#include <algorithm>
-#include <atomic>
-#include <cassert>
-#include <cstdint>
-#include <iterator>
-#include <limits>
-#include <map>
-#include <memory>
-#include <mutex>
-#include <string>
-#include <system_error>
-#include <utility>
-#include <vector>
-
-using namespace clang;
-using namespace vfs;
-using namespace llvm;
-
-using llvm::sys::fs::file_status;
-using llvm::sys::fs::file_type;
-using llvm::sys::fs::perms;
-using llvm::sys::fs::UniqueID;
-
-Status::Status(const file_status &Status)
-    : UID(Status.getUniqueID()), MTime(Status.getLastModificationTime()),
-      User(Status.getUser()), Group(Status.getGroup()), Size(Status.getSize()),
-      Type(Status.type()), Perms(Status.permissions())  {}
-
-Status::Status(StringRef Name, UniqueID UID, sys::TimePoint<> MTime,
-               uint32_t User, uint32_t Group, uint64_t Size, file_type Type,
-               perms Perms)
-    : Name(Name), UID(UID), MTime(MTime), User(User), Group(Group), Size(Size),
-      Type(Type), Perms(Perms) {}
-
-Status Status::copyWithNewName(const Status &In, StringRef NewName) {
-  return Status(NewName, In.getUniqueID(), In.getLastModificationTime(),
-                In.getUser(), In.getGroup(), In.getSize(), In.getType(),
-                In.getPermissions());
-}
-
-Status Status::copyWithNewName(const file_status &In, StringRef NewName) {
-  return Status(NewName, In.getUniqueID(), In.getLastModificationTime(),
-                In.getUser(), In.getGroup(), In.getSize(), In.type(),
-                In.permissions());
-}
-
-bool Status::equivalent(const Status &Other) const {
-  assert(isStatusKnown() && Other.isStatusKnown());
-  return getUniqueID() == Other.getUniqueID();
-}
-
-bool Status::isDirectory() const {
-  return Type == file_type::directory_file;
-}
-
-bool Status::isRegularFile() const {
-  return Type == file_type::regular_file;
-}
-
-bool Status::isOther() const {
-  return exists() && !isRegularFile() && !isDirectory() && !isSymlink();
-}
-
-bool Status::isSymlink() const {
-  return Type == file_type::symlink_file;
-}
-
-bool Status::isStatusKnown() const {
-  return Type != file_type::status_error;
-}
-
-bool Status::exists() const {
-  return isStatusKnown() && Type != file_type::file_not_found;
-}
-
-File::~File() = default;
-
-FileSystem::~FileSystem() = default;
-
-ErrorOr<std::unique_ptr<MemoryBuffer>>
-FileSystem::getBufferForFile(const llvm::Twine &Name, int64_t FileSize,
-                             bool RequiresNullTerminator, bool IsVolatile) {
-  auto F = openFileForRead(Name);
-  if (!F)
-    return F.getError();
-
-  return (*F)->getBuffer(Name, FileSize, RequiresNullTerminator, IsVolatile);
-}
-
-std::error_code FileSystem::makeAbsolute(SmallVectorImpl<char> &Path) const {
-  if (llvm::sys::path::is_absolute(Path))
-    return {};
-
-  auto WorkingDir = getCurrentWorkingDirectory();
-  if (!WorkingDir)
-    return WorkingDir.getError();
-
-  return llvm::sys::fs::make_absolute(WorkingDir.get(), Path);
-}
-
-std::error_code FileSystem::getRealPath(const Twine &Path,
-                                        SmallVectorImpl<char> &Output) const {
-  return errc::operation_not_permitted;
-}
-
-bool FileSystem::exists(const Twine &Path) {
-  auto Status = status(Path);
-  return Status && Status->exists();
-}
-
-#ifndef NDEBUG
-static bool isTraversalComponent(StringRef Component) {
-  return Component.equals("..") || Component.equals(".");
-}
-
-static bool pathHasTraversal(StringRef Path) {
-  using namespace llvm::sys;
-
-  for (StringRef Comp : llvm::make_range(path::begin(Path), path::end(Path)))
-    if (isTraversalComponent(Comp))
-      return true;
-  return false;
-}
-#endif
-
-//===-----------------------------------------------------------------------===/
-// RealFileSystem implementation
-//===-----------------------------------------------------------------------===/
-
-namespace {
-
-/// Wrapper around a raw file descriptor.
-class RealFile : public File {
-  friend class RealFileSystem;
-
-  int FD;
-  Status S;
-  std::string RealName;
-
-  RealFile(int FD, StringRef NewName, StringRef NewRealPathName)
-      : FD(FD), S(NewName, {}, {}, {}, {}, {},
-                  llvm::sys::fs::file_type::status_error, {}),
-        RealName(NewRealPathName.str()) {
-    assert(FD >= 0 && "Invalid or inactive file descriptor");
-  }
-
-public:
-  ~RealFile() override;
-
-  ErrorOr<Status> status() override;
-  ErrorOr<std::string> getName() override;
-  ErrorOr<std::unique_ptr<MemoryBuffer>> getBuffer(const Twine &Name,
-                                                   int64_t FileSize,
-                                                   bool RequiresNullTerminator,
-                                                   bool IsVolatile) override;
-  std::error_code close() override;
-};
-
-} // namespace
-
-RealFile::~RealFile() { close(); }
-
-ErrorOr<Status> RealFile::status() {
-  assert(FD != -1 && "cannot stat closed file");
-  if (!S.isStatusKnown()) {
-    file_status RealStatus;
-    if (std::error_code EC = sys::fs::status(FD, RealStatus))
-      return EC;
-    S = Status::copyWithNewName(RealStatus, S.getName());
-  }
-  return S;
-}
-
-ErrorOr<std::string> RealFile::getName() {
-  return RealName.empty() ? S.getName().str() : RealName;
-}
-
-ErrorOr<std::unique_ptr<MemoryBuffer>>
-RealFile::getBuffer(const Twine &Name, int64_t FileSize,
-                    bool RequiresNullTerminator, bool IsVolatile) {
-  assert(FD != -1 && "cannot get buffer for closed file");
-  return MemoryBuffer::getOpenFile(FD, Name, FileSize, RequiresNullTerminator,
-                                   IsVolatile);
-}
-
-std::error_code RealFile::close() {
-  std::error_code EC = sys::Process::SafelyCloseFileDescriptor(FD);
-  FD = -1;
-  return EC;
-}
-
-namespace {
-
-/// The file system according to your operating system.
-class RealFileSystem : public FileSystem {
-public:
-  ErrorOr<Status> status(const Twine &Path) override;
-  ErrorOr<std::unique_ptr<File>> openFileForRead(const Twine &Path) override;
-  directory_iterator dir_begin(const Twine &Dir, std::error_code &EC) override;
-
-  llvm::ErrorOr<std::string> getCurrentWorkingDirectory() const override;
-  std::error_code setCurrentWorkingDirectory(const Twine &Path) override;
-  std::error_code getRealPath(const Twine &Path,
-                              SmallVectorImpl<char> &Output) const override;
-private:
-  mutable std::mutex CWDMutex;
-  mutable std::string CWDCache;
-};
-
-} // namespace
-
-ErrorOr<Status> RealFileSystem::status(const Twine &Path) {
-  sys::fs::file_status RealStatus;
-  if (std::error_code EC = sys::fs::status(Path, RealStatus))
-    return EC;
-  return Status::copyWithNewName(RealStatus, Path.str());
-}
-
-ErrorOr<std::unique_ptr<File>>
-RealFileSystem::openFileForRead(const Twine &Name) {
-  int FD;
-  SmallString<256> RealName;
-  if (std::error_code EC =
-          sys::fs::openFileForRead(Name, FD, sys::fs::OF_None, &RealName))
-    return EC;
-  return std::unique_ptr<File>(new RealFile(FD, Name.str(), RealName.str()));
-}
-
-llvm::ErrorOr<std::string> RealFileSystem::getCurrentWorkingDirectory() const {
-  std::lock_guard<std::mutex> Lock(CWDMutex);
-  if (!CWDCache.empty())
-    return CWDCache;
-  SmallString<256> Dir;
-  if (std::error_code EC = llvm::sys::fs::current_path(Dir))
-    return EC;
-  CWDCache = Dir.str();
-  return CWDCache;
-}
-
-std::error_code RealFileSystem::setCurrentWorkingDirectory(const Twine &Path) {
-  // FIXME: chdir is thread hostile; on the other hand, creating the same
-  // behavior as chdir is complex: chdir resolves the path once, thus
-  // guaranteeing that all subsequent relative path operations work
-  // on the same path the original chdir resulted in. This makes a
-  // difference for example on network filesystems, where symlinks might be
-  // switched during runtime of the tool. Fixing this depends on having a
-  // file system abstraction that allows openat() style interactions.
-  if (auto EC = llvm::sys::fs::set_current_path(Path))
-    return EC;
-
-  // Invalidate cache.
-  std::lock_guard<std::mutex> Lock(CWDMutex);
-  CWDCache.clear();
-  return std::error_code();
-}
-
-std::error_code
-RealFileSystem::getRealPath(const Twine &Path,
-                            SmallVectorImpl<char> &Output) const {
-  return llvm::sys::fs::real_path(Path, Output);
-}
-
-IntrusiveRefCntPtr<FileSystem> vfs::getRealFileSystem() {
-  static IntrusiveRefCntPtr<FileSystem> FS = new RealFileSystem();
-  return FS;
-}
-
-namespace {
-
-class RealFSDirIter : public clang::vfs::detail::DirIterImpl {
-  llvm::sys::fs::directory_iterator Iter;
-
-public:
-  RealFSDirIter(const Twine &Path, std::error_code &EC) : Iter(Path, EC) {
-    if (Iter != llvm::sys::fs::directory_iterator())
-      CurrentEntry = directory_entry(Iter->path(), Iter->type());
-  }
-
-  std::error_code increment() override {
-    std::error_code EC;
-    Iter.increment(EC);
-    CurrentEntry = (Iter == llvm::sys::fs::directory_iterator())
-                       ? directory_entry()
-                       : directory_entry(Iter->path(), Iter->type());
-    return EC;
-  }
-};
-
-} // namespace
-
-directory_iterator RealFileSystem::dir_begin(const Twine &Dir,
-                                             std::error_code &EC) {
-  return directory_iterator(std::make_shared<RealFSDirIter>(Dir, EC));
-}
-
-//===-----------------------------------------------------------------------===/
-// OverlayFileSystem implementation
-//===-----------------------------------------------------------------------===/
-
-OverlayFileSystem::OverlayFileSystem(IntrusiveRefCntPtr<FileSystem> BaseFS) {
-  FSList.push_back(std::move(BaseFS));
-}
-
-void OverlayFileSystem::pushOverlay(IntrusiveRefCntPtr<FileSystem> FS) {
-  FSList.push_back(FS);
-  // Synchronize added file systems by duplicating the working directory from
-  // the first one in the list.
-  FS->setCurrentWorkingDirectory(getCurrentWorkingDirectory().get());
-}
-
-ErrorOr<Status> OverlayFileSystem::status(const Twine &Path) {
-  // FIXME: handle symlinks that cross file systems
-  for (iterator I = overlays_begin(), E = overlays_end(); I != E; ++I) {
-    ErrorOr<Status> Status = (*I)->status(Path);
-    if (Status || Status.getError() != llvm::errc::no_such_file_or_directory)
-      return Status;
-  }
-  return make_error_code(llvm::errc::no_such_file_or_directory);
-}
-
-ErrorOr<std::unique_ptr<File>>
-OverlayFileSystem::openFileForRead(const llvm::Twine &Path) {
-  // FIXME: handle symlinks that cross file systems
-  for (iterator I = overlays_begin(), E = overlays_end(); I != E; ++I) {
-    auto Result = (*I)->openFileForRead(Path);
-    if (Result || Result.getError() != llvm::errc::no_such_file_or_directory)
-      return Result;
-  }
-  return make_error_code(llvm::errc::no_such_file_or_directory);
-}
-
-llvm::ErrorOr<std::string>
-OverlayFileSystem::getCurrentWorkingDirectory() const {
-  // All file systems are synchronized, just take the first working directory.
-  return FSList.front()->getCurrentWorkingDirectory();
-}
-
-std::error_code
-OverlayFileSystem::setCurrentWorkingDirectory(const Twine &Path) {
-  for (auto &FS : FSList)
-    if (std::error_code EC = FS->setCurrentWorkingDirectory(Path))
-      return EC;
-  return {};
-}
-
-std::error_code
-OverlayFileSystem::getRealPath(const Twine &Path,
-                               SmallVectorImpl<char> &Output) const {
-  for (auto &FS : FSList)
-    if (FS->exists(Path))
-      return FS->getRealPath(Path, Output);
-  return errc::no_such_file_or_directory;
-}
-
-clang::vfs::detail::DirIterImpl::~DirIterImpl() = default;
-
-namespace {
-
-class OverlayFSDirIterImpl : public clang::vfs::detail::DirIterImpl {
-  OverlayFileSystem &Overlays;
-  std::string Path;
-  OverlayFileSystem::iterator CurrentFS;
-  directory_iterator CurrentDirIter;
-  llvm::StringSet<> SeenNames;
-
-  std::error_code incrementFS() {
-    assert(CurrentFS != Overlays.overlays_end() && "incrementing past end");
-    ++CurrentFS;
-    for (auto E = Overlays.overlays_end(); CurrentFS != E; ++CurrentFS) {
-      std::error_code EC;
-      CurrentDirIter = (*CurrentFS)->dir_begin(Path, EC);
-      if (EC && EC != errc::no_such_file_or_directory)
-        return EC;
-      if (CurrentDirIter != directory_iterator())
-        break; // found
-    }
-    return {};
-  }
-
-  std::error_code incrementDirIter(bool IsFirstTime) {
-    assert((IsFirstTime || CurrentDirIter != directory_iterator()) &&
-           "incrementing past end");
-    std::error_code EC;
-    if (!IsFirstTime)
-      CurrentDirIter.increment(EC);
-    if (!EC && CurrentDirIter == directory_iterator())
-      EC = incrementFS();
-    return EC;
-  }
-
-  std::error_code incrementImpl(bool IsFirstTime) {
-    while (true) {
-      std::error_code EC = incrementDirIter(IsFirstTime);
-      if (EC || CurrentDirIter == directory_iterator()) {
-        CurrentEntry = directory_entry();
-        return EC;
-      }
-      CurrentEntry = *CurrentDirIter;
-      StringRef Name = llvm::sys::path::filename(CurrentEntry.path());
-      if (SeenNames.insert(Name).second)
-        return EC; // name not seen before
-    }
-    llvm_unreachable("returned above");
-  }
-
-public:
-  OverlayFSDirIterImpl(const Twine &Path, OverlayFileSystem &FS,
-                       std::error_code &EC)
-      : Overlays(FS), Path(Path.str()), CurrentFS(Overlays.overlays_begin()) {
-    CurrentDirIter = (*CurrentFS)->dir_begin(Path, EC);
-    EC = incrementImpl(true);
-  }
-
-  std::error_code increment() override { return incrementImpl(false); }
-};
-
-} // namespace
-
-directory_iterator OverlayFileSystem::dir_begin(const Twine &Dir,
-                                                std::error_code &EC) {
-  return directory_iterator(
-      std::make_shared<OverlayFSDirIterImpl>(Dir, *this, EC));
-}
-
-namespace clang {
-namespace vfs {
-
-namespace detail {
-
-enum InMemoryNodeKind { IME_File, IME_Directory, IME_HardLink };
-
-/// The in memory file system is a tree of Nodes. Every node can either be a
-/// file , hardlink or a directory.
-class InMemoryNode {
-  InMemoryNodeKind Kind;
-  std::string FileName;
-
-public:
-  InMemoryNode(llvm::StringRef FileName, InMemoryNodeKind Kind)
-      : Kind(Kind), FileName(llvm::sys::path::filename(FileName)) {}
-  virtual ~InMemoryNode() = default;
-
-  /// Get the filename of this node (the name without the directory part).
-  StringRef getFileName() const { return FileName; }
-  InMemoryNodeKind getKind() const { return Kind; }
-  virtual std::string toString(unsigned Indent) const = 0;
-};
-
-class InMemoryFile : public InMemoryNode {
-  Status Stat;
-  std::unique_ptr<llvm::MemoryBuffer> Buffer;
-
-public:
-  InMemoryFile(Status Stat, std::unique_ptr<llvm::MemoryBuffer> Buffer)
-      : InMemoryNode(Stat.getName(), IME_File), Stat(std::move(Stat)),
-        Buffer(std::move(Buffer)) {}
-
-  /// Return the \p Status for this node. \p RequestedName should be the name
-  /// through which the caller referred to this node. It will override
-  /// \p Status::Name in the return value, to mimic the behavior of \p RealFile.
-  Status getStatus(StringRef RequestedName) const {
-    return Status::copyWithNewName(Stat, RequestedName);
-  }
-  llvm::MemoryBuffer *getBuffer() const { return Buffer.get(); }
-
-  std::string toString(unsigned Indent) const override {
-    return (std::string(Indent, ' ') + Stat.getName() + "\n").str();
-  }
-
-  static bool classof(const InMemoryNode *N) {
-    return N->getKind() == IME_File;
-  }
-};
-
-namespace {
-
-class InMemoryHardLink : public InMemoryNode {
-  const InMemoryFile &ResolvedFile;
-
-public:
-  InMemoryHardLink(StringRef Path, const InMemoryFile &ResolvedFile)
-      : InMemoryNode(Path, IME_HardLink), ResolvedFile(ResolvedFile) {}
-  const InMemoryFile &getResolvedFile() const { return ResolvedFile; }
-
-  std::string toString(unsigned Indent) const override {
-    return std::string(Indent, ' ') + "HardLink to -> " +
-           ResolvedFile.toString(0);
-  }
-
-  static bool classof(const InMemoryNode *N) {
-    return N->getKind() == IME_HardLink;
-  }
-};
-
-/// Adapt a InMemoryFile for VFS' File interface.  The goal is to make
-/// \p InMemoryFileAdaptor mimic as much as possible the behavior of
-/// \p RealFile.
-class InMemoryFileAdaptor : public File {
-  const InMemoryFile &Node;
-  /// The name to use when returning a Status for this file.
-  std::string RequestedName;
-
-public:
-  explicit InMemoryFileAdaptor(const InMemoryFile &Node,
-                               std::string RequestedName)
-      : Node(Node), RequestedName(std::move(RequestedName)) {}
-
-  llvm::ErrorOr<Status> status() override {
-    return Node.getStatus(RequestedName);
-  }
-
-  llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
-  getBuffer(const Twine &Name, int64_t FileSize, bool RequiresNullTerminator,
-            bool IsVolatile) override {
-    llvm::MemoryBuffer *Buf = Node.getBuffer();
-    return llvm::MemoryBuffer::getMemBuffer(
-        Buf->getBuffer(), Buf->getBufferIdentifier(), RequiresNullTerminator);
-  }
-
-  std::error_code close() override { return {}; }
-};
-} // namespace
-
-class InMemoryDirectory : public InMemoryNode {
-  Status Stat;
-  llvm::StringMap<std::unique_ptr<InMemoryNode>> Entries;
-
-public:
-  InMemoryDirectory(Status Stat)
-      : InMemoryNode(Stat.getName(), IME_Directory), Stat(std::move(Stat)) {}
-
-  /// Return the \p Status for this node. \p RequestedName should be the name
-  /// through which the caller referred to this node. It will override
-  /// \p Status::Name in the return value, to mimic the behavior of \p RealFile.
-  Status getStatus(StringRef RequestedName) const {
-    return Status::copyWithNewName(Stat, RequestedName);
-  }
-  InMemoryNode *getChild(StringRef Name) {
-    auto I = Entries.find(Name);
-    if (I != Entries.end())
-      return I->second.get();
-    return nullptr;
-  }
-
-  InMemoryNode *addChild(StringRef Name, std::unique_ptr<InMemoryNode> Child) {
-    return Entries.insert(make_pair(Name, std::move(Child)))
-        .first->second.get();
-  }
-
-  using const_iterator = decltype(Entries)::const_iterator;
-
-  const_iterator begin() const { return Entries.begin(); }
-  const_iterator end() const { return Entries.end(); }
-
-  std::string toString(unsigned Indent) const override {
-    std::string Result =
-        (std::string(Indent, ' ') + Stat.getName() + "\n").str();
-    for (const auto &Entry : Entries)
-      Result += Entry.second->toString(Indent + 2);
-    return Result;
-  }
-
-  static bool classof(const InMemoryNode *N) {
-    return N->getKind() == IME_Directory;
-  }
-};
-
-namespace {
-Status getNodeStatus(const InMemoryNode *Node, StringRef RequestedName) {
-  if (auto Dir = dyn_cast<detail::InMemoryDirectory>(Node))
-    return Dir->getStatus(RequestedName);
-  if (auto File = dyn_cast<detail::InMemoryFile>(Node))
-    return File->getStatus(RequestedName);
-  if (auto Link = dyn_cast<detail::InMemoryHardLink>(Node))
-    return Link->getResolvedFile().getStatus(RequestedName);
-  llvm_unreachable("Unknown node type");
-}
-} // namespace
-} // namespace detail
-
-InMemoryFileSystem::InMemoryFileSystem(bool UseNormalizedPaths)
-    : Root(new detail::InMemoryDirectory(
-          Status("", getNextVirtualUniqueID(), llvm::sys::TimePoint<>(), 0, 0,
-                 0, llvm::sys::fs::file_type::directory_file,
-                 llvm::sys::fs::perms::all_all))),
-      UseNormalizedPaths(UseNormalizedPaths) {}
-
-InMemoryFileSystem::~InMemoryFileSystem() = default;
-
-std::string InMemoryFileSystem::toString() const {
-  return Root->toString(/*Indent=*/0);
-}
-
-bool InMemoryFileSystem::addFile(const Twine &P, time_t ModificationTime,
-                                 std::unique_ptr<llvm::MemoryBuffer> Buffer,
-                                 Optional<uint32_t> User,
-                                 Optional<uint32_t> Group,
-                                 Optional<llvm::sys::fs::file_type> Type,
-                                 Optional<llvm::sys::fs::perms> Perms,
-                                 const detail::InMemoryFile *HardLinkTarget) {
-  SmallString<128> Path;
-  P.toVector(Path);
-
-  // Fix up relative paths. This just prepends the current working directory.
-  std::error_code EC = makeAbsolute(Path);
-  assert(!EC);
-  (void)EC;
-
-  if (useNormalizedPaths())
-    llvm::sys::path::remove_dots(Path, /*remove_dot_dot=*/true);
-
-  if (Path.empty())
-    return false;
-
-  detail::InMemoryDirectory *Dir = Root.get();
-  auto I = llvm::sys::path::begin(Path), E = sys::path::end(Path);
-  const auto ResolvedUser = User.getValueOr(0);
-  const auto ResolvedGroup = Group.getValueOr(0);
-  const auto ResolvedType = Type.getValueOr(sys::fs::file_type::regular_file);
-  const auto ResolvedPerms = Perms.getValueOr(sys::fs::all_all);
-  assert(!(HardLinkTarget && Buffer) && "HardLink cannot have a buffer");
-  // Any intermediate directories we create should be accessible by
-  // the owner, even if Perms says otherwise for the final path.
-  const auto NewDirectoryPerms = ResolvedPerms | sys::fs::owner_all;
-  while (true) {
-    StringRef Name = *I;
-    detail::InMemoryNode *Node = Dir->getChild(Name);
-    ++I;
-    if (!Node) {
-      if (I == E) {
-        // End of the path.
-        std::unique_ptr<detail::InMemoryNode> Child;
-        if (HardLinkTarget)
-          Child.reset(new detail::InMemoryHardLink(P.str(), *HardLinkTarget));
-        else {
-          // Create a new file or directory.
-          Status Stat(P.str(), getNextVirtualUniqueID(),
-                      llvm::sys::toTimePoint(ModificationTime), ResolvedUser,
-                      ResolvedGroup, Buffer->getBufferSize(), ResolvedType,
-                      ResolvedPerms);
-          if (ResolvedType == sys::fs::file_type::directory_file) {
-            Child.reset(new detail::InMemoryDirectory(std::move(Stat)));
-          } else {
-            Child.reset(
-                new detail::InMemoryFile(std::move(Stat), std::move(Buffer)));
-          }
-        }
-        Dir->addChild(Name, std::move(Child));
-        return true;
-      }
-
-      // Create a new directory. Use the path up to here.
-      Status Stat(
-          StringRef(Path.str().begin(), Name.end() - Path.str().begin()),
-          getNextVirtualUniqueID(), llvm::sys::toTimePoint(ModificationTime),
-          ResolvedUser, ResolvedGroup, 0, sys::fs::file_type::directory_file,
-          NewDirectoryPerms);
-      Dir = cast<detail::InMemoryDirectory>(Dir->addChild(
-          Name, llvm::make_unique<detail::InMemoryDirectory>(std::move(Stat))));
-      continue;
-    }
-
-    if (auto *NewDir = dyn_cast<detail::InMemoryDirectory>(Node)) {
-      Dir = NewDir;
-    } else {
-      assert((isa<detail::InMemoryFile>(Node) ||
-              isa<detail::InMemoryHardLink>(Node)) &&
-             "Must be either file, hardlink or directory!");
-
-      // Trying to insert a directory in place of a file.
-      if (I != E)
-        return false;
-
-      // Return false only if the new file is different from the existing one.
-      if (auto Link = dyn_cast<detail::InMemoryHardLink>(Node)) {
-        return Link->getResolvedFile().getBuffer()->getBuffer() ==
-               Buffer->getBuffer();
-      }
-      return cast<detail::InMemoryFile>(Node)->getBuffer()->getBuffer() ==
-             Buffer->getBuffer();
-    }
-  }
-}
-
-bool InMemoryFileSystem::addFile(const Twine &P, time_t ModificationTime,
-                                 std::unique_ptr<llvm::MemoryBuffer> Buffer,
-                                 Optional<uint32_t> User,
-                                 Optional<uint32_t> Group,
-                                 Optional<llvm::sys::fs::file_type> Type,
-                                 Optional<llvm::sys::fs::perms> Perms) {
-  return addFile(P, ModificationTime, std::move(Buffer), User, Group, Type,
-                 Perms, /*HardLinkTarget=*/nullptr);
-}
-
-bool InMemoryFileSystem::addFileNoOwn(const Twine &P, time_t ModificationTime,
-                                      llvm::MemoryBuffer *Buffer,
-                                      Optional<uint32_t> User,
-                                      Optional<uint32_t> Group,
-                                      Optional<llvm::sys::fs::file_type> Type,
-                                      Optional<llvm::sys::fs::perms> Perms) {
-  return addFile(P, ModificationTime,
-                 llvm::MemoryBuffer::getMemBuffer(
-                     Buffer->getBuffer(), Buffer->getBufferIdentifier()),
-                 std::move(User), std::move(Group), std::move(Type),
-                 std::move(Perms));
-}
-
-static ErrorOr<const detail::InMemoryNode *>
-lookupInMemoryNode(const InMemoryFileSystem &FS, detail::InMemoryDirectory *Dir,
-                   const Twine &P) {
-  SmallString<128> Path;
-  P.toVector(Path);
-
-  // Fix up relative paths. This just prepends the current working directory.
-  std::error_code EC = FS.makeAbsolute(Path);
-  assert(!EC);
-  (void)EC;
-
-  if (FS.useNormalizedPaths())
-    llvm::sys::path::remove_dots(Path, /*remove_dot_dot=*/true);
-
-  if (Path.empty())
-    return Dir;
-
-  auto I = llvm::sys::path::begin(Path), E = llvm::sys::path::end(Path);
-  while (true) {
-    detail::InMemoryNode *Node = Dir->getChild(*I);
-    ++I;
-    if (!Node)
-      return errc::no_such_file_or_directory;
-
-    // Return the file if it's at the end of the path.
-    if (auto File = dyn_cast<detail::InMemoryFile>(Node)) {
-      if (I == E)
-        return File;
-      return errc::no_such_file_or_directory;
-    }
-
-    // If Node is HardLink then return the resolved file.
-    if (auto File = dyn_cast<detail::InMemoryHardLink>(Node)) {
-      if (I == E)
-        return &File->getResolvedFile();
-      return errc::no_such_file_or_directory;
-    }
-    // Traverse directories.
-    Dir = cast<detail::InMemoryDirectory>(Node);
-    if (I == E)
-      return Dir;
-  }
-}
-
-bool InMemoryFileSystem::addHardLink(const Twine &FromPath,
-                                     const Twine &ToPath) {
-  auto FromNode = lookupInMemoryNode(*this, Root.get(), FromPath);
-  auto ToNode = lookupInMemoryNode(*this, Root.get(), ToPath);
-  // FromPath must not have been added before. ToPath must have been added
-  // before. Resolved ToPath must be a File.
-  if (!ToNode || FromNode || !isa<detail::InMemoryFile>(*ToNode))
-    return false;
-  return this->addFile(FromPath, 0, nullptr, None, None, None, None,
-                       cast<detail::InMemoryFile>(*ToNode));
-}
-
-llvm::ErrorOr<Status> InMemoryFileSystem::status(const Twine &Path) {
-  auto Node = lookupInMemoryNode(*this, Root.get(), Path);
-  if (Node)
-    return detail::getNodeStatus(*Node, Path.str());
-  return Node.getError();
-}
-
-llvm::ErrorOr<std::unique_ptr<File>>
-InMemoryFileSystem::openFileForRead(const Twine &Path) {
-  auto Node = lookupInMemoryNode(*this, Root.get(), Path);
-  if (!Node)
-    return Node.getError();
-
-  // When we have a file provide a heap-allocated wrapper for the memory buffer
-  // to match the ownership semantics for File.
-  if (auto *F = dyn_cast<detail::InMemoryFile>(*Node))
-    return std::unique_ptr<File>(
-        new detail::InMemoryFileAdaptor(*F, Path.str()));
-
-  // FIXME: errc::not_a_file?
-  return make_error_code(llvm::errc::invalid_argument);
-}
-
-namespace {
-
-/// Adaptor from InMemoryDir::iterator to directory_iterator.
-class InMemoryDirIterator : public clang::vfs::detail::DirIterImpl {
-  detail::InMemoryDirectory::const_iterator I;
-  detail::InMemoryDirectory::const_iterator E;
-  std::string RequestedDirName;
-
-  void setCurrentEntry() {
-    if (I != E) {
-      SmallString<256> Path(RequestedDirName);
-      llvm::sys::path::append(Path, I->second->getFileName());
-      sys::fs::file_type Type;
-      switch (I->second->getKind()) {
-        case detail::IME_File:
-        case detail::IME_HardLink:
-          Type = sys::fs::file_type::regular_file;
-          break;
-        case detail::IME_Directory:
-          Type = sys::fs::file_type::directory_file;
-          break;
-      }
-      CurrentEntry = directory_entry(Path.str(), Type);
-    } else {
-      // When we're at the end, make CurrentEntry invalid and DirIterImpl will
-      // do the rest.
-      CurrentEntry = directory_entry();
-    }
-  }
-
-public:
-  InMemoryDirIterator() = default;
-
-  explicit InMemoryDirIterator(const detail::InMemoryDirectory &Dir,
-                               std::string RequestedDirName)
-      : I(Dir.begin()), E(Dir.end()),
-        RequestedDirName(std::move(RequestedDirName)) {
-    setCurrentEntry();
-  }
-
-  std::error_code increment() override {
-    ++I;
-    setCurrentEntry();
-    return {};
-  }
-};
-
-} // namespace
-
-directory_iterator InMemoryFileSystem::dir_begin(const Twine &Dir,
-                                                 std::error_code &EC) {
-  auto Node = lookupInMemoryNode(*this, Root.get(), Dir);
-  if (!Node) {
-    EC = Node.getError();
-    return directory_iterator(std::make_shared<InMemoryDirIterator>());
-  }
-
-  if (auto *DirNode = dyn_cast<detail::InMemoryDirectory>(*Node))
-    return directory_iterator(
-        std::make_shared<InMemoryDirIterator>(*DirNode, Dir.str()));
-
-  EC = make_error_code(llvm::errc::not_a_directory);
-  return directory_iterator(std::make_shared<InMemoryDirIterator>());
-}
-
-std::error_code InMemoryFileSystem::setCurrentWorkingDirectory(const Twine &P) {
-  SmallString<128> Path;
-  P.toVector(Path);
-
-  // Fix up relative paths. This just prepends the current working directory.
-  std::error_code EC = makeAbsolute(Path);
-  assert(!EC);
-  (void)EC;
-
-  if (useNormalizedPaths())
-    llvm::sys::path::remove_dots(Path, /*remove_dot_dot=*/true);
-
-  if (!Path.empty())
-    WorkingDirectory = Path.str();
-  return {};
-}
-
-std::error_code
-InMemoryFileSystem::getRealPath(const Twine &Path,
-                                SmallVectorImpl<char> &Output) const {
-  auto CWD = getCurrentWorkingDirectory();
-  if (!CWD || CWD->empty())
-    return errc::operation_not_permitted;
-  Path.toVector(Output);
-  if (auto EC = makeAbsolute(Output))
-    return EC;
-  llvm::sys::path::remove_dots(Output, /*remove_dot_dot=*/true);
-  return {};
-}
-
-} // namespace vfs
-} // namespace clang
-
-//===-----------------------------------------------------------------------===/
-// RedirectingFileSystem implementation
-//===-----------------------------------------------------------------------===/
-
-namespace {
-
-enum EntryKind {
-  EK_Directory,
-  EK_File
-};
-
-/// A single file or directory in the VFS.
-class Entry {
-  EntryKind Kind;
-  std::string Name;
-
-public:
-  Entry(EntryKind K, StringRef Name) : Kind(K), Name(Name) {}
-  virtual ~Entry() = default;
-
-  StringRef getName() const { return Name; }
-  EntryKind getKind() const { return Kind; }
-};
-
-class RedirectingDirectoryEntry : public Entry {
-  std::vector<std::unique_ptr<Entry>> Contents;
-  Status S;
-
-public:
-  RedirectingDirectoryEntry(StringRef Name,
-                            std::vector<std::unique_ptr<Entry>> Contents,
-                            Status S)
-      : Entry(EK_Directory, Name), Contents(std::move(Contents)),
-        S(std::move(S)) {}
-  RedirectingDirectoryEntry(StringRef Name, Status S)
-      : Entry(EK_Directory, Name), S(std::move(S)) {}
-
-  Status getStatus() { return S; }
-
-  void addContent(std::unique_ptr<Entry> Content) {
-    Contents.push_back(std::move(Content));
-  }
-
-  Entry *getLastContent() const { return Contents.back().get(); }
-
-  using iterator = decltype(Contents)::iterator;
-
-  iterator contents_begin() { return Contents.begin(); }
-  iterator contents_end() { return Contents.end(); }
-
-  static bool classof(const Entry *E) { return E->getKind() == EK_Directory; }
-};
-
-class RedirectingFileEntry : public Entry {
-public:
-  enum NameKind {
-    NK_NotSet,
-    NK_External,
-    NK_Virtual
-  };
-
-private:
-  std::string ExternalContentsPath;
-  NameKind UseName;
-
-public:
-  RedirectingFileEntry(StringRef Name, StringRef ExternalContentsPath,
-                       NameKind UseName)
-      : Entry(EK_File, Name), ExternalContentsPath(ExternalContentsPath),
-        UseName(UseName) {}
-
-  StringRef getExternalContentsPath() const { return ExternalContentsPath; }
-
-  /// whether to use the external path as the name for this file.
-  bool useExternalName(bool GlobalUseExternalName) const {
-    return UseName == NK_NotSet ? GlobalUseExternalName
-                                : (UseName == NK_External);
-  }
-
-  NameKind getUseName() const { return UseName; }
-
-  static bool classof(const Entry *E) { return E->getKind() == EK_File; }
-};
-
-class VFSFromYamlDirIterImpl : public clang::vfs::detail::DirIterImpl {
-  std::string Dir;
-  RedirectingDirectoryEntry::iterator Current, End;
-
-  std::error_code incrementImpl();
-
-public:
-  VFSFromYamlDirIterImpl(const Twine &Path,
-                         RedirectingDirectoryEntry::iterator Begin,
-                         RedirectingDirectoryEntry::iterator End,
-                         std::error_code &EC);
-
-  std::error_code increment() override;
-};
-
-/// A virtual file system parsed from a YAML file.
-///
-/// Currently, this class allows creating virtual directories and mapping
-/// virtual file paths to existing external files, available in \c ExternalFS.
-///
-/// The basic structure of the parsed file is:
-/// \verbatim
-/// {
-///   'version': <version number>,
-///   <optional configuration>
-///   'roots': [
-///              <directory entries>
-///            ]
-/// }
-/// \endverbatim
-///
-/// All configuration options are optional.
-///   'case-sensitive': <boolean, default=true>
-///   'use-external-names': <boolean, default=true>
-///   'overlay-relative': <boolean, default=false>
-///   'ignore-non-existent-contents': <boolean, default=true>
-///
-/// Virtual directories are represented as
-/// \verbatim
-/// {
-///   'type': 'directory',
-///   'name': <string>,
-///   'contents': [ <file or directory entries> ]
-/// }
-/// \endverbatim
-///
-/// The default attributes for virtual directories are:
-/// \verbatim
-/// MTime = now() when created
-/// Perms = 0777
-/// User = Group = 0
-/// Size = 0
-/// UniqueID = unspecified unique value
-/// \endverbatim
-///
-/// Re-mapped files are represented as
-/// \verbatim
-/// {
-///   'type': 'file',
-///   'name': <string>,
-///   'use-external-name': <boolean> # Optional
-///   'external-contents': <path to external file>
-/// }
-/// \endverbatim
-///
-/// and inherit their attributes from the external contents.
-///
-/// In both cases, the 'name' field may contain multiple path components (e.g.
-/// /path/to/file). However, any directory that contains more than one child
-/// must be uniquely represented by a directory entry.
-class RedirectingFileSystem : public vfs::FileSystem {
-  friend class RedirectingFileSystemParser;
-
-  /// The root(s) of the virtual file system.
-  std::vector<std::unique_ptr<Entry>> Roots;
-
-  /// The file system to use for external references.
-  IntrusiveRefCntPtr<FileSystem> ExternalFS;
-
-  /// If IsRelativeOverlay is set, this represents the directory
-  /// path that should be prefixed to each 'external-contents' entry
-  /// when reading from YAML files.
-  std::string ExternalContentsPrefixDir;
-
-  /// @name Configuration
-  /// @{
-
-  /// Whether to perform case-sensitive comparisons.
-  ///
-  /// Currently, case-insensitive matching only works correctly with ASCII.
-  bool CaseSensitive = true;
-
-  /// IsRelativeOverlay marks whether a ExternalContentsPrefixDir path must
-  /// be prefixed in every 'external-contents' when reading from YAML files.
-  bool IsRelativeOverlay = false;
-
-  /// Whether to use to use the value of 'external-contents' for the
-  /// names of files.  This global value is overridable on a per-file basis.
-  bool UseExternalNames = true;
-
-  /// Whether an invalid path obtained via 'external-contents' should
-  /// cause iteration on the VFS to stop. If 'true', the VFS should ignore
-  /// the entry and continue with the next. Allows YAML files to be shared
-  /// across multiple compiler invocations regardless of prior existent
-  /// paths in 'external-contents'. This global value is overridable on a
-  /// per-file basis.
-  bool IgnoreNonExistentContents = true;
-  /// @}
-
-  /// Virtual file paths and external files could be canonicalized without "..",
-  /// "." and "./" in their paths. FIXME: some unittests currently fail on
-  /// win32 when using remove_dots and remove_leading_dotslash on paths.
-  bool UseCanonicalizedPaths =
-#ifdef _WIN32
-      false;
-#else
-      true;
-#endif
-
-private:
-  RedirectingFileSystem(IntrusiveRefCntPtr<FileSystem> ExternalFS)
-      : ExternalFS(std::move(ExternalFS)) {}
-
-  /// Looks up the path <tt>[Start, End)</tt> in \p From, possibly
-  /// recursing into the contents of \p From if it is a directory.
-  ErrorOr<Entry *> lookupPath(sys::path::const_iterator Start,
-                              sys::path::const_iterator End, Entry *From);
-
-  /// Get the status of a given an \c Entry.
-  ErrorOr<Status> status(const Twine &Path, Entry *E);
-
-public:
-  /// Looks up \p Path in \c Roots.
-  ErrorOr<Entry *> lookupPath(const Twine &Path);
-
-  /// Parses \p Buffer, which is expected to be in YAML format and
-  /// returns a virtual file system representing its contents.
-  static RedirectingFileSystem *
-  create(std::unique_ptr<MemoryBuffer> Buffer,
-         SourceMgr::DiagHandlerTy DiagHandler, StringRef YAMLFilePath,
-         void *DiagContext, IntrusiveRefCntPtr<FileSystem> ExternalFS);
-
-  ErrorOr<Status> status(const Twine &Path) override;
-  ErrorOr<std::unique_ptr<File>> openFileForRead(const Twine &Path) override;
-
-  llvm::ErrorOr<std::string> getCurrentWorkingDirectory() const override {
-    return ExternalFS->getCurrentWorkingDirectory();
-  }
-
-  std::error_code setCurrentWorkingDirectory(const Twine &Path) override {
-    return ExternalFS->setCurrentWorkingDirectory(Path);
-  }
-
-  directory_iterator dir_begin(const Twine &Dir, std::error_code &EC) override{
-    ErrorOr<Entry *> E = lookupPath(Dir);
-    if (!E) {
-      EC = E.getError();
-      return {};
-    }
-    ErrorOr<Status> S = status(Dir, *E);
-    if (!S) {
-      EC = S.getError();
-      return {};
-    }
-    if (!S->isDirectory()) {
-      EC = std::error_code(static_cast<int>(errc::not_a_directory),
-                           std::system_category());
-      return {};
-    }
-
-    auto *D = cast<RedirectingDirectoryEntry>(*E);
-    return directory_iterator(std::make_shared<VFSFromYamlDirIterImpl>(
-        Dir, D->contents_begin(), D->contents_end(), EC));
-  }
-
-  void setExternalContentsPrefixDir(StringRef PrefixDir) {
-    ExternalContentsPrefixDir = PrefixDir.str();
-  }
-
-  StringRef getExternalContentsPrefixDir() const {
-    return ExternalContentsPrefixDir;
-  }
-
-  bool ignoreNonExistentContents() const {
-    return IgnoreNonExistentContents;
-  }
-
-#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
-LLVM_DUMP_METHOD void dump() const {
-    for (const auto &Root : Roots)
-      dumpEntry(Root.get());
-  }
-
-LLVM_DUMP_METHOD void dumpEntry(Entry *E, int NumSpaces = 0) const {
-    StringRef Name = E->getName();
-    for (int i = 0, e = NumSpaces; i < e; ++i)
-      dbgs() << " ";
-    dbgs() << "'" << Name.str().c_str() << "'" << "\n";
-
-    if (E->getKind() == EK_Directory) {
-      auto *DE = dyn_cast<RedirectingDirectoryEntry>(E);
-      assert(DE && "Should be a directory");
-
-      for (std::unique_ptr<Entry> &SubEntry :
-           llvm::make_range(DE->contents_begin(), DE->contents_end()))
-        dumpEntry(SubEntry.get(), NumSpaces+2);
-    }
-  }
-#endif
-};
-
-/// A helper class to hold the common YAML parsing state.
-class RedirectingFileSystemParser {
-  yaml::Stream &Stream;
-
-  void error(yaml::Node *N, const Twine &Msg) {
-    Stream.printError(N, Msg);
-  }
-
-  // false on error
-  bool parseScalarString(yaml::Node *N, StringRef &Result,
-                         SmallVectorImpl<char> &Storage) {
-    const auto *S = dyn_cast<yaml::ScalarNode>(N);
-
-    if (!S) {
-      error(N, "expected string");
-      return false;
-    }
-    Result = S->getValue(Storage);
-    return true;
-  }
-
-  // false on error
-  bool parseScalarBool(yaml::Node *N, bool &Result) {
-    SmallString<5> Storage;
-    StringRef Value;
-    if (!parseScalarString(N, Value, Storage))
-      return false;
-
-    if (Value.equals_lower("true") || Value.equals_lower("on") ||
-        Value.equals_lower("yes") || Value == "1") {
-      Result = true;
-      return true;
-    } else if (Value.equals_lower("false") || Value.equals_lower("off") ||
-               Value.equals_lower("no") || Value == "0") {
-      Result = false;
-      return true;
-    }
-
-    error(N, "expected boolean value");
-    return false;
-  }
-
-  struct KeyStatus {
-    bool Required;
-    bool Seen = false;
-
-    KeyStatus(bool Required = false) : Required(Required) {}
-  };
-
-  using KeyStatusPair = std::pair<StringRef, KeyStatus>;
-
-  // false on error
-  bool checkDuplicateOrUnknownKey(yaml::Node *KeyNode, StringRef Key,
-                                  DenseMap<StringRef, KeyStatus> &Keys) {
-    if (!Keys.count(Key)) {
-      error(KeyNode, "unknown key");
-      return false;
-    }
-    KeyStatus &S = Keys[Key];
-    if (S.Seen) {
-      error(KeyNode, Twine("duplicate key '") + Key + "'");
-      return false;
-    }
-    S.Seen = true;
-    return true;
-  }
-
-  // false on error
-  bool checkMissingKeys(yaml::Node *Obj, DenseMap<StringRef, KeyStatus> &Keys) {
-    for (const auto &I : Keys) {
-      if (I.second.Required && !I.second.Seen) {
-        error(Obj, Twine("missing key '") + I.first + "'");
-        return false;
-      }
-    }
-    return true;
-  }
-
-  Entry *lookupOrCreateEntry(RedirectingFileSystem *FS, StringRef Name,
-                             Entry *ParentEntry = nullptr) {
-    if (!ParentEntry) { // Look for a existent root
-      for (const auto &Root : FS->Roots) {
-        if (Name.equals(Root->getName())) {
-          ParentEntry = Root.get();
-          return ParentEntry;
-        }
-      }
-    } else { // Advance to the next component
-      auto *DE = dyn_cast<RedirectingDirectoryEntry>(ParentEntry);
-      for (std::unique_ptr<Entry> &Content :
-           llvm::make_range(DE->contents_begin(), DE->contents_end())) {
-        auto *DirContent = dyn_cast<RedirectingDirectoryEntry>(Content.get());
-        if (DirContent && Name.equals(Content->getName()))
-          return DirContent;
-      }
-    }
-
-    // ... or create a new one
-    std::unique_ptr<Entry> E = llvm::make_unique<RedirectingDirectoryEntry>(
-        Name,
-        Status("", getNextVirtualUniqueID(), std::chrono::system_clock::now(),
-               0, 0, 0, file_type::directory_file, sys::fs::all_all));
-
-    if (!ParentEntry) { // Add a new root to the overlay
-      FS->Roots.push_back(std::move(E));
-      ParentEntry = FS->Roots.back().get();
-      return ParentEntry;
-    }
-
-    auto *DE = dyn_cast<RedirectingDirectoryEntry>(ParentEntry);
-    DE->addContent(std::move(E));
-    return DE->getLastContent();
-  }
-
-  void uniqueOverlayTree(RedirectingFileSystem *FS, Entry *SrcE,
-                         Entry *NewParentE = nullptr) {
-    StringRef Name = SrcE->getName();
-    switch (SrcE->getKind()) {
-    case EK_Directory: {
-      auto *DE = dyn_cast<RedirectingDirectoryEntry>(SrcE);
-      assert(DE && "Must be a directory");
-      // Empty directories could be present in the YAML as a way to
-      // describe a file for a current directory after some of its subdir
-      // is parsed. This only leads to redundant walks, ignore it.
-      if (!Name.empty())
-        NewParentE = lookupOrCreateEntry(FS, Name, NewParentE);
-      for (std::unique_ptr<Entry> &SubEntry :
-           llvm::make_range(DE->contents_begin(), DE->contents_end()))
-        uniqueOverlayTree(FS, SubEntry.get(), NewParentE);
-      break;
-    }
-    case EK_File: {
-      auto *FE = dyn_cast<RedirectingFileEntry>(SrcE);
-      assert(FE && "Must be a file");
-      assert(NewParentE && "Parent entry must exist");
-      auto *DE = dyn_cast<RedirectingDirectoryEntry>(NewParentE);
-      DE->addContent(llvm::make_unique<RedirectingFileEntry>(
-          Name, FE->getExternalContentsPath(), FE->getUseName()));
-      break;
-    }
-    }
-  }
-
-  std::unique_ptr<Entry> parseEntry(yaml::Node *N, RedirectingFileSystem *FS,
-                                    bool IsRootEntry) {
-    auto *M = dyn_cast<yaml::MappingNode>(N);
-    if (!M) {
-      error(N, "expected mapping node for file or directory entry");
-      return nullptr;
-    }
-
-    KeyStatusPair Fields[] = {
-      KeyStatusPair("name", true),
-      KeyStatusPair("type", true),
-      KeyStatusPair("contents", false),
-      KeyStatusPair("external-contents", false),
-      KeyStatusPair("use-external-name", false),
-    };
-
-    DenseMap<StringRef, KeyStatus> Keys(std::begin(Fields), std::end(Fields));
-
-    bool HasContents = false; // external or otherwise
-    std::vector<std::unique_ptr<Entry>> EntryArrayContents;
-    std::string ExternalContentsPath;
-    std::string Name;
-    yaml::Node *NameValueNode;
-    auto UseExternalName = RedirectingFileEntry::NK_NotSet;
-    EntryKind Kind;
-
-    for (auto &I : *M) {
-      StringRef Key;
-      // Reuse the buffer for key and value, since we don't look at key after
-      // parsing value.
-      SmallString<256> Buffer;
-      if (!parseScalarString(I.getKey(), Key, Buffer))
-        return nullptr;
-
-      if (!checkDuplicateOrUnknownKey(I.getKey(), Key, Keys))
-        return nullptr;
-
-      StringRef Value;
-      if (Key == "name") {
-        if (!parseScalarString(I.getValue(), Value, Buffer))
-          return nullptr;
-
-        NameValueNode = I.getValue();
-        if (FS->UseCanonicalizedPaths) {
-          SmallString<256> Path(Value);
-          // Guarantee that old YAML files containing paths with ".." and "."
-          // are properly canonicalized before read into the VFS.
-          Path = sys::path::remove_leading_dotslash(Path);
-          sys::path::remove_dots(Path, /*remove_dot_dot=*/true);
-          Name = Path.str();
-        } else {
-          Name = Value;
-        }
-      } else if (Key == "type") {
-        if (!parseScalarString(I.getValue(), Value, Buffer))
-          return nullptr;
-        if (Value == "file")
-          Kind = EK_File;
-        else if (Value == "directory")
-          Kind = EK_Directory;
-        else {
-          error(I.getValue(), "unknown value for 'type'");
-          return nullptr;
-        }
-      } else if (Key == "contents") {
-        if (HasContents) {
-          error(I.getKey(),
-                "entry already has 'contents' or 'external-contents'");
-          return nullptr;
-        }
-        HasContents = true;
-        auto *Contents = dyn_cast<yaml::SequenceNode>(I.getValue());
-        if (!Contents) {
-          // FIXME: this is only for directories, what about files?
-          error(I.getValue(), "expected array");
-          return nullptr;
-        }
-
-        for (auto &I : *Contents) {
-          if (std::unique_ptr<Entry> E =
-                  parseEntry(&I, FS, /*IsRootEntry*/ false))
-            EntryArrayContents.push_back(std::move(E));
-          else
-            return nullptr;
-        }
-      } else if (Key == "external-contents") {
-        if (HasContents) {
-          error(I.getKey(),
-                "entry already has 'contents' or 'external-contents'");
-          return nullptr;
-        }
-        HasContents = true;
-        if (!parseScalarString(I.getValue(), Value, Buffer))
-          return nullptr;
-
-        SmallString<256> FullPath;
-        if (FS->IsRelativeOverlay) {
-          FullPath = FS->getExternalContentsPrefixDir();
-          assert(!FullPath.empty() &&
-                 "External contents prefix directory must exist");
-          llvm::sys::path::append(FullPath, Value);
-        } else {
-          FullPath = Value;
-        }
-
-        if (FS->UseCanonicalizedPaths) {
-          // Guarantee that old YAML files containing paths with ".." and "."
-          // are properly canonicalized before read into the VFS.
-          FullPath = sys::path::remove_leading_dotslash(FullPath);
-          sys::path::remove_dots(FullPath, /*remove_dot_dot=*/true);
-        }
-        ExternalContentsPath = FullPath.str();
-      } else if (Key == "use-external-name") {
-        bool Val;
-        if (!parseScalarBool(I.getValue(), Val))
-          return nullptr;
-        UseExternalName = Val ? RedirectingFileEntry::NK_External
-                              : RedirectingFileEntry::NK_Virtual;
-      } else {
-        llvm_unreachable("key missing from Keys");
-      }
-    }
-
-    if (Stream.failed())
-      return nullptr;
-
-    // check for missing keys
-    if (!HasContents) {
-      error(N, "missing key 'contents' or 'external-contents'");
-      return nullptr;
-    }
-    if (!checkMissingKeys(N, Keys))
-      return nullptr;
-
-    // check invalid configuration
-    if (Kind == EK_Directory &&
-        UseExternalName != RedirectingFileEntry::NK_NotSet) {
-      error(N, "'use-external-name' is not supported for directories");
-      return nullptr;
-    }
-
-    if (IsRootEntry && !sys::path::is_absolute(Name)) {
-      assert(NameValueNode && "Name presence should be checked earlier");
-      error(NameValueNode,
-            "entry with relative path at the root level is not discoverable");
-      return nullptr;
-    }
-
-    // Remove trailing slash(es), being careful not to remove the root path
-    StringRef Trimmed(Name);
-    size_t RootPathLen = sys::path::root_path(Trimmed).size();
-    while (Trimmed.size() > RootPathLen &&
-           sys::path::is_separator(Trimmed.back()))
-      Trimmed = Trimmed.slice(0, Trimmed.size()-1);
-    // Get the last component
-    StringRef LastComponent = sys::path::filename(Trimmed);
-
-    std::unique_ptr<Entry> Result;
-    switch (Kind) {
-    case EK_File:
-      Result = llvm::make_unique<RedirectingFileEntry>(
-          LastComponent, std::move(ExternalContentsPath), UseExternalName);
-      break;
-    case EK_Directory:
-      Result = llvm::make_unique<RedirectingDirectoryEntry>(
-          LastComponent, std::move(EntryArrayContents),
-          Status("", getNextVirtualUniqueID(), std::chrono::system_clock::now(),
-                 0, 0, 0, file_type::directory_file, sys::fs::all_all));
-      break;
-    }
-
-    StringRef Parent = sys::path::parent_path(Trimmed);
-    if (Parent.empty())
-      return Result;
-
-    // if 'name' contains multiple components, create implicit directory entries
-    for (sys::path::reverse_iterator I = sys::path::rbegin(Parent),
-                                     E = sys::path::rend(Parent);
-         I != E; ++I) {
-      std::vector<std::unique_ptr<Entry>> Entries;
-      Entries.push_back(std::move(Result));
-      Result = llvm::make_unique<RedirectingDirectoryEntry>(
-          *I, std::move(Entries),
-          Status("", getNextVirtualUniqueID(), std::chrono::system_clock::now(),
-                 0, 0, 0, file_type::directory_file, sys::fs::all_all));
-    }
-    return Result;
-  }
-
-public:
-  RedirectingFileSystemParser(yaml::Stream &S) : Stream(S) {}
-
-  // false on error
-  bool parse(yaml::Node *Root, RedirectingFileSystem *FS) {
-    auto *Top = dyn_cast<yaml::MappingNode>(Root);
-    if (!Top) {
-      error(Root, "expected mapping node");
-      return false;
-    }
-
-    KeyStatusPair Fields[] = {
-      KeyStatusPair("version", true),
-      KeyStatusPair("case-sensitive", false),
-      KeyStatusPair("use-external-names", false),
-      KeyStatusPair("overlay-relative", false),
-      KeyStatusPair("ignore-non-existent-contents", false),
-      KeyStatusPair("roots", true),
-    };
-
-    DenseMap<StringRef, KeyStatus> Keys(std::begin(Fields), std::end(Fields));
-    std::vector<std::unique_ptr<Entry>> RootEntries;
-
-    // Parse configuration and 'roots'
-    for (auto &I : *Top) {
-      SmallString<10> KeyBuffer;
-      StringRef Key;
-      if (!parseScalarString(I.getKey(), Key, KeyBuffer))
-        return false;
-
-      if (!checkDuplicateOrUnknownKey(I.getKey(), Key, Keys))
-        return false;
-
-      if (Key == "roots") {
-        auto *Roots = dyn_cast<yaml::SequenceNode>(I.getValue());
-        if (!Roots) {
-          error(I.getValue(), "expected array");
-          return false;
-        }
-
-        for (auto &I : *Roots) {
-          if (std::unique_ptr<Entry> E =
-                  parseEntry(&I, FS, /*IsRootEntry*/ true))
-            RootEntries.push_back(std::move(E));
-          else
-            return false;
-        }
-      } else if (Key == "version") {
-        StringRef VersionString;
-        SmallString<4> Storage;
-        if (!parseScalarString(I.getValue(), VersionString, Storage))
-          return false;
-        int Version;
-        if (VersionString.getAsInteger<int>(10, Version)) {
-          error(I.getValue(), "expected integer");
-          return false;
-        }
-        if (Version < 0) {
-          error(I.getValue(), "invalid version number");
-          return false;
-        }
-        if (Version != 0) {
-          error(I.getValue(), "version mismatch, expected 0");
-          return false;
-        }
-      } else if (Key == "case-sensitive") {
-        if (!parseScalarBool(I.getValue(), FS->CaseSensitive))
-          return false;
-      } else if (Key == "overlay-relative") {
-        if (!parseScalarBool(I.getValue(), FS->IsRelativeOverlay))
-          return false;
-      } else if (Key == "use-external-names") {
-        if (!parseScalarBool(I.getValue(), FS->UseExternalNames))
-          return false;
-      } else if (Key == "ignore-non-existent-contents") {
-        if (!parseScalarBool(I.getValue(), FS->IgnoreNonExistentContents))
-          return false;
-      } else {
-        llvm_unreachable("key missing from Keys");
-      }
-    }
-
-    if (Stream.failed())
-      return false;
-
-    if (!checkMissingKeys(Top, Keys))
-      return false;
-
-    // Now that we sucessefully parsed the YAML file, canonicalize the internal
-    // representation to a proper directory tree so that we can search faster
-    // inside the VFS.
-    for (auto &E : RootEntries)
-      uniqueOverlayTree(FS, E.get());
-
-    return true;
-  }
-};
-
-} // namespace
-
-RedirectingFileSystem *
-RedirectingFileSystem::create(std::unique_ptr<MemoryBuffer> Buffer,
-                              SourceMgr::DiagHandlerTy DiagHandler,
-                              StringRef YAMLFilePath, void *DiagContext,
-                              IntrusiveRefCntPtr<FileSystem> ExternalFS) {
-  SourceMgr SM;
-  yaml::Stream Stream(Buffer->getMemBufferRef(), SM);
-
-  SM.setDiagHandler(DiagHandler, DiagContext);
-  yaml::document_iterator DI = Stream.begin();
-  yaml::Node *Root = DI->getRoot();
-  if (DI == Stream.end() || !Root) {
-    SM.PrintMessage(SMLoc(), SourceMgr::DK_Error, "expected root node");
-    return nullptr;
-  }
-
-  RedirectingFileSystemParser P(Stream);
-
-  std::unique_ptr<RedirectingFileSystem> FS(
-      new RedirectingFileSystem(std::move(ExternalFS)));
-
-  if (!YAMLFilePath.empty()) {
-    // Use the YAML path from -ivfsoverlay to compute the dir to be prefixed
-    // to each 'external-contents' path.
-    //
-    // Example:
-    //    -ivfsoverlay dummy.cache/vfs/vfs.yaml
-    // yields:
-    //  FS->ExternalContentsPrefixDir => /<absolute_path_to>/dummy.cache/vfs
-    //
-    SmallString<256> OverlayAbsDir = sys::path::parent_path(YAMLFilePath);
-    std::error_code EC = llvm::sys::fs::make_absolute(OverlayAbsDir);
-    assert(!EC && "Overlay dir final path must be absolute");
-    (void)EC;
-    FS->setExternalContentsPrefixDir(OverlayAbsDir);
-  }
-
-  if (!P.parse(Root, FS.get()))
-    return nullptr;
-
-  return FS.release();
-}
-
-ErrorOr<Entry *> RedirectingFileSystem::lookupPath(const Twine &Path_) {
-  SmallString<256> Path;
-  Path_.toVector(Path);
-
-  // Handle relative paths
-  if (std::error_code EC = makeAbsolute(Path))
-    return EC;
-
-  // Canonicalize path by removing ".", "..", "./", etc components. This is
-  // a VFS request, do bot bother about symlinks in the path components
-  // but canonicalize in order to perform the correct entry search.
-  if (UseCanonicalizedPaths) {
-    Path = sys::path::remove_leading_dotslash(Path);
-    sys::path::remove_dots(Path, /*remove_dot_dot=*/true);
-  }
-
-  if (Path.empty())
-    return make_error_code(llvm::errc::invalid_argument);
-
-  sys::path::const_iterator Start = sys::path::begin(Path);
-  sys::path::const_iterator End = sys::path::end(Path);
-  for (const auto &Root : Roots) {
-    ErrorOr<Entry *> Result = lookupPath(Start, End, Root.get());
-    if (Result || Result.getError() != llvm::errc::no_such_file_or_directory)
-      return Result;
-  }
-  return make_error_code(llvm::errc::no_such_file_or_directory);
-}
-
-ErrorOr<Entry *>
-RedirectingFileSystem::lookupPath(sys::path::const_iterator Start,
-                                  sys::path::const_iterator End, Entry *From) {
-#ifndef _WIN32
-  assert(!isTraversalComponent(*Start) &&
-         !isTraversalComponent(From->getName()) &&
-         "Paths should not contain traversal components");
-#else
-  // FIXME: this is here to support windows, remove it once canonicalized
-  // paths become globally default.
-  if (Start->equals("."))
-    ++Start;
-#endif
-
-  StringRef FromName = From->getName();
-
-  // Forward the search to the next component in case this is an empty one.
-  if (!FromName.empty()) {
-    if (CaseSensitive ? !Start->equals(FromName)
-                      : !Start->equals_lower(FromName))
-      // failure to match
-      return make_error_code(llvm::errc::no_such_file_or_directory);
-
-    ++Start;
-
-    if (Start == End) {
-      // Match!
-      return From;
-    }
-  }
-
-  auto *DE = dyn_cast<RedirectingDirectoryEntry>(From);
-  if (!DE)
-    return make_error_code(llvm::errc::not_a_directory);
-
-  for (const std::unique_ptr<Entry> &DirEntry :
-       llvm::make_range(DE->contents_begin(), DE->contents_end())) {
-    ErrorOr<Entry *> Result = lookupPath(Start, End, DirEntry.get());
-    if (Result || Result.getError() != llvm::errc::no_such_file_or_directory)
-      return Result;
-  }
-  return make_error_code(llvm::errc::no_such_file_or_directory);
-}
-
-static Status getRedirectedFileStatus(const Twine &Path, bool UseExternalNames,
-                                      Status ExternalStatus) {
-  Status S = ExternalStatus;
-  if (!UseExternalNames)
-    S = Status::copyWithNewName(S, Path.str());
-  S.IsVFSMapped = true;
-  return S;
-}
-
-ErrorOr<Status> RedirectingFileSystem::status(const Twine &Path, Entry *E) {
-  assert(E != nullptr);
-  if (auto *F = dyn_cast<RedirectingFileEntry>(E)) {
-    ErrorOr<Status> S = ExternalFS->status(F->getExternalContentsPath());
-    assert(!S || S->getName() == F->getExternalContentsPath());
-    if (S)
-      return getRedirectedFileStatus(Path, F->useExternalName(UseExternalNames),
-                                     *S);
-    return S;
-  } else { // directory
-    auto *DE = cast<RedirectingDirectoryEntry>(E);
-    return Status::copyWithNewName(DE->getStatus(), Path.str());
-  }
-}
-
-ErrorOr<Status> RedirectingFileSystem::status(const Twine &Path) {
-  ErrorOr<Entry *> Result = lookupPath(Path);
-  if (!Result)
-    return Result.getError();
-  return status(Path, *Result);
-}
-
-namespace {
-
-/// Provide a file wrapper with an overriden status.
-class FileWithFixedStatus : public File {
-  std::unique_ptr<File> InnerFile;
-  Status S;
-
-public:
-  FileWithFixedStatus(std::unique_ptr<File> InnerFile, Status S)
-      : InnerFile(std::move(InnerFile)), S(std::move(S)) {}
-
-  ErrorOr<Status> status() override { return S; }
-  ErrorOr<std::unique_ptr<llvm::MemoryBuffer>>
-
-  getBuffer(const Twine &Name, int64_t FileSize, bool RequiresNullTerminator,
-            bool IsVolatile) override {
-    return InnerFile->getBuffer(Name, FileSize, RequiresNullTerminator,
-                                IsVolatile);
-  }
-
-  std::error_code close() override { return InnerFile->close(); }
-};
-
-} // namespace
-
-ErrorOr<std::unique_ptr<File>>
-RedirectingFileSystem::openFileForRead(const Twine &Path) {
-  ErrorOr<Entry *> E = lookupPath(Path);
-  if (!E)
-    return E.getError();
-
-  auto *F = dyn_cast<RedirectingFileEntry>(*E);
-  if (!F) // FIXME: errc::not_a_file?
-    return make_error_code(llvm::errc::invalid_argument);
-
-  auto Result = ExternalFS->openFileForRead(F->getExternalContentsPath());
-  if (!Result)
-    return Result;
-
-  auto ExternalStatus = (*Result)->status();
-  if (!ExternalStatus)
-    return ExternalStatus.getError();
-
-  // FIXME: Update the status with the name and VFSMapped.
-  Status S = getRedirectedFileStatus(Path, F->useExternalName(UseExternalNames),
-                                     *ExternalStatus);
-  return std::unique_ptr<File>(
-      llvm::make_unique<FileWithFixedStatus>(std::move(*Result), S));
-}
-
-IntrusiveRefCntPtr<FileSystem>
-vfs::getVFSFromYAML(std::unique_ptr<MemoryBuffer> Buffer,
-                    SourceMgr::DiagHandlerTy DiagHandler,
-                    StringRef YAMLFilePath,
-                    void *DiagContext,
-                    IntrusiveRefCntPtr<FileSystem> ExternalFS) {
-  return RedirectingFileSystem::create(std::move(Buffer), DiagHandler,
-                                       YAMLFilePath, DiagContext,
-                                       std::move(ExternalFS));
-}
-
-static void getVFSEntries(Entry *SrcE, SmallVectorImpl<StringRef> &Path,
-                          SmallVectorImpl<YAMLVFSEntry> &Entries) {
-  auto Kind = SrcE->getKind();
-  if (Kind == EK_Directory) {
-    auto *DE = dyn_cast<RedirectingDirectoryEntry>(SrcE);
-    assert(DE && "Must be a directory");
-    for (std::unique_ptr<Entry> &SubEntry :
-         llvm::make_range(DE->contents_begin(), DE->contents_end())) {
-      Path.push_back(SubEntry->getName());
-      getVFSEntries(SubEntry.get(), Path, Entries);
-      Path.pop_back();
-    }
-    return;
-  }
-
-  assert(Kind == EK_File && "Must be a EK_File");
-  auto *FE = dyn_cast<RedirectingFileEntry>(SrcE);
-  assert(FE && "Must be a file");
-  SmallString<128> VPath;
-  for (auto &Comp : Path)
-    llvm::sys::path::append(VPath, Comp);
-  Entries.push_back(YAMLVFSEntry(VPath.c_str(), FE->getExternalContentsPath()));
-}
-
-void vfs::collectVFSFromYAML(std::unique_ptr<MemoryBuffer> Buffer,
-                             SourceMgr::DiagHandlerTy DiagHandler,
-                             StringRef YAMLFilePath,
-                             SmallVectorImpl<YAMLVFSEntry> &CollectedEntries,
-                             void *DiagContext,
-                             IntrusiveRefCntPtr<FileSystem> ExternalFS) {
-  RedirectingFileSystem *VFS = RedirectingFileSystem::create(
-      std::move(Buffer), DiagHandler, YAMLFilePath, DiagContext,
-      std::move(ExternalFS));
-  ErrorOr<Entry *> RootE = VFS->lookupPath("/");
-  if (!RootE)
-    return;
-  SmallVector<StringRef, 8> Components;
-  Components.push_back("/");
-  getVFSEntries(*RootE, Components, CollectedEntries);
-}
-
-UniqueID vfs::getNextVirtualUniqueID() {
-  static std::atomic<unsigned> UID;
-  unsigned ID = ++UID;
-  // The following assumes that uint64_t max will never collide with a real
-  // dev_t value from the OS.
-  return UniqueID(std::numeric_limits<uint64_t>::max(), ID);
-}
-
-void YAMLVFSWriter::addFileMapping(StringRef VirtualPath, StringRef RealPath) {
-  assert(sys::path::is_absolute(VirtualPath) && "virtual path not absolute");
-  assert(sys::path::is_absolute(RealPath) && "real path not absolute");
-  assert(!pathHasTraversal(VirtualPath) && "path traversal is not supported");
-  Mappings.emplace_back(VirtualPath, RealPath);
-}
-
-namespace {
-
-class JSONWriter {
-  llvm::raw_ostream &OS;
-  SmallVector<StringRef, 16> DirStack;
-
-  unsigned getDirIndent() { return 4 * DirStack.size(); }
-  unsigned getFileIndent() { return 4 * (DirStack.size() + 1); }
-  bool containedIn(StringRef Parent, StringRef Path);
-  StringRef containedPart(StringRef Parent, StringRef Path);
-  void startDirectory(StringRef Path);
-  void endDirectory();
-  void writeEntry(StringRef VPath, StringRef RPath);
-
-public:
-  JSONWriter(llvm::raw_ostream &OS) : OS(OS) {}
-
-  void write(ArrayRef<YAMLVFSEntry> Entries, Optional<bool> UseExternalNames,
-             Optional<bool> IsCaseSensitive, Optional<bool> IsOverlayRelative,
-             Optional<bool> IgnoreNonExistentContents, StringRef OverlayDir);
-};
-
-} // namespace
-
-bool JSONWriter::containedIn(StringRef Parent, StringRef Path) {
-  using namespace llvm::sys;
-
-  // Compare each path component.
-  auto IParent = path::begin(Parent), EParent = path::end(Parent);
-  for (auto IChild = path::begin(Path), EChild = path::end(Path);
-       IParent != EParent && IChild != EChild; ++IParent, ++IChild) {
-    if (*IParent != *IChild)
-      return false;
-  }
-  // Have we exhausted the parent path?
-  return IParent == EParent;
-}
-
-StringRef JSONWriter::containedPart(StringRef Parent, StringRef Path) {
-  assert(!Parent.empty());
-  assert(containedIn(Parent, Path));
-  return Path.slice(Parent.size() + 1, StringRef::npos);
-}
-
-void JSONWriter::startDirectory(StringRef Path) {
-  StringRef Name =
-      DirStack.empty() ? Path : containedPart(DirStack.back(), Path);
-  DirStack.push_back(Path);
-  unsigned Indent = getDirIndent();
-  OS.indent(Indent) << "{\n";
-  OS.indent(Indent + 2) << "'type': 'directory',\n";
-  OS.indent(Indent + 2) << "'name': \"" << llvm::yaml::escape(Name) << "\",\n";
-  OS.indent(Indent + 2) << "'contents': [\n";
-}
-
-void JSONWriter::endDirectory() {
-  unsigned Indent = getDirIndent();
-  OS.indent(Indent + 2) << "]\n";
-  OS.indent(Indent) << "}";
-
-  DirStack.pop_back();
-}
-
-void JSONWriter::writeEntry(StringRef VPath, StringRef RPath) {
-  unsigned Indent = getFileIndent();
-  OS.indent(Indent) << "{\n";
-  OS.indent(Indent + 2) << "'type': 'file',\n";
-  OS.indent(Indent + 2) << "'name': \"" << llvm::yaml::escape(VPath) << "\",\n";
-  OS.indent(Indent + 2) << "'external-contents': \""
-                        << llvm::yaml::escape(RPath) << "\"\n";
-  OS.indent(Indent) << "}";
-}
-
-void JSONWriter::write(ArrayRef<YAMLVFSEntry> Entries,
-                       Optional<bool> UseExternalNames,
-                       Optional<bool> IsCaseSensitive,
-                       Optional<bool> IsOverlayRelative,
-                       Optional<bool> IgnoreNonExistentContents,
-                       StringRef OverlayDir) {
-  using namespace llvm::sys;
-
-  OS << "{\n"
-        "  'version': 0,\n";
-  if (IsCaseSensitive.hasValue())
-    OS << "  'case-sensitive': '"
-       << (IsCaseSensitive.getValue() ? "true" : "false") << "',\n";
-  if (UseExternalNames.hasValue())
-    OS << "  'use-external-names': '"
-       << (UseExternalNames.getValue() ? "true" : "false") << "',\n";
-  bool UseOverlayRelative = false;
-  if (IsOverlayRelative.hasValue()) {
-    UseOverlayRelative = IsOverlayRelative.getValue();
-    OS << "  'overlay-relative': '"
-       << (UseOverlayRelative ? "true" : "false") << "',\n";
-  }
-  if (IgnoreNonExistentContents.hasValue())
-    OS << "  'ignore-non-existent-contents': '"
-       << (IgnoreNonExistentContents.getValue() ? "true" : "false") << "',\n";
-  OS << "  'roots': [\n";
-
-  if (!Entries.empty()) {
-    const YAMLVFSEntry &Entry = Entries.front();
-    startDirectory(path::parent_path(Entry.VPath));
-
-    StringRef RPath = Entry.RPath;
-    if (UseOverlayRelative) {
-      unsigned OverlayDirLen = OverlayDir.size();
-      assert(RPath.substr(0, OverlayDirLen) == OverlayDir &&
-             "Overlay dir must be contained in RPath");
-      RPath = RPath.slice(OverlayDirLen, RPath.size());
-    }
-
-    writeEntry(path::filename(Entry.VPath), RPath);
-
-    for (const auto &Entry : Entries.slice(1)) {
-      StringRef Dir = path::parent_path(Entry.VPath);
-      if (Dir == DirStack.back())
-        OS << ",\n";
-      else {
-        while (!DirStack.empty() && !containedIn(DirStack.back(), Dir)) {
-          OS << "\n";
-          endDirectory();
-        }
-        OS << ",\n";
-        startDirectory(Dir);
-      }
-      StringRef RPath = Entry.RPath;
-      if (UseOverlayRelative) {
-        unsigned OverlayDirLen = OverlayDir.size();
-        assert(RPath.substr(0, OverlayDirLen) == OverlayDir &&
-               "Overlay dir must be contained in RPath");
-        RPath = RPath.slice(OverlayDirLen, RPath.size());
-      }
-      writeEntry(path::filename(Entry.VPath), RPath);
-    }
-
-    while (!DirStack.empty()) {
-      OS << "\n";
-      endDirectory();
-    }
-    OS << "\n";
-  }
-
-  OS << "  ]\n"
-     << "}\n";
-}
-
-void YAMLVFSWriter::write(llvm::raw_ostream &OS) {
-  llvm::sort(Mappings, [](const YAMLVFSEntry &LHS, const YAMLVFSEntry &RHS) {
-    return LHS.VPath < RHS.VPath;
-  });
-
-  JSONWriter(OS).write(Mappings, UseExternalNames, IsCaseSensitive,
-                       IsOverlayRelative, IgnoreNonExistentContents,
-                       OverlayDir);
-}
-
-VFSFromYamlDirIterImpl::VFSFromYamlDirIterImpl(
-    const Twine &_Path, RedirectingDirectoryEntry::iterator Begin,
-    RedirectingDirectoryEntry::iterator End, std::error_code &EC)
-    : Dir(_Path.str()), Current(Begin), End(End) {
-  EC = incrementImpl();
-}
-
-std::error_code VFSFromYamlDirIterImpl::increment() {
-  assert(Current != End && "cannot iterate past end");
-  ++Current;
-  return incrementImpl();
-}
-
-std::error_code VFSFromYamlDirIterImpl::incrementImpl() {
-  while (Current != End) {
-    SmallString<128> PathStr(Dir);
-    llvm::sys::path::append(PathStr, (*Current)->getName());
-    sys::fs::file_type Type;
-    switch ((*Current)->getKind()) {
-      case EK_Directory:
-        Type = sys::fs::file_type::directory_file;
-        break;
-      case EK_File:
-        Type = sys::fs::file_type::regular_file;
-        break;
-    }
-    CurrentEntry = directory_entry(PathStr.str(), Type);
-    break;
-  }
-
-  if (Current == End)
-    CurrentEntry = directory_entry();
-  return {};
-}
-
-vfs::recursive_directory_iterator::recursive_directory_iterator(FileSystem &FS_,
-                                                           const Twine &Path,
-                                                           std::error_code &EC)
-    : FS(&FS_) {
-  directory_iterator I = FS->dir_begin(Path, EC);
-  if (I != directory_iterator()) {
-    State = std::make_shared<IterState>();
-    State->push(I);
-  }
-}
-
-vfs::recursive_directory_iterator &
-recursive_directory_iterator::increment(std::error_code &EC) {
-  assert(FS && State && !State->empty() && "incrementing past end");
-  assert(!State->top()->path().empty() && "non-canonical end iterator");
-  vfs::directory_iterator End;
-  if (State->top()->type() == sys::fs::file_type::directory_file) {
-    vfs::directory_iterator I = FS->dir_begin(State->top()->path(), EC);
-    if (I != End) {
-      State->push(I);
-      return *this;
-    }
-  }
-
-  while (!State->empty() && State->top().increment(EC) == End)
-    State->pop();
-
-  if (State->empty())
-    State.reset(); // end iterator
-
-  return *this;
-}