vendor/clang/clang-trunk-r366426

5 files changed, 688 insertions, 0 deletions

diff --git a/lib/DirectoryWatcher/DirectoryScanner.cpp b/lib/DirectoryWatcher/DirectoryScanner.cpp
new file mode 100644
index 0000000000000..ecfec52f459e2
--- /dev/null
+++ b/lib/DirectoryWatcher/DirectoryScanner.cpp
@@ -0,0 +1,54 @@
+//===- DirectoryScanner.cpp - Utility functions for DirectoryWatcher ------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "DirectoryScanner.h"
+
+#include "llvm/Support/Path.h"
+
+namespace clang {
+
+using namespace llvm;
+
+Optional<sys::fs::file_status> getFileStatus(StringRef Path) {
+  sys::fs::file_status Status;
+  std::error_code EC = status(Path, Status);
+  if (EC)
+    return None;
+  return Status;
+}
+
+std::vector<std::string> scanDirectory(StringRef Path) {
+  using namespace llvm::sys;
+  std::vector<std::string> Result;
+
+  std::error_code EC;
+  for (auto It = fs::directory_iterator(Path, EC),
+            End = fs::directory_iterator();
+       !EC && It != End; It.increment(EC)) {
+    auto status = getFileStatus(It->path());
+    if (!status.hasValue())
+      continue;
+    Result.emplace_back(sys::path::filename(It->path()));
+  }
+
+  return Result;
+}
+
+std::vector<DirectoryWatcher::Event>
+getAsFileEvents(const std::vector<std::string> &Scan) {
+  std::vector<DirectoryWatcher::Event> Events;
+  Events.reserve(Scan.size());
+
+  for (const auto &File : Scan) {
+    Events.emplace_back(DirectoryWatcher::Event{
+        DirectoryWatcher::Event::EventKind::Modified, File});
+  }
+  return Events;
+}
+
+} // namespace clang
\ No newline at end of file
diff --git a/lib/DirectoryWatcher/DirectoryScanner.h b/lib/DirectoryWatcher/DirectoryScanner.h
new file mode 100644
index 0000000000000..55731225e251b
--- /dev/null
+++ b/lib/DirectoryWatcher/DirectoryScanner.h
@@ -0,0 +1,29 @@
+//===- DirectoryScanner.h - Utility functions for DirectoryWatcher --------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/DirectoryWatcher/DirectoryWatcher.h"
+#include "llvm/Support/FileSystem.h"
+#include <string>
+#include <vector>
+
+namespace clang {
+
+/// Gets names (filenames) of items in directory at \p Path.
+/// \returns empty vector if \p Path is not a directory, doesn't exist or can't
+/// be read from.
+std::vector<std::string> scanDirectory(llvm::StringRef Path);
+
+/// Create event with EventKind::Added for every element in \p Scan.
+std::vector<DirectoryWatcher::Event>
+getAsFileEvents(const std::vector<std::string> &Scan);
+
+/// Gets status of file (or directory) at \p Path.
+/// \returns llvm::None if \p Path doesn't exist or can't get the status.
+llvm::Optional<llvm::sys::fs::file_status> getFileStatus(llvm::StringRef Path);
+
+} // namespace clang
\ No newline at end of file
diff --git a/lib/DirectoryWatcher/default/DirectoryWatcher-not-implemented.cpp b/lib/DirectoryWatcher/default/DirectoryWatcher-not-implemented.cpp
new file mode 100644
index 0000000000000..e330ff06f504d
--- /dev/null
+++ b/lib/DirectoryWatcher/default/DirectoryWatcher-not-implemented.cpp
@@ -0,0 +1,19 @@
+//===- DirectoryWatcher-not-implemented.cpp -------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "clang/DirectoryWatcher/DirectoryWatcher.h"
+
+using namespace llvm;
+using namespace clang;
+
+std::unique_ptr<DirectoryWatcher> clang::DirectoryWatcher::create(
+    StringRef Path,
+    std::function<void(llvm::ArrayRef<DirectoryWatcher::Event>, bool)> Receiver,
+    bool WaitForInitialSync) {
+  return nullptr;
+}
\ No newline at end of file
diff --git a/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp b/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp
new file mode 100644
index 0000000000000..6d7d69da4db5a
--- /dev/null
+++ b/lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp
@@ -0,0 +1,353 @@
+//===- DirectoryWatcher-linux.cpp - Linux-platform directory watching -----===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "DirectoryScanner.h"
+#include "clang/DirectoryWatcher/DirectoryWatcher.h"
+
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/ScopeExit.h"
+#include "llvm/Support/AlignOf.h"
+#include "llvm/Support/Errno.h"
+#include "llvm/Support/Mutex.h"
+#include "llvm/Support/Path.h"
+#include <atomic>
+#include <condition_variable>
+#include <mutex>
+#include <queue>
+#include <string>
+#include <thread>
+#include <vector>
+
+#include <fcntl.h>
+#include <linux/version.h>
+#include <sys/epoll.h>
+#include <sys/inotify.h>
+#include <unistd.h>
+
+namespace {
+
+using namespace llvm;
+using namespace clang;
+
+/// Pipe for inter-thread synchronization - for epoll-ing on multiple
+/// conditions. It is meant for uni-directional 1:1 signalling - specifically:
+/// no multiple consumers, no data passing. Thread waiting for signal should
+/// poll the FDRead. Signalling thread should call signal() which writes single
+/// character to FDRead.
+struct SemaphorePipe {
+  // Expects two file-descriptors opened as a pipe in the canonical POSIX
+  // order: pipefd[0] refers to the read end of the pipe. pipefd[1] refers to
+  // the write end of the pipe.
+  SemaphorePipe(int pipefd[2])
+      : FDRead(pipefd[0]), FDWrite(pipefd[1]), OwnsFDs(true) {}
+  SemaphorePipe(const SemaphorePipe &) = delete;
+  void operator=(const SemaphorePipe &) = delete;
+  SemaphorePipe(SemaphorePipe &&other)
+      : FDRead(other.FDRead), FDWrite(other.FDWrite),
+        OwnsFDs(other.OwnsFDs) // Someone could have moved from the other
+                               // instance before.
+  {
+    other.OwnsFDs = false;
+  };
+
+  void signal() {
+#ifndef NDEBUG
+    ssize_t Result =
+#endif
+    llvm::sys::RetryAfterSignal(-1, write, FDWrite, "A", 1);
+    assert(Result != -1);
+  }
+  ~SemaphorePipe() {
+    if (OwnsFDs) {
+      close(FDWrite);
+      close(FDRead);
+    }
+  }
+  const int FDRead;
+  const int FDWrite;
+  bool OwnsFDs;
+
+  static llvm::Optional<SemaphorePipe> create() {
+    int InotifyPollingStopperFDs[2];
+    if (pipe2(InotifyPollingStopperFDs, O_CLOEXEC) == -1)
+      return llvm::None;
+    return SemaphorePipe(InotifyPollingStopperFDs);
+  }
+};
+
+/// Mutex-protected queue of Events.
+class EventQueue {
+  std::mutex Mtx;
+  std::condition_variable NonEmpty;
+  std::queue<DirectoryWatcher::Event> Events;
+
+public:
+  void push_back(const DirectoryWatcher::Event::EventKind K,
+                 StringRef Filename) {
+    {
+      std::unique_lock<std::mutex> L(Mtx);
+      Events.emplace(K, Filename);
+    }
+    NonEmpty.notify_one();
+  }
+
+  // Blocks on caller thread and uses codition_variable to wait until there's an
+  // event to return.
+  DirectoryWatcher::Event pop_front_blocking() {
+    std::unique_lock<std::mutex> L(Mtx);
+    while (true) {
+      // Since we might have missed all the prior notifications on NonEmpty we
+      // have to check the queue first (under lock).
+      if (!Events.empty()) {
+        DirectoryWatcher::Event Front = Events.front();
+        Events.pop();
+        return Front;
+      }
+      NonEmpty.wait(L, [this]() { return !Events.empty(); });
+    }
+  }
+};
+
+class DirectoryWatcherLinux : public clang::DirectoryWatcher {
+public:
+  DirectoryWatcherLinux(
+      llvm::StringRef WatchedDirPath,
+      std::function<void(llvm::ArrayRef<Event>, bool)> Receiver,
+      bool WaitForInitialSync, int InotifyFD, int InotifyWD,
+      SemaphorePipe &&InotifyPollingStopSignal);
+
+  ~DirectoryWatcherLinux() override {
+    StopWork();
+    InotifyPollingThread.join();
+    EventsReceivingThread.join();
+    inotify_rm_watch(InotifyFD, InotifyWD);
+    llvm::sys::RetryAfterSignal(-1, close, InotifyFD);
+  }
+
+private:
+  const std::string WatchedDirPath;
+  // inotify file descriptor
+  int InotifyFD = -1;
+  // inotify watch descriptor
+  int InotifyWD = -1;
+
+  EventQueue Queue;
+
+  // Make sure lifetime of Receiver fully contains lifetime of
+  // EventsReceivingThread.
+  std::function<void(llvm::ArrayRef<Event>, bool)> Receiver;
+
+  // Consumes inotify events and pushes directory watcher events to the Queue.
+  void InotifyPollingLoop();
+  std::thread InotifyPollingThread;
+  // Using pipe so we can epoll two file descriptors at once - inotify and
+  // stopping condition.
+  SemaphorePipe InotifyPollingStopSignal;
+
+  // Does the initial scan of the directory - directly calling Receiver,
+  // bypassing the Queue. Both InitialScan and EventReceivingLoop use Receiver
+  // which isn't necessarily thread-safe.
+  void InitialScan();
+
+  // Processing events from the Queue.
+  // In case client doesn't want to do the initial scan synchronously
+  // (WaitForInitialSync=false in ctor) we do the initial scan at the beginning
+  // of this thread.
+  std::thread EventsReceivingThread;
+  // Push event of WatcherGotInvalidated kind to the Queue to stop the loop.
+  // Both InitialScan and EventReceivingLoop use Receiver which isn't
+  // necessarily thread-safe.
+  void EventReceivingLoop();
+
+  // Stops all the async work. Reentrant.
+  void StopWork() {
+    Queue.push_back(DirectoryWatcher::Event::EventKind::WatcherGotInvalidated,
+                    "");
+    InotifyPollingStopSignal.signal();
+  }
+};
+
+void DirectoryWatcherLinux::InotifyPollingLoop() {
+  // We want to be able to read ~30 events at once even in the worst case
+  // (obscenely long filenames).
+  constexpr size_t EventBufferLength =
+      30 * (sizeof(struct inotify_event) + NAME_MAX + 1);
+  // http://man7.org/linux/man-pages/man7/inotify.7.html
+  // Some systems cannot read integer variables if they are not
+  // properly aligned. On other systems, incorrect alignment may
+  // decrease performance. Hence, the buffer used for reading from
+  // the inotify file descriptor should have the same alignment as
+  // struct inotify_event.
+
+  auto ManagedBuffer =
+      llvm::make_unique<llvm::AlignedCharArray<alignof(struct inotify_event),
+                                               EventBufferLength>>();
+  char *const Buf = ManagedBuffer->buffer;
+
+  const int EpollFD = epoll_create1(EPOLL_CLOEXEC);
+  if (EpollFD == -1) {
+    StopWork();
+    return;
+  }
+  auto EpollFDGuard = llvm::make_scope_exit([EpollFD]() { close(EpollFD); });
+
+  struct epoll_event EventSpec;
+  EventSpec.events = EPOLLIN;
+  EventSpec.data.fd = InotifyFD;
+  if (epoll_ctl(EpollFD, EPOLL_CTL_ADD, InotifyFD, &EventSpec) == -1) {
+    StopWork();
+    return;
+  }
+
+  EventSpec.data.fd = InotifyPollingStopSignal.FDRead;
+  if (epoll_ctl(EpollFD, EPOLL_CTL_ADD, InotifyPollingStopSignal.FDRead,
+                &EventSpec) == -1) {
+    StopWork();
+    return;
+  }
+
+  std::array<struct epoll_event, 2> EpollEventBuffer;
+
+  while (true) {
+    const int EpollWaitResult = llvm::sys::RetryAfterSignal(
+        -1, epoll_wait, EpollFD, EpollEventBuffer.data(),
+        EpollEventBuffer.size(), /*timeout=*/-1 /*== infinity*/);
+    if (EpollWaitResult == -1) {
+      StopWork();
+      return;
+    }
+
+    // Multiple epoll_events can be received for a single file descriptor per
+    // epoll_wait call.
+    for (int i = 0; i < EpollWaitResult; ++i) {
+      if (EpollEventBuffer[i].data.fd == InotifyPollingStopSignal.FDRead) {
+        StopWork();
+        return;
+      }
+    }
+
+    // epoll_wait() always return either error or >0 events. Since there was no
+    // event for stopping, it must be an inotify event ready for reading.
+    ssize_t NumRead = llvm::sys::RetryAfterSignal(-1, read, InotifyFD, Buf,
+                                                  EventBufferLength);
+    for (char *P = Buf; P < Buf + NumRead;) {
+      if (P + sizeof(struct inotify_event) > Buf + NumRead) {
+        StopWork();
+        llvm_unreachable("an incomplete inotify_event was read");
+        return;
+      }
+
+      struct inotify_event *Event = reinterpret_cast<struct inotify_event *>(P);
+      P += sizeof(struct inotify_event) + Event->len;
+
+      if (Event->mask & (IN_CREATE | IN_MODIFY | IN_MOVED_TO | IN_DELETE) &&
+          Event->len <= 0) {
+        StopWork();
+        llvm_unreachable("expected a filename from inotify");
+        return;
+      }
+
+      if (Event->mask & (IN_CREATE | IN_MOVED_TO | IN_MODIFY)) {
+        Queue.push_back(DirectoryWatcher::Event::EventKind::Modified,
+                        Event->name);
+      } else if (Event->mask & (IN_DELETE | IN_MOVED_FROM)) {
+        Queue.push_back(DirectoryWatcher::Event::EventKind::Removed,
+                        Event->name);
+      } else if (Event->mask & (IN_DELETE_SELF | IN_MOVE_SELF)) {
+        Queue.push_back(DirectoryWatcher::Event::EventKind::WatchedDirRemoved,
+                        "");
+        StopWork();
+        return;
+      } else if (Event->mask & IN_IGNORED) {
+        StopWork();
+        return;
+      } else {
+        StopWork();
+        llvm_unreachable("Unknown event type.");
+        return;
+      }
+    }
+  }
+}
+
+void DirectoryWatcherLinux::InitialScan() {
+  this->Receiver(getAsFileEvents(scanDirectory(WatchedDirPath)),
+                 /*IsInitial=*/true);
+}
+
+void DirectoryWatcherLinux::EventReceivingLoop() {
+  while (true) {
+    DirectoryWatcher::Event Event = this->Queue.pop_front_blocking();
+    this->Receiver(Event, false);
+    if (Event.Kind ==
+        DirectoryWatcher::Event::EventKind::WatcherGotInvalidated) {
+      StopWork();
+      return;
+    }
+  }
+}
+
+DirectoryWatcherLinux::DirectoryWatcherLinux(
+    StringRef WatchedDirPath,
+    std::function<void(llvm::ArrayRef<Event>, bool)> Receiver,
+    bool WaitForInitialSync, int InotifyFD, int InotifyWD,
+    SemaphorePipe &&InotifyPollingStopSignal)
+    : WatchedDirPath(WatchedDirPath), InotifyFD(InotifyFD),
+      InotifyWD(InotifyWD), Receiver(Receiver),
+      InotifyPollingStopSignal(std::move(InotifyPollingStopSignal)) {
+
+  InotifyPollingThread = std::thread([this]() { InotifyPollingLoop(); });
+  // We have no guarantees about thread safety of the Receiver which is being
+  // used in both InitialScan and EventReceivingLoop. We shouldn't run these
+  // only synchronously.
+  if (WaitForInitialSync) {
+    InitialScan();
+    EventsReceivingThread = std::thread([this]() { EventReceivingLoop(); });
+  } else {
+    EventsReceivingThread = std::thread([this]() {
+      // FIXME: We might want to terminate an async initial scan early in case
+      // of a failure in EventsReceivingThread.
+      InitialScan();
+      EventReceivingLoop();
+    });
+  }
+}
+
+} // namespace
+
+std::unique_ptr<DirectoryWatcher> clang::DirectoryWatcher::create(
+    StringRef Path,
+    std::function<void(llvm::ArrayRef<DirectoryWatcher::Event>, bool)> Receiver,
+    bool WaitForInitialSync) {
+  if (Path.empty())
+    return nullptr;
+
+  const int InotifyFD = inotify_init1(IN_CLOEXEC);
+  if (InotifyFD == -1)
+    return nullptr;
+
+  const int InotifyWD = inotify_add_watch(
+      InotifyFD, Path.str().c_str(),
+      IN_CREATE | IN_DELETE | IN_DELETE_SELF | IN_MODIFY |
+      IN_MOVED_FROM | IN_MOVE_SELF | IN_MOVED_TO | IN_ONLYDIR | IN_IGNORED
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,36)
+      | IN_EXCL_UNLINK
+#endif
+      );
+  if (InotifyWD == -1)
+    return nullptr;
+
+  auto InotifyPollingStopper = SemaphorePipe::create();
+
+  if (!InotifyPollingStopper)
+    return nullptr;
+
+  return llvm::make_unique<DirectoryWatcherLinux>(
+      Path, Receiver, WaitForInitialSync, InotifyFD, InotifyWD,
+      std::move(*InotifyPollingStopper));
+}
\ No newline at end of file
diff --git a/lib/DirectoryWatcher/mac/DirectoryWatcher-mac.cpp b/lib/DirectoryWatcher/mac/DirectoryWatcher-mac.cpp
new file mode 100644
index 0000000000000..3df79ac48a4ac
--- /dev/null
+++ b/lib/DirectoryWatcher/mac/DirectoryWatcher-mac.cpp
@@ -0,0 +1,233 @@
+//===- DirectoryWatcher-mac.cpp - Mac-platform directory watching ---------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "DirectoryScanner.h"
+#include "clang/DirectoryWatcher/DirectoryWatcher.h"
+
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Path.h"
+#include <CoreServices/CoreServices.h>
+
+using namespace llvm;
+using namespace clang;
+
+static FSEventStreamRef createFSEventStream(
+    StringRef Path,
+    std::function<void(llvm::ArrayRef<DirectoryWatcher::Event>, bool)>,
+    dispatch_queue_t);
+static void stopFSEventStream(FSEventStreamRef);
+
+namespace {
+
+class DirectoryWatcherMac : public clang::DirectoryWatcher {
+public:
+  DirectoryWatcherMac(
+      FSEventStreamRef EventStream,
+      std::function<void(llvm::ArrayRef<DirectoryWatcher::Event>, bool)>
+          Receiver,
+      llvm::StringRef WatchedDirPath)
+      : EventStream(EventStream), Receiver(Receiver),
+        WatchedDirPath(WatchedDirPath) {}
+
+  ~DirectoryWatcherMac() override {
+    stopFSEventStream(EventStream);
+    EventStream = nullptr;
+    // Now it's safe to use Receiver as the only other concurrent use would have
+    // been in EventStream processing.
+    Receiver(DirectoryWatcher::Event(
+                 DirectoryWatcher::Event::EventKind::WatcherGotInvalidated, ""),
+             false);
+  }
+
+private:
+  FSEventStreamRef EventStream;
+  std::function<void(llvm::ArrayRef<Event>, bool)> Receiver;
+  const std::string WatchedDirPath;
+};
+
+struct EventStreamContextData {
+  std::string WatchedPath;
+  std::function<void(llvm::ArrayRef<DirectoryWatcher::Event>, bool)> Receiver;
+
+  EventStreamContextData(
+      std::string &&WatchedPath,
+      std::function<void(llvm::ArrayRef<DirectoryWatcher::Event>, bool)>
+          Receiver)
+      : WatchedPath(std::move(WatchedPath)), Receiver(Receiver) {}
+
+  // Needed for FSEvents
+  static void dispose(const void *ctx) {
+    delete static_cast<const EventStreamContextData *>(ctx);
+  }
+};
+} // namespace
+
+constexpr const FSEventStreamEventFlags StreamInvalidatingFlags =
+    kFSEventStreamEventFlagUserDropped | kFSEventStreamEventFlagKernelDropped |
+    kFSEventStreamEventFlagMustScanSubDirs;
+
+constexpr const FSEventStreamEventFlags ModifyingFileEvents =
+    kFSEventStreamEventFlagItemCreated | kFSEventStreamEventFlagItemRenamed |
+    kFSEventStreamEventFlagItemModified;
+
+static void eventStreamCallback(ConstFSEventStreamRef Stream,
+                                void *ClientCallBackInfo, size_t NumEvents,
+                                void *EventPaths,
+                                const FSEventStreamEventFlags EventFlags[],
+                                const FSEventStreamEventId EventIds[]) {
+  auto *ctx = static_cast<EventStreamContextData *>(ClientCallBackInfo);
+
+  std::vector<DirectoryWatcher::Event> Events;
+  for (size_t i = 0; i < NumEvents; ++i) {
+    StringRef Path = ((const char **)EventPaths)[i];
+    const FSEventStreamEventFlags Flags = EventFlags[i];
+
+    if (Flags & StreamInvalidatingFlags) {
+      Events.emplace_back(DirectoryWatcher::Event{
+          DirectoryWatcher::Event::EventKind::WatcherGotInvalidated, ""});
+      break;
+    } else if (!(Flags & kFSEventStreamEventFlagItemIsFile)) {
+      // Subdirectories aren't supported - if some directory got removed it
+      // must've been the watched directory itself.
+      if ((Flags & kFSEventStreamEventFlagItemRemoved) &&
+          Path == ctx->WatchedPath) {
+        Events.emplace_back(DirectoryWatcher::Event{
+            DirectoryWatcher::Event::EventKind::WatchedDirRemoved, ""});
+        Events.emplace_back(DirectoryWatcher::Event{
+            DirectoryWatcher::Event::EventKind::WatcherGotInvalidated, ""});
+        break;
+      }
+      // No support for subdirectories - just ignore everything.
+      continue;
+    } else if (Flags & kFSEventStreamEventFlagItemRemoved) {
+      Events.emplace_back(DirectoryWatcher::Event::EventKind::Removed,
+                          llvm::sys::path::filename(Path));
+      continue;
+    } else if (Flags & ModifyingFileEvents) {
+      if (!getFileStatus(Path).hasValue()) {
+        Events.emplace_back(DirectoryWatcher::Event::EventKind::Removed,
+                            llvm::sys::path::filename(Path));
+      } else {
+        Events.emplace_back(DirectoryWatcher::Event::EventKind::Modified,
+                            llvm::sys::path::filename(Path));
+      }
+      continue;
+    }
+
+    // default
+    Events.emplace_back(DirectoryWatcher::Event{
+        DirectoryWatcher::Event::EventKind::WatcherGotInvalidated, ""});
+    llvm_unreachable("Unknown FSEvent type.");
+  }
+
+  if (!Events.empty()) {
+    ctx->Receiver(Events, /*IsInitial=*/false);
+  }
+}
+
+FSEventStreamRef createFSEventStream(
+    StringRef Path,
+    std::function<void(llvm::ArrayRef<DirectoryWatcher::Event>, bool)> Receiver,
+    dispatch_queue_t Queue) {
+  if (Path.empty())
+    return nullptr;
+
+  CFMutableArrayRef PathsToWatch = [&]() {
+    CFMutableArrayRef PathsToWatch =
+        CFArrayCreateMutable(nullptr, 0, &kCFTypeArrayCallBacks);
+    CFStringRef CfPathStr =
+        CFStringCreateWithBytes(nullptr, (const UInt8 *)Path.data(),
+                                Path.size(), kCFStringEncodingUTF8, false);
+    CFArrayAppendValue(PathsToWatch, CfPathStr);
+    CFRelease(CfPathStr);
+    return PathsToWatch;
+  }();
+
+  FSEventStreamContext Context = [&]() {
+    std::string RealPath;
+    {
+      SmallString<128> Storage;
+      StringRef P = llvm::Twine(Path).toNullTerminatedStringRef(Storage);
+      char Buffer[PATH_MAX];
+      if (::realpath(P.begin(), Buffer) != nullptr)
+        RealPath = Buffer;
+      else
+        RealPath = Path;
+    }
+
+    FSEventStreamContext Context;
+    Context.version = 0;
+    Context.info = new EventStreamContextData(std::move(RealPath), Receiver);
+    Context.retain = nullptr;
+    Context.release = EventStreamContextData::dispose;
+    Context.copyDescription = nullptr;
+    return Context;
+  }();
+
+  FSEventStreamRef Result = FSEventStreamCreate(
+      nullptr, eventStreamCallback, &Context, PathsToWatch,
+      kFSEventStreamEventIdSinceNow, /* latency in seconds */ 0.0,
+      kFSEventStreamCreateFlagFileEvents | kFSEventStreamCreateFlagNoDefer);
+  CFRelease(PathsToWatch);
+
+  return Result;
+}
+
+void stopFSEventStream(FSEventStreamRef EventStream) {
+  if (!EventStream)
+    return;
+  FSEventStreamStop(EventStream);
+  FSEventStreamInvalidate(EventStream);
+  FSEventStreamRelease(EventStream);
+}
+
+std::unique_ptr<DirectoryWatcher> clang::DirectoryWatcher::create(
+    StringRef Path,
+    std::function<void(llvm::ArrayRef<DirectoryWatcher::Event>, bool)> Receiver,
+    bool WaitForInitialSync) {
+  dispatch_queue_t Queue =
+      dispatch_queue_create("DirectoryWatcher", DISPATCH_QUEUE_SERIAL);
+
+  if (Path.empty())
+    return nullptr;
+
+  auto EventStream = createFSEventStream(Path, Receiver, Queue);
+  if (!EventStream) {
+    return nullptr;
+  }
+
+  std::unique_ptr<DirectoryWatcher> Result =
+      llvm::make_unique<DirectoryWatcherMac>(EventStream, Receiver, Path);
+
+  // We need to copy the data so the lifetime is ok after a const copy is made
+  // for the block.
+  const std::string CopiedPath = Path;
+
+  auto InitWork = ^{
+    // We need to start watching the directory before we start scanning in order
+    // to not miss any event. By dispatching this on the same serial Queue as
+    // the FSEvents will be handled we manage to start watching BEFORE the
+    // inital scan and handling events ONLY AFTER the scan finishes.
+    FSEventStreamSetDispatchQueue(EventStream, Queue);
+    FSEventStreamStart(EventStream);
+    // We need to decrement the ref count for Queue as initialize() will return
+    // and FSEvents has incremented it. Since we have to wait for FSEvents to
+    // take ownership it's the easiest to do it here rather than main thread.
+    dispatch_release(Queue);
+    Receiver(getAsFileEvents(scanDirectory(CopiedPath)), /*IsInitial=*/true);
+  };
+
+  if (WaitForInitialSync) {
+    dispatch_sync(Queue, InitWork);
+  } else {
+    dispatch_async(Queue, InitWork);
+  }
+
+  return Result;
+}