Reland [clang] DirectoryWatcher

This reverts commit abce8c457dd3de6b156756e547cc0eefb7653c79.

+ Fix the build for platforms that don't have DW implementated.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@365947 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/DirectoryWatcher/DirectoryWatcher.h

@@ -0,0 +1,123 @@
+//===- DirectoryWatcher.h - Listens for directory file changes --*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_DIRECTORYWATCHER_DIRECTORYWATCHER_H
+#define LLVM_CLANG_DIRECTORYWATCHER_DIRECTORYWATCHER_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/StringRef.h"
+#include <functional>
+#include <memory>
+#include <string>
+
+namespace clang {
+/// Provides notifications for file changes in a directory.
+///
+/// Invokes client-provided function on every filesystem event in the watched
+/// directory. Initially the the watched directory is scanned and for every file
+/// found, an event is synthesized as if the file was added.
+///
+/// This is not a general purpose directory monitoring tool - list of
+/// limitations follows.
+///
+/// Only flat directories with no subdirectories are supported. In case
+/// subdirectories are present the behavior is unspecified - events *might* be
+/// passed to Receiver on macOS (due to FSEvents being used) while they
+/// *probably* won't be passed on Linux (due to inotify being used).
+///
+/// Known potential inconsistencies
+/// - For files that are deleted befor the initial scan processed them, clients
+/// might receive Removed notification without any prior Added notification.
+/// - Multiple notifications might be produced when a file is added to the
+/// watched directory during the initial scan. We are choosing the lesser evil
+/// here as the only known alternative strategy would be to invalidate the
+/// watcher instance and force user to create a new one whenever filesystem
+/// event occurs during the initial scan but that would introduce continuous
+/// restarting failure mode (watched directory is not always "owned" by the same
+/// process that is consuming it). Since existing clients can handle duplicate
+/// events well, we decided for simplicity.
+///
+/// Notifications are provided only for changes done through local user-space
+/// filesystem interface. Specifically, it's unspecified if notification would
+/// be provided in case of a:
+/// - a file mmap-ed and changed
+/// - a file changed via remote (NFS) or virtual (/proc) FS access to monitored
+/// directory
+/// - another filesystem mounted to the watched directory
+///
+/// No support for LLVM VFS.
+///
+/// It is unspecified whether notifications for files being deleted are sent in
+/// case the whole watched directory is sent.
+///
+/// Directories containing "too many" files and/or receiving events "too
+/// frequently" are not supported - if the initial scan can't be finished before
+/// the watcher instance gets invalidated (see WatcherGotInvalidated) there's no
+/// good error handling strategy - the only option for client is to destroy the
+/// watcher, restart watching with new instance and hope it won't repeat.
+class DirectoryWatcher {
+public:
+  struct Event {
+    enum class EventKind {
+      Removed,
+      /// Content of a file was modified.
+      Modified,
+      /// The watched directory got deleted.
+      WatchedDirRemoved,
+      /// The DirectoryWatcher that originated this event is no longer valid and
+      /// its behavior is unspecified.
+      ///
+      /// The prime case is kernel signalling to OS-specific implementation of
+      /// DirectoryWatcher some resource limit being hit.
+      /// *Usually* kernel starts dropping or squashing events together after
+      /// that and so would DirectoryWatcher. This means that *some* events
+      /// might still be passed to Receiver but this behavior is unspecified.
+      ///
+      /// Another case is after the watched directory itself is deleted.
+      /// WatcherGotInvalidated will be received at least once during
+      /// DirectoryWatcher instance lifetime - when handling errors this is done
+      /// on best effort basis, when an instance is being destroyed then this is
+      /// guaranteed.
+      ///
+      /// The only proper response to this kind of event is to destruct the
+      /// originating DirectoryWatcher instance and create a new one.
+      WatcherGotInvalidated
+    };
+
+    EventKind Kind;
+    /// Filename that this event is related to or an empty string in
+    /// case this event is related to the watched directory itself.
+    std::string Filename;
+
+    Event(EventKind Kind, llvm::StringRef Filename)
+        : Kind(Kind), Filename(Filename) {}
+  };
+
+  /// Returns nullptr if \param Path doesn't exist.
+  /// Returns nullptr if \param Path isn't a directory.
+  /// Returns nullptr if OS kernel API told us we can't start watching. In such
+  /// case it's unclear whether just retrying has any chance to succeeed.
+  static std::unique_ptr<DirectoryWatcher>
+  create(llvm::StringRef Path,
+         std::function<void(llvm::ArrayRef<DirectoryWatcher::Event> Events,
+                            bool IsInitial)>
+             Receiver,
+         bool WaitForInitialSync);
+
+  virtual ~DirectoryWatcher() = default;
+  DirectoryWatcher(const DirectoryWatcher &) = delete;
+  DirectoryWatcher &operator=(const DirectoryWatcher &) = delete;
+  DirectoryWatcher(DirectoryWatcher &&) = default;
+
+protected:
+  DirectoryWatcher() = default;
+};
+
+} // namespace clang
+
+#endif // LLVM_CLANG_DIRECTORYWATCHER_DIRECTORYWATCHER_H

lib/CMakeLists.txt

@@ -18,6 +18,7 @@ add_subdirectory(Serialization)
 add_subdirectory(Frontend)
 add_subdirectory(FrontendTool)
 add_subdirectory(Tooling)
+add_subdirectory(DirectoryWatcher)
 add_subdirectory(Index)
 if(CLANG_ENABLE_STATIC_ANALYZER)
   add_subdirectory(StaticAnalyzer)

lib/DirectoryWatcher/CMakeLists.txt

@@ -0,0 +1,29 @@
+include(CheckIncludeFiles)
+
+set(LLVM_LINK_COMPONENTS support)
+
+set(DIRECTORY_WATCHER_SOURCES DirectoryScanner.cpp)
+set(DIRECTORY_WATCHER_LINK_LIBS "")
+
+if(APPLE)
+  check_include_files("CoreServices/CoreServices.h" HAVE_CORESERVICES)
+  if(HAVE_CORESERVICES)
+    list(APPEND DIRECTORY_WATCHER_SOURCES mac/DirectoryWatcher-mac.cpp)
+    set(DIRECTORY_WATCHER_LINK_LIBS "-framework CoreServices")
+  endif()
+elseif(CMAKE_SYSTEM_NAME MATCHES "Linux")
+  check_include_files("sys/inotify.h" HAVE_INOTIFY)
+  if(HAVE_INOTIFY)
+    list(APPEND DIRECTORY_WATCHER_SOURCES linux/DirectoryWatcher-linux.cpp)
+    find_package(Threads REQUIRED)
+    set(DIRECTORY_WATCHER_LINK_LIBS ${CMAKE_THREAD_LIBS_INIT})
+  endif()
+else()
+  list(APPEND DIRECTORY_WATCHER_SOURCES default/DirectoryWatcher-not-implemented.cpp)
+endif()
+
+add_clang_library(clangDirectoryWatcher
+  ${DIRECTORY_WATCHER_SOURCES}
+  )
+
+target_link_libraries(clangDirectoryWatcher PRIVATE ${DIRECTORY_WATCHER_LINK_LIBS})

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

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

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;
+}

lib/DirectoryWatcher/linux/DirectoryWatcher-linux.cpp

@@ -0,0 +1,345 @@
+//===- 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 <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() {
+    ssize_t Result = 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 (const auto &EpollEvent : EpollEventBuffer) {
+      if (EpollEvent.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_EXCL_UNLINK | IN_MODIFY |
+          IN_MOVED_FROM | IN_MOVE_SELF | IN_MOVED_TO | IN_ONLYDIR | IN_IGNORED);
+  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));
+}

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;
+}

unittests/CMakeLists.txt

@@ -30,6 +30,7 @@ add_subdirectory(CodeGen)
 if(NOT WIN32 AND CLANG_TOOL_LIBCLANG_BUILD) 
   add_subdirectory(libclang)
 endif()
+add_subdirectory(DirectoryWatcher)
 add_subdirectory(Rename)
 add_subdirectory(Index)
 add_subdirectory(Serialization)

unittests/DirectoryWatcher/CMakeLists.txt

@@ -0,0 +1,17 @@
+if(APPLE OR CMAKE_SYSTEM_NAME MATCHES "Linux")
+
+  set(LLVM_LINK_COMPONENTS
+    Support
+    )
+
+  add_clang_unittest(DirectoryWatcherTests
+    DirectoryWatcherTest.cpp
+    )
+
+  target_link_libraries(DirectoryWatcherTests
+    PRIVATE
+    clangDirectoryWatcher
+    clangBasic
+    )
+
+endif()

unittests/DirectoryWatcher/DirectoryWatcherTest.cpp

@@ -0,0 +1,426 @@
+//===- unittests/DirectoryWatcher/DirectoryWatcherTest.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"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Mutex.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/raw_ostream.h"
+#include "gtest/gtest.h"
+#include <condition_variable>
+#include <future>
+#include <mutex>
+#include <thread>
+
+using namespace llvm;
+using namespace llvm::sys;
+using namespace llvm::sys::fs;
+using namespace clang;
+
+namespace clang {
+static bool operator==(const DirectoryWatcher::Event &lhs,
+                       const DirectoryWatcher::Event &rhs) {
+  return lhs.Filename == rhs.Filename &&
+         static_cast<int>(lhs.Kind) == static_cast<int>(rhs.Kind);
+}
+} // namespace clang
+
+namespace {
+
+struct DirectoryWatcherTestFixture {
+  std::string TestRootDir;
+  std::string TestWatchedDir;
+
+  DirectoryWatcherTestFixture() {
+    SmallString<128> pathBuf;
+    std::error_code UniqDirRes = createUniqueDirectory("dirwatcher", pathBuf);
+    assert(!UniqDirRes);
+    TestRootDir = pathBuf.str();
+    path::append(pathBuf, "watch");
+    TestWatchedDir = pathBuf.str();
+    std::error_code CreateDirRes = create_directory(TestWatchedDir, false);
+    assert(!CreateDirRes);
+  }
+
+  ~DirectoryWatcherTestFixture() { remove_directories(TestRootDir); }
+
+  SmallString<128> getPathInWatched(const std::string &testFile) {
+    SmallString<128> pathBuf;
+    pathBuf = TestWatchedDir;
+    path::append(pathBuf, testFile);
+    return pathBuf;
+  }
+
+  void addFile(const std::string &testFile) {
+    Expected<file_t> ft = openNativeFileForWrite(getPathInWatched(testFile),
+                                                 CD_CreateNew, OF_None);
+    if (ft) {
+      closeFile(*ft);
+    } else {
+      llvm::errs() << llvm::toString(ft.takeError()) << "\n";
+      llvm::errs() << getPathInWatched(testFile) << "\n";
+      llvm_unreachable("Couldn't create test file.");
+    }
+  }
+
+  void deleteFile(const std::string &testFile) {
+    std::error_code EC =
+        remove(getPathInWatched(testFile), /*IgnoreNonExisting=*/false);
+    ASSERT_FALSE(EC);
+  }
+};
+
+std::string eventKindToString(const DirectoryWatcher::Event::EventKind K) {
+  switch (K) {
+  case DirectoryWatcher::Event::EventKind::Removed:
+    return "Removed";
+  case DirectoryWatcher::Event::EventKind::Modified:
+    return "Modified";
+  case DirectoryWatcher::Event::EventKind::WatchedDirRemoved:
+    return "WatchedDirRemoved";
+  case DirectoryWatcher::Event::EventKind::WatcherGotInvalidated:
+    return "WatcherGotInvalidated";
+  }
+  llvm_unreachable("unknown event kind");
+}
+
+struct VerifyingConsumer {
+  std::vector<DirectoryWatcher::Event> ExpectedInitial;
+  std::vector<DirectoryWatcher::Event> ExpectedNonInitial;
+  std::vector<DirectoryWatcher::Event> OptionalNonInitial;
+  std::vector<DirectoryWatcher::Event> UnexpectedInitial;
+  std::vector<DirectoryWatcher::Event> UnexpectedNonInitial;
+  std::mutex Mtx;
+  std::condition_variable ResultIsReady;
+
+  VerifyingConsumer(
+      const std::vector<DirectoryWatcher::Event> &ExpectedInitial,
+      const std::vector<DirectoryWatcher::Event> &ExpectedNonInitial,
+      const std::vector<DirectoryWatcher::Event> &OptionalNonInitial = {})
+      : ExpectedInitial(ExpectedInitial),
+        ExpectedNonInitial(ExpectedNonInitial),
+        OptionalNonInitial(OptionalNonInitial) {}
+
+  // This method is used by DirectoryWatcher.
+  void consume(DirectoryWatcher::Event E, bool IsInitial) {
+    if (IsInitial)
+      consumeInitial(E);
+    else
+      consumeNonInitial(E);
+  }
+
+  void consumeInitial(DirectoryWatcher::Event E) {
+    std::unique_lock<std::mutex> L(Mtx);
+    auto It = std::find(ExpectedInitial.begin(), ExpectedInitial.end(), E);
+    if (It == ExpectedInitial.end()) {
+      UnexpectedInitial.push_back(E);
+    } else {
+      ExpectedInitial.erase(It);
+    }
+    if (result())
+      ResultIsReady.notify_one();
+  }
+
+  void consumeNonInitial(DirectoryWatcher::Event E) {
+    std::unique_lock<std::mutex> L(Mtx);
+    auto It =
+        std::find(ExpectedNonInitial.begin(), ExpectedNonInitial.end(), E);
+    if (It == ExpectedNonInitial.end()) {
+      auto OptIt =
+          std::find(OptionalNonInitial.begin(), OptionalNonInitial.end(), E);
+      if (OptIt != OptionalNonInitial.end()) {
+        OptionalNonInitial.erase(OptIt);
+      } else {
+        UnexpectedNonInitial.push_back(E);
+      }
+    } else {
+      ExpectedNonInitial.erase(It);
+    }
+    if (result())
+      ResultIsReady.notify_one();
+  }
+
+  // This method is used by DirectoryWatcher.
+  void consume(llvm::ArrayRef<DirectoryWatcher::Event> Es, bool IsInitial) {
+    for (const auto &E : Es)
+      consume(E, IsInitial);
+  }
+
+  // Not locking - caller has to lock Mtx.
+  llvm::Optional<bool> result() const {
+    if (ExpectedInitial.empty() && ExpectedNonInitial.empty() &&
+        UnexpectedInitial.empty() && UnexpectedNonInitial.empty())
+      return true;
+    if (!UnexpectedInitial.empty() || !UnexpectedNonInitial.empty())
+      return false;
+    return llvm::None;
+  }
+
+  // This method is used by tests.
+  // \returns true on success
+  bool blockUntilResult() {
+    std::unique_lock<std::mutex> L(Mtx);
+    while (true) {
+      if (result())
+        return *result();
+
+      ResultIsReady.wait(L, [this]() { return result().hasValue(); });
+    }
+    return false; // Just to make compiler happy.
+  }
+
+  void printUnmetExpectations(llvm::raw_ostream &OS) {
+    if (!ExpectedInitial.empty()) {
+      OS << "Expected but not seen initial events: \n";
+      for (const auto &E : ExpectedInitial) {
+        OS << eventKindToString(E.Kind) << " " << E.Filename << "\n";
+      }
+    }
+    if (!ExpectedNonInitial.empty()) {
+      OS << "Expected but not seen non-initial events: \n";
+      for (const auto &E : ExpectedNonInitial) {
+        OS << eventKindToString(E.Kind) << " " << E.Filename << "\n";
+      }
+    }
+    if (!UnexpectedInitial.empty()) {
+      OS << "Unexpected initial events seen: \n";
+      for (const auto &E : UnexpectedInitial) {
+        OS << eventKindToString(E.Kind) << " " << E.Filename << "\n";
+      }
+    }
+    if (!UnexpectedNonInitial.empty()) {
+      OS << "Unexpected non-initial events seen: \n";
+      for (const auto &E : UnexpectedNonInitial) {
+        OS << eventKindToString(E.Kind) << " " << E.Filename << "\n";
+      }
+    }
+  }
+};
+
+void checkEventualResultWithTimeout(VerifyingConsumer &TestConsumer) {
+  std::packaged_task<int(void)> task(
+      [&TestConsumer]() { return TestConsumer.blockUntilResult(); });
+  std::future<int> WaitForExpectedStateResult = task.get_future();
+  std::thread worker(std::move(task));
+  worker.detach();
+
+  EXPECT_TRUE(WaitForExpectedStateResult.wait_for(std::chrono::seconds(3)) ==
+              std::future_status::ready)
+      << "The expected result state wasn't reached before the time-out.";
+  EXPECT_TRUE(TestConsumer.result().hasValue());
+  if (TestConsumer.result().hasValue()) {
+    EXPECT_TRUE(*TestConsumer.result());
+  }
+  if ((TestConsumer.result().hasValue() && !TestConsumer.result().getValue()) ||
+      !TestConsumer.result().hasValue())
+    TestConsumer.printUnmetExpectations(llvm::outs());
+}
+
+} // namespace
+
+TEST(DirectoryWatcherTest, InitialScanSync) {
+  DirectoryWatcherTestFixture fixture;
+
+  fixture.addFile("a");
+  fixture.addFile("b");
+  fixture.addFile("c");
+
+  VerifyingConsumer TestConsumer{
+      {{DirectoryWatcher::Event::EventKind::Modified, "a"},
+       {DirectoryWatcher::Event::EventKind::Modified, "b"},
+       {DirectoryWatcher::Event::EventKind::Modified, "c"}},
+      {}};
+
+  auto DW = DirectoryWatcher::create(
+      fixture.TestWatchedDir,
+      [&TestConsumer](llvm::ArrayRef<DirectoryWatcher::Event> Events,
+                      bool IsInitial) {
+        TestConsumer.consume(Events, IsInitial);
+      },
+      /*waitForInitialSync=*/true);
+
+  checkEventualResultWithTimeout(TestConsumer);
+}
+
+TEST(DirectoryWatcherTest, InitialScanAsync) {
+  DirectoryWatcherTestFixture fixture;
+
+  fixture.addFile("a");
+  fixture.addFile("b");
+  fixture.addFile("c");
+
+  VerifyingConsumer TestConsumer{
+      {{DirectoryWatcher::Event::EventKind::Modified, "a"},
+       {DirectoryWatcher::Event::EventKind::Modified, "b"},
+       {DirectoryWatcher::Event::EventKind::Modified, "c"}},
+      {}};
+
+  auto DW = DirectoryWatcher::create(
+      fixture.TestWatchedDir,
+      [&TestConsumer](llvm::ArrayRef<DirectoryWatcher::Event> Events,
+                      bool IsInitial) {
+        TestConsumer.consume(Events, IsInitial);
+      },
+      /*waitForInitialSync=*/false);
+
+  checkEventualResultWithTimeout(TestConsumer);
+}
+
+TEST(DirectoryWatcherTest, AddFiles) {
+  DirectoryWatcherTestFixture fixture;
+
+  VerifyingConsumer TestConsumer{
+      {},
+      {{DirectoryWatcher::Event::EventKind::Modified, "a"},
+       {DirectoryWatcher::Event::EventKind::Modified, "b"},
+       {DirectoryWatcher::Event::EventKind::Modified, "c"}}};
+
+  auto DW = DirectoryWatcher::create(
+      fixture.TestWatchedDir,
+      [&TestConsumer](llvm::ArrayRef<DirectoryWatcher::Event> Events,
+                      bool IsInitial) {
+        TestConsumer.consume(Events, IsInitial);
+      },
+      /*waitForInitialSync=*/true);
+
+  fixture.addFile("a");
+  fixture.addFile("b");
+  fixture.addFile("c");
+
+  checkEventualResultWithTimeout(TestConsumer);
+}
+
+TEST(DirectoryWatcherTest, ModifyFile) {
+  DirectoryWatcherTestFixture fixture;
+
+  fixture.addFile("a");
+
+  VerifyingConsumer TestConsumer{
+      {{DirectoryWatcher::Event::EventKind::Modified, "a"}},
+      {{DirectoryWatcher::Event::EventKind::Modified, "a"}}};
+
+  auto DW = DirectoryWatcher::create(
+      fixture.TestWatchedDir,
+      [&TestConsumer](llvm::ArrayRef<DirectoryWatcher::Event> Events,
+                      bool IsInitial) {
+        TestConsumer.consume(Events, IsInitial);
+      },
+      /*waitForInitialSync=*/true);
+
+  // modify the file
+  {
+    std::error_code error;
+    llvm::raw_fd_ostream bStream(fixture.getPathInWatched("a"), error,
+                                 CD_OpenExisting);
+    assert(!error);
+    bStream << "foo";
+  }
+
+  checkEventualResultWithTimeout(TestConsumer);
+}
+
+TEST(DirectoryWatcherTest, DeleteFile) {
+  DirectoryWatcherTestFixture fixture;
+
+  fixture.addFile("a");
+
+  VerifyingConsumer TestConsumer{
+      {{DirectoryWatcher::Event::EventKind::Modified, "a"}},
+      {{DirectoryWatcher::Event::EventKind::Removed, "a"}}};
+
+  auto DW = DirectoryWatcher::create(
+      fixture.TestWatchedDir,
+      [&TestConsumer](llvm::ArrayRef<DirectoryWatcher::Event> Events,
+                      bool IsInitial) {
+        TestConsumer.consume(Events, IsInitial);
+      },
+      /*waitForInitialSync=*/true);
+
+  fixture.deleteFile("a");
+
+  checkEventualResultWithTimeout(TestConsumer);
+}
+
+TEST(DirectoryWatcherTest, DeleteWatchedDir) {
+  DirectoryWatcherTestFixture fixture;
+
+  VerifyingConsumer TestConsumer{
+      {},
+      {{DirectoryWatcher::Event::EventKind::WatchedDirRemoved, ""},
+       {DirectoryWatcher::Event::EventKind::WatcherGotInvalidated, ""}}};
+
+  auto DW = DirectoryWatcher::create(
+      fixture.TestWatchedDir,
+      [&TestConsumer](llvm::ArrayRef<DirectoryWatcher::Event> Events,
+                      bool IsInitial) {
+        TestConsumer.consume(Events, IsInitial);
+      },
+      /*waitForInitialSync=*/true);
+
+  remove_directories(fixture.TestWatchedDir);
+
+  checkEventualResultWithTimeout(TestConsumer);
+}
+
+TEST(DirectoryWatcherTest, InvalidatedWatcher) {
+  DirectoryWatcherTestFixture fixture;
+
+  VerifyingConsumer TestConsumer{
+      {}, {{DirectoryWatcher::Event::EventKind::WatcherGotInvalidated, ""}}};
+
+  {
+    auto DW = DirectoryWatcher::create(
+        fixture.TestWatchedDir,
+        [&TestConsumer](llvm::ArrayRef<DirectoryWatcher::Event> Events,
+                        bool IsInitial) {
+          TestConsumer.consume(Events, IsInitial);
+        },
+        /*waitForInitialSync=*/true);
+  } // DW is destructed here.
+
+  checkEventualResultWithTimeout(TestConsumer);
+}
+
+TEST(DirectoryWatcherTest, ChangeMetadata) {
+  DirectoryWatcherTestFixture fixture;
+  fixture.addFile("a");
+
+  VerifyingConsumer TestConsumer{
+      {{DirectoryWatcher::Event::EventKind::Modified, "a"}},
+      // We don't expect any notification for file having access file changed.
+      {},
+      // Given the timing we are ok with receiving the duplicate event.
+      {{DirectoryWatcher::Event::EventKind::Modified, "a"}}};
+
+  auto DW = DirectoryWatcher::create(
+      fixture.TestWatchedDir,
+      [&TestConsumer](llvm::ArrayRef<DirectoryWatcher::Event> Events,
+                      bool IsInitial) {
+        TestConsumer.consume(Events, IsInitial);
+      },
+      /*waitForInitialSync=*/true);
+
+  { // Change access and modification time of file a.
+    Expected<file_t> HopefullyTheFD = llvm::sys::fs::openNativeFileForWrite(
+        fixture.getPathInWatched("a"), CD_OpenExisting, OF_None);
+    if (!HopefullyTheFD) {
+      llvm::outs() << HopefullyTheFD.takeError();
+    }
+
+    const int FD = HopefullyTheFD.get();
+    const TimePoint<> NewTimePt =
+        std::chrono::system_clock::now() - std::chrono::minutes(1);
+
+    std::error_code setTimeRes =
+        llvm::sys::fs::setLastAccessAndModificationTime(FD, NewTimePt,
+                                                        NewTimePt);
+    assert(!setTimeRes);
+  }
+
+  checkEventualResultWithTimeout(TestConsumer);
+}