Use FSEvents for recursive file watch on Mac

base/files/file_path_watcher_mac.cc

+// Copyright (c) 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/files/file_path_watcher.h"
+#include "base/files/file_path_watcher_kqueue.h"
+
+#if !defined(OS_IOS)
+#include "base/files/file_path_watcher_fsevents.h"
+#include "base/mac/mac_util.h"
+#endif
+
+namespace base {
+
+namespace {
+
+class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate {
+ public:
+  virtual bool Watch(const FilePath& path,
+                     bool recursive,
+                     const FilePathWatcher::Callback& callback) OVERRIDE {
+    // Use kqueue for non-recursive watches and FSEvents for recursive ones.
+    DCHECK(!impl_.get());
+#if !defined(OS_IOS)
+    if (recursive) {
+      // FSEvents is broken on 10.6 and earlier. See http://crbug.com/54822#c31
+      if (mac::IsOSSnowLeopard())
+        return false;
+
+      impl_ = new FilePathWatcherFSEvents();
+    } else
+#endif  // OS_IOS

[Mattias Nissler (ping if slow), 2014/05/28 08:08:32]

Uh, I'm not so fond of intermixing preprocessor and language control flow (and
the resulting style guide violation). How about wrapping the
FilePathWatcherKQueue initialization in an if (!impl_) conditional so it does
the right thing regardless of defined(OS_IOS)?

[vandebo (ex-Chrome), 2014/05/28 18:54:52]

Thanks, made it even a bit cleaner.

+      impl_ = new FilePathWatcherKQueue();
+    return impl_->Watch(path, recursive, callback);
+  }
+
+  virtual void Cancel() OVERRIDE {
+    if (impl_)
+      impl_->Cancel();
+  }
+
+  virtual void CancelOnMessageLoopThread() OVERRIDE {
+    if (impl_)
+      impl_->Cancel();
+  }
+
+ protected:
+  virtual ~FilePathWatcherImpl() {}
+
+  scoped_refptr<PlatformDelegate> impl_;
+};
+
+}  // namespace
+
+FilePathWatcher::FilePathWatcher() {
+  impl_ = new FilePathWatcherImpl();
+}
+
+}  // namespace base