Fix git branch name sometimes getting stuck with inotify

If you try to checkout the already current branch in git, git creates
HEAD.lock and renames it to HEAD. This causes the inode of HEAD to
change and so the inotify file watcher stops tracking HEAD.

The fix is to re-create the inotify watch when the file attributes
change. This is a bit of a performance penalty as most of the time the
attribute changes are simple last modified time/size changes, but since
inotify provides no way to know specifically when the inode has changed,
this is the best we can do.

powerline/lib/file_watcher.py

@@ -54,7 +54,24 @@ class INotifyWatch(INotify):
 					self.modified.pop(path, None)
 					self.last_query.pop(path, None)
 				else:
-					self.modified[path] = True
+					if mask & self.ATTRIB:
+						# The watched file could have had its inode changed, in
+						# which case we will not get any more events for this
+						# file, so re-register the watch. For example by some
+						# other file being renamed as this file.
+						try:
+							self.unwatch(path)
+						except OSError:
+							pass
+						try:
+							self.watch(path)
+						except OSError as e:
+							if getattr(e, 'errno', None) != errno.ENOENT:
+								raise
+						else:
+							self.modified[path] = True
+					else:
+						self.modified[path] = True
 
 	def unwatch(self, path):
 		''' Remove the watch for path. Raises an OSError if removing the watch

powerline/lib/vcs/__init__.py

@@ -31,6 +31,15 @@ def file_watcher():
 		_file_watcher = create_file_watcher()
 	return _file_watcher
 
+_branch_watcher = None
+
+def branch_watcher():
+	global _branch_watcher
+	if _branch_watcher is None:
+		from powerline.lib.file_watcher import create_file_watcher
+		_branch_watcher = create_file_watcher()
+	return _branch_watcher
+
 branch_name_cache = {}
 branch_lock = Lock()
 file_status_lock = Lock()
@@ -39,7 +48,7 @@ def get_branch_name(directory, config_file, get_func):
 	global branch_name_cache
 	with branch_lock:
 		# Check if the repo directory was moved/deleted
-		fw = file_watcher()
+		fw = branch_watcher()
 		is_watched = fw.is_watched(directory)
 		try:
 			changed = fw(directory)

tests/test_lib.py

@@ -54,10 +54,11 @@ class TestFilesystemWatchers(TestCase):
 		w = create_file_watcher(use_stat=False)
 		if w.is_stat_based:
 			raise SkipTest('This test is not suitable for a stat based file watcher')
-		f1, f2 = os.path.join(INOTIFY_DIR, 'file1'), os.path.join(INOTIFY_DIR, 'file2')
+		f1, f2, f3 = map(lambda x: os.path.join(INOTIFY_DIR, 'file%d' % x), (1, 2, 3))
 		with open(f1, 'wb'):
 			with open(f2, 'wb'):
-				pass
+				with open(f3, 'wb'):
+					pass
 		ne = os.path.join(INOTIFY_DIR, 'notexists')
 		self.assertRaises(OSError, w, ne)
 		self.assertTrue(w(f1))
@@ -85,6 +86,13 @@ class TestFilesystemWatchers(TestCase):
 		# Check that deleting a file registers as a change
 		os.unlink(f1)
 		self.do_test_for_change(w, f1)
+		# Test that changing the inode of a file does not cause it to stop
+		# being watched
+		os.rename(f3, f2)
+		self.do_test_for_change(w, f2)
+		self.assertFalse(w(f2), 'Spurious change detected')
+		os.utime(f2, None)
+		self.do_test_for_change(w, f2)
 
 	def test_tree_watcher(self):
 		from powerline.lib.tree_watcher import TreeWatcher