owners.py: Use os.path.split to handle file separators correctly

The script gets confused on Windows, because the path delimieter is \,
not /.

Bug: 899724
Change-Id: Id907aceb4f7bb6fcc0460245890b9e4716054ff9
Reviewed-on: https://chromium-review.googlesource.com/c/1308897Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>

owners.py

@@ -149,6 +149,12 @@ class Database(object):
     # File with global status lines for owners.
     self._status_file = None
 
+  def _file_affects_ownership(self, path):
+    """Returns true if the path refers to a file that could affect ownership."""
+    filename = self.os_path.split(path)[-1]
+    return filename == 'OWNERS' or filename.endswith('_OWNERS')
+
+
   def reviewers_for(self, files, author):
     """Returns a suggested set of reviewers that will cover the files.
 
@@ -395,7 +401,7 @@ class Database(object):
     # Paths included via "file:" must end in OWNERS or _OWNERS. Files that can
     # affect ownership have a different set of ownership rules, so that users
     # cannot self-approve changes adding themselves to an OWNERS file.
-    if not (owners_path.endswith('/OWNERS') or owners_path.endswith('_OWNERS')):
+    if not self._file_affects_ownership(owners_path):
       raise SyntaxErrorInOwnersFile(start, lineno, 'file: include must specify '
                                     'a file named OWNERS or ending in _OWNERS')
 

testing_support/filesystem_mock.py

@@ -30,9 +30,6 @@ class MockFileSystem(object):
   def sep(self):
     return self._sep
 
-  def _split(self, path):
-    return path.rsplit(self.sep, 1)
-
   def abspath(self, path):
     if path.endswith(self.sep):
       return path[:-1]
@@ -41,12 +38,12 @@ class MockFileSystem(object):
   def basename(self, path):
     if self.sep not in path:
       return ''
-    return self._split(path)[-1] or self.sep
+    return self.split(path)[-1] or self.sep
 
   def dirname(self, path):
     if self.sep not in path:
       return ''
-    return self._split(path)[0] or self.sep
+    return self.split(path)[0] or self.sep
 
   def exists(self, path):
     return self.isfile(path) or self.isdir(path)
@@ -92,3 +89,6 @@ class MockFileSystem(object):
       base += self.sep
     assert path.startswith(base)
     return path[len(base):]
+
+  def split(self, path):
+    return path.rsplit(self.sep, 1)