config: Raise ValueError if Path is asked to serialize unicode

If we accept unicode and try to encode using sys.getfilesystemencoding() then
it may work most of the time, but will fail if we get non-ASCII chars in the
unicode string and the file system encoding is e.g. ANSI-something because the
locale is C. Thus, I figure it is better to always fail if we try to serialize
Path from unicode strings. Paths should be maintained as bytes all the time.

mopidy/config/types.py

@@ -3,7 +3,6 @@ from __future__ import unicode_literals
 import logging
 import re
 import socket
-import sys
 
 from mopidy.utils import path
 from mopidy.config import validators
@@ -257,7 +256,7 @@ class Path(ConfigValue):
 
     def serialize(self, value, display=False):
         if isinstance(value, unicode):
-            value = value.encode(sys.getfilesystemencoding())
+            raise ValueError('paths should always be bytes')
         if isinstance(value, ExpandedPath):
             return value.original
         return value

tests/config/types_test.py

@@ -5,7 +5,6 @@ from __future__ import unicode_literals
 import logging
 import mock
 import socket
-import sys
 import unittest
 
 from mopidy.config import types
@@ -367,7 +366,4 @@ class PathTest(unittest.TestCase):
 
     def test_serialize_unicode_string(self):
         value = types.Path()
-        expected = 'æøå'.encode(sys.getfilesystemencoding())
-        result = value.serialize('æøå')
-        self.assertEqual(expected, result)
-        self.assertIsInstance(result, bytes)
+        self.assertRaises(ValueError, value.serialize, 'æøå')