Allow passing in fs encoding to _fs_to_tree_path.

sys.getfilesystemencoding() may be 'ascii' in which case some characters can not be encoded.

dulwich/index.py

@@ -557,15 +557,18 @@ def _tree_to_fs_path(root_path, tree_path):
     return os.path.join(root_path, sep_corrected_path)
 
 
-def _fs_to_tree_path(fs_path):
+def _fs_to_tree_path(fs_path, fs_encoding=None):
     """Convert a file system path to a git tree path.
 
     :param fs_path: File system path.
+    :param fs_encoding: File system encoding
 
     :return:  Git tree path as bytes
     """
+    if fs_encoding is None:
+        fs_encoding = sys.getfilesystemencoding()
     if not isinstance(fs_path, bytes):
-        fs_path_bytes = fs_path.encode(sys.getfilesystemencoding())
+        fs_path_bytes = fs_path.encode(fs_encoding)
     else:
         fs_path_bytes = fs_path
     if os_sep_bytes != b'/':

dulwich/tests/test_index.py

@@ -491,10 +491,10 @@ class TestTreeFSPathConversion(TestCase):
 
     def test_fs_to_tree_path_str(self):
         fs_path = os.path.join(os.path.join(u'délwíçh', u'foo'))
-        tree_path = _fs_to_tree_path(fs_path)
-        self.assertEqual(tree_path, u'délwíçh/foo'.encode(sys.getfilesystemencoding()))
+        tree_path = _fs_to_tree_path(fs_path, "utf-8")
+        self.assertEqual(tree_path, u'délwíçh/foo'.encode("utf-8"))
 
     def test_fs_to_tree_path_bytes(self):
         fs_path = os.path.join(os.path.join(u'délwíçh', u'foo').encode('utf8'))
-        tree_path = _fs_to_tree_path(fs_path)
+        tree_path = _fs_to_tree_path(fs_path, "utf-8")
         self.assertEqual(tree_path, u'délwíçh/foo'.encode('utf8'))