Allow empty string as encoding value (to re-activate default).

Value `None` cannot be specified on the command line.
Use ``--input-encoding=""`` go back to Docutil's default behaviur
(use encoding indicated in the file or fallbacks)
if a config file sets "input_encoding" to another value.

git-svn-id: https://svn.code.sf.net/p/docutils/code/trunk@9303 929543f6-e4f2-0310-98a6-ba3bd3dd1d04

2 files changed, 5 insertions, 1 deletions

diff --git a/docutils/docutils/frontend.py b/docutils/docutils/frontend.py
index 2f4ca405f..62769aa30 100644
--- a/docutils/docutils/frontend.py
+++ b/docutils/docutils/frontend.py
@@ -92,6 +92,8 @@ def read_config_file(option, opt, value, parser):
 
 def validate_encoding(setting, value, option_parser,
                       config_parser=None, config_section=None):
+    if value == '':
+        return None  # allow overwriting a config file value
     try:
         codecs.lookup(value)
     except LookupError:
diff --git a/docutils/test/test_io.py b/docutils/test/test_io.py
index f545ab923..17b77eaa1 100755
--- a/docutils/test/test_io.py
+++ b/docutils/test/test_io.py
@@ -70,8 +70,9 @@ class HelperTests(unittest.TestCase):
         self.assertEqual(io.check_encoding(io.FileInput(), 'ascii'), None)
         # stream.encoding does not exist:
         self.assertEqual(io.check_encoding(BBuf, 'ascii'), None)
-        # encoding is None:
+        # encoding is None or empty string:
         self.assertEqual(io.check_encoding(mock_stdout, None), None)
+        self.assertEqual(io.check_encoding(mock_stdout, ''), None)
         # encoding is invalid
         self.assertEqual(io.check_encoding(mock_stdout, 'UTF-9'), None)
 
@@ -142,6 +143,7 @@ print("hello world")
     def test_heuristics_no_utf8(self):
         # if no encoding is given and decoding with 'utf-8' fails,
         # use either the locale encoding (if specified) or 'latin-1':
+        # Provisional: the second fallback 'latin-1' will be dropped
         probed_encodings = (io._locale_encoding, 'latin-1')  # noqa
         input = io.FileInput(
             source_path=os.path.join(DATA_ROOT, 'latin1.txt'))