bpo-46659: Update the test on the mbcs codec alias (GH-31168)

encodings registers the _alias_mbcs() codec search function before the search_function() codec search function. Previously, the _alias_mbcs() was never used. Fix the test_codecs.test_mbcs_alias() test: use the current ANSI code page, not a fake ANSI code page number. Remove the test_site.test_aliasing_mbcs() test: the alias is now implemented in the encodings module, no longer in the site module.

Author: vstinner

Lib/encodings/__init__.py

@@ -152,9 +152,6 @@ def search_function(encoding):
  # Return the registry entry
  return entry
 
-# Register the search_function in the Python codec registry
-codecs.register(search_function)
-
 if sys.platform == 'win32':
  def _alias_mbcs(encoding):
  try:
@@ -167,4 +164,8 @@ def _alias_mbcs(encoding):
  # Imports may fail while we are shutting down
  pass
 
+ # It must be registered before search_function()
  codecs.register(_alias_mbcs)
+
+# Register the search_function in the Python codec registry
+codecs.register(search_function)

Lib/test/test_codecs.py

@@ -1904,7 +1904,10 @@ def test_basics(self):
  name += "_codec"
  elif encoding == "latin_1":
  name = "latin_1"
- self.assertEqual(encoding.replace("_", "-"), name.replace("_", "-"))
+ # Skip the mbcs alias on Windows
+ if name != "mbcs":
+ self.assertEqual(encoding.replace("_", "-"),
+ name.replace("_", "-"))
 
  (b, size) = codecs.getencoder(encoding)(s)
  self.assertEqual(size, len(s), "encoding=%r" % encoding)
@@ -3188,11 +3191,13 @@ def test_incremental(self):
  self.assertEqual(decoded, ('abc', 3))
 
  def test_mbcs_alias(self):
- # Check that looking up our 'default' codepage will return
- # mbcs when we don't have a more specific one available
- with mock.patch('_winapi.GetACP', return_value=123):
- codec = codecs.lookup('cp123')
- self.assertEqual(codec.name, 'mbcs')
+ # On Windows, the encoding name must be the ANSI code page
+ encoding = locale.getpreferredencoding(False)
+ self.assertTrue(encoding.startswith('cp'), encoding)
+
+ # The encodings module create a "mbcs" alias to the ANSI code page
+ codec = codecs.lookup(encoding)
+ self.assertEqual(codec.name, "mbcs")
 
  @support.bigmemtest(size=2**31, memuse=7, dry_run=False)
  def test_large_input(self, size):

Lib/test/test_site.py

@@ -456,16 +456,6 @@ def test_setting_help(self):
  # 'help' should be set in builtins
  self.assertTrue(hasattr(builtins, "help"))
 
- def test_aliasing_mbcs(self):
- if sys.platform == "win32":
- import locale
- if locale.getdefaultlocale()[1].startswith('cp'):
- for value in encodings.aliases.aliases.values():
- if value == "mbcs":
- break
- else:
- self.fail("did not alias mbcs")
-
  def test_sitecustomize_executed(self):
  # If sitecustomize is available, it should have been imported.
  if "sitecustomize" not in sys.modules: