typing: mark the argument to mercurial.i18n.gettext() non-Optional

Few if any of the callers are handling a `None` return, which is making pytype
complain.  I tried adding @overload definitions to indicate the bytes -> bytes
and None -> None relationship, but pytype doesn't seem to apply that to `_()`
through the function assignment.  What did work was to change `_()` into its own
function that called `gettext()`, but that has an extra function call overhead.
Even putting that function into an `if pycompat.TYPE_CHECKING` block and leaving
the existing assignments in the `else` block caused pytype to lose track of the
@overloads.

At that point, I simply gave up.  PyCharm doesn't like that it can return None,
given the new type hints, but pytype doesn't complain about this nor does it
see any callers passing None.  The most important thing here is to catch str
being passed anyway.

Differential Revision: https://phab.mercurial-scm.org/D10235

mercurial/i18n.py

@@ -1,127 +1,126 b''
 # i18n.py - internationalization support for mercurial
 #
 # Copyright 2005, 2006 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import gettext as gettextmod
 import locale
 import os
 import sys
 
 from .pycompat import getattr
 from .utils import resourceutil
 from . import (
     encoding,
     pycompat,
 )
 
 if pycompat.TYPE_CHECKING:
     from typing import (
         Callable,
         List,
-        Optional,
     )
 
 
 # modelled after templater.templatepath:
 if getattr(sys, 'frozen', None) is not None:
     module = pycompat.sysexecutable
 else:
     module = pycompat.fsencode(__file__)
 
 _languages = None
 if (
     pycompat.iswindows
     and b'LANGUAGE' not in encoding.environ
     and b'LC_ALL' not in encoding.environ
     and b'LC_MESSAGES' not in encoding.environ
     and b'LANG' not in encoding.environ
 ):
     # Try to detect UI language by "User Interface Language Management" API
     # if no locale variables are set. Note that locale.getdefaultlocale()
     # uses GetLocaleInfo(), which may be different from UI language.
     # (See http://msdn.microsoft.com/en-us/library/dd374098(v=VS.85).aspx )
     try:
         import ctypes
 
         # pytype: disable=module-attr
         langid = ctypes.windll.kernel32.GetUserDefaultUILanguage()
         # pytype: enable=module-attr
 
         _languages = [locale.windows_locale[langid]]
     except (ImportError, AttributeError, KeyError):
         # ctypes not found or unknown langid
         pass
 
 
 datapath = pycompat.fsdecode(resourceutil.datapath)
 localedir = os.path.join(datapath, 'locale')
 t = gettextmod.translation('hg', localedir, _languages, fallback=True)
 try:
     _ugettext = t.ugettext  # pytype: disable=attribute-error
 except AttributeError:
     _ugettext = t.gettext
 
 
 _msgcache = {}  # encoding: {message: translation}
 
 
 def gettext(message):
-    # type: (Optional[bytes]) -> Optional[bytes]
+    # type: (bytes) -> bytes
     """Translate message.
 
     The message is looked up in the catalog to get a Unicode string,
     which is encoded in the local encoding before being returned.
 
     Important: message is restricted to characters in the encoding
     given by sys.getdefaultencoding() which is most likely 'ascii'.
     """
     # If message is None, t.ugettext will return u'None' as the
     # translation whereas our callers expect us to return None.
     if message is None or not _ugettext:
         return message
 
     cache = _msgcache.setdefault(encoding.encoding, {})
     if message not in cache:
         if type(message) is pycompat.unicode:
             # goofy unicode docstrings in test
             paragraphs = message.split(u'\n\n')  # type: List[pycompat.unicode]
         else:
             # should be ascii, but we have unicode docstrings in test, which
             # are converted to utf-8 bytes on Python 3.
             paragraphs = [p.decode("utf-8") for p in message.split(b'\n\n')]
         # Be careful not to translate the empty string -- it holds the
         # meta data of the .po file.
         u = u'\n\n'.join([p and _ugettext(p) or u'' for p in paragraphs])
         try:
             # encoding.tolocal cannot be used since it will first try to
             # decode the Unicode string. Calling u.decode(enc) really
             # means u.encode(sys.getdefaultencoding()).decode(enc). Since
             # the Python encoding defaults to 'ascii', this fails if the
             # translated string use non-ASCII characters.
             encodingstr = pycompat.sysstr(encoding.encoding)
             cache[message] = u.encode(encodingstr, "replace")
         except LookupError:
             # An unknown encoding results in a LookupError.
             cache[message] = message
     return cache[message]
 
 
 def _plain():
     if (
         b'HGPLAIN' not in encoding.environ
         and b'HGPLAINEXCEPT' not in encoding.environ
     ):
         return False
     exceptions = encoding.environ.get(b'HGPLAINEXCEPT', b'').strip().split(b',')
     return b'i18n' not in exceptions
 
 
 if _plain():
     _ = lambda message: message  # type: Callable[[bytes], bytes]
 else:
     _ = gettext