encoding: improve handling of buggy getpreferredencoding() on Mac OS X

Prior to version 2.7, calling locale.getpreferredencoding() would
always return 'mac-roman' on Mac OS X. Previously, this was handled by
a call to locale.setlocale(). Unfortunately, Python 2.6.5 and older
have a bug where isspace() would incorrectly report True for 0x85 and
0xa0 after such a call.

In order to fix this, we replace the previous _encodingfixup mapping
to an _encodingfixers mapping. Rather than mapping encodings to their
replacement, it maps them to a function returning the
replacement. This allows us to provide an simplified implementation of
getpreferredencoding() which extracts the expected encoding and
restores the locale.

This fix is based on a patch originally submitted by Martijn Pieters
as well as feedback from Brodie Rao.

mercurial/encoding.py

@@ -1,77 +1,97 b''
 # encoding.py - character transcoding support for Mercurial
 #
 #  Copyright 2005-2009 Matt Mackall <[e-mail]> and others
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 import error
 import sys, unicodedata, locale, os
 
-_encodingfixup = {'646': 'ascii', 'ANSI_X3.4-1968': 'ascii'}
+def _getpreferredencoding():
+    '''
+    On darwin, getpreferredencoding ignores the locale environment and
+    always returns mac-roman. http://bugs.python.org/issue6202 fixes this
+    for Python 2.7 and up. This is the same corrected code for earlier
+    Python versions.
+
+    However, we can't use a version check for this method, as some distributions 
+    patch Python to fix this. Instead, we use it as a 'fixer' for the mac-roman
+    encoding, as it is unlikely that this encoding is the actually expected.
+    '''
+    try:
+        locale.CODESET
+    except AttributeError:
+        # Fall back to parsing environment variables :-(
+        return locale.getdefaultlocale()[1]
+
+    oldloc = locale.setlocale(locale.LC_CTYPE)
+    locale.setlocale(locale.LC_CTYPE, "")
+    result = locale.nl_langinfo(locale.CODESET)
+    locale.setlocale(locale.LC_CTYPE, oldloc)
+
+    return result
+
+_encodingfixers = {
+    '646': lambda: 'ascii',
+    'ANSI_X3.4-1968': lambda: 'ascii',
+    'mac-roman': _getpreferredencoding
+}
 
 try:
     encoding = os.environ.get("HGENCODING")
-    if sys.platform == 'darwin' and not encoding:
-        # On darwin, getpreferredencoding ignores the locale environment and
-        # always returns mac-roman. We override this if the environment is
-        # not C (has been customized by the user).
-        lc = locale.setlocale(locale.LC_CTYPE, '')
-        if lc == 'UTF-8':
-            locale.setlocale(locale.LC_CTYPE, 'en_US.UTF-8')
-        encoding = locale.getlocale()[1]
     if not encoding:
         encoding = locale.getpreferredencoding() or 'ascii'
-        encoding = _encodingfixup.get(encoding, encoding)
+        encoding = _encodingfixers.get(encoding, lambda: encoding)()
 except locale.Error:
     encoding = 'ascii'
 encodingmode = os.environ.get("HGENCODINGMODE", "strict")
 fallbackencoding = 'ISO-8859-1'
 
 def tolocal(s):
     """
     Convert a string from internal UTF-8 to local encoding
 
     All internal strings should be UTF-8 but some repos before the
     implementation of locale support may contain latin1 or possibly
     other character sets. We attempt to decode everything strictly
     using UTF-8, then Latin-1, and failing that, we use UTF-8 and
     replace unknown characters.
     """
     for e in ('UTF-8', fallbackencoding):
         try:
             u = s.decode(e) # attempt strict decoding
             return u.encode(encoding, "replace")
         except LookupError, k:
             raise error.Abort("%s, please check your locale settings" % k)
         except UnicodeDecodeError:
             pass
     u = s.decode("utf-8", "replace") # last ditch
     return u.encode(encoding, "replace")
 
 def fromlocal(s):
     """
     Convert a string from the local character encoding to UTF-8
 
     We attempt to decode strings using the encoding mode set by
     HGENCODINGMODE, which defaults to 'strict'. In this mode, unknown
     characters will cause an error message. Other modes include
     'replace', which replaces unknown characters with a special
     Unicode character, and 'ignore', which drops the character.
     """
     try:
         return s.decode(encoding, encodingmode).encode("utf-8")
     except UnicodeDecodeError, inst:
         sub = s[max(0, inst.start - 10):inst.start + 10]
         raise error.Abort("decoding near '%s': %s!" % (sub, inst))
     except LookupError, k:
         raise error.Abort("%s, please check your locale settings" % k)
 
 def colwidth(s):
     "Find the column width of a UTF-8 string for display"
     d = s.decode(encoding, 'replace')
     if hasattr(unicodedata, 'east_asian_width'):
         w = unicodedata.east_asian_width
         return sum([w(c) in 'WFA' and 2 or 1 for c in d])
     return len(d)