py3: add a bytes version of os.name

os.name returns unicodes on py3. Most of our checks are like
    os.name == 'nt'

Because of the transformer, on the right hand side we have b'nt'. The
condition will never satisfy even if os.name returns 'nt' as that will be an
unicode.
We either need to encode every occurence of os.name or have a
new variable which is much cleaner. Now we have pycompat.osname.
There are around 53 occurences of os.name in the codebase which needs to
be replaced by pycompat.osname to support Python 3.

mercurial/pycompat.py

@@ -1,202 +1,206 b''
 # pycompat.py - portability shim for python 3
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 """Mercurial portability shim for python 3.
 
 This contains aliases to hide python version-specific details from the core.
 """
 
 from __future__ import absolute_import
 
+import os
 import sys
 
 ispy3 = (sys.version_info[0] >= 3)
 
 if not ispy3:
     import cPickle as pickle
     import cStringIO as io
     import httplib
     import Queue as _queue
     import SocketServer as socketserver
     import urlparse
     import xmlrpclib
 else:
     import http.client as httplib
     import io
     import pickle
     import queue as _queue
     import socketserver
     import urllib.parse as urlparse
     import xmlrpc.client as xmlrpclib
 
 if ispy3:
     import builtins
     import functools
-    import os
     fsencode = os.fsencode
     fsdecode = os.fsdecode
+    # A bytes version of os.name.
+    osname = os.name.encode('ascii')
 
     def sysstr(s):
         """Return a keyword str to be passed to Python functions such as
         getattr() and str.encode()
 
         This never raises UnicodeDecodeError. Non-ascii characters are
         considered invalid and mapped to arbitrary but unique code points
         such that 'sysstr(a) != sysstr(b)' for all 'a != b'.
         """
         if isinstance(s, builtins.str):
             return s
         return s.decode(u'latin-1')
 
     def _wrapattrfunc(f):
         @functools.wraps(f)
         def w(object, name, *args):
             return f(object, sysstr(name), *args)
         return w
 
     # these wrappers are automagically imported by hgloader
     delattr = _wrapattrfunc(builtins.delattr)
     getattr = _wrapattrfunc(builtins.getattr)
     hasattr = _wrapattrfunc(builtins.hasattr)
     setattr = _wrapattrfunc(builtins.setattr)
     xrange = builtins.range
 
 else:
     def sysstr(s):
         return s
 
     # Partial backport from os.py in Python 3, which only accepts bytes.
     # In Python 2, our paths should only ever be bytes, a unicode path
     # indicates a bug.
     def fsencode(filename):
         if isinstance(filename, str):
             return filename
         else:
             raise TypeError(
                 "expect str, not %s" % type(filename).__name__)
 
     # In Python 2, fsdecode() has a very chance to receive bytes. So it's
     # better not to touch Python 2 part as it's already working fine.
     def fsdecode(filename):
         return filename
 
+    osname = os.name
+
 stringio = io.StringIO
 empty = _queue.Empty
 queue = _queue.Queue
 
 class _pycompatstub(object):
     def __init__(self):
         self._aliases = {}
 
     def _registeraliases(self, origin, items):
         """Add items that will be populated at the first access"""
         items = map(sysstr, items)
         self._aliases.update(
             (item.replace(sysstr('_'), sysstr('')).lower(), (origin, item))
             for item in items)
 
     def __getattr__(self, name):
         try:
             origin, item = self._aliases[name]
         except KeyError:
             raise AttributeError(name)
         self.__dict__[name] = obj = getattr(origin, item)
         return obj
 
 httpserver = _pycompatstub()
 urlreq = _pycompatstub()
 urlerr = _pycompatstub()
 if not ispy3:
     import BaseHTTPServer
     import CGIHTTPServer
     import SimpleHTTPServer
     import urllib2
     import urllib
     urlreq._registeraliases(urllib, (
         "addclosehook",
         "addinfourl",
         "ftpwrapper",
         "pathname2url",
         "quote",
         "splitattr",
         "splitpasswd",
         "splitport",
         "splituser",
         "unquote",
         "url2pathname",
         "urlencode",
     ))
     urlreq._registeraliases(urllib2, (
         "AbstractHTTPHandler",
         "BaseHandler",
         "build_opener",
         "FileHandler",
         "FTPHandler",
         "HTTPBasicAuthHandler",
         "HTTPDigestAuthHandler",
         "HTTPHandler",
         "HTTPPasswordMgrWithDefaultRealm",
         "HTTPSHandler",
         "install_opener",
         "ProxyHandler",
         "Request",
         "urlopen",
     ))
     urlerr._registeraliases(urllib2, (
         "HTTPError",
         "URLError",
     ))
     httpserver._registeraliases(BaseHTTPServer, (
         "HTTPServer",
         "BaseHTTPRequestHandler",
     ))
     httpserver._registeraliases(SimpleHTTPServer, (
         "SimpleHTTPRequestHandler",
     ))
     httpserver._registeraliases(CGIHTTPServer, (
         "CGIHTTPRequestHandler",
     ))
 
 else:
     import urllib.request
     urlreq._registeraliases(urllib.request, (
         "AbstractHTTPHandler",
         "addclosehook",
         "addinfourl",
         "BaseHandler",
         "build_opener",
         "FileHandler",
         "FTPHandler",
         "ftpwrapper",
         "HTTPHandler",
         "HTTPSHandler",
         "install_opener",
         "pathname2url",
         "HTTPBasicAuthHandler",
         "HTTPDigestAuthHandler",
         "HTTPPasswordMgrWithDefaultRealm",
         "ProxyHandler",
         "quote",
         "Request",
         "splitattr",
         "splitpasswd",
         "splitport",
         "splituser",
         "unquote",
         "url2pathname",
         "urlopen",
     ))
     import urllib.error
     urlerr._registeraliases(urllib.error, (
         "HTTPError",
         "URLError",
     ))
     import http.server
     httpserver._registeraliases(http.server, (
         "HTTPServer",
         "BaseHTTPRequestHandler",
         "SimpleHTTPRequestHandler",
         "CGIHTTPRequestHandler",
     ))