windows: degrade to py2 behavior when reading a non-symlink as a symlink

While waiting for the push to hg-committed in WSL to complete, I ran a
`phabimport` from Windows and got this traceback:

    $ hg phabimport 11313
    ** Unknown exception encountered with possibly-broken third-party extension "mercurial_keyring" (version N/A)
    ** which supports versions unknown of Mercurial.
    ** Please disable "mercurial_keyring" and try your action again.
    ** If that fixes the bug please report it to https://foss.heptapod.net/mercurial/mercurial_keyring/issues
    ** Python 3.9.5 (default, May  6 2021, 17:29:31) [MSC v.1928 64 bit (AMD64)]
    ** Mercurial Distributed SCM (version 5.9rc1+hg32.0e2f5733563d)
    ** Extensions loaded: absorb, blackbox, evolve 10.3.3, extdiff, fastannotate, fix, mercurial_keyring, mq, phabblocker 20210126, phabricator, rebase, show, strip, topic 0.22.3
    Traceback (most recent call last):
      File "mercurial.lock", line 279, in _trylock
      File "mercurial.vfs", line 202, in makelock
      File "mercurial.util", line 2147, in makelock
    FileExistsError: [WinError 183] Cannot create a file when that file already exists: b'hp-omen:78348' -> b'C:\\Users\\Matt\\hg/.hg/store/lock'

    During handling of the above exception, another exception occurred:

    Traceback (most recent call last):
      File "<string>", line 24, in <module>
      File "mercurial.dispatch", line 144, in run
      File "mercurial.dispatch", line 250, in dispatch
      File "mercurial.dispatch", line 294, in _rundispatch
      File "mercurial.dispatch", line 470, in _runcatch
      File "mercurial.dispatch", line 480, in _callcatch
      File "mercurial.scmutil", line 153, in callcatch
      File "mercurial.dispatch", line 460, in _runcatchfunc
      File "mercurial.dispatch", line 1273, in _dispatch
      File "mercurial.dispatch", line 918, in runcommand
      File "mercurial.dispatch", line 1285, in _runcommand
      File "mercurial.dispatch", line 1271, in <lambda>
      File "mercurial.util", line 1886, in check
      File "mercurial.util", line 1886, in check
      File "hgext.mq", line 4239, in mqcommand
      File "mercurial.util", line 1886, in check
      File "mercurial.util", line 1886, in check
      File "hgext.phabricator", line 314, in inner
      File "hgext.phabricator", line 2222, in phabimport
      File "hgext.phabricator", line 2123, in readpatch
      File "hgext.phabricator", line 2199, in _write
      File "mercurial.localrepo", line 2956, in lock
      File "mercurial.localrepo", line 2918, in _lock
      File "mercurial.lock", line 152, in trylock
      File "mercurial.lock", line 283, in _trylock
      File "mercurial.lock", line 314, in _readlock
      File "mercurial.vfs", line 221, in readlock
      File "mercurial.util", line 2163, in readlock
      File "mercurial.windows", line 619, in readlink
    ValueError: not a symbolic link

Both exceptions look accurate (the file exists, and the Windows side can't read
WSL side symlinks).  I didn't try to reproduce this entirely within the Windows
side, but we can do better than a cryptic stacktrace.  With this change, the
same scenario results in this abort:

    abort: C:\Users\Matt\hg/.hg/store/lock: The file cannot be accessed by the system

When both the `push` and `phabimport` are done on the Windows side, it prints a
message about waiting for the lock, and successfully applies the patch after the
push completes.

I'm not sure if there's enough info to be able to convert the abort into the
wait scenario.  As it stands now, we don't support symlinks on Windows, which
requires either a UAC Administrator level process or an opt-in in developer
mode, and there are several places where the new symlink on Windows support in
py3 was explicitly disabled in order to get tests to pass quicker.

Differential Revision: https://phab.mercurial-scm.org/D11333

mercurial/windows.py

@@ -1,732 +1,741 b''
 # windows.py - Windows utility function implementations for Mercurial
 #
 #  Copyright 2005-2009 Olivia 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.
 
 from __future__ import absolute_import
 
 import errno
 import getpass
 import msvcrt
 import os
 import re
 import stat
 import string
 import sys
 
 from .i18n import _
 from .pycompat import getattr
 from . import (
     encoding,
     error,
     policy,
     pycompat,
     win32,
 )
 
 try:
     import _winreg as winreg  # pytype: disable=import-error
 
     winreg.CloseKey
 except ImportError:
     # py2 only
     import winreg  # pytype: disable=import-error
 
 osutil = policy.importmod('osutil')
 
 getfsmountpoint = win32.getvolumename
 getfstype = win32.getfstype
 getuser = win32.getuser
 hidewindow = win32.hidewindow
 makedir = win32.makedir
 nlinks = win32.nlinks
 oslink = win32.oslink
 samedevice = win32.samedevice
 samefile = win32.samefile
 setsignalhandler = win32.setsignalhandler
 spawndetached = win32.spawndetached
 split = os.path.split
 testpid = win32.testpid
 unlink = win32.unlink
 
 umask = 0o022
 
 
 class mixedfilemodewrapper(object):
     """Wraps a file handle when it is opened in read/write mode.
 
     fopen() and fdopen() on Windows have a specific-to-Windows requirement
     that files opened with mode r+, w+, or a+ make a call to a file positioning
     function when switching between reads and writes. Without this extra call,
     Python will raise a not very intuitive "IOError: [Errno 0] Error."
 
     This class wraps posixfile instances when the file is opened in read/write
     mode and automatically adds checks or inserts appropriate file positioning
     calls when necessary.
     """
 
     OPNONE = 0
     OPREAD = 1
     OPWRITE = 2
 
     def __init__(self, fp):
         object.__setattr__(self, '_fp', fp)
         object.__setattr__(self, '_lastop', 0)
 
     def __enter__(self):
         self._fp.__enter__()
         return self
 
     def __exit__(self, exc_type, exc_val, exc_tb):
         self._fp.__exit__(exc_type, exc_val, exc_tb)
 
     def __getattr__(self, name):
         return getattr(self._fp, name)
 
     def __setattr__(self, name, value):
         return self._fp.__setattr__(name, value)
 
     def _noopseek(self):
         self._fp.seek(0, os.SEEK_CUR)
 
     def seek(self, *args, **kwargs):
         object.__setattr__(self, '_lastop', self.OPNONE)
         return self._fp.seek(*args, **kwargs)
 
     def write(self, d):
         if self._lastop == self.OPREAD:
             self._noopseek()
 
         object.__setattr__(self, '_lastop', self.OPWRITE)
         return self._fp.write(d)
 
     def writelines(self, *args, **kwargs):
         if self._lastop == self.OPREAD:
             self._noopeseek()
 
         object.__setattr__(self, '_lastop', self.OPWRITE)
         return self._fp.writelines(*args, **kwargs)
 
     def read(self, *args, **kwargs):
         if self._lastop == self.OPWRITE:
             self._noopseek()
 
         object.__setattr__(self, '_lastop', self.OPREAD)
         return self._fp.read(*args, **kwargs)
 
     def readline(self, *args, **kwargs):
         if self._lastop == self.OPWRITE:
             self._noopseek()
 
         object.__setattr__(self, '_lastop', self.OPREAD)
         return self._fp.readline(*args, **kwargs)
 
     def readlines(self, *args, **kwargs):
         if self._lastop == self.OPWRITE:
             self._noopseek()
 
         object.__setattr__(self, '_lastop', self.OPREAD)
         return self._fp.readlines(*args, **kwargs)
 
 
 class fdproxy(object):
     """Wraps osutil.posixfile() to override the name attribute to reflect the
     underlying file name.
     """
 
     def __init__(self, name, fp):
         self.name = name
         self._fp = fp
 
     def __enter__(self):
         self._fp.__enter__()
         # Return this wrapper for the context manager so that the name is
         # still available.
         return self
 
     def __exit__(self, exc_type, exc_value, traceback):
         self._fp.__exit__(exc_type, exc_value, traceback)
 
     def __iter__(self):
         return iter(self._fp)
 
     def __getattr__(self, name):
         return getattr(self._fp, name)
 
 
 def posixfile(name, mode=b'r', buffering=-1):
     '''Open a file with even more POSIX-like semantics'''
     try:
         fp = osutil.posixfile(name, mode, buffering)  # may raise WindowsError
 
         # PyFile_FromFd() ignores the name, and seems to report fp.name as the
         # underlying file descriptor.
         if pycompat.ispy3:
             fp = fdproxy(name, fp)
 
         # The position when opening in append mode is implementation defined, so
         # make it consistent with other platforms, which position at EOF.
         if b'a' in mode:
             fp.seek(0, os.SEEK_END)
 
         if b'+' in mode:
             return mixedfilemodewrapper(fp)
 
         return fp
     except WindowsError as err:
         # convert to a friendlier exception
         raise IOError(
             err.errno, '%s: %s' % (encoding.strfromlocal(name), err.strerror)
         )
 
 
 # may be wrapped by win32mbcs extension
 listdir = osutil.listdir
 
 
 # copied from .utils.procutil, remove after Python 2 support was dropped
 def _isatty(fp):
     try:
         return fp.isatty()
     except AttributeError:
         return False
 
 
 def get_password():
     """Prompt for password with echo off, using Windows getch().
 
     This shouldn't be called directly- use ``ui.getpass()`` instead, which
     checks if the session is interactive first.
     """
     pw = u""
     while True:
         c = msvcrt.getwch()  # pytype: disable=module-attr
         if c == u'\r' or c == u'\n':
             break
         if c == u'\003':
             raise KeyboardInterrupt
         if c == u'\b':
             pw = pw[:-1]
         else:
             pw = pw + c
     msvcrt.putwch(u'\r')  # pytype: disable=module-attr
     msvcrt.putwch(u'\n')  # pytype: disable=module-attr
     return encoding.unitolocal(pw)
 
 
 class winstdout(object):
     """Some files on Windows misbehave.
 
     When writing to a broken pipe, EINVAL instead of EPIPE may be raised.
 
     When writing too many bytes to a console at the same, a "Not enough space"
     error may happen. Python 3 already works around that.
     """
 
     def __init__(self, fp):
         self.fp = fp
         self.throttle = not pycompat.ispy3 and _isatty(fp)
 
     def __getattr__(self, key):
         return getattr(self.fp, key)
 
     def close(self):
         try:
             self.fp.close()
         except IOError:
             pass
 
     def write(self, s):
         try:
             if not self.throttle:
                 return self.fp.write(s)
             # This is workaround for "Not enough space" error on
             # writing large size of data to console.
             limit = 16000
             l = len(s)
             start = 0
             while start < l:
                 end = start + limit
                 self.fp.write(s[start:end])
                 start = end
         except IOError as inst:
             if inst.errno != 0 and not win32.lasterrorwaspipeerror(inst):
                 raise
             self.close()
             raise IOError(errno.EPIPE, 'Broken pipe')
 
     def flush(self):
         try:
             return self.fp.flush()
         except IOError as inst:
             if not win32.lasterrorwaspipeerror(inst):
                 raise
             raise IOError(errno.EPIPE, 'Broken pipe')
 
 
 def openhardlinks():
     return True
 
 
 def parsepatchoutput(output_line):
     """parses the output produced by patch and returns the filename"""
     pf = output_line[14:]
     if pf[0] == b'`':
         pf = pf[1:-1]  # Remove the quotes
     return pf
 
 
 def sshargs(sshcmd, host, user, port):
     '''Build argument list for ssh or Plink'''
     pflag = b'plink' in sshcmd.lower() and b'-P' or b'-p'
     args = user and (b"%s@%s" % (user, host)) or host
     if args.startswith(b'-') or args.startswith(b'/'):
         raise error.Abort(
             _(b'illegal ssh hostname or username starting with - or /: %s')
             % args
         )
     args = shellquote(args)
     if port:
         args = b'%s %s %s' % (pflag, shellquote(port), args)
     return args
 
 
 def setflags(f, l, x):
     pass
 
 
 def copymode(src, dst, mode=None, enforcewritable=False):
     pass
 
 
 def checkexec(path):
     return False
 
 
 def checklink(path):
     return False
 
 
 def setbinary(fd):
     # When run without console, pipes may expose invalid
     # fileno(), usually set to -1.
     fno = getattr(fd, 'fileno', None)
     if fno is not None and fno() >= 0:
         msvcrt.setmode(fno(), os.O_BINARY)  # pytype: disable=module-attr
 
 
 def pconvert(path):
     return path.replace(pycompat.ossep, b'/')
 
 
 def localpath(path):
     return path.replace(b'/', b'\\')
 
 
 def normpath(path):
     return pconvert(os.path.normpath(path))
 
 
 def normcase(path):
     return encoding.upper(path)  # NTFS compares via upper()
 
 
 DRIVE_RE_B = re.compile(b'^[a-z]:')
 DRIVE_RE_S = re.compile('^[a-z]:')
 
 
 def abspath(path):
     abs_path = os.path.abspath(path)  # re-exports
     # Python on Windows is inconsistent regarding the capitalization of drive
     # letter and this cause issue with various path comparison along the way.
     # So we normalize the drive later to upper case here.
     #
     # See https://bugs.python.org/issue40368 for and example of this hell.
     if isinstance(abs_path, bytes):
         if DRIVE_RE_B.match(abs_path):
             abs_path = abs_path[0:1].upper() + abs_path[1:]
     elif DRIVE_RE_S.match(abs_path):
         abs_path = abs_path[0:1].upper() + abs_path[1:]
     return abs_path
 
 
 # see posix.py for definitions
 normcasespec = encoding.normcasespecs.upper
 normcasefallback = encoding.upperfallback
 
 
 def samestat(s1, s2):
     return False
 
 
 def shelltocmdexe(path, env):
     r"""Convert shell variables in the form $var and ${var} inside ``path``
     to %var% form.  Existing Windows style variables are left unchanged.
 
     The variables are limited to the given environment.  Unknown variables are
     left unchanged.
 
     >>> e = {b'var1': b'v1', b'var2': b'v2', b'var3': b'v3'}
     >>> # Only valid values are expanded
     >>> shelltocmdexe(b'cmd $var1 ${var2} %var3% $missing ${missing} %missing%',
     ...               e)
     'cmd %var1% %var2% %var3% $missing ${missing} %missing%'
     >>> # Single quote prevents expansion, as does \$ escaping
     >>> shelltocmdexe(b"cmd '$var1 ${var2} %var3%' \$var1 \${var2} \\", e)
     'cmd "$var1 ${var2} %var3%" $var1 ${var2} \\'
     >>> # $$ is not special. %% is not special either, but can be the end and
     >>> # start of consecutive variables
     >>> shelltocmdexe(b"cmd $$ %% %var1%%var2%", e)
     'cmd $$ %% %var1%%var2%'
     >>> # No double substitution
     >>> shelltocmdexe(b"$var1 %var1%", {b'var1': b'%var2%', b'var2': b'boom'})
     '%var1% %var1%'
     >>> # Tilde expansion
     >>> shelltocmdexe(b"~/dir ~\dir2 ~tmpfile \~/", {})
     '%USERPROFILE%/dir %USERPROFILE%\\dir2 ~tmpfile ~/'
     """
     if not any(c in path for c in b"$'~"):
         return path
 
     varchars = pycompat.sysbytes(string.ascii_letters + string.digits) + b'_-'
 
     res = b''
     index = 0
     pathlen = len(path)
     while index < pathlen:
         c = path[index : index + 1]
         if c == b'\'':  # no expansion within single quotes
             path = path[index + 1 :]
             pathlen = len(path)
             try:
                 index = path.index(b'\'')
                 res += b'"' + path[:index] + b'"'
             except ValueError:
                 res += c + path
                 index = pathlen - 1
         elif c == b'%':  # variable
             path = path[index + 1 :]
             pathlen = len(path)
             try:
                 index = path.index(b'%')
             except ValueError:
                 res += b'%' + path
                 index = pathlen - 1
             else:
                 var = path[:index]
                 res += b'%' + var + b'%'
         elif c == b'$':  # variable
             if path[index + 1 : index + 2] == b'{':
                 path = path[index + 2 :]
                 pathlen = len(path)
                 try:
                     index = path.index(b'}')
                     var = path[:index]
 
                     # See below for why empty variables are handled specially
                     if env.get(var, b'') != b'':
                         res += b'%' + var + b'%'
                     else:
                         res += b'${' + var + b'}'
                 except ValueError:
                     res += b'${' + path
                     index = pathlen - 1
             else:
                 var = b''
                 index += 1
                 c = path[index : index + 1]
                 while c != b'' and c in varchars:
                     var += c
                     index += 1
                     c = path[index : index + 1]
                 # Some variables (like HG_OLDNODE) may be defined, but have an
                 # empty value.  Those need to be skipped because when spawning
                 # cmd.exe to run the hook, it doesn't replace %VAR% for an empty
                 # VAR, and that really confuses things like revset expressions.
                 # OTOH, if it's left in Unix format and the hook runs sh.exe, it
                 # will substitute to an empty string, and everything is happy.
                 if env.get(var, b'') != b'':
                     res += b'%' + var + b'%'
                 else:
                     res += b'$' + var
 
                 if c != b'':
                     index -= 1
         elif (
             c == b'~'
             and index + 1 < pathlen
             and path[index + 1 : index + 2] in (b'\\', b'/')
         ):
             res += b"%USERPROFILE%"
         elif (
             c == b'\\'
             and index + 1 < pathlen
             and path[index + 1 : index + 2] in (b'$', b'~')
         ):
             # Skip '\', but only if it is escaping $ or ~
             res += path[index + 1 : index + 2]
             index += 1
         else:
             res += c
 
         index += 1
     return res
 
 
 # A sequence of backslashes is special iff it precedes a double quote:
 # - if there's an even number of backslashes, the double quote is not
 #   quoted (i.e. it ends the quoted region)
 # - if there's an odd number of backslashes, the double quote is quoted
 # - in both cases, every pair of backslashes is unquoted into a single
 #   backslash
 # (See http://msdn2.microsoft.com/en-us/library/a1y7w461.aspx )
 # So, to quote a string, we must surround it in double quotes, double
 # the number of backslashes that precede double quotes and add another
 # backslash before every double quote (being careful with the double
 # quote we've appended to the end)
 _quotere = None
 _needsshellquote = None
 
 
 def shellquote(s):
     r"""
     >>> shellquote(br'C:\Users\xyz')
     '"C:\\Users\\xyz"'
     >>> shellquote(br'C:\Users\xyz/mixed')
     '"C:\\Users\\xyz/mixed"'
     >>> # Would be safe not to quote too, since it is all double backslashes
     >>> shellquote(br'C:\\Users\\xyz')
     '"C:\\\\Users\\\\xyz"'
     >>> # But this must be quoted
     >>> shellquote(br'C:\\Users\\xyz/abc')
     '"C:\\\\Users\\\\xyz/abc"'
     """
     global _quotere
     if _quotere is None:
         _quotere = re.compile(br'(\\*)("|\\$)')
     global _needsshellquote
     if _needsshellquote is None:
         # ":" is also treated as "safe character", because it is used as a part
         # of path name on Windows.  "\" is also part of a path name, but isn't
         # safe because shlex.split() (kind of) treats it as an escape char and
         # drops it.  It will leave the next character, even if it is another
         # "\".
         _needsshellquote = re.compile(br'[^a-zA-Z0-9._:/-]').search
     if s and not _needsshellquote(s) and not _quotere.search(s):
         # "s" shouldn't have to be quoted
         return s
     return b'"%s"' % _quotere.sub(br'\1\1\\\2', s)
 
 
 def _unquote(s):
     if s.startswith(b'"') and s.endswith(b'"'):
         return s[1:-1]
     return s
 
 
 def shellsplit(s):
     """Parse a command string in cmd.exe way (best-effort)"""
     return pycompat.maplist(_unquote, pycompat.shlexsplit(s, posix=False))
 
 
 # if you change this stub into a real check, please try to implement the
 # username and groupname functions above, too.
 def isowner(st):
     return True
 
 
 def findexe(command):
     """Find executable for command searching like cmd.exe does.
     If command is a basename then PATH is searched for command.
     PATH isn't searched if command is an absolute or relative path.
     An extension from PATHEXT is found and added if not present.
     If command isn't found None is returned."""
     pathext = encoding.environ.get(b'PATHEXT', b'.COM;.EXE;.BAT;.CMD')
     pathexts = [ext for ext in pathext.lower().split(pycompat.ospathsep)]
     if os.path.splitext(command)[1].lower() in pathexts:
         pathexts = [b'']
 
     def findexisting(pathcommand):
         """Will append extension (if needed) and return existing file"""
         for ext in pathexts:
             executable = pathcommand + ext
             if os.path.exists(executable):
                 return executable
         return None
 
     if pycompat.ossep in command:
         return findexisting(command)
 
     for path in encoding.environ.get(b'PATH', b'').split(pycompat.ospathsep):
         executable = findexisting(os.path.join(path, command))
         if executable is not None:
             return executable
     return findexisting(os.path.expanduser(os.path.expandvars(command)))
 
 
 _wantedkinds = {stat.S_IFREG, stat.S_IFLNK}
 
 
 def statfiles(files):
     """Stat each file in files. Yield each stat, or None if a file
     does not exist or has a type we don't care about.
 
     Cluster and cache stat per directory to minimize number of OS stat calls."""
     dircache = {}  # dirname -> filename -> status | None if file does not exist
     getkind = stat.S_IFMT
     for nf in files:
         nf = normcase(nf)
         dir, base = os.path.split(nf)
         if not dir:
             dir = b'.'
         cache = dircache.get(dir, None)
         if cache is None:
             try:
                 dmap = {
                     normcase(n): s
                     for n, k, s in listdir(dir, True)
                     if getkind(s.st_mode) in _wantedkinds
                 }
             except OSError as err:
                 # Python >= 2.5 returns ENOENT and adds winerror field
                 # EINVAL is raised if dir is not a directory.
                 if err.errno not in (errno.ENOENT, errno.EINVAL, errno.ENOTDIR):
                     raise
                 dmap = {}
             cache = dircache.setdefault(dir, dmap)
         yield cache.get(base, None)
 
 
 def username(uid=None):
     """Return the name of the user with the given uid.
 
     If uid is None, return the name of the current user."""
     if not uid:
         return pycompat.fsencode(getpass.getuser())
     return None
 
 
 def groupname(gid=None):
     """Return the name of the group with the given gid.
 
     If gid is None, return the name of the current group."""
     return None
 
 
 def readlink(pathname):
-    return pycompat.fsencode(os.readlink(pycompat.fsdecode(pathname)))
+    path = pycompat.fsdecode(pathname)
+    try:
+        link = os.readlink(path)
+    except ValueError as e:
+        # On py2, os.readlink() raises an AttributeError since it is
+        # unsupported.  On py3, reading a non-link raises a ValueError.  Simply
+        # treat this as the error the locking code has been expecting up to now
+        # until an effort can be made to enable symlink support on Windows.
+        raise AttributeError(e)
+    return pycompat.fsencode(link)
 
 
 def removedirs(name):
     """special version of os.removedirs that does not remove symlinked
     directories or junction points if they actually contain files"""
     if listdir(name):
         return
     os.rmdir(name)
     head, tail = os.path.split(name)
     if not tail:
         head, tail = os.path.split(head)
     while head and tail:
         try:
             if listdir(head):
                 return
             os.rmdir(head)
         except (ValueError, OSError):
             break
         head, tail = os.path.split(head)
 
 
 def rename(src, dst):
     '''atomically rename file src to dst, replacing dst if it exists'''
     try:
         os.rename(src, dst)
     except OSError as e:
         if e.errno != errno.EEXIST:
             raise
         unlink(dst)
         os.rename(src, dst)
 
 
 def gethgcmd():
     return [encoding.strtolocal(arg) for arg in [sys.executable] + sys.argv[:1]]
 
 
 def groupmembers(name):
     # Don't support groups on Windows for now
     raise KeyError
 
 
 def isexec(f):
     return False
 
 
 class cachestat(object):
     def __init__(self, path):
         pass
 
     def cacheable(self):
         return False
 
 
 def lookupreg(key, valname=None, scope=None):
     """Look up a key/value name in the Windows registry.
 
     valname: value name. If unspecified, the default value for the key
     is used.
     scope: optionally specify scope for registry lookup, this can be
     a sequence of scopes to look up in order. Default (CURRENT_USER,
     LOCAL_MACHINE).
     """
     if scope is None:
         scope = (winreg.HKEY_CURRENT_USER, winreg.HKEY_LOCAL_MACHINE)
     elif not isinstance(scope, (list, tuple)):
         scope = (scope,)
     for s in scope:
         try:
             with winreg.OpenKey(s, encoding.strfromlocal(key)) as hkey:
                 name = valname and encoding.strfromlocal(valname) or valname
                 val = winreg.QueryValueEx(hkey, name)[0]
                 # never let a Unicode string escape into the wild
                 return encoding.unitolocal(val)
         except EnvironmentError:
             pass
 
 
 expandglobs = True
 
 
 def statislink(st):
     '''check whether a stat result is a symlink'''
     return False
 
 
 def statisexec(st):
     '''check whether a stat result is an executable file'''
     return False
 
 
 def poll(fds):
     # see posix.py for description
     raise NotImplementedError()
 
 
 def readpipe(pipe):
     """Read all available data from a pipe."""
     chunks = []
     while True:
         size = win32.peekpipe(pipe)
         if not size:
             break
 
         s = pipe.read(size)
         if not s:
             break
         chunks.append(s)
 
     return b''.join(chunks)
 
 
 def bindunixsocket(sock, path):
     raise NotImplementedError('unsupported platform')