comparison mercurial/utils/procutil.py @ 43076:2372284d9457

formatting: blacken the codebase

This is using my patch to black
(https://github.com/psf/black/pull/826) so we don't un-wrap collection
literals.

Done with:

  hg files 'set:**.py - mercurial/thirdparty/** - "contrib/python-zstandard/**"' | xargs black -S

# skip-blame mass-reformatting only

# no-check-commit reformats foo_bar functions

Differential Revision: https://phab.mercurial-scm.org/D6971

43075:57875cf423c9

stderr = pycompat.stderr
stdin = pycompat.stdin
stdout = pycompat.stdout

def isatty(fp):
    try:
        return fp.isatty()
    except AttributeError:
        return False

# glibc determines buffering on first write to stdout - if we replace a TTY
# destined stdout with a pipe destined stdout (e.g. pager), we want line
# buffering (or unbuffered, on Windows)
if isatty(stdout):

    else:
        stdout = os.fdopen(stdout.fileno(), r'wb', 1)

if pycompat.iswindows:
    from .. import windows as platform
    stdout = platform.winstdout(stdout)
else:
    from .. import posix as platform

findexe = platform.findexe

except AttributeError:
    pass

closefds = pycompat.isposix

def explainexit(code):
    """return a message describing a subprocess status
    (codes from kill are negative - not os.system/wait encoding)"""
    if code >= 0:
        return _("exited with status %d") % code
    return _("killed by signal %d") % -code

class _pfile(object):
    """File-like wrapper for a stream opened by subprocess.Popen()"""

    def __init__(self, proc, fp):
        self._proc = proc

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, exc_tb):
        self.close()

def popen(cmd, mode='rb', bufsize=-1):
    if mode == 'rb':
        return _popenreader(cmd, bufsize)
    elif mode == 'wb':
        return _popenwriter(cmd, bufsize)
    raise error.ProgrammingError('unsupported mode: %r' % mode)

def _popenreader(cmd, bufsize):
    p = subprocess.Popen(tonativestr(quotecommand(cmd)),
                         shell=True, bufsize=bufsize,
                         close_fds=closefds,
                         stdout=subprocess.PIPE)
    return _pfile(p, p.stdout)

def _popenwriter(cmd, bufsize):
    p = subprocess.Popen(tonativestr(quotecommand(cmd)),
                         shell=True, bufsize=bufsize,
                         close_fds=closefds,
                         stdin=subprocess.PIPE)
    return _pfile(p, p.stdin)

def popen2(cmd, env=None):
    # Setting bufsize to -1 lets the system decide the buffer size.
    # The default for bufsize is 0, meaning unbuffered. This leads to
    # poor performance on Mac OS X: http://bugs.python.org/issue4194
    p = subprocess.Popen(tonativestr(cmd),
                         shell=True, bufsize=-1,
                         close_fds=closefds,
                         stdin=subprocess.PIPE, stdout=subprocess.PIPE,
                         env=tonativeenv(env))
    return p.stdin, p.stdout

def popen3(cmd, env=None):
    stdin, stdout, stderr, p = popen4(cmd, env)
    return stdin, stdout, stderr

def popen4(cmd, env=None, bufsize=-1):
    p = subprocess.Popen(tonativestr(cmd),
                         shell=True, bufsize=bufsize,
                         close_fds=closefds,
                         stdin=subprocess.PIPE, stdout=subprocess.PIPE,
                         stderr=subprocess.PIPE,
                         env=tonativeenv(env))
    return p.stdin, p.stdout, p.stderr, p

def pipefilter(s, cmd):
    '''filter string S through command CMD, returning its output'''
    p = subprocess.Popen(tonativestr(cmd),
                         shell=True, close_fds=closefds,
                         stdin=subprocess.PIPE, stdout=subprocess.PIPE)
    pout, perr = p.communicate(s)
    return pout

def tempfilter(s, cmd):
    '''filter string S through a pair of temporary files with CMD.
    CMD is used as a template to create the real command to be run,
    with the strings INFILE and OUTFILE replaced by the real names of

        cmd = cmd.replace('OUTFILE', outname)
        code = system(cmd)
        if pycompat.sysplatform == 'OpenVMS' and code & 1:
            code = 0
        if code:
            raise error.Abort(_("command '%s' failed: %s") %
                              (cmd, explainexit(code)))
        with open(outname, 'rb') as fp:
            return fp.read()
    finally:
        try:
            if inname:

            if outname:
                os.unlink(outname)
        except OSError:
            pass

_filtertable = {
    'tempfile:': tempfilter,
    'pipe:': pipefilter,
}

def filter(s, cmd):
    "filter a string through a command that transforms its input to its output"
    for name, fn in _filtertable.iteritems():
        if cmd.startswith(name):
            return fn(s, cmd[len(name):].lstrip())
    return pipefilter(s, cmd)

def mainfrozen():
    """return True if we are a frozen executable.

    The code supports py2exe (most common, Windows only) and tools/freeze
    (portable, not much used).
    """
    return (pycompat.safehasattr(sys, "frozen") or # new py2exe
            pycompat.safehasattr(sys, "importers") or # old py2exe
            imp.is_frozen(r"__main__")) # tools/freeze

_hgexecutable = None

def hgexecutable():
    """return location of the 'hg' executable.

    Defaults to $HG or 'hg' in the search path.

            if getattr(sys, 'frozen', None) == 'macosx_app':
                # Env variable set by py2app
                _sethgexecutable(encoding.environ['EXECUTABLEPATH'])
            else:
                _sethgexecutable(pycompat.sysexecutable)
        elif (not pycompat.iswindows and os.path.basename(
            pycompat.fsencode(getattr(mainmod, '__file__', ''))) == 'hg'):
            _sethgexecutable(pycompat.fsencode(mainmod.__file__))
        else:
            _sethgexecutable(findexe('hg') or
                             os.path.basename(pycompat.sysargv[0]))
    return _hgexecutable

def _sethgexecutable(path):
    """set location of the 'hg' executable"""
    global _hgexecutable
    _hgexecutable = path

def _testfileno(f, stdf):
    fileno = getattr(f, 'fileno', None)
    try:
        return fileno and fileno() == stdf.fileno()
    except io.UnsupportedOperation:
        return False # fileno() raised UnsupportedOperation

def isstdin(f):
    return _testfileno(f, sys.__stdin__)

def isstdout(f):
    return _testfileno(f, sys.__stdout__)

def protectstdio(uin, uout):
    """Duplicate streams and redirect original if (uin, uout) are stdio

    If uin is stdin, it's redirected to /dev/null. If uout is stdout, it's

        newfd = os.dup(uout.fileno())
        os.dup2(stderr.fileno(), uout.fileno())
        fout = os.fdopen(newfd, r'wb')
    return fin, fout

def restorestdio(uin, uout, fin, fout):
    """Restore (uin, uout) streams from possibly duplicated (fin, fout)"""
    uout.flush()
    for f, uif in [(fin, uin), (fout, uout)]:
        if f is not uif:
            os.dup2(f.fileno(), uif.fileno())
            f.close()

def shellenviron(environ=None):
    """return environ with optional override, useful for shelling out"""
    def py2shell(val):
        'convert python object into string that is useful to shell'
        if val is None or val is False:
            return '0'
        if val is True:
            return '1'
        return pycompat.bytestr(val)
    env = dict(encoding.environ)
    if environ:
        env.update((k, py2shell(v)) for k, v in environ.iteritems())
    env['HG'] = hgexecutable()
    return env

if pycompat.iswindows:
    def shelltonative(cmd, env):
        return platform.shelltocmdexe(cmd, shellenviron(env))

    tonativestr = encoding.strfromlocal
else:
    def shelltonative(cmd, env):
        return cmd

    tonativestr = pycompat.identity

def tonativeenv(env):
    '''convert the environment from bytes to strings suitable for Popen(), etc.
    '''
    return pycompat.rapply(tonativestr, env)

def system(cmd, environ=None, cwd=None, out=None):
    '''enhanced shell command execution.
    run with environment maybe modified, maybe in different dir.

    except Exception:
        pass
    cmd = quotecommand(cmd)
    env = shellenviron(environ)
    if out is None or isstdout(out):
        rc = subprocess.call(tonativestr(cmd),
                             shell=True, close_fds=closefds,
                             env=tonativeenv(env),
                             cwd=pycompat.rapply(tonativestr, cwd))
    else:
        proc = subprocess.Popen(tonativestr(cmd),
                                shell=True, close_fds=closefds,
                                env=tonativeenv(env),
                                cwd=pycompat.rapply(tonativestr, cwd),
                                stdout=subprocess.PIPE,
                                stderr=subprocess.STDOUT)
        for line in iter(proc.stdout.readline, ''):
            out.write(line)
        proc.wait()
        rc = proc.returncode
    if pycompat.sysplatform == 'OpenVMS' and rc & 1:
        rc = 0
    return rc

def gui():
    '''Are we running in a GUI?'''
    if pycompat.isdarwin:
        if 'SSH_CONNECTION' in encoding.environ:

            # pure build; use a safe default
            return True
    else:
        return pycompat.iswindows or encoding.environ.get("DISPLAY")

def hgcmd():
    """Return the command used to execute current hg

    This is different from hgexecutable() because on Windows we want
    to avoid things opening new shell windows like batch files, so we

            # Env variable set by py2app
            return [encoding.environ['EXECUTABLEPATH']]
        else:
            return [pycompat.sysexecutable]
    return _gethgcmd()

def rundetached(args, condfn):
    """Execute the argument list in a detached process.

    condfn is a callable which is called repeatedly and should return

    # process fails to start, it will be left in a zombie state until
    # the parent wait on it, which we cannot do since we expect a long
    # running process on success. Instead we listen for SIGCHLD telling
    # us our child process terminated.
    terminated = set()
    def handler(signum, frame):
        terminated.add(os.wait())
    prevhandler = None
    SIGCHLD = getattr(signal, 'SIGCHLD', None)
    if SIGCHLD is not None:
        prevhandler = signal.signal(SIGCHLD, handler)
    try:
        pid = spawndetached(args)
        while not condfn():
            if ((pid in terminated or not testpid(pid))
                and not condfn()):
                return -1
            time.sleep(0.1)
        return pid
    finally:
        if prevhandler is not None:
            signal.signal(signal.SIGCHLD, prevhandler)

@contextlib.contextmanager
def uninterruptible(warn):
    """Inhibit SIGINT handling on a region of code.

        if oldsiginthandler:
            signal.signal(signal.SIGINT, oldsiginthandler[0])
        if shouldbail:
            raise KeyboardInterrupt

if pycompat.iswindows:
    # no fork on Windows, but we can create a detached process
    # https://msdn.microsoft.com/en-us/library/windows/desktop/ms684863.aspx
    # No stdlib constant exists for this value
    DETACHED_PROCESS = 0x00000008

    # Using subprocess.CREATE_NEW_CONSOLE might helps.
    # See https://phab.mercurial-scm.org/D1701 for discussion
    _creationflags = DETACHED_PROCESS | subprocess.CREATE_NEW_PROCESS_GROUP

    def runbgcommand(
      script, env, shell=False, stdout=None, stderr=None, ensurestart=True):
        '''Spawn a command without waiting for it to finish.'''
        # we can't use close_fds *and* redirect stdin. I'm not sure that we
        # need to because the detached process has no console connection.
        subprocess.Popen(
            tonativestr(script),
            shell=shell, env=tonativeenv(env), close_fds=True,
            creationflags=_creationflags, stdout=stdout,
            stderr=stderr)
else:
    def runbgcommand(
      cmd, env, shell=False, stdout=None, stderr=None, ensurestart=True):
        '''Spawn a command without waiting for it to finish.'''
        # double-fork to completely detach from the parent process
        # based on http://code.activestate.com/recipes/278731
        pid = os.fork()
        if pid:

            # Parent process
            (_pid, status) = os.waitpid(pid, 0)
            if os.WIFEXITED(status):
                returncode = os.WEXITSTATUS(status)
            else:
                returncode = -os.WTERMSIG(status)
            if returncode != 0:
                # The child process's return code is 0 on success, an errno
                # value on failure, or 255 if we don't have a valid errno
                # value.
                #
                # (It would be slightly nicer to return the full exception info
                # over a pipe as the subprocess module does.  For now it
                # doesn't seem worth adding that complexity here, though.)
                if returncode == 255:
                    returncode = errno.EINVAL
                raise OSError(returncode, 'error running %r: %s' %
                              (cmd, os.strerror(returncode)))
            return

        returncode = 255
        try:
            # Start a new session

                stderr = open(os.devnull, 'w')

            # connect stdin to devnull to make sure the subprocess can't
            # muck up that stream for mercurial.
            subprocess.Popen(
                cmd, shell=shell, env=env, close_fds=True,
                stdin=stdin, stdout=stdout, stderr=stderr)
            returncode = 0
        except EnvironmentError as ex:
            returncode = (ex.errno & 0xff)
            if returncode == 0:
                # This shouldn't happen, but just in case make sure the
                # return code is never 0 here.
                returncode = 255
        except Exception:

43076:2372284d9457

stderr = pycompat.stderr
stdin = pycompat.stdin
stdout = pycompat.stdout


def isatty(fp):
    try:
        return fp.isatty()
    except AttributeError:
        return False


# glibc determines buffering on first write to stdout - if we replace a TTY
# destined stdout with a pipe destined stdout (e.g. pager), we want line
# buffering (or unbuffered, on Windows)
if isatty(stdout):

    else:
        stdout = os.fdopen(stdout.fileno(), r'wb', 1)

if pycompat.iswindows:
    from .. import windows as platform

    stdout = platform.winstdout(stdout)
else:
    from .. import posix as platform

findexe = platform.findexe

except AttributeError:
    pass

closefds = pycompat.isposix


def explainexit(code):
    """return a message describing a subprocess status
    (codes from kill are negative - not os.system/wait encoding)"""
    if code >= 0:
        return _("exited with status %d") % code
    return _("killed by signal %d") % -code


class _pfile(object):
    """File-like wrapper for a stream opened by subprocess.Popen()"""

    def __init__(self, proc, fp):
        self._proc = proc

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, exc_tb):
        self.close()


def popen(cmd, mode='rb', bufsize=-1):
    if mode == 'rb':
        return _popenreader(cmd, bufsize)
    elif mode == 'wb':
        return _popenwriter(cmd, bufsize)
    raise error.ProgrammingError('unsupported mode: %r' % mode)


def _popenreader(cmd, bufsize):
    p = subprocess.Popen(
        tonativestr(quotecommand(cmd)),
        shell=True,
        bufsize=bufsize,
        close_fds=closefds,
        stdout=subprocess.PIPE,
    )
    return _pfile(p, p.stdout)


def _popenwriter(cmd, bufsize):
    p = subprocess.Popen(
        tonativestr(quotecommand(cmd)),
        shell=True,
        bufsize=bufsize,
        close_fds=closefds,
        stdin=subprocess.PIPE,
    )
    return _pfile(p, p.stdin)


def popen2(cmd, env=None):
    # Setting bufsize to -1 lets the system decide the buffer size.
    # The default for bufsize is 0, meaning unbuffered. This leads to
    # poor performance on Mac OS X: http://bugs.python.org/issue4194
    p = subprocess.Popen(
        tonativestr(cmd),
        shell=True,
        bufsize=-1,
        close_fds=closefds,
        stdin=subprocess.PIPE,
        stdout=subprocess.PIPE,
        env=tonativeenv(env),
    )
    return p.stdin, p.stdout


def popen3(cmd, env=None):
    stdin, stdout, stderr, p = popen4(cmd, env)
    return stdin, stdout, stderr


def popen4(cmd, env=None, bufsize=-1):
    p = subprocess.Popen(
        tonativestr(cmd),
        shell=True,
        bufsize=bufsize,
        close_fds=closefds,
        stdin=subprocess.PIPE,
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
        env=tonativeenv(env),
    )
    return p.stdin, p.stdout, p.stderr, p


def pipefilter(s, cmd):
    '''filter string S through command CMD, returning its output'''
    p = subprocess.Popen(
        tonativestr(cmd),
        shell=True,
        close_fds=closefds,
        stdin=subprocess.PIPE,
        stdout=subprocess.PIPE,
    )
    pout, perr = p.communicate(s)
    return pout


def tempfilter(s, cmd):
    '''filter string S through a pair of temporary files with CMD.
    CMD is used as a template to create the real command to be run,
    with the strings INFILE and OUTFILE replaced by the real names of

        cmd = cmd.replace('OUTFILE', outname)
        code = system(cmd)
        if pycompat.sysplatform == 'OpenVMS' and code & 1:
            code = 0
        if code:
            raise error.Abort(
                _("command '%s' failed: %s") % (cmd, explainexit(code))
            )
        with open(outname, 'rb') as fp:
            return fp.read()
    finally:
        try:
            if inname:

            if outname:
                os.unlink(outname)
        except OSError:
            pass


_filtertable = {
    'tempfile:': tempfilter,
    'pipe:': pipefilter,
}


def filter(s, cmd):
    "filter a string through a command that transforms its input to its output"
    for name, fn in _filtertable.iteritems():
        if cmd.startswith(name):
            return fn(s, cmd[len(name) :].lstrip())
    return pipefilter(s, cmd)


def mainfrozen():
    """return True if we are a frozen executable.

    The code supports py2exe (most common, Windows only) and tools/freeze
    (portable, not much used).
    """
    return (
        pycompat.safehasattr(sys, "frozen")
        or pycompat.safehasattr(sys, "importers")  # new py2exe
        or imp.is_frozen(r"__main__")  # old py2exe
    )  # tools/freeze


_hgexecutable = None


def hgexecutable():
    """return location of the 'hg' executable.

    Defaults to $HG or 'hg' in the search path.

            if getattr(sys, 'frozen', None) == 'macosx_app':
                # Env variable set by py2app
                _sethgexecutable(encoding.environ['EXECUTABLEPATH'])
            else:
                _sethgexecutable(pycompat.sysexecutable)
        elif (
            not pycompat.iswindows
            and os.path.basename(
                pycompat.fsencode(getattr(mainmod, '__file__', ''))
            )
            == 'hg'
        ):
            _sethgexecutable(pycompat.fsencode(mainmod.__file__))
        else:
            _sethgexecutable(
                findexe('hg') or os.path.basename(pycompat.sysargv[0])
            )
    return _hgexecutable


def _sethgexecutable(path):
    """set location of the 'hg' executable"""
    global _hgexecutable
    _hgexecutable = path


def _testfileno(f, stdf):
    fileno = getattr(f, 'fileno', None)
    try:
        return fileno and fileno() == stdf.fileno()
    except io.UnsupportedOperation:
        return False  # fileno() raised UnsupportedOperation


def isstdin(f):
    return _testfileno(f, sys.__stdin__)


def isstdout(f):
    return _testfileno(f, sys.__stdout__)


def protectstdio(uin, uout):
    """Duplicate streams and redirect original if (uin, uout) are stdio

    If uin is stdin, it's redirected to /dev/null. If uout is stdout, it's

        newfd = os.dup(uout.fileno())
        os.dup2(stderr.fileno(), uout.fileno())
        fout = os.fdopen(newfd, r'wb')
    return fin, fout


def restorestdio(uin, uout, fin, fout):
    """Restore (uin, uout) streams from possibly duplicated (fin, fout)"""
    uout.flush()
    for f, uif in [(fin, uin), (fout, uout)]:
        if f is not uif:
            os.dup2(f.fileno(), uif.fileno())
            f.close()


def shellenviron(environ=None):
    """return environ with optional override, useful for shelling out"""

    def py2shell(val):
        'convert python object into string that is useful to shell'
        if val is None or val is False:
            return '0'
        if val is True:
            return '1'
        return pycompat.bytestr(val)

    env = dict(encoding.environ)
    if environ:
        env.update((k, py2shell(v)) for k, v in environ.iteritems())
    env['HG'] = hgexecutable()
    return env


if pycompat.iswindows:

    def shelltonative(cmd, env):
        return platform.shelltocmdexe(cmd, shellenviron(env))

    tonativestr = encoding.strfromlocal
else:

    def shelltonative(cmd, env):
        return cmd

    tonativestr = pycompat.identity


def tonativeenv(env):
    '''convert the environment from bytes to strings suitable for Popen(), etc.
    '''
    return pycompat.rapply(tonativestr, env)


def system(cmd, environ=None, cwd=None, out=None):
    '''enhanced shell command execution.
    run with environment maybe modified, maybe in different dir.

    except Exception:
        pass
    cmd = quotecommand(cmd)
    env = shellenviron(environ)
    if out is None or isstdout(out):
        rc = subprocess.call(
            tonativestr(cmd),
            shell=True,
            close_fds=closefds,
            env=tonativeenv(env),
            cwd=pycompat.rapply(tonativestr, cwd),
        )
    else:
        proc = subprocess.Popen(
            tonativestr(cmd),
            shell=True,
            close_fds=closefds,
            env=tonativeenv(env),
            cwd=pycompat.rapply(tonativestr, cwd),
            stdout=subprocess.PIPE,
            stderr=subprocess.STDOUT,
        )
        for line in iter(proc.stdout.readline, ''):
            out.write(line)
        proc.wait()
        rc = proc.returncode
    if pycompat.sysplatform == 'OpenVMS' and rc & 1:
        rc = 0
    return rc


def gui():
    '''Are we running in a GUI?'''
    if pycompat.isdarwin:
        if 'SSH_CONNECTION' in encoding.environ:

            # pure build; use a safe default
            return True
    else:
        return pycompat.iswindows or encoding.environ.get("DISPLAY")


def hgcmd():
    """Return the command used to execute current hg

    This is different from hgexecutable() because on Windows we want
    to avoid things opening new shell windows like batch files, so we

            # Env variable set by py2app
            return [encoding.environ['EXECUTABLEPATH']]
        else:
            return [pycompat.sysexecutable]
    return _gethgcmd()


def rundetached(args, condfn):
    """Execute the argument list in a detached process.

    condfn is a callable which is called repeatedly and should return

    # process fails to start, it will be left in a zombie state until
    # the parent wait on it, which we cannot do since we expect a long
    # running process on success. Instead we listen for SIGCHLD telling
    # us our child process terminated.
    terminated = set()

    def handler(signum, frame):
        terminated.add(os.wait())

    prevhandler = None
    SIGCHLD = getattr(signal, 'SIGCHLD', None)
    if SIGCHLD is not None:
        prevhandler = signal.signal(SIGCHLD, handler)
    try:
        pid = spawndetached(args)
        while not condfn():
            if (pid in terminated or not testpid(pid)) and not condfn():
                return -1
            time.sleep(0.1)
        return pid
    finally:
        if prevhandler is not None:
            signal.signal(signal.SIGCHLD, prevhandler)


@contextlib.contextmanager
def uninterruptible(warn):
    """Inhibit SIGINT handling on a region of code.

        if oldsiginthandler:
            signal.signal(signal.SIGINT, oldsiginthandler[0])
        if shouldbail:
            raise KeyboardInterrupt


if pycompat.iswindows:
    # no fork on Windows, but we can create a detached process
    # https://msdn.microsoft.com/en-us/library/windows/desktop/ms684863.aspx
    # No stdlib constant exists for this value
    DETACHED_PROCESS = 0x00000008

    # Using subprocess.CREATE_NEW_CONSOLE might helps.
    # See https://phab.mercurial-scm.org/D1701 for discussion
    _creationflags = DETACHED_PROCESS | subprocess.CREATE_NEW_PROCESS_GROUP

    def runbgcommand(
        script, env, shell=False, stdout=None, stderr=None, ensurestart=True
    ):
        '''Spawn a command without waiting for it to finish.'''
        # we can't use close_fds *and* redirect stdin. I'm not sure that we
        # need to because the detached process has no console connection.
        subprocess.Popen(
            tonativestr(script),
            shell=shell,
            env=tonativeenv(env),
            close_fds=True,
            creationflags=_creationflags,
            stdout=stdout,
            stderr=stderr,
        )


else:

    def runbgcommand(
        cmd, env, shell=False, stdout=None, stderr=None, ensurestart=True
    ):
        '''Spawn a command without waiting for it to finish.'''
        # double-fork to completely detach from the parent process
        # based on http://code.activestate.com/recipes/278731
        pid = os.fork()
        if pid:

            # Parent process
            (_pid, status) = os.waitpid(pid, 0)
            if os.WIFEXITED(status):
                returncode = os.WEXITSTATUS(status)
            else:
                returncode = -(os.WTERMSIG(status))
            if returncode != 0:
                # The child process's return code is 0 on success, an errno
                # value on failure, or 255 if we don't have a valid errno
                # value.
                #
                # (It would be slightly nicer to return the full exception info
                # over a pipe as the subprocess module does.  For now it
                # doesn't seem worth adding that complexity here, though.)
                if returncode == 255:
                    returncode = errno.EINVAL
                raise OSError(
                    returncode,
                    'error running %r: %s' % (cmd, os.strerror(returncode)),
                )
            return

        returncode = 255
        try:
            # Start a new session

                stderr = open(os.devnull, 'w')

            # connect stdin to devnull to make sure the subprocess can't
            # muck up that stream for mercurial.
            subprocess.Popen(
                cmd,
                shell=shell,
                env=env,
                close_fds=True,
                stdin=stdin,
                stdout=stdout,
                stderr=stderr,
            )
            returncode = 0
        except EnvironmentError as ex:
            returncode = ex.errno & 0xFF
            if returncode == 0:
                # This shouldn't happen, but just in case make sure the
                # return code is never 0 here.
                returncode = 255
        except Exception: