view mercurial/txnutil.py @ 40527:1b49b84d5ed5

pycompat: adding Linux detection and fixing Mac

Python 3 recommends detecting OSs with the prefix of the platform, but we were
comparing the full string for macOS. We also didn't have Linux detection, which
is convenient for extensions to use (rather than have some OSs detected by hg
and some by the extension).

Reference:
https://docs.python.org/3/library/sys.html#sys.platform

Differential Revision: https://phab.mercurial-scm.org/D5227

# txnutil.py - transaction related utilities
#
#  Copyright FUJIWARA Katsunori <[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

from . import (
    encoding,
)

def mayhavepending(root):
    '''return whether 'root' may have pending changes, which are
    visible to this process.
    '''
    return root == encoding.environ.get('HG_PENDING')

def trypending(root, vfs, filename, **kwargs):
    '''Open  file to be read according to HG_PENDING environment variable

    This opens '.pending' of specified 'filename' only when HG_PENDING
    is equal to 'root'.

    This returns '(fp, is_pending_opened)' tuple.
    '''
    if mayhavepending(root):
        try:
            return (vfs('%s.pending' % filename, **kwargs), True)
        except IOError as inst:
            if inst.errno != errno.ENOENT:
                raise
    return (vfs(filename, **kwargs), False)