view mercurial/txnutil.py @ 45203:ae5c1a3bc339

commitctx: extract the function in a dedicated module

the function have few callers (< 15) is quite long a mostly independent from the
repository itself. It seems like a good candidate to reduce the bloatness of the
localrepository class. Extracting it will help us cleaning the code up and
splitting it into more reasonable-size function.

We don't use a copy trick because the amount of code extract is quite small
(<5%) and the de-indent means every single line change anyway. So this is not
deemed valuable to do so.

This is part of a larger refactoring/cleanup of the commitctx code to clarify
and augment the logic gathering metadata useful for copy tracing. The current
code is a tad too long and entangled to make such update easy.

Differential Revision: https://phab.mercurial-scm.org/D8709

# 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(b'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(b'%s.pending' % filename, **kwargs), True)
        except IOError as inst:
            if inst.errno != errno.ENOENT:
                raise
    return (vfs(filename, **kwargs), False)