view mercurial/txnutil.py @ 45098:20a65e397943

patch: refactor content diffing part in separate fn so extensions can wrap

Right now extdiff uses it's own logic using archival to diff two versions of
file using external diff tools. This makes the extdiff functionality
non-extensible.

This series is an attempt to refactor core patch and diff functionality so that
extdiff can wrap and reuse it. This will help us in using external diffing tools
at more places and not just extdiff command only then.

Differential Revision: https://phab.mercurial-scm.org/D8685

# 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)