view mercurial/txnutil.py @ 47589:f5c24c124e07

dirstate: introduce an internal `_add` method

We want to split current user of `dirstate.add` between `hg add`-like cases and
update of the dirstate coming from update/merge.

To do this we will introduce new API. The first step is to introduces an
internal function that these new API migh use (or not use) to distinct between
the migrated users and the others.

Differential Revision: https://phab.mercurial-scm.org/D11010

# 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)