view mercurial/txnutil.py @ 43114:8197b395710e

destutil: provide hint on rebase+merge for how to specify destination/rev

Without a destination specified, rebase and merge attempt to identify a good
candidate; this fails if there's too many heads, the heads have a bookmark, or
other reasons.

Complicating the issue, users may have specified -t, thinking it means target,
and are confused when the error message says that they need to specify an
explicit rev or explicit destination - they feel like they already have.

Differential Revision: https://phab.mercurial-scm.org/D7024

# 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)