mercurial/txnutil.py

graft: add a new `--stop` flag to stop interrupted graft

This patch adds a new flag `--stop` to `hg graft` command which stops the
interrupted graft.

The `--stop` flag takes back you to the last successful step i.e. it will keep
your grafted commits, it will just clear the mergestate and interrupted graft
state.

The `--stop` is different from `--abort` flag as the latter also undoes all the
work done till now which is sometimes not what the user wants.

Suppose you grafted a lot of changesets, you encountered conflicts, you resolved
them, did `hg graft --continue`, again encountered conflicts, continue, again
encountered conflicts. Now you are tired of solving merge conflicts and want to
resume this sometimes later. If you use the `--abort` functionality, it will
strip your already grafted changesets, making you loose the work you have done
resolving merge conflicts.

A general goal related to this flag is to add this flag to `rebase` and
`histedit` too. The evolve command already has this --stop flag.

Tests are added for the new flag.

.. feature::

   `hg graft` now has a `--stop` flag to stop interrupted graft.

Differential Revision: https://phab.mercurial-scm.org/D3668

# 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)