mercurial/txnutil.py

filemerge: show warning if chosen tool has no binary files capability

While matching patterns in "merge-patterns" configuration, Mercurial
silently assumes that all merge tools have binary files
capability. This implementation comes from 5af5f0f9d724 (or Mercurial
1.0).

At failure of merging binary files with incorrect internal merge tool,
there is no hint about this silent ignorance of binary files
capability.

This patch shows warning message, if chosen internal merge tool has no
binary files capability. This will help users to investigate why a
binary file isn't merged as expected.

# 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)