mercurial/txnutil.py

crecord: redraw the screen when starting up chunkselector

Failure to do this can cause screen corruption like:

    <headerline>
     [X] filename.cc
    <several blank lines>
    <output from previous iteration of split that happened to be here>

I believe this might only happen in some terminals, and maybe only when using
the "alternate screen". Regardless of the exact conditions to reproduce, it
should be safe to always clear it when starting up and is probably the correct
thing to do anyway :)

Differential Revision: https://phab.mercurial-scm.org/D6131

# 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)