mercurial/txnutil.py

help: show "[no-]" only for default-on Flags

As Anton (av6) pointed out, the "[no-]" is confusing for action flags
like `hg bookmark --delete`. We could come up with a way of indicating
which flags are action flags (e.g. use None for the default value
instead of False). However, it's probably also unlikely that users
will want to negate even non-action flags like --hidden.

One of the more common flags where the "[no-]" prefix would be useful
is `hg evolve --update`. The reason it's helpful there is that it
defaults to on. So I think we can simply include "[no-]" only for
flags that are on by default (and thus require the user to add the
"[no-]" for the option to have any effect).

Note that there are use cases for negating flags that already off by
default. For example, you may have an alias for `hg log -G --hidden -T
foo` and now want to pass "--no-hidden" to that alias. However, I
think that users who want that are likely to be advanced enough that
they've already learnt about the "no-" prefix by seeing it somewhere
else.

Differential Revision: https://phab.mercurial-scm.org/D5454

# 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)