view mercurial/txnutil.py @ 33137:99ce2f586cd4

show: config option to register aliases for views

As part of using `hg show` in my daily workflow, I've found it slightly
annoying to have to type full view names, complete with a space. I've
locally registered an alias for "swork = show work."

I think others will have this same complaint and could benefit from
some automation to streamline the creation of aliases. So, this
commit introduces a config option that allows `hg show` views to be
automatically aliased using a given prefix. e.g. a value of "s"
will automatically register "swork" and "sbookmarks." Multiple
values can be given for ultimate flexibility. This arguably isn't
needed now. But since we don't register aliases if there will be
a collision and we're bound to have a collision, it makes sense to
allow multiple prefixes so specific views can avoid collisions by
using different prefixes.

# 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)