view mercurial/txnutil.py @ 38853:3588e41f796d

shortest: cache disambiguation revset

This makes it actually useful. In compared the time in my hg repo with
69.6k revisions and with a disambiguation revset of "not public()"
that matches 563 visible revisions. I ran "time hg log -T
'{shortest(node1,)}' -r 0:1000" (no revisions within the revset in
that revision range). Before this patch, it took 57s and after it took
0.7s.

Differential Revision: https://phab.mercurial-scm.org/D4039

# 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)