annotate mercurial/txnutil.py @ 39244:73cf21b2e8a6

manifest: add getstorage() to manifestlog and use it globally

It is a common pattern to obtain a directory manifest storage instance
(a manifestrevlog) by going through manifestlog._revlog.dirlog().

Why access to storage and caching of other manifests is done through
manifestrevlog instead of manifestlog, I don't know.

This commit establishes a getstorage(tree) API on manifestlog and
imanifestlog that provides a public API for accessing manifest storage.

All consumers previously using private attributes have been updated
to use this new method.

.. api:: manifestlog now has a getstorage(tree) method

   It should be used for obtaining an object representing the
   manifest's storage implementation. Accessing
   manifestlog._revlog should be avoided.

Differential Revision: https://phab.mercurial-scm.org/D4277

# 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)