mercurial/txnutil.py

simplestore: use a custom store for the simple store repo

Before, we used the default store, which was based on fncache
and dotencode. After attempting to port tests to work with the
simple store, I realized that fncache was more trouble than it is
worth.

This commit implements a proper store type for the simple repo -
one that isn't based off fncache.

This causes a number of new test failures because of tests
expecting the full fncache store filename encoding. I may
extend the store format in a subsequent commit to take the
filename encoding parts of fncache that we can take
(basically everything except hash encoding, since that isn't
reversible). But for now, let's use encoded store.

As part of this, we implement proper requirements support for
repos created with the simple store. This should have been
done from the beginning, as a requirement is needed to lock
out clients that don't understand a storage format.

A new hghave feature advertising the presence of fncache in repos
has been added. Most tests touching the fncache are now conditional
on that feature.

Other tests have added the optional repo requirement to output.

Differential Revision: https://phab.mercurial-scm.org/D3095

# 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)