mercurial/txnutil.py

revlog: using two new functions in C capsule from Rust code

We expose `index_length` and `index_node` in the C capsule, so that
the Rust representation of the C index can implement the `RevlogIndex`
trait.

Because our `Node` is actually a one-field struct, we have
to decorate it for direct FFI exchange with the C `char*`

It would be a good thing to get a length from the C layer, but doing
so right now would probably interfere with the upcoming changes that
will happen there for the hash length.

Differential Revision: https://phab.mercurial-scm.org/D8152

# 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(b'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(b'%s.pending' % filename, **kwargs), True)
        except IOError as inst:
            if inst.errno != errno.ENOENT:
                raise
    return (vfs(filename, **kwargs), False)