annotate mercurial/txnutil.py @ 51725:bbe59cc5d2e1

rust-changelog: accessing the index

The `Index` object is currently the one providing all DAG related
algorithms, starting with simple ancestors iteration up to more
advanced ones (ranges, common ancestors…).

From pure Rust code, there was no way to access the changelog index for
a given `Repository`, probably because `rhg` does not use any such algorithm
yet.

# 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 . 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 FileNotFoundError:
            pass
    return (vfs(filename, **kwargs), False)