view mercurial/txnutil.py @ 50175:0ab92dabea6e

typing: add type hints to pycompat.maplist()

The typeshed hints define 5 overloads with an increasing number of parameters on
the passed function, and then a catchall that ignores the argument list on the
passed function and allows an `*iterators` arg.  All of our uses are fulfilled
by the 1 function + 1 iterable overload, but add the second overload as a hint
in case it's needed in the future.

# 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)