view mercurial/txnutil.py @ 45308:dc10bcd5c08d

templater: start passing resource to read from into _readmapfile()

This patch makes it so we pass in a file-like resource to read from
instead of having `_readmapfile()` open the file. This is one more
step towards making `_readmapfile()` able to read resources opened by
from `importlib.resources`. We still need to pass in the mapfile path
because it's used for loading dependent mapfiles from `%include` and
`__base__`, and it's also used for giving the user better error
messages. Besides that, one can safely call `_readmapfile()` with any
file-like resource after this patch.

Differential Revision: https://phab.mercurial-scm.org/D8891

# 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)