view mercurial/txnutil.py @ 45264:8cce9f77ca73

templatespec: create a factory function for each type there is

Most of the arguments to the `templatespec` constructor are mutually
exclusive, so each combination creates a different type of
templatespec. Let's clarify that by creating factory functions.

I've left the callers in `logcmdutil` unchanged for now because they
are more complex and `logcmdutil.templatespec()` is slightly higher
level in that it is specific to changesets.

My larger goal is to add support frozen binaries (specifically
PyOxidizer) by adding a specific type of `templatespec` for built-in
templates. That will get its own factory function.

Differential Revision: https://phab.mercurial-scm.org/D8845

# 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)