annotate mercurial/txnutil.py @ 47770:460e479be66e

typing: add several assertions to dirstatemap to appease pytype

I think it's been mentioned in IRC that these can't be None in this case.  This
fixes:

    File "/mnt/c/Users/Matt/hg/mercurial/dirstatemap.py", line 213, in addfile: unsupported operand type(s) for &: 'None' and 'int' [unsupported-operands]
      No attribute '__and__' on None or '__rand__' on int
    Called from (traceback):
      line 290, in reset_state
    File "/mnt/c/Users/Matt/hg/mercurial/dirstatemap.py", line 214, in addfile: unsupported operand type(s) for &: 'None' and 'int' [unsupported-operands]
      No attribute '__and__' on None or '__rand__' on int
    Called from (traceback):
      line 290, in reset_state

Differential Revision: https://phab.mercurial-scm.org/D11235

# 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)