view mercurial/txnutil.py @ 49012:5b65721a75eb

revlog: recommit 49fd21f32695 with a fix for issue6528

`filelog.size` currently special cases two forms of metadata encoding:
- copy data via the parent order as flag bit
- censor data by peaking into the raw delta
All other forms of metadata encoding including the empty metadata block
are mishandled. In `basefilectx.cmp` the empty metadata block is
explicitly checked to compensate for this.

Restore 49fd21f32695, but disable it for filelog, so that the original
flag bit use contines to work. Document all this mess for now in
preparation of a proper rework.

Differential Revision: https://phab.mercurial-scm.org/D11203

# 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.


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)