view mercurial/txnutil.py @ 49034:079197e94b24

crecord: avoid duplicating lines when reverting noeol->eol change

When reversing a patch that looks like this while using crecord:

```
@@ -301,4 +302,4 @@ zza
 zzb
 zzc
 zzd
-zze
\ No newline at end of file
+zze
```

we would previously reverse the `-zze` line to be an add, encounter the "no
newline" line and stop inspecting lines. This caused us to duplicate the line,
producing `zzezze` (still without a newline).

`break` is the correct action if we know there will be no lines afterwards, as
would be the case in an eol -> noeol transition. It is incorrect if there are
lines afterward, such as if both sides are missing the newline or if only the
lhs is missing the newline.

Differential Revision: https://phab.mercurial-scm.org/D12441

# 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)