mercurial/dirstateguard.py

test-rebase: add a brute force test

Rebase is becoming more complex and it looks like a good idea to try some
brute force enumeration to cover cases that are hard to find manually.

Using brute force to generate repos in different shapes and enumerating the
rebase source and destination would generate too many cases that takes too
long to compute. This patch limits the "brute force" to only the "rebase
source" part. Repo and destination are still manual.

The added test cases are crafted manually to reveal some behaviors that are
not covered by other tests:

  - "revlog index out of range" crash
  - after rebase, p1 == p2, p2 != null
  - "nothing to merge" abort

In the future we might want to add more tests here. For now I'm more
interested in revealing interesting behaviors in a minified way. I tried
some more complex cases but didn't find other interesting behaviors.

Differential Revision: https://phab.mercurial-scm.org/D262

# dirstateguard.py - class to allow restoring dirstate after failure
#
# Copyright 2005-2007 Matt Mackall <[e-mail]>
#
# 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

from .i18n import _

from . import (
    error,
)

class dirstateguard(object):
    '''Restore dirstate at unexpected failure.

    At the construction, this class does:

    - write current ``repo.dirstate`` out, and
    - save ``.hg/dirstate`` into the backup file

    This restores ``.hg/dirstate`` from backup file, if ``release()``
    is invoked before ``close()``.

    This just removes the backup file at ``close()`` before ``release()``.
    '''

    def __init__(self, repo, name):
        self._repo = repo
        self._active = False
        self._closed = False
        self._backupname = 'dirstate.backup.%s.%d' % (name, id(self))
        repo.dirstate.savebackup(repo.currenttransaction(), self._backupname)
        self._active = True

    def __del__(self):
        if self._active: # still active
            # this may occur, even if this class is used correctly:
            # for example, releasing other resources like transaction
            # may raise exception before ``dirstateguard.release`` in
            # ``release(tr, ....)``.
            self._abort()

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        try:
            if exc_type is None:
                self.close()
        finally:
            self.release()

    def close(self):
        if not self._active: # already inactivated
            msg = (_("can't close already inactivated backup: %s")
                   % self._backupname)
            raise error.Abort(msg)

        self._repo.dirstate.clearbackup(self._repo.currenttransaction(),
                                         self._backupname)
        self._active = False
        self._closed = True

    def _abort(self):
        self._repo.dirstate.restorebackup(self._repo.currenttransaction(),
                                           self._backupname)
        self._active = False

    def release(self):
        if not self._closed:
            if not self._active: # already inactivated
                msg = (_("can't release already inactivated backup: %s")
                       % self._backupname)
                raise error.Abort(msg)
            self._abort()