view CONTRIBUTORS @ 24991:4169a4f83548

cmdutil: add class to restore dirstate during unexpected failure

Before this patch, after "dirstate.write()" execution, there was no way to
restore dirstate to the original status before "dirstate.write()".

In some code paths, "dirstate.invalidate()" is used as a kind of "restore
.hg/dirstate to the original status", but it just avoids writing changes in
memory out, and doesn't actually restore the ".hg/dirstate" file.

To fix the issue that the recent (in memory) dirstate isn't visible to external
processes (e.g. "precommit" hooks), "dirstate.write()" should be invoked before
invocation of external processes. But at the same time, ".hg/dirstate" should be
restored to its content before "dirstate.write()" during an unexpected failure
in some cases.

This patch adds the class "dirstateguard" to easily restore ".hg/dirstate"
during unexpected failures. Typical usecase of it is:

    # (1) build dirstate up
    ....

    # (2) write dirstate out, and backup ".hg/dirstate"
    dsguard = dirstateguard(repo, 'scopename')
    try:
        # (3) execute somethig to do:
        #     this may imply making some additional changes on dirstate
        ....

        # (4) unlink backed-up dirstate file at the end of dsguard scope
        dsguard.close()
    finally:
        # (5) if execution is aborted before "dsguard.close()",
        #     ".hg/dirstate" is restored from the backup
        dsguard.release()

For this kind of issue, an "extending transaction" approach (in
https://titanpad.com/mercurial32-sprint) seems to not be suitable, because:

  - transaction nesting occurs in some cases (e.g. "shelve => rebase"), and

  - "dirstate" may be already modified since the beginning of OUTER
    transaction scope, then

  - dirstate should be backed up into the file other than
    "dirstate.journal" at the beginning of INNER transaction scope, but

  - such alternative backup files are useless for transaction itself,
    and increases complication of its implementation

"transaction" and "dirstateguard" differ from each other also in "what
it should do for .hg/dirstate" in cases other than success.

  ============== ======= ======== =============
  type           success fail     "hg rollback"
  ============== ======= ======== =============
  transaction    keep     keep     restore
  dirstateguard  keep     restore  (not implied)
  ============== ======= ======== =============

Some collaboration between transaction and dirstate will probably be introduced
in the future. But this layer is needed in all cases.

[This file is here for historical purposes, all recent contributors
should appear in the changelog directly]

Andrea Arcangeli <andrea at suse.de>
Thomas Arendsen Hein <thomas at intevation.de>
Goffredo Baroncelli <kreijack at libero.it>
Muli Ben-Yehuda <mulix at mulix.org>
Mikael Berthe <mikael at lilotux.net>
Benoit Boissinot <bboissin at gmail.com>
Brendan Cully <brendan at kublai.com>
Vincent Danjean <vdanjean.ml at free.fr>
Jake Edge <jake at edge2.net>
Michael Fetterman <michael.fetterman at intel.com>
Edouard Gomez <ed.gomez at free.fr>
Eric Hopper <hopper at omnifarious.org>
Alecs King <alecsk at gmail.com>
Volker Kleinfeld <Volker.Kleinfeld at gmx.de>
Vadim Lebedev <vadim at mbdsys.com>
Christopher Li <hg at chrisli.org>
Chris Mason <mason at suse.com>
Colin McMillen <mcmillen at cs.cmu.edu>
Wojciech Milkowski <wmilkowski at interia.pl>
Chad Netzer <chad.netzer at gmail.com>
Bryan O'Sullivan <bos at serpentine.com>
Vicent Seguí Pascual <vseguip at gmail.com>
Sean Perry <shaleh at speakeasy.net>
Nguyen Anh Quynh <aquynh at gmail.com>
Ollivier Robert <roberto at keltia.freenix.fr>
Alexander Schremmer <alex at alexanderweb.de>
Arun Sharma <arun at sharma-home.net>
Josef "Jeff" Sipek <jeffpc at optonline.net>
Kevin Smith <yarcs at qualitycode.com>
TK Soh <teekaysoh at yahoo.com>
Radoslaw Szkodzinski <astralstorm at gorzow.mm.pl>
Samuel Tardieu <sam at rfc1149.net>
K Thananchayan <thananck at yahoo.com>
Andrew Thompson <andrewkt at aktzero.com>
Michael S. Tsirkin <mst at mellanox.co.il>
Rafael Villar Burke <pachi at mmn-arquitectos.com>
Tristan Wibberley <tristan at wibberley.org>
Mark Williamson <mark.williamson at cl.cam.ac.uk>