========================================
Safe Mutable History
========================================


Here are various materials on planned improvement to Mercurial regarding
rewriting history.

First read about what challenge arise while rewriting history and how we plan to
solve them once and for all.

.. toctree::
   :maxdepth: 2

   instability

The effort is split in two parts:

 * The **obsolete marker** concept aims to provide an alternative to ``strip``
   to get rid of changesets.

 * The **evolve** mercurial extension rewrites history using obsolete
   *marker* under the hood.

The first and most important step is by far the **obsolete marker**. However
most users will never be directly exposed to the concept. For this reason
this manual starts with changeset evolution.

Evolve: A robust alternative to MQ
====================================

Evolve is an experimental history rewriting extension that uses obsolete
markers. It is inspired from MQ and pbranch but have multiple advantages over
them:

* Focus on your current work.

    You can focus your work on a single changeset and take care of adapting
    descendent changeset later.

* Handle **non-linear history with branches and merges**

* Rely internally on **robust merge** mechanism of mercurial.

  Simple conflict are handled by real merge tools using appropriate ancestor.
  Conflict are much rarer and much more user friendly.

*  Mutable history **fully available all the time**.

  always use 'hg update' and forget about (un)applying patches to access the
  mutable part of your history.


* Use only **plain changeset** and forget about patches. Evole will create and
  exchange real changesets. Mutable history can be used in all usual operations:
  pull, push, log, diff, etc.

* Allow **sharing and collaboration** mutable history without fear of duplicate
  (thanks to obsolete marker).

* Cover all mq usage but guard.

.. warning:: The evolve extention and the obsolete marker are at an experimental
            stage. While using obsolete you'll likely be exposed to complex
            implication of the **obsolete marker** concept. I do not recommend
            non-power user to test this at this stage.

            XXX make sure to read the XXX section before using it.

            Production ready version should hide such details to normal user.

To enable the evolve extension use::

    $ hg clone https://bitbucket.org/marmoute/mutable-history -u stable
    $ mutable-history/enable.sh >> ~/.hgrc

You will probably want to use the associated version of hgview (qt viewer
recommended). ::

    $ hg clone http://hg-lab.logilab.org/wip/hgview/
    $ cd hgview
    $ python setup.py install --user

works with mercurial 2.1 and 2.2 (recommended)

 ---

For more information see documents below:

.. toctree::
   :maxdepth: 1

   tutorials/tutorial
   evolve-good-practice
   evolve-faq
   from-mq
   evolve-collaboration
   qsync

Smart changeset deletion: Obsolete Marker
==========================================

Obsolete marker is a powerful concept that allow mercurial to safely handle
history rewriting operations. It is a new type of relation between Mercurial
changesets that track the result of history rewriting operations.

This concept is simple to define and provides a very solid base to:

- Very fast history rewriting operations,

- auditable and reversible history rewriting process,

- clean final history,

- share and collaborate on mutable parts of the history,

- gracefully handle history rewriting conflicts,

- allow various history rewriting UI to collaborate with a underlying common API.

 ---

For more information see documents below

.. toctree::
   :maxdepth: 1

   obs-concept
   obs-implementation
   obs-road-map


Known caveats
=============

Here is a list of known issues that will be fixed later:

* Unstable changeset turn secret.

* ``hg stabilize`` does not handle conflicts.

Known limitation and bug
=================================

Here is a list of know issue that will be fixed later:


* ``hg stabilize`` does not handle merge conflict.

    You must fallback to graft or rebase when that happen.

* rewriting conflict are not detected yet``hg stabilize`` does not
  handle them.

* ``hg update`` can move an obsolete parent

* you need to provide to `graft --continue -O` if you started you
  graft using `-O`.

* ``hg merge`` considers an extinct head to be a valid target, hence requiring
  you to manually specify target all the time.

* trying to exchange obsolete relations with a static http repo will crash.

* Extinct changesets are turned secret by various commands.

* Extinct changesets are hidden using the *hidden* feature of mercurial only
  supported by a few commands.

  Only ``hg log``, ``hgview`` and `hg glog` (2.2 only) support it. ``hg head`` or other visual viewer don't.

* hg heads show extinct changeset

Fixed in 2.2
---------------------------------

* hg graphlog show extinct changeset

* Mercurial 2.1 think you are pushing additional heads even when the new head
  obsolete another one. You have to use hg push -f more often than necessary.


* ``hg heads`` shows extinct changeset

* ``hg merge`` considers an extinct head to be a valid target, hence requiring
  you to manually specify target all the time.

* trying to exchange obsolete relations with a static http repo will crash.

Annexe
======

.. toctree::
   :maxdepth: 1

   glossary