author | Boris Feld <boris.feld@octobus.net> |
Fri, 16 Jun 2017 09:22:39 +0200 | |
changeset 2593 | ed977325cd2a |
parent 2066 | a35f6b1e4a41 |
child 2557 | e3acb8823900 |
permissions | -rw-r--r-- |
.. Copyright © 2014 Greg Ward <greg@gerg.ca> ================================== Changeset Evolution with Mercurial ================================== .. toctree:: :maxdepth: 2 user-guide sharing concepts from-mq `evolve`_ is an experimental Mercurial extension for safe mutable history. .. _`evolve`: https://www.mercurial-scm.org/wiki/EvolveExtension With core Mercurial, changesets are permanent and immutable. You can commit new changesets to modify your source code, but you cannot modify or remove old changesets—they are carved in stone for all eternity. For years, Mercurial has included various extensions that allow history modification: ``rebase``, ``mq``, ``histedit``, and so forth. These are useful and popular extensions, and in fact history modification is one of the big reasons DVCSes (distributed version control systems) like Mercurial took off. But there's a catch: until now, Mercurial's various mechanisms for modifying history have been *unsafe*, in that changesets were destroyed (“stripped”) rather than simply made invisible. ``evolve`` makes things better in a couple of ways: * It changes the behaviour of most existing history modification extensions (``rebase``, ``histedit``, etc.) so they use a safer mechanism (*changeset obsolescence*, covered below) rather than the older, less safe *strip* operation. * It provides a new way of modifying history that is roughly equivalent to ``mq`` (but much nicer and safer). It helps to understand that ``evolve`` builds on infrastructure already in core Mercurial: * *Phases* (starting in Mercurial 2.1) allow you to distinguish mutable and immutable changesets. We'll cover phases early in the user guide, since understanding phases is essential to understanding ``evolve``. * *Changeset obsolescence* (starting in Mercurial 2.3) is how Mercurial knows how history has been modified, specifically when one changeset replaces another. In the obsolescence model, a changeset is neither removed nor modified, but is instead marked *obsolete* and typically replaced by a *successor*. Obsolete changesets usually become *hidden* as well. Obsolescence is an invisible feature until you start using ``evolve``, so we'll cover it in the user guide too. Some of the things you can do with ``evolve`` are: * Fix a mistake immediately: “Oops! I just committed a changeset with a syntax error—I'll fix that and amend the changeset so no one sees my mistake.” (While this is possible using existing features of core Mercurial, ``evolve`` makes it safer.) * Fix a mistake a little bit later: “Oops! I broke the tests three commits back, but only noticed it now—I'll just update back to the bad changeset, fix my mistake, amend the changeset, and evolve history to update the affected changesets.” * Remove unwanted changes: “I hacked in some debug output two commits back; everything is working now, so I'll just prune that unwanted changeset and evolve history before pushing.” * Share mutable history with yourself: say you do most of your programming work locally, but need to test on a big remote server somewhere before you know everything is good. You can use ``evolve`` to share mutable history between two computers, pushing finely polished changesets to a public repository only after testing on the test server. * Share mutable history for code review: you don't want to publish unreviewed changesets, but you can't block every commit waiting for code review. The solution is to share mutable history with your reviewer, amending each changeset until it passes review. ``evolve`` is experimental! --------------------------- The long-term plan for ``evolve`` is to add it to core Mercurial. However, it is not yet stable enough for that. In particular: * The UI is unstable: ``evolve``'s command names and command options are not completely nailed down yet. They are subject to occasional backwards-incompatible changes. If you write scripts that use evolve commands, a future release could break your scripts. * There are still some corner cases that aren't handled yet. If you think you have found such a case, please check if it's already described in the Mercurial bug tracker (https://bz.mercurial-scm.org/). Bugs in ``evolve`` are files under component "evolution": use `this query`_ to view open bugs in ``evolve``. .. _`this query`: https://bz.mercurial-scm.org/buglist.cgi?component=evolution&bug_status=UNCONFIRMED&bug_status=CONFIRMED&bug_status=NEED_EXAMPLE Installation and setup ---------------------- To use ``evolve``, you must: #. Clone the ``evolve`` repository:: cd ~/src hg clone http://hg.netv6.net/evolve-main #. Configure the extension, either locally :: hg config --local or for all your repositories :: hg config --edit Then add :: evolve=~/src/evolve-main/hgext3rd/evolve/ in the ``[extensions]`` section (adding the section if necessary). Use the directory that you actually cloned to, of course. Next steps: ----------- * For a practical guide to using ``evolve`` in a single repository, see the `user guide`_. * For more advanced tricks, see `sharing mutable history`_. * To learn about the concepts underlying ``evolve``, see `concepts`_ (incomplete). * If you're coming from MQ, see the `MQ migration guide`_ (incomplete). .. _`user guide`: user-guide.html .. _`sharing mutable history`: sharing.html .. _`concepts`: concepts.html .. _`MQ migration guide`: from-mq.html