view README @ 3846:f9dad99a90d5

evolve: create a new commit instead of amending one of the divergents

This patch changes the behavior of evolve command while resolving
content-divergence to create a new commit instead of amending one of the
divergent ones.

In past, I have made this change, backed out this change and now today again I
am doing this change, so let's dive in some history.

Using cmdrewrite.amend() was never a good option as that requires hack to delete
the evolvestate and also gives us less control over things. We can't make the
commit on top of different parents as that of content-divergent ones. Due to all
these, I first made this change to create a new commit instead of amending one.

But, after few days, there was flakiness observed in the tests and turned out
that we need to do some dirstate dance as repo.dirstate.setparents() does not
always fix the dirstate. That flakiness was a blocker for progress at that time
and we decided to switch to amend back so that we can have things working with
some hacks and we can later fix the implementation part.

Now, yesterday while tackling resolving content-divergence of a stack which is
as follows:

C1 C2
 | |
B1 B2
 | |
A1 A2
 \/
base

where, A1-A2, B1-B2, C1-C2 are content-divergent with each other. Now we can
resolve A1-A2 very well because they have the same parent and let's say that
resolution leads to A3.
Now, we want to resolve B1-B2 and make the new resolution commit on top of A3 so
that we can end up something like:

C3
 |
B3
 |
A3
 |
base

however, amending one of the divergent changesets, it's not possible to create a
commit on a different parent like A3 here without some relocation. We should
prevent relocation as that may leads to some conflicts and should change the
parent before committing.

So, looking ahead, we can't move with using amend as still using that we will
need some relocation hacks making code ugly and prone to bad behaviors, bugs.
Let's change back to creating a new commit so that we can move forward in a good
way.

About repo.dirstate.setparents() not setting the dirstate, I have researched
yesterday night about how we can do that and found out that we can use
cmdrewrite._uncommitdirstate() here. Expect upcoming patches to improve the
documentation of that function.

There are lot of test changes because of change in hash but there is no behavior
change. The only behavior change is in test-evolve-abort-contentdiv.t which is
nice because creating a new commit helps us in stripping that while aborting.
We have a lot of testing of content-divergence and no behavior change gives
enough confidence for making this change.

I reviewed the patch carefully to make sure there is no behavior change and I
suggest reviewer to do the same.

=============================
Mutable History For Mercurial
=============================

Evolve Extension
=================

This package supplies the ``evolve`` extension for Mercurial,

**The full implementation of the changeset evolution concept is still in
progress.**  Please subscribe to the `evolve-testers mailing list
<https://www.mercurial-scm.org/mailman/listinfo/evolve-testers>`_ to stay up to
date with changes.

This extension:

* enables the “changeset evolution” feature of Mercurial core,

* provides a set of commands to mutate your history,

* issues several warning messages when troubles from some mutable appears in
  your repository,

* provides an ``hg evolve`` command to deal with such "troubles",

* improves performance of obsolescence marker exchanges and discovery during
  push and pull.

Documentation
-------------

We recommend reading the documentation first. An online version is
available here:

    https://www.mercurial-scm.org/doc/evolution/

How to Install
==============

Using Pip
---------

You can install the latest evolution version usin pip::

    $ pip install --user hg-evolve

Then just enable it in you hgrc::

    $ hg config --edit # adds the two line below:
    [extensions]
    evolve =

From Source
-----------

To install a local version from source::

    $ hg clone https://www.mercurial-scm.org/repo/evolve/
    $ cd evolve
    $ pip install --user .

Then just enable it in you hgrc::

    $ hg config --edit # adds the two line below:
    [extensions]
    evolve =

Documentation lives in ``doc/``.

Server Only Setup
=================

It is possible to enable a smaller subset of the extensions aimed at server
serving repository. It skips the additions of the new commands and local UI
messages that might add performance overheads. To use the server only
extension, install the package and use::

    $ hg config --edit # adds the two line below:
    [extensions]
    evolve.serveronly =


How to Contribute
=================

Discussion happens on the #hg-evolve IRC on freenode_.

.. _freenode: https://freenode.net/

Bugs are to be reported on the mercurial's bug tracker (component: `evolution`_):

.. _evolution: https://bz.mercurial-scm.org/buglist.cgi?component=evolution&query_format=advanced&resolution=---

You can use the patchbomb extension to send email to `mercurial devel
<https://www.mercurial-scm.org/mailman/listinfo/mercurial-devel>`_. Please make
sure to use the evolve-ext flag when doing so. You can use a command like
this::

    $ hg email --to [e-mail] --flag evolve-ext --rev '<your patches>'

Some of development happens on a public bitbucket repository (`evolve-devel`_) using the topic extension.

.. _`evolve-devel`: https://bitbucket.org/octobus/evolve-devel

For guidelines on the patch description, see the `official Mercurial guideline`_.

.. _`official Mercurial guideline`: https://mercurial-scm.org/wiki/ContributingChanges#Patch_descriptions

Please don't forget to update and run the tests when you fix a bug or
add a feature. To run the tests, you need a working copy of Mercurial,
say in $HGSRC::

    $ cd tests
    $ python $HGSRC/tests/run-tests.py

Branch policy
-------------

The evolve test are highly impacted by changes in core. To deal with this, we use named branches.

There are two main branches: "stable" and "default". Tests on these branch are
supposed to pass with the corresponding "default" and "stable" branch from core
Mercurial. The documentation is built from the tip of stable.

In addition, we have compatibility branches to check tests on older version of
Mercurial. They are the "mercurial-x.y" branches. They are used to apply
expected test change only, no code change should happen there.