=============================
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 core Mercurial,

* provides a set of commands to rewrite history in a distributed way,

* issues various warning messages when "troubles" from changeset evolution
  appear in your repository,

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

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

.. _`changeset evolution`: https://wiki.mercurial-scm.org/ChangesetEvolution

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

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

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

Source of the documentation can be found in ``docs/``.

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

Using Pip
---------

You can install the latest released version using pip::

    $ pip install --user hg-evolve

Note: some distributions have adopted PEP 668 and made using ``pip install
--user`` more difficult than it should be. One of the cleanest ways around this
issue is to install both Mercurial and this extension in a separate virtual
environment. If you don't want to manage the virtual environment manually, you
can use Pipx.

Using Pipx
----------

Its documentation explains that "pipx is made specifically for application
installation", and the idea is that for every application it can create and
maintain a separate virtual environment and make all executables available on a
single path (e.g. ~/.local/bin/ on Linux, check ``pipx ensurepath``).

To create a virtual environment for hg and install evolve::

    $ pipx install mercurial
    $ pipx inject mercurial hg-evolve
    # or pipx runpip mercurial install hg-evolve

Note: it's recommended to use ``inject`` command to install evolve, but
sometimes ``runpip`` could be used. On some setups ``inject`` might require
specifying the full path to the extension in the configuration file, while
``runpip`` might not.

Using Your Package Manager
--------------------------

Sometimes your distribution's package manager might have the newest (or recent
enough) version of the extension. For example, both `Debian`_ and `Ubuntu`_
currently have a package called ``mercurial-evolve``.  Similarly, other
distributions might have it packaged, possibly under a slightly different name.
Try searching your package manager's database or see `this Repology page`_.

.. _`Debian`: https://packages.debian.org/search?keywords=mercurial-evolve&searchon=names&exact=1&suite=all&section=all
.. _`Ubuntu`: https://packages.ubuntu.com/search?keywords=mercurial-evolve&searchon=names&exact=1&suite=all&section=all
.. _`this Repology page`: https://repology.org/project/mercurial-evolve/related

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

To obtain a local version from source::

    $ hg clone https://repo.mercurial-scm.org/evolve

There's no need to compile anything or run ``make``.

This method keeps the extension in its own repo, and you can use it by
specifying the full path to the ``hgext3rd/evolve/``.

Alternatively, you can install it::

    $ cd evolve
    # optionally `hg update <target revision>`
    $ pip install --user .

This should avoid the need to specify the full path to the extension.

Enabling the Extension
----------------------

After installing the extension, you need to enable it before you can use it.

To do that, edit your hgrc::

    $ hg config --edit # add these two lines:
    [extensions]
    evolve =

If you didn't install the extension or Mercurial can't find it on one of the
default paths, you need to specify the full path to ``hgext3rd/evolve/``::

    [extensions]
    evolve = ~/evolve/hgext3rd/evolve

Similarly, if you want to enable topic extension, do this::

    $ hg config --edit
    [extensions]
    topic =
    # or
    topic = ~/evolve/hgext3rd/topic

Pitfalls
--------

If you get ``"failed to import extension evolve: No module named 'evolve'"``
error, there are a couple of things to check:

* make sure you gave pip/pipx the correct package name (it's ``hg-evolve``),

* make sure evolve is installed for the same version of Python that you use for
  running Mercurial (``hg debuginstall | grep Python``),

* try specifying the full path to the ``hgext3rd/evolve/`` directory.

Extension Purpose
=================

The goal of this extension is to provide an appropriate place for code and
concepts related to `changeset evolution`_ to mature. In this extension we
allow hackier code, unlocking quick experimentation and faster iterations.

In addition, evolve extension supports a wide range of Mercurial versions,
allowing us to reach a larger user base for feedback. The extension is not tied
to the Mercurial release cycle and can release new features and bug fixes at a
higher rate if necessary.

Once a concept is deemed ready, its implementation is moved into core
Mercurial. The maturation period helped us to get a clearer picture of what was
needed. During the upstreaming process, we can use this clearer picture to
clean up the code and upgrade it to an appropriate quality for core Mercurial.

Python 3 Support
================

Mercurial announced official `support for Python 3`_ starting with its 5.2
release. Since 9.3.0, evolve has official support for Python 3.6+.

.. _`support for Python 3`: https://wiki.mercurial-scm.org/Python3

Python 2 Support
================

Python 2 is supported by evolve. However, Mercurial 6.2 release dropped support
for it, so evolve can work on Python 2 only on earlier versions.

Debian packages that are built using Heptapod CI only install files for Python
3, because they target current Debian stable.

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

Discussion happens in #hg-evolve and #mercurial on libera_ IRC network.

.. _libera: https://libera.chat/

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=---

The recommended way to submit a patch is to create a Merge Request on
https://foss.heptapod.net/mercurial/evolve. To do so, create an account and
request access. You'll then be able to create a topic-based merge request.

Alternatively, 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 mercurial-devel@mercurial-scm.org --flag evolve-ext --rev '<your patches>'

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

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

When certain blocks of code need to cope with API changes in core Mercurial,
they should have comments in the ``hg <= x.y (commit hash)`` format. For
example, if a function needs another code path because of changes introduced in
02802fa87b74 that was first included in Mercurial 5.3, then the comment should
be::

    # hg <= 5.2 (02802fa87b74)

See also tests/test-check-compat-strings.t.

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

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

There are two main branches: "stable" and "default". Tests on these branches
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 versions of
Mercurial. They are the "mercurial-x.y" branches. They are used to apply
expected test changes only, no code changes should happen there.

Test output changes from a changeset in core should add the following line to
their patch description::

    CORE-TEST-OUTPUT-UPDATE: <changeset hash>

Format-source config
====================

Format-source helps smooth out the pain of merging after auto-formatting.
Follow the installation instructions at the `format-source`_ repo.

.. _`format-source`: https://foss.heptapod.net/mercurial/format-source

Then update your per-repo config file::

    $ hg config --local --edit # add these lines:
    [extensions]
    formatsource =

    [format-source]
    byteify-strings = python3 ~/hg/contrib/byteify-strings.py --dictiter --treat-as-kwargs kwargs opts commitopts TROUBLES --allow-attr-methods
    byteify-strings:mode.input = file
    byteify-strings:mode.output = pipe

Release Checklist
=================

* use contrib/merge-test-compat.sh to merge with the test compatibility
  branches,

* make sure the tests are happy on all supported versions,

* make sure there is no code difference between the compatibility branches and
  stable (no diff within hgext3rd/),

* update the ``testedwith`` variable for all extensions (remove '.dev0'):

  - hgext3rd/evolve/metadata.py
  - hgext3rd/topic/__init__.py
  - hgext3rd/pullbundle.py

* make sure CHANGELOG is up-to-date,

* add a date to the CHANGELOG entry for the target version,

* update the ``__version__`` field of all relevant extensions:

  - hgext3rd/evolve/metadata.py
  - hgext3rd/topic/__init__.py
  - hgext3rd/pullbundle.py (if touched)

* create a new Debian changelog entry:

  - debchange --newversion x.y.z-1 "new upstream release"
  - debchange --release

* sanity check install and sdist targets of setup.py:

  - python setup.py install --home=$(mktemp -d)
  - python setup.py sdist

* tag the commit,

* push and publish the tag,

* upload the tarball to PyPI,

* build .deb on Heptapod CI for the tagged commit,

* make an announcement on evolve-testers@mercurial-scm.org and
  mercurial@mercurial-scm.org,

* bump versions of all extensions and add ``.dev0`` (see existing commits as an
  example):

  - hgext3rd/evolve/metadata.py
  - hgext3rd/topic/__init__.py
  - hgext3rd/pullbundle.py

  Version bump rules:

  - stable branch x.y.z+1.dev0
  - default branch x.y+1.0.dev0

* merge stable into default.
