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Flexible evolution of Mercurial history.

Project description

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 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.


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

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

Then enable it in your hgrc:

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

From Source

To install a local version from source:

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

Then enable it in your hgrc:

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

It’s also possible to use evolve without installing it, in which case you will need to provide the full path to hgext3rd/evolve/, for example:

evolve = ~/evolve/hgext3rd/evolve


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 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).

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+.

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.

Bugs are to be reported on the Mercurial’s bug tracker (component: evolution).

The recommended way to submit a patch is to create a Merge Request on 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. Please make sure to use the evolve-ext flag when doing so. You can use a command like this:

$ hg email --to --flag evolve-ext --rev '<your patches>'

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

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/

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.

Then update your per-repo config file:

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

byteify-strings = python3 ~/hg/contrib/ --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/ 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/

    • hgext3rd/topic/

    • hgext3rd/

  • 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/

    • hgext3rd/topic/

    • hgext3rd/ (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

    • python install –home=$(mktemp -d)

    • python sdist

  • tag the commit,

  • move @ bookmark to the new tag,

  • push and publish the tag,

  • upload the tarball to PyPI,

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

  • make an announcement on and,

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

    • hgext3rd/evolve/

    • hgext3rd/topic/

    • hgext3rd/

    Version bump rules:

    • stable branch x.y.z+1.dev0

    • default branch x.y+1.0.dev0

  • merge stable into default.

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