Version Control in CI

Upgrading Mercurial

Upgrading Mercurial in CI requires touching a handful of different components.

Vendored robustcheckout

The robustcheckout Mercurial extension is used throughout CI to perform clones and working directory updates. The canonical home of the extension is in the repository at the path hgext/robustcheckout/ A copy of the extension is vendored at testing/mozharness/external_tools/

When upgrading Mercurial, the robustcheckout extension should also be updated to ensure it is compatible with the version of Mercurial being upgraded to. Typically, one simplies copies the latest version from version-control-tools into the vendored location.

Debian Packages for Debian Based Docker Images

taskcluster/ci/packages/kind.yml defines custom Debian packages for Mercurial. These are installed in various Docker images.

To upgrade Mercurial, typically you just need to update the source URL and its hash in this file.

Non-Debian Linux Docker Images

The taskcluster/docker/recipes/ script is sourced by a handful of Docker images to install Mercurial.

The script references 3 tooltool artifacts:

  • A Mercurial source tarball (for pip installs).
  • A mercurial_*_amd64.deb Debian package.
  • A mercurial-common_*_all.deb Debian package.

The source tarball is a vanilla Mercurial source distribution. The Debian archives will need to be produced manually.

To produce the Debian archives, hg clone and hg update to the tag being built. Then run make docker-ubuntu-xenial. This will build the Mercurial Debian packages in a Docker container. It will deposit the produced packages in packages/ubuntu-xenial/.

Once all 3 files are available, copy them to the same directory and upload them to tooltool.

$ add –public mercurial-x.y.z.tar.gz mercurial*.deb $ upload –message ‘Bug XXX - Mercurial x.y.z’ –authentication-file ~/.tooltoolauth


See for how to use tooltool and where to obtain

Next, copy values from the file into taskcluster/docker/recipes/ See revision 977768c296ca for an example upgrade.

Windows AMIs defines the Windows environment for various Windows AMIs used by Taskcluster. Several of the files reference a mercurial-x.y.z-*.msi installer. These references will need to be updated to the Mercurial version being upgraded to.

The robustcheckout extension is also vendored into this repository at userdata/Configuration/FirefoxBuildResources/ It should also be updated if needed.

Puppet Maintained Hosts

Some hosts (namely macOS machines) are managed by Puppet and Puppet is used to install Mercurial.

Puppet code lives in the repository. Relevant files are in modules/mercurial/, modules/packages/manifests/mozilla/mozilla-python27-mercurial-debian/, and modules/packages/manifests/mozilla/py27_mercurial*. A copy of robustcheckout is also vendored at modules/mercurial/files/


The steps to upgrade Mercurial in Puppet aren’t currently captured here. Someone should capture those…