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/

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 simply copies the latest version from version-control-tools into the vendored locations.

The locations are as follows:

  • In-tree: testing/mozharness/external_tools/

  • Treescript:

  • build-puppet:

  • ronin_puppet:

  • OpenCloudConfig:

Debian Packages for Debian and Ubuntu Based Docker Images

taskcluster/ci/packages/debian.yml and taskcluster/ci/packages/ubuntu.yml define 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.

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…