Vendoring Application Services into mozilla-central

Some of these components are used in mozilla-central. This document describes how to update existing components or add new components.

The general process for vendoring rust code into mozilla-central has its own documentation - please make sure you read that before continuing.

When to vendor

We want to keep our versions in moz-central relatively up-to-date, but it takes some manual effort to do. The main possibility of breakage is from a dependency mismatch, so our current vendoring policy is:

  • Whenever a 3rd-party dependency is added or updated, the dev who made the change is responsible for vendoring.
  • At the start of the release cycle the triage owner is response for vendoring.

Updating existing components.

To update components which are already in mozilla-central, follow these steps:

  1. Ensure your mozilla-central build environment is setup correctly to make "non-artifact" builds - check you can get a full working build before starting this process.

  2. Run ./tools/update-moz-central-vendoring.py [path-to-moz-central] from the application-services root directory.

  3. If this generates errors regarding duplicate crates, you will enter a world of pain, and probably need to ask for advice from the application-services team, and/or the #build channel on matrix.

  4. Run ./mach cargo vet to check if there any any new dependencies that need to be vetted. If there are ask for advice from the application-services team.

  5. Build and test your tree. Ideally make a try run.

  6. Put your patch up to phabricator, requesting review from, at least, someone on the application-services team and one of the "build peers" - asking on #build on matrix for a suitable reviewer might help. Alternatively, try and find the bug which made the most recent update and ask the same reviewer in that patch.

  7. Profit!

Adding a new component

Follow the Uniffi documentation on mozilla-central to understand where you'll need to add your crate path and UDL. In general:

  • The consuming component will specify the dependency as a nominal "version 0.1"
  • The top-level Cargo.toml will override that dependency with a specific git revision.

For example, consider the webext-storage crate:

Adding a new component implies there will be related mozilla-central changes which leverage it. The best practice here is to land both the vendoring of the new component and the related mozilla-central changes in the same bug, but in different phabricator patches. As noted above, the best-practice is that all application-services components are on the same revision, so adding a new component implies you will generally also be updating all the existing components.

For an example of a recently added component, the tabs was recently added to mozilla-central with uniffi and shows a general process to follow.

Vendoring an unreleased version for testing purposes

Sometimes you will need to make changes in application-services and in mozilla-central simultaneously - for example, you may need to add new features or capabilities to a component, and matching changes in mozilla-central to use that new feature.

In that scenario, you don't want to check your changes in and re-vendor as you iterate - it would be far better to use a local checkout of application-services with uncommitted changes with your mozilla-central tree which also has uncommited changes.

To do this, you can edit the top-level Cargo.toml to specify a path. Note however that in this scenario, you need to specify the path to the individual component rather than to the top-level of the repo.

For example, you might end up with something like:

# application-services overrides to make updating them all simpler.
interrupt-support = { path = "../application-services/components/support/interrupt" }
sql-support = { path = "../application-services/components/support/sql" }
sync15-traits = { path = "../application-services/components/support/sync15-traits" }
viaduct = { path = "../application-services/components/viaduct" }
webext-storage = { path = "../application-services/components/webext-storage" }

Note that when you first do this, it will still be necessary to run ./mach vendor rust and to re-build.

After you make a change to the local repository, you do not need to run ./mach vendor rust, but you do still obviously need to rebuild.

Once you are happy with all the changes, you would:

  • Open a PR up in application-services and land your changes there.
  • Follow the process above to re-vendor your new changes, and in that same bug (although not necessarily the same phabricator patch), include the other mozilla-central changes which rely on the new version.