# Updating the Glean SDK

Project FOG uses the published Glean SDK.
It currently depends on [glean-core] from crates.io.

[glean-core]: https://crates.io/crates/glean-core

To update the dependency:

1. Bump the version of the `glean-core` crate in and `toolkit/components/glean/Cargo.toml` and `toolkit/components/glean/api/Cargo.toml`.
2. Run `mach vendor rust`. This fetches all dependencies and adds them to `mozilla-central/third_pary/rust`.

## Version mismatches of Rust dependencies

Other crates that are already vendored might require a different version of the same dependencies that the Glean SDK requires.
The general strategy for Rust dependencies is to keep one single version of the dependency in-tree
(see [comment #8 in bug 1591555](https://bugzilla.mozilla.org/show_bug.cgi?id=1591555#c8)).
This might be hard to do in reality since some dependencies might require tweaks in order to work.
The following strategy can be followed to decide on version mismatches:

* If the versions only **differ by the patch version**, Cargo will keep the vendored version,
  unless some other dependency pinned specific patch versions;
  assuming it doesn’t break the Glean SDK;
  if it does, follow the next steps;
* If the version of the **vendored dependency is newer** (greater major or minor version) than the version required by the Glean SDK,
  [file a bug in the Glean SDK component][glean-bug] to get Glean to require the same version;
* If the version of the **vendored dependency is older** (lower major or minor version), consider updating the vendored version to the newer one;
  seek review from the person who vendored that dependency in the first place;
  if that is not possible or breaks mozilla-central build, then consider keeping both versions vendored in-tree; please note that this option will probably only be approved for small crates.

## Keeping versions in sync

The Glean SDK and `glean_parser` are currently released as separate projects.
However each Glean SDK release requires a specific `glean_parser` version.
When updating one or the other ensure versions stay compatible.
You can find the currently used `glean_parser` version in the Glean SDK source tree, e.g. in [sdk_generator.sh].

[sdk_generator.sh]: https://github.com/mozilla/glean/blob/main/glean-core/ios/sdk_generator.sh#L28
[glean-bug]: https://bugzilla.mozilla.org/enter_bug.cgi?product=Data+Platform+and+Tools&component=Glean%3A+SDK&priority=P3&status_whiteboard=%5Btelemetry%3Aglean-rs%3Am%3F%5D