Bug 1716955: Initial implementation of the rate metric

[ChinYing-Li]

Pull Request checklist

• Quality: Make sure this PR builds and runs cleanly.
  • Inside the glean/ folder, run:
    • npm run test Runs all tests
    • npm run lint Runs all linters
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry to CHANGELOG.md or an explanation of why it does not need one
• Documentation: This PR includes documentation changes, an explanation of why it does not need that or a follow-up bug has been filed to do that work
  • Documentation should be added to The Glean Book when making changes to Glean's user facing API
    • When changes to the Glean Book are necessary, link to the corresponding PR on the mozilla/glean repository
  • Documentation should be added to the Glean.js developer documentation when making internal code changes

[ChinYing-Li]

Hello,
I just realized that in the glean library (https://github.com/mozilla/glean), there's no unit test for the rate metric. Is this by purpose?

[Dexterp37]

Hello, I just realized that in the glean library (https://github.com/mozilla/glean), there's no unit test for the rate metric. Is this by purpose?

There's a smoke test here and a schema test here. I believe that given the time pressure, no other test was added.

[ChinYing-Li]

The PR is now ready for review; any suggestion is appreciated!

[chutten]

This is looking good to me so far. I'll bring in @brizental to make sure I'm not allowing strange patterns in just because I'm unfamiliar with how metric types are implemented in the Glean JS SDK.

[brizental]

Hey @ChinYing-Li this is looking really great. I like the way you implemented the metric, very clean.

I left some comments. Implementation looks really good. I would like to have more tests as well.

Once we are done with these changes we will also need to update the docs. Feel free to simply file a follow up for that if you don't want to work on it.

[brizental]

Thanks for adding the tests! Not much is missing, left some inline commments and through the tests found a bug in the implementation. Easy to fix though.

[brizental]

Some final nits, otherwise, looks god!

Thanks so much for the work here @ChinYing-Li 🎉

[brizental]

Oh, yeah. Also, please add a changelog entry for this.