Add a coverage artifact to web-features releases

[ddbeck]

We should have an artifact like coverage.json on web-features releases on GitHub that reports:

• How many BCD keys exist (in scope for web-features, i.e., not webextensions)
• How many BCD keys have been assigned to a feature

Eventually, we'll cover all of BCD and this will not be interesting, so I don't think we need to add it to the package itself.

Prompted by GoogleChrome/webstatus.dev#793.

[jcscottiii]

Initially, I assumed this would be a temporary statistic that would be tracked. But I wanted to ask if you think this will be something that will be tracked long term (as more features are added)?

If it is something truly temporary, we can discuss some options like manually hosting a publicly accessible JSON blob. Then the webstatus.dev frontend can request it.

But if it is actually a long term statistic, we could build a coverage.json schema and release it alongside data.json. Then, I would modify my existing process to download and store coverage.json and create an endpoint to serve it.

Also, there are options in between these two approaches too.

[ddbeck]

But I wanted to ask if you think this will be something that will be tracked long term (as more features are added)?

I don't think so. My expectation is that we'll (hopefully soon) get to the point where every BCD feature is tagged and new BCD features get tagged at inception (we're looking at ways to assign feature IDs before the feature ships). 100% coverage ought to be the norm.

If it is something truly temporary, we can discuss some options like manually hosting a publicly accessible JSON blob.

Honestly, I expect to reach >95% coverage in November or December (and the last fraction will likely be non-standard and deprecated features). This ought to be very short-lived. 😄

[jcscottiii]

If it's that short term, you could just tell me a number. Or put it in the release notes text to let everyone know the progress. It doesn't have to be machine readable. Either way, I'll grab it and update the score on the site.

[ddbeck]

If it's that short term, you could just tell me a number. Or put it in the release notes text to let everyone know the progress

Can do. https://github.com/web-platform-dx/web-features/releases/tag/v2.2.0 includes the overall percentage in the release notes. I'll start doing this until we get to 100%.

Also, there are finer-grained stats in #788 if you want them, but they're done weekly, not pinned to a specific release.