Add FID deprecation warn on web vital measure

[ankur22]

What?

When the FID metric is measured, a warning will be logged to let users know to move away from working with browser_web_vital_fid and instead use browser_web_vital_inp.

Why?

FID has been deprecated -- ttps://web.dev/blog/fid.

Checklist

• I have performed a self-review of my code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have added tests for my changes.
• I have run linter and tests locally (make check) and all pass.

Checklist: Documentation (only for k6 maintainers and if relevant)

Please do not merge this PR until the following items are filled out.

• I have added the correct milestone and labels to the PR.
• I have updated the release notes: link
• I have updated or added an issue to the k6-documentation: grafana/k6-docs#NUMBER if applicable
• I have updated or added an issue to the TypeScript definitions: grafana/k6-DefinitelyTyped#NUMBER if applicable

Related PR(s)/Issue(s)

#5179

[ankur22]

I'm not entirely happy with this approach. Is there something I'm missing, maybe a state that I can rely on that allows me to log a single warning log regardless of how many iterations, VUs and scenarios are in the test?

[mstoykov]

This seems like it will ALWAYS log this instead of only when this is used. I am not aware how this is used, but if it is going to always be logged and we will just drop it ... maybe just drop a warning that will be useless for most people and lets just drop it in v2 ?

[ankur22]

What about logging a warning when the FID metric is about to be emitted?

[mstoykov]

Wouldn't that still happen each time someone uses browser - irregardless of what they are using it for /

[ankur22]

Ok, i see what you're saying. The user could be relying on the metric in a threshold, what about adding a log when a threshold uses the metric? Any other ideas?

[ankur22]

as a quick POC, placing a warn log line here produces this:

> k6 run e2e/quickpizza-admin-user.js
WARN[0000] browser_web_vital_fid has been deprecated and superseded by browser_web_vital_inp 

         /\      Grafana   /‾‾/  
    /\  /  \     |\  __   /  /   
   /  \/    \    | |/ /  /   ‾‾\ 
  /          \   |   (  |  (‾)  |
 / __________ \  |_|\_\  \_____/ 

So pretty hidden, whereas i would want the log line to be more visible. I also don't want to spend too long on this with lots of changes just to get the log line in the correct place, since this is temporary and FID will be removed in v2.

[mstoykov]

I do not feel like this is a good solution and I think that thsi will just get a lot of users to report that they do not care and this shouldn't have been printed.

Given that we will be dropping this in k6 v2 ... I feel like maybe a better way will be for this to go in the Release notes "Future breaking changes and plans" section and stay there until v2 and then we can have it in there.

If this is such a bad idea that it has been deprecated by everyone, I do expect most users will not be that suprised, and it is likely v2 will have more changes that require user interferance than just this.

I am approving this in case the rest of @grafana/k6-core is off different opinion

[joanlopez]

👋🏻 I have no strong opinion because I'd say I don't know our Browser users enough to have so. For instance, I don't know how important the FID metric is for those k6 users that run Browser tests, and whether the deprecation is more because it's not relevant for them or because the standards have changed and now others are considered "vital", but FID remains important for them.

Compared to our HTTP metrics, if we would be dropping a metric like TLS handshake, or similar, that I'm pretty sure almost nobody cares about, then I'd probably prefer to not leave a warning.

Given that we will be dropping this in k6 v2 ... I feel like maybe a better way will be for this to go in the Release notes "Future breaking changes and plans" section and stay there until v2 and then we can have it in there.

I do like this idea, and indeed I think we might want to use it also for other changes that we plan by v2.0.