mention "modern" fake timers implementation in docs

[PavelPolyakov]

Summary

Docs update. It's currently difficult to find out, that it's even possible to try this new implementation. I've accidentally met it in the release notes.

Test plan

none

[facebook-github-bot]

Hi @PavelPolyakov!

Thank you for your pull request and welcome to our community.We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file.

In order for us to review and merge your code, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

If you have received this in error or have any questions, please contact us at [email protected]. Thanks!

[jeysal]

Thanks! @SimenB does this go far enough or would you want this guide to explicitly recommend using 'modern'?

[SimenB]

I think we should recommend it. It'll be the default in the next major, and the sooner people migrate the better 😀

[jeysal]

I wonder though: What will happen after the default changes? Lots of people with unnecessary 'modern' in their codebase :|
If the change is non-breaking for the majority of people (no idea if it is) maybe it's fine to not give the recommendation to everyone now?

[facebook-github-bot]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!

[SimenB]

Lots of people with unnecessary 'modern' in their codebase :|

Not sure I think this is an issue. It's a search&replace away. Can probably add a lint rule or codemod that can fix it (we probably want one so FB can go the other way - add 'legacy' to all without arguments)

If the change is non-breaking for the majority of people (no idea if it is)

It should be

[codecov-io]

Codecov Report

Merging #10022 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #10022   +/-   ##
=======================================
  Coverage   64.00%   64.00%           
=======================================
  Files         297      297           
  Lines       12528    12528           
  Branches     3093     3093           
=======================================
  Hits         8018     8018           
  Misses       3860     3860           
  Partials      650      650           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0e0eeed...fc640bd. Read the comment docs.

[facebook-github-bot]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!

[SimenB]

Landed in #12317

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.
Please note this issue tracker is not a help forum. We recommend using StackOverflow or our discord channel for questions.