One reason there's no Perforce support for Gerrit/Rietveld is that Google doesn't use those tools for changes to code that's stored in Piper. Instead, they use Critique:

- https://abseil.io/resources/swe-book/html/ch19.html

- https://read.engineerscodex.com/p/how-google-takes-the-pain-...

I haven't found anything external that's as good, and am astounded that GitHub's incredibly lackluster PR review tooling is acceptable to most people. If anyone is aware of something in Critique's league, I'd love to hear about it!

Edit: I tried to do a reasonably thorough survey a couple of years ago when I left Google and https://codeapprove.com/ was the closest I found, but there were still many gaps.

> which lives in Piper, a fork of Perforce

This is incorrect. Piper is API-compatible with Perforce but is a totally different implementation, not a fork.

Don't worry, they accept PRs on that repo. They just merge them internally and then re-export them.

There are some variations, but this is generally the same with all open source projects which live in their internal monorepo, such as gVisor or Bazel.