Enable ZJIT on the available version

[moznion]

This pull request adds the --enable-zjit option to each configure invocation to enable ZJIT.

Example after this patch is applied:

root@47c230db30e9:/# ruby --zjit --version
ruby 4.0.0preview2 (2025-11-17 master 4fa6e9938c) +ZJIT +PRISM [aarch64-linux]

And this also upgrades the rustc version because the ZJIT runtime requires edition2024.

Note: On versions that do not support ZJIT, the --enable-zjit option is ignored (ref: https://github.com/ruby/docker-images/blob/7589c4dad2d112bcfc255324363c91616741261a/install_ruby.sh#L99).

[moznion]

Oops sorry, this seems like duplicated by #509 but is it still progress?

[Earlopain]

Yeah, I'm still on it. I want to wait until the first release candiate to see how the developers feel about the status of zjit. I don't really want to expose here it if they don't think it's ready yet.

For now the release notes have this to say:

As of Ruby 4.0.0-preview1, ZJIT is not yet ready for speeding up most benchmarks. Please refrain from evaluating ZJIT just yet. Stay tuned for the Ruby 4.0 release.

[tianon]

Thank you (both) for the contribution! I'm indeed going to close in favor of #509 for tracking this, since @Earlopain has been really on top of it and waiting seems sane to me too ❤️

[moznion]

Thank you for the information. I understand the current situation.
The motivation behind this pull request is that we want to try ZJIT in a production (or production-like) environment. In my opinion, it would be more useful if this Docker repository provided images with ZJIT enabled for that purpose.

[moznion]

Anyway, I appreciate your support and maintenance of this repository ❤️

[tianon]

With the important echoed caveat that upstream doesn't officially recommend it for production yet, you should be able to create a build directly from #509 with something like this:

docker build 'https://github.com/docker-library/ruby.git#refs/pull/509/merge:4.0-rc/trixie'
(adjusting for taste, especially adding --tag)