ruby: re-enable yjit, and fix, on cross

[samueldr]

This PR fixes yjit support, after re-enabling it (see: #449938).

This was authored sometimes last year when working on fixing Mobile NixOS cross-compilation issues with Ruby. I never got around to sending the fix.

Currently verified with:

 $ nix-build --attr pkgsCross.aarch64-multiplatform.ruby_3_3 --attr pkgsCross.aarch64-multiplatform.ruby_3_4

~/tmp/nixpkgs/nixos-unstable $ nix-shell -p qemu-user

[nix-shell:~/tmp/nixpkgs/nixos-unstable]$ qemu-aarch64 ./result/bin/ruby --yjit-stats -e 'pp RUBY_VERSION'
"3.3.10"
***YJIT: Printing YJIT statistics on exit***
[...]

For the record, before this change:

[nix-shell:~/tmp/nixpkgs/nixos-unstable]$ qemu-aarch64 ./result/bin/ruby --yjit-stats -e 'pp RUBY_VERSION'
./result/bin/ruby: warning: Ruby was built without YJIT support. You may need to install rustc to build Ruby with YJIT.
"3.3.10"

Ruby 3.5 has an unrelated failure, same as on nixos-unstable:

error: output '/nix/store/0f1s4lmddng92rwi28l1ibajiyq3ky22-ruby-aarch64-unknown-linux-> gnu-3.5.0-preview1' is not allowed to refer to the following paths:
         /nix/store/41virlkphdik7jnvagaas5lxaqbii1hn-ruby-3.3.10

Note that the build otherwise fully succeeds.

---

• cc @nim65s, who turned the feature off.
• cc @kirillrdy, who reviewed the previous change (and is getting deeper into Ruby maintenance?)

Things done

• Built on platform:
  • x86_64-linux [yes, cross]
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

---

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[samueldr]

I can fold back the Revert commit into the other commits, but I feel this is better showing what was done, rather than making the other commits include the revert.

[nim65s]

Great, thanks !

Diff LGTM, and I can confirm this fix the issue that got me to deactivate this, so I'm happy for the revert

[kirillrdy]

i think this is cause of mass rebuild, can it be split ? if not, this should go to staging

[samueldr]

Not in this case, it's the removal of cargo from the inputs that changes the ruby derivation.

The env input attribute in mkDerivation is special-cased and when it's an empty set, it has no effect.

nix-repl> stdenv.mkDerivation { name = "foo"; }                                             
«derivation /nix/store/w0ps5bzjcc5x3xcv8b327jfzmd5k5nsp-foo.drv»

nix-repl> stdenv.mkDerivation { name = "foo"; env = lib.optionalAttrs false { x = "x"; }; }
«derivation /nix/store/w0ps5bzjcc5x3xcv8b327jfzmd5k5nsp-foo.drv»

nix-repl> stdenv.mkDerivation { name = "foo"; env = lib.optionalAttrs true { x = "x"; }; }  
«derivation /nix/store/216b6l77hb1n2s6n6n7asfdj4b49qcg4-foo.drv»

I'll split that (cargo) change out if ruby cross-compiles fine without that change.

[samueldr]

Follow-up: #462631

[samueldr]

(Previous force-push is a simple rebase on top of current nixos-unstable)

[samueldr]

With the following force-push'd changes:

 $ git checkout -B nixos-unstable NixOS/nixos-unstable

 $ nix-instantiate --attr ruby_3_3
/nix/store/maym3jairjj8mybhf06vfks8ak2mchh3-ruby-3.3.10.drv

 $ git checkout fix/ruby-cross-ynojit-lets-yjit 

~/tmp/nixpkgs/nixos-unstable $ nix-instantiate --attr ruby_3_3
/nix/store/maym3jairjj8mybhf06vfks8ak2mchh3-ruby-3.3.10.drv

And it still cross-compiles.

~/tmp/nixpkgs/nixos-unstable $ nix-build --attr pkgsCross.aarch64-multiplatform.ruby_3_3
/nix/store/57v2sv3lx61y3rd59bnyl5g99rdff9n3-ruby-aarch64-unknown-linux-gnu-3.3.10