ruby: check disallowed references with jitSupport disabled

[danieldk]

Motivation for this change

This makes it easier to detect regressions.

cc @doronbehar

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[doronbehar]

Maybe:

Suggested change

	disallowedReferences = op (!jitSupport) stdenv.cc;
	disallowedReferences = lib.optionals (!jitSupport) [ stdenv.cc stdenv.cc.cc ];

[danieldk]

Then I propose

        disallowedRequisites = op (!jitSupport) stdenv.cc.cc;

Since that checks the transitive closure and stdenv.cc will have stdenv.cc.cc in its closure.

[doronbehar]

LGTM but I wonder if it'll actually be detected and fixed if at some point, a future version of ruby will add another point of reference to cc (not handled currently).. @lilyball thinks (I think) there should be a ruby derivation built by Hydra that doesn't reference cc.

[danieldk]

LGTM but I wonder if it'll actually be detected and fixed if at some point, a future version of ruby will add another point of reference to cc (not handled currently).. @lilyball thinks (I think) there should be a ruby derivation built by Hydra that doesn't reference cc.

I don't really have an opinion, I don't use Ruby (aside from one website that uses Jekyll for historical reasons). I just happened to see the topic on Discourse & it's usually good to match a removeReferencesTo with a disallowedReferences. Saved the day in a private Nix repo a few times ;).

[doronbehar]

OK. We can make another PR in the future, this is good enough as a start.