Upstream cross-compilation support

[alyssais]

It would be really great if Nixpkgs could cross-compile OCaml out of the box. What would need to happen to get the cross-compilation support from this overlay upstream? I would be willing to put work into this, but if you already have thought about what would need to happen it would be great to hear from you.

[anmonteiro]

I agree this would be desirable to upstream. I haven't made many strides towards that however. Here's the current state of cross compilation support in this repo:

• changes live in the cross/ folder
• the OCaml compiler needs a small patch + a custom build process which you can find here
• then we need to make the OCaml package set (esp. findlib) aware of the 2 toolchains (buildPackages and the cross-compilation environment). This is all done in cross/ocaml.nix
  • IMO this is where most of the complexity lies: nixpkgs uses OCAMLPATH to tell findlib about OCaml packages, but we need to actually write down findlib.conf files for both the build and cross toolchains.

I hope the above information gives you something to start with. Feel free to reach out for more questions otherwise.