ocamlPackages.findlib: Allow built-in libraries to clash

[ulrikstrid]

Description of changes

This change allows the builtin libraries in OCaml to clash which is the case when you cross-compile since you'll have both the target and system OCaml available

Follow-up on #205646

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.05 Release Notes (or backporting 22.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[ulrikstrid]

Added those involved in the last PR as reviwers

[Mindavi]

Seems like a good idea but I don't know anything about ocaml :)

[symphorien]

I cannot reproduce the issue, inside nix-shell -A pkgsStatic.ocamlPackages.batteries I get

[nix-shell:~/src/nixpkgs]$ ocamlfind list
bigarray            (version: [distributed with Ocaml])
bytes               (version: [distributed with OCaml 4.02 or above])
camlp-streams       (version: n/a)
compiler-libs       (version: [distributed with Ocaml])
compiler-libs.bytecomp (version: [distributed with Ocaml])
compiler-libs.common (version: [distributed with Ocaml])
compiler-libs.native-toplevel (version: [distributed with Ocaml])
compiler-libs.optcomp (version: [distributed with Ocaml])
compiler-libs.toplevel (version: [distributed with Ocaml])
dynlink             (version: [distributed with Ocaml])
findlib             (version: 1.9.6)
findlib.dynload     (version: 1.9.6)
findlib.internal    (version: 1.9.6)
findlib.top         (version: 1.9.6)
num                 (version: 1.0)
num-top             (version: 1.1)
num.core            (version: 1.0)
oUnit               (version: 2.2.6)
oUnit.advanced      (version: n/a)
oUnit.threads       (version: n/a)
ocamldoc            (version: [distributed with Ocaml])
ounit2              (version: 2.2.6)
ounit2.advanced     (version: 2.2.6)
ounit2.threads      (version: 2.2.6)
qcheck              (version: 0.20)
qcheck-core         (version: 0.20)
qcheck-core.runner  (version: 0.20)
qcheck-ounit        (version: 0.20)
seq                 (version: [distributed with OCaml 4.07 or above])
stdlib              (version: [distributed with Ocaml])
stdlib-shims        (version: 0.3.0)
str                 (version: [distributed with Ocaml])
threads             (version: [distributed with Ocaml])
threads.none        (version: [internal])
threads.posix       (version: [internal])
unix                (version: [distributed with Ocaml])

so no clash

---

An alternative to hard coding the list of builtins would be to run ocamlfind list with empty OCAMLPATH.

[ulrikstrid]

@symphorien i think that's because you only have the musl compiler. We saw it in our OCaml overlays when compiling to arm64.

[symphorien]

does cross x86 -> arm64 work at all with ocaml? I thought it only worked for platforms which can execute one-another

[anmonteiro]

does cross x86 -> arm64 work at all with ocaml? I thought it only worked for platforms which can execute one-another

yup, a few patches are required but we set it up successfully in our ocaml-focused nix-overlays. Example working PR:

nix-ocaml/nix-overlays#621

[symphorien]

cool!

However it would be nice to provide a way to reproduce the issue on vanilla nixpkgs so that I can review.

[Et7f3]

Could we split ocaml compiler instead ? so that it has native stdlib when compiling native binary and cross stdlib to compile cross library ?

[ulrikstrid]

Could we split ocaml compiler instead ? so that it has native stdlib when compiling native binary and cross stdlib to compile cross library ?

I think this is a bigger effort 😅

@symphorien I'm trying to find a way to repro in this repo.

@anmonteiro what would need to be upstreamed here to have good crosscompilation? The OCaml patches + what?

[Mindavi]

This doesn't seem that bad to merge anyway to me, but a comment might be warranted on the line above?

[phanirithvij]

bumping to know whether it is still relevant