Naive question after a quick look at the changes: why is findlib often both in buildInputs and nativeBuildInputs?

@vbgl Because it doesn't appear to be working otherwise :)

My guess is that it needs to find both host and target libraries, thus requiring both host and target findlib.

@balsoft commit 7263951 mentions it fixes the static build of OCaml for versions <= 4.07. I got OCaml 4.08 and 4.09 going under musl with the following (I think they switched the build to autoconf since 4.08):

(_: super:
    {
      ocaml = super.ocaml.overrideDerivation (o: {
        preConfigure = ''
          configureFlagsArray+=("CC=$CC" "AS=$AS" "PARTIALLD=$LD -r")
        '';
        configureFlags = (lib.remove "--no-shared-libs" o.configureFlags) ++ [
          "--disable-shared"
           "--host ${o.stdenv.hostPlatform.config}"
          "--target ${o.stdenv.targetPlatform.config}"
        ];
      });
    })

Ideally this would make it upstream to nixpkgs -- I'm looking for pointers on how to add these flags conditionally based on the OCaml version.

The configureFlags attribute of the derivation for the OCaml compilers has a “flag” function that should help to deal with the discrepancies between old and new configure flags:

I'm happy to submit a PR adding support for OCaml >= 4.08, but I'm still having an issue where I can't use packages that build with topkg. I keep getting e.g.:

building
No such package: topkg
File "./pkg/pkg.ml", line 4, characters 5-10:
4 | open Topkg
         ^^^^^
Error: Unbound module Topkg
builder for '/nix/store/7gfy9f8ai9bwbv1q112v3d40nwgas8w4-ocaml4.09.0-fmt-0.8.5-x86_64-unknown-linux-musl.drv' failed with exit code 2

Any pointers on what to look for here would be appreciated. I tried messing with nativeBuildInputs (added both topkg and findlib) but it doesn't seem to change anything.