build any ocaml package with dune

[intermet]

Hello,
In the context of reproducible builds (e.g. guix/nix), I was wondering how can I use to dune to build any ocaml package. When doing dune pkg lock, build “recipes” are written in .pkg files. For example fmt doesn't use dune for its build system, yet we can build it with dune thanks to the action defined in fmt.pkg. Is there any lib exposed by dune that lets build fmt? (independently of any dune-project and locking).

Thanks for helping

[Leonidas-from-XIV]

No, there is not. The way Dune builds and installs is by unpacking them to a sandbox location, building and installing them using the instructions extracted from the .opam files into .pkg files and then storing the installed artifacts in the _build folder. When some program needs it to build, it gets moved into the path so the compiler can access it.

So the only way to trigger that behavior for any project is to create an empty dune project with your desired library as dependency and locking and building from there.