`ocamlbuild` compatibility with `dune pkg` and OxCaml

[Sudha247]

Desired Behavior

We can use ocamlbuild in a project with an OxCaml compiler and build with dune pkg

Example

Currently, there are two separate forks of ocamlbuild, one in the OxCaml opam-repository and one in dune opam overlays. The forks ensure they retain compatibility for their own use cases - for OxCaml, with the OxCaml compiler, and for the overlays that it works with dune pkg.

• Dune pkg patch: ocaml/ocamlbuild@master...gridbugs:ocamlbuild:0.16.1+dune
• OxCaml patch: https://github.com/oxcaml/opam-repository/blob/main/packages/ocamlbuild/ocamlbuild.0.15.0%2Box/files/flambda2.patch

Right now, what happens is when you build an OxCaml project that requires ocamlbuild with dune pkg, the solver tries to use the dune version, but a lot of OxCaml packages, including the compiler, have a conflict with any ocamlbuild that's not 0.15.0+ox. However, dune pkg can't use it because it has symlinks (c.f. #9873).

It would be good to have a version of ocamlbuild that supports both OxCaml and dune pkg. This version should ideally be able to support both OxCaml projects built with dune pkg and OxCaml projects build with opam.

[Sudha247]

I have a version here that seems to satisfy the conditions listed above: https://github.com/Sudha247/ocamlbuild/tree/oxcaml%2Bdune. I'd be interested to know if folks have opinions on whether we host this somewhere and where.

[shonfeder]

If the oxcaml patch is backward compatible with mainline ocaml (and is an improvement), then adopting those changes into the dune pkg overlays desirable? If not, then maybe we need to go the other way, and ask oxcaml's overlay to become downstream of our fork?

I wonder also if there has been work to try to upstream our fixes with the symlinks to ocamlbuild?

[shonfeder]

Did it get fixed already via ocaml/ocamlbuild#362 ?

[Sudha247]

Also related to ocaml/ocamlbuild#327, but I see the fix above hasn't been released yet. If we get upstream ocamlbuild working with dune pkg, it could be hosted in the OxCaml repo with the compat patches, and we won't have multiple overlays.