Add support for OCaml 4.12

[kit-ty-kate]

This requires the OCaml 4.12 support in omp to be merged first: ocaml-ppx/ocaml-migrate-parsetree#107

This is just a PR to make ppxlib compile in case someone needs to test packages requiring ppxlib with OCaml 4.12. I do not know the internal nor have i tested if the tests ran correctly.

This branch will temporary be used in opam-alpha-repository

[kit-ty-kate]

I did not use cinaps to generate this, however when I tried to use it, it failed with the following warning/error and failed to produce ast/versions.mli file:

File "ast/versions.mli", line 131, characters 23-32:
Error (warning 49 [no-cmi-file]): no cmi file was found in path for module OCaml_412

Is that something to do with ocaml-ppx/ocaml-migrate-parsetree#107 maybe?

[NathanReb]

I did not use cinaps to generate this, however when I tried to use it, it failed with the following warning/error and failed to produce ast/versions.mli file:

File "ast/versions.mli", line 131, characters 23-32:
Error (warning 49 [no-cmi-file]): no cmi file was found in path for module OCaml_412

Is that something to do with ocaml-ppx/ocaml-migrate-parsetree#107 maybe?

I tried it locally myself and it seems to work just fine. I did get a few errors but that's probably related to the fact that you have to promote multiple times. After a couple dune runtest && dune promote runs, both the ml and mli files were updated and everything builds and passes the test!

Thanks for working on this, I'll merge as soon as we release the corresponding ocaml-migrate-parsetree!

[NathanReb]

Can you allow push from maintainers please? I'd like to update a couple things like the changelog and the opam file.

[NathanReb]

Nevermind I was doing it all wrong!