Support OCaml 5.4.0

[patricoferris]

We now have a dune 3.18.0 with 5.4.0 support (afaict). See the conversation in #566

[NathanReb]

There are a few missing promotions it seems!

[patricoferris]

I think we're just waiting for the magic numbers to be bumped in OCaml.

[NathanReb]

I think we're just waiting for the magic numbers to be bumped in OCaml

I thought they were bumped on the development branch now.

It also seems the dune version we're using for the trunk CI build does not build.

[NathanReb]

Looks great! Thanks for taking the time to work on this.

From the top of your head, do you know which functions in the migration need to be reviewed?

[NathanReb]

I think we should have a Longident module in ast_504 similar to what we have for Asttypes. That way if the type is further modified, it'll be treated as a regular AST change.

I think we should still have a Longident module in astlib but it should only provide the utility functions on Longidents from the compiler, same as the Parse, or Pprintast modules do for other moving Ast types.

Since Astlib is supposed to provide the stable layer on top of the compiler-libs that's necessary for ppxlib, we should maybe make it provide the exact set of functions we need and nothing more.

What would you think about the following:

• Make Legacy_longident define only the type
• Make Longident provide the functions we use, conditionnally compiled to work with the current compiler
• Have a Longident module in Ppxlib that expose the functions corresponding to our internal AST.

As I write this I wonder if, in fact, we don't need any compiler functions on longidents but simply need the ones for our internal AST. Making a compat layer for functions unnecessary as we can simply have a local copy of the correct version.

[kit-ty-kate]

the magic numbers have been bumped

[patricoferris]

Thanks for the review @NathanReb -- I think I followed what you were suggesting and applied the changes. To reiterate:

• We know version Longident in the AST itself for 504
• Our Internal AST Longident is still that from 502 so nothing else needs changed there

And everything just works.

Presumably when we bump the internal AST to 504 we will have to almost invert this in order to migrate from below to 504.

[patricoferris]

Also, we're waiting on a new version of dune that support 5.4.0 too.

[kit-ty-kate]

the dune PR has been merged in opam-repository