Fix build for OCaml 5

[samoht]

No description provided.

[bikallem]

Any chance of this PR getting merged? I am getting ocaml-ci issues since lru is not compatible with OCaml 5.0 yet. mirage/ocaml-dns#312

[patricoferris]

Bumped into this issue recently with Irmin. Trying to install irmin-graphql.3.4.2 on a 5.0.0 switch can't be done:

[ERROR] Package conflict!
  * No agreement on the version of ocaml:
    - (invariant) → ocaml-base-compiler >= 5.0.0~beta1 → ocaml = 5.0.0
    - git-unix >= 3.9.1 → tcpip >= 7.0.0 → lru >= 0.3.0 → ocaml < 5.0
    You can temporarily relax the switch invariant with `--update-invariant'

No solution found, exiting

[pqwy]

There's no way to make this compatible with pre-5.0, right?

[edwintorok]

Why is this using MakeSeeded and then providing a seeded hash function that is not seeded?
Wouldn't it be better for Make to use Hashtbl.Make and MakeSeeded to use Hashtbl.MakeSeeded and that might even work with both versions?

[edwintorok]

I haven't tried, but in principle would this work?

 module FakeSeededHash (H: Hashtbl.HashedType) = struct
    include H 
    let seeded_hash _ x = hash x
    let hash _ x = hash x
  end
  module Make (K: Hashtbl.HashedType) (V: Weighted) =
    Bake (Hashtbl.MakeSeeded (FakeSeededHash (K))) (V)
  module MakeSeeded (K : Hashtbl.SeededHashedType) (V: Weighted) =
    Bake (Hashtbl.MakeSeeded (K)) (V)

Then 4.x can pick hash _ x from SeededHash module, and 5.x can pick seeded_hash _ x and neither would mind having an extra value defined (worst case you get some dead code warning?) that the other version needs.

[pqwy]

@edwintorok Right, of course! :)