Adapt to ppxlib 0.22.0

[copy]

It's currently constrained to < "0.18.0":

% opam show ppx_protocol_conv |grep ppxlib
              "ppxlib" {>= "0.9.0" & < "0.18.0"}

[andersfugmann]

This limit was added as part of ocaml/opam-repository#17360. I cannot access the logs referenced in the PR, so I do not know the rationale for this, other than rev-deps was complaining about this package.

You are welcome to create a PR against the opam-repository. The code compiles just fine against ppxlib 0.22.0 (although the tests implicitly requires ppxlib 0.21.0)

[copy]

Thanks. I went ahead and proposed to adjust the constraints on opam-repository: ocaml/opam-repository#18172