Automatic instrumentation via landmarks-ppx and inherited constructors without module name

[maroneze]

This is a simplified example of an issue that happened with Frama-C's visitors:

(* a.ml *)
type visitAction = Go | Skip
class visitor = object
  method visit () = Go
end

(* b.ml *)
class skip_visitor = object
  inherit A.visitor
  method! visit () = Skip (* Could be A.Skip, but due to inheritance, the module name is unnecessary *)
end

OCAML_LANDMARKS=auto ocamlfind ocamlopt -package landmarks -package landmarks-ppx a.ml b.ml

This fails with:

File "b.ml", line 4, characters 21-25:
4 |   method! visit () = Skip
                         ^^^^
Error: Unbound constructor Skip

Without Landmarks instrumentation, the above compiles, since the Skip constructor is found in module A.

If I explicitly write A.Skip in b.ml, it works fine.

If this is hard to fix, I believe a small addition to the Known issues section with the workaround should suffice to help people find it. Classes and inheritance are rarely used anyway in OCaml.