Check arity of %compare primitive

[nojb]

See MPR#7846.

[hhugo]

The problem exists with other primitives as well.

external a : ('a -> 'b) -> 'a = "%apply"
let () = a (fun x -> x)

[nojb]

Yes, this is known (see e.g https://caml.inria.fr/mantis/view.php?id=7408). Checking the arity of comparison primitives is easy but the general case is more work, and am not sure it is worth it given that it is an undocumented feature not meant for general use.

[hhugo]

I gave it a quick shot in #2015

[nojb]

Subsumed by #2015.