Incomplete error messages

[xvw]

cc @gasche

Consider this minimal OCaml program, that defines a functor with two arguments, but then applies it with only the second argument, resulting in a functor-application type error.

module F(K : Map.OrderedType) (V : sig type value end) = struct
  module S = Map.Make(K)
  type t = V.value S.t
end

module Val = struct type value = string end
module IValMap = F(Val)

displays in error buffer:

ocamllsp: This application of the functor F is ill-typed.
These arguments:
  Val
do not match these parameters:
  (K : Map.OrderedType) (V : ...) -> ...

[xvw]

The way additional messages (1, 2) are added uses the sub field, which, on the LSP side, is transformed into DiagnosticRelatedInformation. So the server does return the two sub-messages, but it seems that Eglot does not support them :/