merlin is missing unused (type|open|value|constructor|field) warnings

e.g.:

open Printf

module type X = sig end

let x =
  let y = 42 in
  ()

let _f x = ()

type x = {
  foo: int }
type y =
  | Foo

let () = for i = 0 to 0 do () done

with an empty test.mli and the following dune:

(executable (name test))

There are a bunch of different unused warnings (I didn't manage to get an unused module warning out of the compiler):

% dune clean && dune build test.exe
File "test.ml", line 1, characters 0-11:
1 | open Printf
    ^^^^^^^^^^^
Error (warning 33 [unused-open]): unused open Stdlib.Printf.
File "test.ml", line 5, characters 4-5:
5 | let x =
        ^
Error (warning 32 [unused-value-declaration]): unused value x.
File "test.ml", line 6, characters 6-7:
6 |   let y = 42 in
          ^
Error (warning 26 [unused-var]): unused variable y.
File "test.ml", line 9, characters 7-8:
9 | let _f x = ()
           ^
Error (warning 27 [unused-var-strict]): unused variable x.
File "test.ml", lines 11-12, characters 0-12:
11 | type x = {
12 |   foo: int }
Error (warning 34 [unused-type-declaration]): unused type x.
File "test.ml", line 12, characters 2-10:
12 |   foo: int }
       ^^^^^^^^
Error (warning 69 [unused-field]): unused record field foo.
File "test.ml", lines 13-14, characters 0-7:
13 | type y =
14 |   | Foo
Error (warning 34 [unused-type-declaration]): unused type y.
File "test.ml", line 14, characters 2-7:
14 |   | Foo
       ^^^^^
Error (warning 37 [unused-constructor]): unused constructor Foo.
File "test.ml", line 16, characters 9-34:
16 | let () = for i = 0 to 0 do () done
              ^^^^^^^^^^^^^^^^^^^^^^^^^
Error (warning 35 [unused-for-index]): unused for-loop index i.

But merlin only reports warning 26:

% ocamlmerlin single errors < test.ml |jq
{
  "class": "return",
  "value": [
    {
      "start": {
        "line": 6,
        "col": 6
      },
      "end": {
        "line": 6,
        "col": 7
      },
      "type": "warning",
      "sub": [],
      "valid": true,
      "message": "Warning 26: unused variable y."
    }
  ],
  "notifications": [],
  "timing": {
    "clock": 2,
    "cpu": 2,
    "query": 0,
    "pp": 0,
    "reader": 0,
    "ppx": 0,
    "typer": 2,
    "error": 0
  }
}

This is with merlin 4.8-500.

ocaml / merlin

merlin is missing unused (type|open|value|constructor|field) warnings #1593