[BUG] object%js with references to self can trigger false unused variable warnings

[johnridesabike]

Describe the bug

If using references to "self"/"this" with object%js, and any methods do not use that variable, it triggers an unused variable warning. Minimal example:

let () =
  Js_of_ocaml.Js.export_all
    object%js (self)
      method foo = self
      method bar = ()
    end

3 |     object%js (self)
                  ^^^^^^
Error (warning 27 [unused-var-strict]): unused variable self.

Expected behavior
The above example should not trigger the warning.

Looking at the PPX output, it seems that self gets added as an argument to each method function, so the presence of bar is what triggers the warning in this case. Adding more methods triggers the warning more times.

Versions
Version of packages used to reproduce the bug

$ opam list --search js_of_ocaml --installed
# Packages matching: match(*js_of_ocaml*) & installed
# Name               # Installed # Synopsis
brr                  0.0.8       Browser programming toolkit for OCaml
js_of_ocaml          6.2.0       Compiler from OCaml bytecode to JavaScript
js_of_ocaml-compiler 6.2.0       Compiler from OCaml bytecode to JavaScript
js_of_ocaml-ppx      6.2.0       Compiler from OCaml bytecode to JavaScript
js_of_ocaml-toplevel 6.2.0       Compiler from OCaml bytecode to JavaScript
tyxml                4.6.0       A library for building correct HTML and SVG documents

[hhugo]

I had a look at the generated code. We emit one function per method with "self" as the first argument. A warning is emitted anytime a method doesn't use "self" (the first argument of the generated function). I think the best we can do is to disable the warning entirely for "self" by prefixing the body by a dummy let _ = "self_id".

[johnridesabike]

My current workaround is prefixing it with an underscore (_self) to suppress the warning, so that solution would work just as well for me.