ocamlformat doesn't work on the following code (reduced example):

module M = struct
  let f x = x
end

let g=M.f ((let open M in f) [@ocaml.warning "-33"])

The error message is BUG: ast changed (although I got BUG: generating invalid ocaml syntax for the file where this originally occurred).

This is for ocamlformat 0.12 on OCaml 4.07.0 with the default configuration (the same thing also happened on my custom configuration).