Thanks!
Btw. I always thought it would be nice to upstream that to compilation mode itself. I routinely use the format outside OCaml to dump AST representations (see e.g. cmarkit locs or jsont locs if you have cmarkit or jsont installed) instead of the GNU error format whose default regexp does not match when the location print out is indented.
But for that I would likely be good that upstream acts on this issue to have a proper reference to mention.