Completion in Emacs not working correctly

[patrick-nicodemus]

I have a project with a top-level module A and a submodule, B_submodule, so that I can access things in the submodule as A.B_submodule.foo.

If I run dune utop from the terminal and type A., a list of completions appears at the bottom, including B_submodule, and I can select this.

However, in Emacs this feature appears not to work. If I run opam exec -- dune utop . -- -emacs and do A.B_s and try to use the completion feature, it says "No match." If I just type A and use the completion feature, the completion feature suggests the name-mangled submodule A__B_submodule, but I'd like to be able to use the dot operator appropriately.