No prompt in SQL modes?

[Eric Abrahamsen <eric@ericabrahamsen.net>]

I'm using GNU Emacs 26.0.50 on Arch linux.

None of the sql interactive modes are showing me the prompt in the
process buffer, which messes up things like `sql-list-all'.

I run `sql-sqlite', choose the database, and the process buffer opens.
It's totally empty, no "sqlite> " prompt. I can enter commands into the
buffer and get correct output, but the prompt never appears. Commands
like `sql-list-all' don't work, because comint does a sanity check to
make sure there's a prompt available.

`comint-use-prompt-regexp' is t, and `comint-prompt-regexp' is correctly
set to "^sqlite> ". I tried following through the code, but don't see
where the prompt would (or wouldn't) be inserted on server response.

Prompts work fine in other interactive process buffers like Python and
Ocaml. I don't think I have any other relevant customizations...

Any hints?

Thanks,
Eric