I think we’re close now. The attached patch should be ready to
install or at least review.

Use of advice has been removed, byte-compiler and checkdoc
warnings are fixed and tests have been added. For the tests I just
copied the lua-ts-mode files and adjusted for the current state of
lua-mode.

Once landed I’ll follow up with some improvements and work out how
to share code between the Lua modes (following the Ruby model
unless there is some other preference).