The (merlin) instruction is only needed in a jbuild-workspace file, not in a jbuild file. Are you not getting .merlin files auto-generated? They should be generated in the same directory as each of your jbuild files.
Whoops, you are both correct. Brain spasm on my end, I wasn’t using ls -a so didn’t see .merlin. I just set up a dead-simple project and indeed have full Merlin support. JBuilder looks great.
If I may squeeze in another question here: does JBuilder support inferring and printing out an interface for a given module, like ocamlbuild mymodule.inferred.mli? Nothing pops out from the documentation.