None exist. So far the best solution is to use Emacs with [2]

* merlin-mode, for autocompletion

* ocp-indent, for external code formating... think running gofmt on every enter press (surprisingly, it's fast enough unless your file is 2k lines long)

* tuareg-mode (everything else, REPL etc.)

* flycheck-ocaml for syntax checking

The "real" IDE plugins aren't even close and that's saying a lot since the hodge-podge of addons I just listed isn't

The default Emacs user experience is awful so if you're a Vim user, just install the "evil" package and enable it inside Emacs by doing M-x evil-mode, then you have Vim inside Emacs. Or use Vim, but the experience isn't as complete w.r.t. tooling[3]. There's always Spacemacs as well[1].

[1] https://github.com/syl20bnr/spacemacs

[2] https://github.com/the-lambda-church/merlin/wiki/emacs-from-...

[3] https://github.com/the-lambda-church/merlin/wiki/vim-from-sc...