ESS language modes with use-package

Question

I've recenly started to convert my init.el to using use-package, and have so far not found any problems with that -- except that I can't get ESS to work for all languages.

I have installed the package ess from Melpa. If I don't mention this at all in the init file, normal ".r" files get opened with ess-mode (showing as up as ESS[S]) as major mode, so there seems to be some automatic configuration going on. ".Rnw" files, on the other hand, don't get opened in ESS. Additionally, I want to use julia-mode in ESS (which is supposed to work automatically; the julia-mode package is also installed). So I added the following:

(use-package ess
  :mode (("\\.[rR]\\'" . R-mode)
         ("\\.[rR]nw\\'" . Rnw-mode)
         ("\\.jl\\'" . julia-mode)))

However, this does not help anything. When opening a ".jl" file, there is no julia function available, as there should; and there's always a warning

File mode specification error: (error Autoloading failed to define function Rnw-mode)

So, how am I supposed to set that up? I see that in most documentations, ESS mode is compiled by hand and loaded by (require 'ess-site) -- does that make the difference?

I'm using Emacs 25.1.

Answer 1

The file associations should all be set up for you. It works for me on Emacs 25.1 with just the following in my init:

(use-package ess
  :init (require 'ess-site))

This will set the associations for R-mode, julia-mode and Rnw-mode. If that doesn't work for you, the most likely explanation is that something else in your configuration is causing the problem (ie., by changing the assocations with R-mode etc).