How to stop ESS overriding AUCTeX's TeX-newline in LaTeX parts of .Rnw?

Question

I'm new to Emacs, and am trying to learn it for knitting LaTeX and R (using AUCTeX and ESS). In my ~/.emacs I have:

(setq-default TeX-newline-function 'reindent-then-newline-and-indent)

which means that when I press RET AUCTeX applies the proper LaTeX indentation automatically for me. However, in an .Rnw file it seems that ESS overrides the TeX-newline. In an .Rnw file C-h m returns:

RET     TeX-newline
(that binding is currently shadowed by another mode)

and C-h k RET returns:

RET (translated from <return>) runs the command ess-noweb-newline,
which is an interactive compiled Lisp function in `ess-noweb-mode.el'.

It is bound to RET.

(ess-noweb-newline &optional ARG)

A kludge to get round very odd behaviour of newline in quoted code.

Basically I only want ESS to override RET when the point is inside an R chunk (<<>> @) or the brackets of an \Sexpr{} expression. Seems to me that this should be the default behaviour, but is there any way to force it?

Answer 1

I worked this one out, you need to use polymode. After installing polymode (I added the MELPA repository for that), you then set up whatever polymode bits you need in your ~/.emacs file. This is what I had to put for .Rnw support:

; enable polymode stuff
(require 'poly-R)
(require 'poly-markdown)
(require 'poly-noweb)
; add .Rnw filetype
(add-to-list 'auto-mode-alist '("\\.Rnw" . poly-noweb+r-mode))

With that you get everything working as it should be for LaTeX and R sections of the code. In .Rnw files RET works correctly, and syntax highlighting is more accurate too.