Thinking about this some more, C-h v keeps telling me that the bad value for ess-etc-directory is coming from ess-site.el even though the string 'ess-etc-directory' does not appear in ess-site.el. So I got suspicious.
$ find / -name 'ess-site.el*' -ls 2> /dev/null 33614087 4 -rw-r--r-- 1 root root 3821 Aug 22 12:49 /usr/share/emacs/site-lisp/ess/ess-site.elc 16804888 12 -rw-r--r-- 1 root root 8345 Aug 24 07:57 /usr/share/emacs/site-lisp/elpa-src/ess-17.11/ess-site.el 33736809 0 lrwxrwxrwx 1 root root 58 Aug 28 11:47 /usr/share/emacs/site-lisp/elpa/ess-17.11/ess-site.el -> /usr/share/emacs/site-lisp/elpa-src/ess-17.11//ess-site.el 33746754 4 -rw-r--r-- 1 root root 3646 Aug 28 11:47 /usr/share/emacs/site-lisp/elpa/ess-17.11/ess-site.elc 17260428 4 -rw-r--r-- 1 root root 3821 Aug 17 16:12 /usr/share/emacs/25.2/site-lisp/ess/ess-site.elc After 'dpkg --purge elpa-ess', the oldest two of those are still present: 33614087 4 -rw-r--r-- 1 root root 3821 Aug 22 12:49 /usr/share/emacs/site-lisp/ess/ess-site.elc 17260428 4 -rw-r--r-- 1 root root 3821 Aug 17 16:12 /usr/share/emacs/25.2/site-lisp/ess/ess-site.elc These files are identical, and they contain a setting for ess-etc-directory: $ grep -a etc /usr/share/emacs/site-lisp/ess/ess-site.elc #@130 Location of the ESS etc/ directory. The ESS etc directory stores various auxillary files that are useful (defvar ess-etc-directory "/usr/share/ess/etc/" (#$ . 695)) (A copy of the whole file is attached.) In fact, both /usr/share/emacs/25.2/site-lisp/ess and /usr/share/emacs/site-lisp/ess appear to be detritus from older versions of the ESS packages, containing a full set of .elc files for the ESS code. After deleting both directories and their contents and re-installing the elpa-ess package (but not the transitional 'ess' package), M-x R no longer throws errors, and C-c v works correctly in buffers containing R code. So, if there is a bug here, it involves upgrading from the pre-ELPA versions of the ESS packages, to the ELPA-ified versions. zw
ess-site.elc.gz
Description: application/gzip
