[Bug-AUCTeX] Cite lookup failure in presence of escaped %

[sword]

Hi Auctex maints and devs,

Great package, thanks for making life with LaTeX easy.

I've encountered a problem with RefTeX's cite lookup. I've got a
document where I use a lot of percents (escaped) and that happens to
be causing cite lookup to fail.

To reproduce, in emacs-snapshot of October, reftex 4.31, with -Q, with
my long LaTeX document which works otherwise, after turning on reftex,
etc:

Blah \% in mumble.\cite{abcd:efg}

When point is placed in the cite and C-c & (reftex-view-crossref) I
get "Not on a crossref macro argument". I can make it look it up by
deleting the \% however, so it's not a problem with the biblio, etc.

I believe this is related to a simplistic lookup in reftex-in-comment
(reftex.el) where it only scans backwards for a % and ignores
that it can be escaped. AIUI, \% is a legal escape - LaTeX is
accepting it, so I think it's okay to have it in my document. I
can make it kinda work by redefining in my .emacs with the
following code based on the current defun:

; Ensure that the comment char isn't escaped.
; We are in a comment if % is there and the character before it is not \
(defun reftex-in-comment ()
  (save-excursion
    (skip-chars-backward "^%\n\r")
    (and (eq (char-before) ?%) 
         (not (eq ?\ (char-before (- (point) 2))))))) 

However, this simple version should fail in the presence of mixed \%
and %, like this:

Blah \% foo % in mumble \%.\cite{abcd:efg}

since it will only go back to the last \% and thinks it's still a live
cite but the cite is still commented overall.

It would be best to start at the beginning of the current line and
look forwards for a % not preceeded by a \:

(defun reftex-in-comment ()
  (save-excursion
    (beginning-of-line)
    (re-search-forward 
     (rx (not (any "\\")) "%")
     ; If you prefer, "\\(?:[^\\]%\\)" is what the rx evals to
     (line-end-position)
     t)))

and this appears to work in the above mixed case.