emacs24: cperl-mode and which-function-mode oddity

[Frank Terbeck <ft@bewatermyfriend.org>]

Hey there.

I'm encountering odd behaviour when using `which-function-mode' with
`cperl-mode' in emacs version 24. It's a fairly recent development
build:

% emacs --version
GNU Emacs 24.0.50.1
[...]


Consider these two files:

foo.el:

[snip]
(mapc
  (lambda (pair)
    (if (eq (cdr pair) 'perl-mode)
      (setcdr pair 'cperl-mode)))
  (append auto-mode-alist interpreter-mode-alist))

(which-function-mode t)
[snap]

And foo.pl:

[snip]
$foo = qq{I'm just another Perl Hacker.};
[snap]

Now, I'd start emacs like this:

% emacs -nw -Q

...and then:

M-x load-file RET foo.el RET
C-x C-f foo.pl RET

Now font locking is screwed up. The "qq" is highlighted as
`cperl-nonoverridable-face', which is correct. But "{I" shows up in
`default'. Which is wrong. Now, the ' looks like the start of a string
and it's highlighted as `font-lock-string-face'. But because the "q{"
isn't the start of the string but the single quote, the closing "}"
doesn't end the string and so the ";" (and in fact, any following lines
would be too, until another single quote would be encountered) is
highlighted in `font-lock-string-face', as well.

When I'm removing the "(which-function-mode t)" line from "foo.el", the
problem goes away.

I've been browsing emacs' BTS for a while, but AFAICS this wasn't
reported yet. My question is if anybody is seeing this, too. And by
extension, whether `which-function-mode' is supposed to work with
`cperl-mode', in which case I'd "M-x report-emacs-bug" it.

Regards, Frank

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