bug#15867: 24.3.50; cperl-mode: Fix default value of cperl-invalid-face

[Jambunathan K]

Fix cperl-invalid-face.  It is quite distracting.

Leo, Nathan, RJoe on Emacswiki and myself all seem to say this is a bad
default.  That means 4 upvotes that this is not good default.

ps: Since editing with cperl-mode may introduce leading whitespaces on
empty lines, it might actually be better to introduce a
'cperl-cleanup-trailing-whitespace' (or some such variable) to
compensate for cperl's smartness.


----------------------------------------------------------------

>From a private thread.
=====================

Leo Liu <sdl.web@gmail.com> writes:

> On 2013-11-11 20:03 +0800, Nathan Trapuzzano wrote:
>> (defalias 'perl-mode 'cperl-mode)
>> (setq cperl-continued-brace-offset -4
>>       cperl-invalid-face 'default
>> )

From: RJH on http://www.emacswiki.org/emacs/CPerlMode
====================================================

First of all, there’s a very peculiar feature which many people want to
disable: trailing whitespace is indicated with an underline (see
discussion below). Consider that whitespace is rarely significant in
perl code, but that underlines often are (e.g. “$_”) and with this
feature an underscore appears every time you hit the space bar, and will
not disappear until you enter another character. Adding this line to
your .emacs works to disable this feature in GnuEmacs 21:

    (setq cperl-invalid-face (quote off)) 

However, in at least GNU Emacs 21.2.1, this has been known to cause
problems with font-locking, in which case:

    (setq cperl-invalid-face nil) 


In GNU Emacs 24.3.50.4 (i686-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2013-11-09 on debian-6.05
Bzr revision: 115051 jan.h.d@swipnet.se-20131109111953-cysfi19meuidy96q
Windowing system distributor `The X.Org Foundation', version 11.0.10707000
System Description:     Debian GNU/Linux 6.0.5 (squeeze)