perl-mode font-lock flaky around $' &c.

[Edward Welbourne]

Put the following (complete with its tabs) into a buffer in perl-mode,
with font-lock mode active.  (tab-width 4 is recommended, but incidental).

                        for ( $arg ) {
                                /^-([bcdghLpuv]+)$/ && do { $short = $1; last; 
};
                                /^--usage/              && do { 
$self->report(0, &usage()); return 0; };
                                /^--help/               && do { 
$self->report(0, &help()); return 0; };
                                /^--config=/    && do { $config = $'; last; };
                                /^--config$/    && do { $short = 'c'; last; };
                                /^--unstripped$/&& do { $self->{debug} = 1; 
last; };
                                /^--version=/   && do { $self->{version} = $'; 
last; };
                                /^--version$/   && do { $short = 'v'; last; };
                                /^--build=/             && do { $self->{build} 
= $'; last; };
                                /^--build$/             && do { $short = 'b'; 
last; };
                                /^--manifest=/  && do { $self->{manifest} = $'; 
last; };
                                /^--manifest$/  && do { $short = 'm'; last; };
                                /^--date=/              && do { $self->{date} = 
$'; last; };
                                /^--date/               && do { $short = 'd'; 
last; };
                        /^--lang(uage)?s?=/     && do { push @{$self->{langs}}, 
split(/,/, $'); last; };
                        /^--lang(uage)?s?$/     && do { $short = 'L'; last; };
                                /^--all-clean/  && do { $self->{cleanly} = 1; 
last; };
                                /^--no-clean/   && do { $self->{cleanly} = -1; 
last; };
                                /^--ok-clean/   && do { $self->{cleanly} = 0; 
last; };
                                /^--debug=/             && do { $self->{dbglvl} 
= $'; last; };
                                /^--debug$/             && do { $short = 'g'; 
last; };
                                /^--verbose=/   && do { $self->{verbose} = $'; 
last; };
                                /^--verbose$/   && do { $short = 'p'; last; };
                                /^-/ && do { die &usage("Unrecognized 
command-line flag: $arg"); };

                                if (!defined($config)) { $config = $arg; }
                                elsif (!defined($self->{version})) { 
$self->{version} = $arg; }
                                elsif (!defined($self->{build})) { 
$self->{build} = $arg; }
                                elsif (!defined($self->{date})) { $self->{date} 
= $arg; }
                                else { die &usage("Stray or unrecognized cruft 
at end of command-line: $arg"); }
                        }


Notice, first, that $' confuses the syntax highlighting.
Next, delete some of the tab characters used for spacing.
Notice that syntax colouring changes.

I used to be able to quite sensibly deal with $' (and other $X where X
would, without a preceding $, complicate font-lock or
sexp-recognition) by putting an end-of-line comment like #')}
which would suffice to un-confuse everything.
This no longer seems to work :-(

My attempts at it prove highly volatile; seemingly innocuous changes
elsewhere in the file (e.g. hspace changes, as above) can change how
everything is displayed.  I can make no sense of it.


In GNU Emacs 22.1.1 (i486-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2007-07-07 on raven, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.10300000
configured using `configure  '--build=i486-linux-gnu' '--host=i486-linux-gnu' 
'--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' 
'--localstatedir=/var/lib' '--infodir=/usr/share/info' 
'--mandir=/usr/share/man' '--with-pop=yes' 
'--enable-locallisppath=/etc/emacs22:/etc/emacs:/usr/local/share/emacs/22.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/22.1/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/22.1/leim'
 '--with-x=yes' '--with-x-toolkit=athena' '--with-toolkit-scroll-bars' 
'build_alias=i486-linux-gnu' 'host_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -g 
-O2''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_GB.ISO-8859-15
  locale-coding-system: iso-8859-15
  default-enable-multibyte-characters: t

Major mode: Perl

Minor modes in effect:
  tooltip-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  unify-8859-on-encoding-mode: t
  utf-translate-cjk-mode: t
  auto-compression-mode: t
  line-number-mode: t

Recent input:
C-x C-s C-p C-d C-d C-d C-n C-d C-d C-d C-n C-d C-d 
C-d C-n C-d C-d C-d C-n C-d C-d C-d C-n C-d C-d C-d 
C-n C-d C-d C-d C-n C-d C-d C-d C-n C-d C-d C-d C-n 
C-d C-d C-d C-n C-d C-d C-d C-n C-d C-d C-d C-n C-d 
C-d C-d C-n C-d C-d C-d C-n C-d C-d C-d C-n C-d C-d 
C-d C-n C-d C-d C-d C-n C-d C-d C-d C-n C-d C-d C-d 
C-n C-d C-d C-d C-n C-d C-d C-d C-n C-p C-d C-/ C-n 
C-d C-d C-d C-n C-d C-d C-d C-n C-d C-d C-d C-n C-d 
C-d C-d C-n C-n C-d C-d C-d C-n C-d C-d C-d C-n C-d 
C-d C-d C-n C-d C-d C-d C-n C-d C-d C-d C-n C-d C-d 
C-d C-n C-M-b C-n C-n C-f C-f C-f C-f C-f C-f C-d C-n 
C-d C-n C-n C-n C-n C-n C-n C-d C-n C-d C-n C-n C-n 
C-d C-n C-d C-n C-n C-n C-n C-n C-n C-d C-n C-d C-/ 
C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ 
C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ 
C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ 
C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ 
C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ 
C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ 
C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ 
C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-/ C-n C-l 
C-d C-/ C-p C-d C-/ C-x o C-x C-s M-x e m a <tab> b 
u <tab> <M-backspace> <M-backspace> r e p o <tab> r 
<tab> <return>

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