bug#30549: 25.2; perl-mode: font lock improvement

[Evgeni Kolev <evgeni.d.kolev@gmail.com>]

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I'm reporting an issue with perl-mode's font lock for perl keywords, and
suggesting a fix.

To reproduce:

- emacs -Q
- clear the scratch buffer
- M-x perl-mode
- enter the following text:

    use Fake;
    my $use = 123;
    my $var = 123;

- observe the issue: `$use` is incorrectly highlighted - it should be
highlighted with the same color as `$var`, but it's highlighted with the
same color as `use` (on the first line).

The fix I suggest is borrowed from cperl-mode - extend the font lock regex
to *not* match keywords if they start with a perl sigil.

The diff is below, please let me know if it can be improved. I've signed
the copyright assignment.

From 8d1977cfc6c4884b231270c33c3bdabbd16b14aa Mon Sep 17 00:00:00 2001
From: Evgeni Kolev <evgenysw@gmail.com>
Date: Tue, 20 Feb 2018 18:14:29 +0200
Subject: [PATCH] lisp/progmodes/perl-mode.el: keyword regex must not match
 sigils

---
 lisp/progmodes/perl-mode.el | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lisp/progmodes/perl-mode.el b/lisp/progmodes/perl-mode.el
index 9948078..c1d94ac 100644
--- a/lisp/progmodes/perl-mode.el
+++ b/lisp/progmodes/perl-mode.el
@@ -165,7 +165,7 @@ perl-font-lock-keywords-1
     ;; Fontify function and package names in declarations.
     ("\\<\\(package\\|sub\\)\\>[ \t]*\\(\\sw+\\)?"
      (1 font-lock-keyword-face) (2 font-lock-function-name-face nil t))
-    ("\\<\\(import\\|no\\|require\\|use\\)\\>[ \t]*\\(\\sw+\\)?"
+    ("\\(^\\|[^$@%&\\]\\)\\<\\(import\\|no\\|require\\|use\\)\\>[
\t]*\\(\\sw+\\)?"
      (1 font-lock-keyword-face) (2 font-lock-constant-face nil t)))
   "Subdued level highlighting for Perl mode.")

--
2.9.0

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