Yes, my change does break the indentation test case.
So changing the class doesn't seem like a good option.

After giving some thought to this, I think we can instead
make the regex more strict so that it matches only the
allowed characters in perl's prototypes. The allowed chars
are: $%&*;@[\]

This is what I have in mind - diff is pasted below.
However, please note the change below doesn't handle
these 3 chars [ / ]  I'll add them if you think this is the correct
approach:

diff --git a/lisp/progmodes/perl-mode.el b/lisp/progmodes/perl-mode.el
index a516f07..840aa4e 100644
--- a/lisp/progmodes/perl-mode.el
+++ b/lisp/progmodes/perl-mode.el
@@ -257,7 +257,7 @@
        (1 (prog1 "\"" (perl-syntax-propertize-special-constructs end))))
       ;; Funny things in `sub' arg-specs like `sub myfun ($)' or `sub ($)'.
       ;; Be careful not to match "sub { (...) ... }".
-      ("\\<sub\\(?:[\s\t\n]+\\(?:\\sw\\|\\s_\\)+\\)?[\s\t\n]*(\\([^)]+\\))"
+      ("\\<sub\\(?:[\s\t\n]+\\(?:\\sw\\|\\s_\\)+\\)?[\s\t\n]*(\\([$%&*;@]+\\))"
        (1 "."))
       ;; Turn __DATA__ trailer into a comment.
       ("^\\(_\\)_\\(?:DATA\\|END\\)__[ \t]*\\(?:\\(\n\\)#.-\\*-.*perl.*-\\*-\\|\n.*\\)"

On Thu, Mar 16, 2017 at 2:49 AM, <npostavs@users.sourceforge.net> wrote:
[Please use Reply All to keep 26037@debbugs.gnu.org on CC]



---------- Forwarded message ----------
From: Evgeni Kolev <evgeni.d.kolev@gmail.com>
To: npostavs@users.sourceforge.net
Cc: 
Bcc: 
Date: Wed, 15 Mar 2017 12:00:32 +0200
Subject: Re: bug#26037: 25.1; perl-mode add syntax support for subroutine signatures
OK, I see.

After a bit of testing with C-u C-x =, I see that with my proposed
change the sigils in 'sub test ($)' will *not* have punctuation class
as they did before the chagne.

I see these options:

1. I can try to improve the proposed change to preserve backward
compatibility - I can try to add another rule which will strictly
match only the allowed prototype-sigils $%&*;@[\]

2. discard my proposed change as it might have undesired side effects -
at this point, I don't see anything in perl-mode which depends on
these prototype-sigils having punctioation class, however, I could be
missing something.

3. accept my proposed change as-is, but we must be sure nothing will
be broken as a result.  I'm sure syntax highlighting will not be
broken (I've tested with different themes, different perl sub
definitions).

Please let me know what you think.



I ran git blame against the relevant lines, and turned up Bug#18502.
Please check if your change breaks the indentation test case at
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=18502#5.