cperl-mode.el: Support Perl 5.38 syntax for subroutine signatures

* lisp/progmodes/cperl-mode.el (defconst): New rx sequence
describing a signature with initialization.
(cperl-init-faces): integrate the new rx sequence into the
font-lock-defaults init routine (Bug#64190) (Bug#64364).

* test/lisp/progmodes/cperl-mode-resources/cperl-bug-64364.pl: Add
test data for a signature with initialization (tests indentation).

* test/lisp/progmodes/cperl-mode-resources/proto-and-attrs.pl: Add
test data for a signature with initialization (tests fontification).

2 files changed, 38 insertions, 1 deletions

diff --git a/test/lisp/progmodes/cperl-mode-resources/cperl-bug-64364.pl b/test/lisp/progmodes/cperl-mode-resources/cperl-bug-64364.pl
index af188cbedac..62ef6982f38 100644
--- a/test/lisp/progmodes/cperl-mode-resources/cperl-bug-64364.pl
+++ b/test/lisp/progmodes/cperl-mode-resources/cperl-bug-64364.pl
@@ -24,3 +24,32 @@ package P {
     }
 }
 # -------- Bug#64364: end -------
+
+# Now do this with multiline initializers
+# -------- signature with init: input -------
+package P {
+sub way { ...; }
+# perl 5.38 or newer
+sub bus
+:lvalue
+($sig,
+$na //= 42,
+@ture)
+{
+...;
+}
+}
+# -------- signature with init: expected output -------
+package P {
+    sub way { ...; }
+    # perl 5.38 or newer
+    sub bus
+        :lvalue
+        ($sig,
+         $na //= 42,
+         @ture)
+    {
+        ...;
+    }
+}
+# -------- signature with init: end -------
diff --git a/test/lisp/progmodes/cperl-mode-resources/proto-and-attrs.pl b/test/lisp/progmodes/cperl-mode-resources/proto-and-attrs.pl
index 6ed5c0dfc41..1f898250252 100644
--- a/test/lisp/progmodes/cperl-mode-resources/proto-and-attrs.pl
+++ b/test/lisp/progmodes/cperl-mode-resources/proto-and-attrs.pl
@@ -34,9 +34,17 @@ sub sub_4 :prototype($$$) ($foo,$bar,$baz) { ...; }
 # A signature with a trailing comma (weird, but legal)
 sub sub_5 ($foo,$bar,) { ...; }
 
+# Perl 5.38-style initializer
+sub sub_6
+    ($foo,
+     $bar //= "baz")
+{
+}
+
+
 # Part 2: Same constructs for anonymous subs
 # A plain named subroutine without any optional stuff
-my $subref_0 = sub { ...; }
+my $subref_0 = sub { ...; };
 
 # A prototype and a trivial subroutine attribute
 {