From 492ebabafba699f4c29cfd76c551ec1f342f08e9 Mon Sep 17 00:00:00 2001
From: Father Chrysostomos <sprout@cpan.org>
Date: Thu, 5 Jan 2012 16:47:54 -0800
Subject: [PATCH] [perl #91850] utf8::decode: croak for ro scalars

---
 lib/utf8.t  | 11 +++++++++++
 universal.c |  2 +-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/lib/utf8.t b/lib/utf8.t
index b13bb5377d65..e56eebf626df 100644
--- a/lib/utf8.t
+++ b/lib/utf8.t
@@ -438,6 +438,17 @@ SKIP: {
     is join('', keys $h), $k2, 'utf8::decode respects copy-on-write';
 }
 
+{
+    # Make sure utf8::decode does not modify read-only scalars
+    # [perl #91850].
+    
+    my $name = "\x{c3}\x{b3}";
+    Internals::SvREADONLY($name, 1);
+    eval { utf8::decode($name) };
+    like $@, qr/^Modification of a read-only/,
+	'utf8::decode respects readonliness';
+}
+
 {
     my $a = "456\xb6";
     utf8::upgrade($a);
diff --git a/universal.c b/universal.c
index 9d743abaaa1e..dd8ae74372f4 100644
--- a/universal.c
+++ b/universal.c
@@ -812,7 +812,7 @@ XS(XS_utf8_decode)
     else {
 	SV * const sv = ST(0);
 	bool RETVAL;
-	if (SvIsCOW(sv)) sv_force_normal(sv);
+	if (SvREADONLY(sv)) sv_force_normal(sv);
 	RETVAL = sv_utf8_decode(sv);
 	ST(0) = boolSV(RETVAL);
     }