2nd try: [perl #91834] utf8::decode does not respect copy-on-write

I reverted the first version of this patch because I put the if()
statement before a declaration. I did a revert, rather than a correc-
tion, to make back-porting easier.

2 files changed, 15 insertions, 1 deletions

diff --git a/lib/utf8.t b/lib/utf8.t
index ae81ccdc46..6cd2d3fe30 100644
--- a/lib/utf8.t
+++ b/lib/utf8.t
@@ -427,6 +427,18 @@ SKIP: {
 }
 
 {
+    # Make sure utf8::decode respects copy-on-write [perl #91834].
+    # Hash keys are the easiest way to test this.
+    my $name = "\x{c3}\x{b3}";
+    my ($k1) = keys %{ { $name=>undef } };
+    my $k2 = $name;
+    utf8::decode($k1);
+    utf8::decode($k2);
+    my $h = { $k1 => 1, $k2 => 2 };
+    is join('', keys %$h), $k2, 'utf8::decode respects copy-on-write';
+}
+
+{
     my $a = "456\xb6";
     utf8::upgrade($a);
 
diff --git a/universal.c b/universal.c
index 07bbe96504..092ee80079 100644
--- a/universal.c
+++ b/universal.c
@@ -695,7 +695,9 @@ XS(XS_utf8_decode)
 	croak_xs_usage(cv, "sv");
     else {
 	SV * const sv = ST(0);
-	const bool RETVAL = sv_utf8_decode(sv);
+	bool RETVAL;
+	if (SvIsCOW(sv)) sv_force_normal(sv);
+	RETVAL = sv_utf8_decode(sv);
 	ST(0) = boolSV(RETVAL);
 	sv_2mortal(ST(0));
     }