In sv.c:sv_magic don’t allow tying ro COWs

Read-only COWs are read-only and should not be treated as though they
were not.  This logic is left over from when READONLY+FAKE meant
copy-on-write.

1 files changed, 7 insertions, 0 deletions

diff --git a/t/op/tie.t b/t/op/tie.t
index 7aff015276..eb53030e21 100644
--- a/t/op/tie.t
+++ b/t/op/tie.t
@@ -1030,6 +1030,13 @@ EXPECT
 ok
 Modification of a read-only value attempted at - line 16.
 ########
+#
+# And one should not be able to tie read-only COWs
+for(__PACKAGE__) { tie $_, "" }
+sub TIESCALAR {bless []}
+EXPECT
+Modification of a read-only value attempted at - line 3.
+########
 
 # Similarly, read-only regexps cannot be tied.
 sub TIESCALAR { bless [] }