Don't attempt UTF-8 cache assertion for SVs with invalid SvPVX() (eg overloaded)

Fixes RT 69422.

However, I'm not actually sure whether we should even be caching the results of
UTF-8 operations on overloading, given that nothing stops overloading returning
a different value every time it's called.

1 files changed, 22 insertions, 1 deletions

diff --git a/t/uni/overload.t b/t/uni/overload.t
index e4f4e132ea..d44d1711cf 100644
--- a/t/uni/overload.t
+++ b/t/uni/overload.t
@@ -7,7 +7,7 @@ BEGIN {
     }
 }
 
-use Test::More tests => 208;
+use Test::More tests => 215;
 
 package UTF8Toggle;
 use strict;
@@ -264,6 +264,27 @@ foreach my $value ("\243", UTF8Toggle->new("\243")) {
     is (pack ("A/A", $value), pack ("A/A", "\243"));
 }
 
+foreach my $value ("\243", UTF8Toggle->new("\243")) {
+    my $v;
+    $v = substr $value, 0, 1;
+    is ($v, "\243");
+    $v = substr $value, 0, 1;
+    is ($v, "\243");
+    $v = substr $value, 0, 1;
+    is ($v, "\243");
+}
+
+{
+    package RT69422;
+    use overload '""' => sub { $_[0]->{data} }
+}
+
+{
+    my $text = bless { data => "\x{3075}" }, 'RT69422';
+    my $p = substr $text, 0, 1;
+    is ($p, "\x{3075}");
+}
+
 END {
     1 while -f $tmpfile and unlink $tmpfile || die "unlink '$tmpfile': $!";
 }