fix utf8 length magic handling for scalar reverse

fixes #17737

1 files changed, 10 insertions, 1 deletions

diff --git a/t/op/reverse.t b/t/op/reverse.t
index 16c732bc3f..babf3cf3ac 100644
--- a/t/op/reverse.t
+++ b/t/op/reverse.t
@@ -6,7 +6,7 @@ BEGIN {
     set_up_inc('../lib');
 }
 
-plan tests => 24;
+plan tests => 25;
 
 is(reverse("abc"), "cba", 'simple reverse');
 
@@ -92,6 +92,15 @@ use Tie::Array;
     is($a, $c, 'Unicode string double reversal matches original');
 }
 
+{
+    # https://github.com/Perl/perl5/issues/17737
+    # utf8 length magic handling
+    # threw an assertion failure with -DDEBUGGING
+    my @x;
+    push @x, length reverse for split "-", "\x{100}--0";
+    is($x[1], 0, "check set magic being called to clear length magic");
+}
+
 # [perl #132544] stack pointer used to go wild when nullary reverse
 # required extending the stack
 for(0..1000){()=(0..$_,scalar reverse )}