Test reference to unavailable lexical variable

This is related to #123172.

v5.21.3-644-ge52eb89 inadvertently fixed this old bug, which was prob-
ably introduced by the jumbo closure patch:

$ perl5.8.9 -le 'sub { my $f; BEGIN { $ref = \$f; $f = 7; $$ref = 8; print $f } }'
8
$ perl5.10 -le 'sub { my $f; BEGIN { $ref = \$f; $f = 7; $$ref = 8; print $f } }'
7
$ perl5.20.1 -le 'sub { my $f; BEGIN { $ref = \$f; $f = 7; $$ref = 8; print $f } }'
7
$ perl5.21.5 -le 'sub { my $f; BEGIN { $ref = \$f; $f = 7; $$ref = 8; print $f } }'
8

\ was returning a *copy* of its referent if the latter closed over an
anonymous sub’s stale variable.

1 files changed, 10 insertions, 0 deletions

diff --git a/t/op/closure.t b/t/op/closure.t
index 569724f62d..9a4e50dc2a 100644
--- a/t/op/closure.t
+++ b/t/op/closure.t
@@ -815,4 +815,14 @@ SKIP: {
         'closures in source filters do not interfere with pad names';
 }
 
+sub {
+    my $f;
+    sub test_ref_to_unavailable {
+	my $ref = \$f;
+        $$ref = 7;
+        is $f, 7, 'taking a ref to unavailable var should not copy it';
+    }
+};
+test_ref_to_unavailable();
+
 done_testing();