#!/usr/bin/env perl
use v5.38;
use Scalar::Util qw(weaken);
my $wref;
{
    my $x;
    my $subject = sub {
        $x = $_[0];
        my $y;
        return sub { $y };
    };
    my $subscriber = {};
    weaken($wref = $subscriber);
    $subscriber->{foo} = $subject->($subscriber);
}
!defined $wref or die "Leak";