G'day hurricup,

++ Good catch!

The code itself parses as legal Perl:

$ perl -MO=Deparse,-p -e 'my $l = ref $a eq "ARRAY" ? ($a->[0] || $->[
+1]) : $a;'
(my $l = ((ref($a) eq 'ARRAY') ? ($a->[0] || ($- > [1])) : $a));
-e syntax OK
[download]

And, as you can see, your analysis is correct: '$-' is being compared with '[1]'.

There's actually two adjacent lines like that in the source code:

    # Deal with the case of an item actually being an array ref to 1 o
+r 2
    # hashrefs. Don't assign to $a or $b, as they're aliases to the or
+ignal
    my $l = ref $a eq 'ARRAY' ? ($a->[0] || $->[1]) : $a;
    my $r = ref $b eq 'ARRAY' ? ($b->[0] || $->[1]) : $b;
[download]

I suspect those should be:

    my $l = ref $a eq 'ARRAY' ? ($a->[0] || $a->[1]) : $a;
    my $r = ref $b eq 'ARRAY' ? ($b->[0] || $b->[1]) : $b;
[download]

although, I haven't delved deeply enough into the code to say for certain.

I suggest you raise a bug report for this.