`subset` could use better diagnostic output

[benb-zr]

use strict;
use warnings;
use Test2::V0;
my $a = [
  map {
    [ $_ ]
  } qw(a b c d e f),
];
is $a, subset {
  item ["a"];
  item ["c"];
  item ["g"];
}, "got subset";
done_testing;

(Fails due to non-existence of g)

not ok 1 - got subset
# Failed test 'got subset'
# at test66.pl line 14.
# +------+-----------------------+------------------+--------+
# | PATH | GOT                   | CHECK            | LNs    |
# +------+-----------------------+------------------+--------+
# |      | ARRAY(0x7f94b2af2468) | <ORDERED SUBSET> | 10, 14 |
# | [?]  | <DOES NOT EXIST>      | <ARRAY>          | 13     |
# +------+-----------------------+------------------+--------+

Doesn't really indicate the nature of the failure.

[exodist]

oh, I see now.

In this case the error message is not wrong, you are missing an entire array. <ARRAY> is not useful, however the line 13 indicator is because it tells you which item caused the failure.

I am not sure how to improve this message as an array can literally contain any number of anything and there is no compact form for that. This is exactly the kind of situation the line number of the check was added for.