The current version of Rakudo (after Jonathan's merge) now reports:
$ cat 66182
my $x;
[$x.WHAT, $x.HOW, $x]>>.say;
$ ./perl6 66182
Failure()
Method 'say' not found for invocant of class 'P6metaclass'
$
I don't know if this is more along the lines of what you were looking
for. If so, close the ticket, if not, tell us what you expect. :-)
Pm
