[perl #61364] sort() should implement a stable sort

[via RT]

# New Ticket Created by  Moritz Lenz 
# Please include the string:  [perl #61364]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=61364 >


S29 says:

: If all criteria are exhausted when comparing two elements, sort should
: return them in the same relative order they had in @values.

or in terms of computer science, the sort should be stable.

Rakudo r33895 doesn't do this, as a few tests show that I've added to
t/spec/S29-list/sort.t, for example:



my @a = ([5, 4], [5, 5], [5, 6], [0, 0], [1, 2], [1, 3], [0, 1], [5, 7]);

{
    my @s = @a.sort: { .[0] };
    say @s.perl;

    ok ([<] @s.map({.[1]})), 'sort with arity 1 closure is stable';
}

Cheers,
Moritz