[perl #97508] "sub is rw {}" allowed in return causing Null PMC access

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# New Ticket Created by  Paweł Pabian 
# Please include the string:  [perl #97508]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org:443/rt3/Ticket/Display.html?id=97508 >


[16:15] <bbkr_> rakudo: my $s = sub foo { return sub is rw { 1; } }; $s.
().WHAT.say
[16:15] <p6eval> rakudo a55346: OUTPUT«Null PMC access in getprop()␤  
in '&infix:<=>' at line 1:src/metamodel/RoleToInstanceApplier.nqp␤  in main 
program body at line 22:/tmp/oD_Bf6ik2y␤»

But according to STD, this syntax should not parse in the first place.

[16:11] <bbkr_> std: sub foo { return sub is rw { 1; } };
[16:11] <p6eval> std 516268a: OUTPUT«===SORRY!===␤Malformed 
block at /tmp/HOlwPG8lqb line 1:␤------> sub foo { return sub is ⏏
[31mrw { 1; } };␤    expecting any of:␤   routine_def␤    trait␤Parse 
failed␤FAILED 00:01 119m␤»

Rakudo Perl 6, version 2011.07 built on parrot 3.6.0 0