[perl #67992] [BUG] Null PMC Access when referring to attributes in roles used by classes which also have attributes in Rakudo

[Carl Mäsak]

# New Ticket Created by  "Carl Mäsak" 
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<masak> rakudo: role A { has @!foo; method bar() { @!foo ~~ (1,2); }
}; class B does A { has $.baz; }; B.new().bar()
<p6eval> rakudo 6999e5: OUTPUT«Null PMC access in isa()␤in method A[]::bar [...]
* masak submits rakudobug
<masak> rakudo: role A { has @!foo; method bar() { say @!foo } };
class B does A { has $.baz; }; B.new().bar()
<p6eval> rakudo 6999e5: OUTPUT«Null PMC access in isa()␤in method A[]::bar [...]

I've been testing the phenomenon pretty extensively, and it doesn't
seem to matter whether it's @!foo, $!foo or %!foo -- the error occurs
in all those cases. Also doesn't matter if it's $.baz or $!baz.
Removing $.baz entirely makes the error go away. Defining &bar in B
instead of A also doesn't make any difference.