[perl #129874] [BUG] Strange closure-related issue in block interpolation

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# New Ticket Created by  Zoffix Znet 
# Please include the string:  [perl #129874]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=129874 >



<Zoffix> Hm. Found a strange bug in core that I can't reproduce.
<Zoffix> m: Bag.new-from-pairs: 1 => -1;
<camelia> rakudo-moar a09c8d: OUTPUT«Use of Nil in string context␤  in  
block <unit> at <tmp> line 1␤Use of Nil in string context␤  in block  
<unit> at <tmp> line 1␤Found negative values for  in ␤  in block  
<unit> at <tmp> line 1␤␤Actually thrown at:␤  in block <unit> at <tmp>  
l…»
<Zoffix> Those Nils? It's the two interpolated blocks on this line:  
https://github.com/rakudo/rakudo/blob/a09c8dc99ef7ae60876ad7a7cc478f7e303eb804/src/core/Baggy.pm#L48
<Zoffix> If I change it to this: my $wat = @toolow.join:  ' '; my  
$name = self.^name; fail "Found negative values for $wat in $name" if  
@toolow;      then the bug goes away.
<Zoffix> m: role Foo { method !meow { my @meows = <foo bar ber>; fail  
"some {@meows}" if @meows; }; method moo { self!meow; 42 } }; class ::  
does Foo {}.moo
<camelia> rakudo-moar a09c8d: OUTPUT«some foo bar ber␤  in method meow  
at <tmp> line 1␤  in method moo at <tmp> line 1␤  in block <unit> at  
<tmp> line 1␤␤Actually thrown at:␤  in method moo at <tmp> line 1␤  in  
block <unit> at <tmp> line 1␤␤»
<Zoffix> But can't reproduce it ^ :/

https://irclog.perlgeek.de/perl6-dev/2016-10-14#i_13399643