[perl #123072] 'for' loop in sink context isn't invoking block in sink context

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# New Ticket Created by  Patrick R. Michaud 
# Please include the string:  [perl #123072]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=123072 >


This is a reminder/placeholder ticket for a bug I found tonight while
researching GLR-related topics.  A "for" loop executed in sink context
isn't executing its block in sink context.  From #perl6:

  04:50 <pmichaud> m:  class Sinker { method sink() { say "Blub" } };  my $i = 
0; while $i < 5 { $i++; Sinker.new(); }; 1 
  04:50 <camelia> rakudo-moar 315ec6: OUTPUT«Blub␤Blub␤Blub␤Blub␤Blub␤»
  04:50 <pmichaud> m:  class Sinker { method sink() { say "Blub" } };  for ^5 { 
Sinker.new(); }; 1 
  04:50 <camelia> rakudo-moar 315ec6: ( no output )

Earlier in the conversation:

  00:38 <pmichaud> ...which one is "correct"?  (post-GLR)
  00:41 <pmichaud> i.e., does a loop executed in sink context execute its body 
in sink context?
  03:16 <TimToady> pmichaud: why would a loop in sink context ever want a value 
from its loop body?
  03:16 <TimToady> I'm a bit surprised the 2nd one isn't sunk already
  03:21 <TimToady> well, not really, given what I know about internals :)
  04:39 <pmichaud> TimToady: I'm not surprised the second one isn't sunk 
already; sink context in Rakudo is (still) somewhat inconsistently handled.
  04:40 <pmichaud> Implementors sometimes remembered to throw away the values, 
but forgot to tell the values they were being thrown away.
  04:41 <pmichaud> anyway, I'll be looking at fixing that shortly

The bug will likely be taken care of as part of the GLR; this ticket is to 
remind us that we need a test for it.  :)

Pm