[perl #129263] [CONC] Outer dynamic variable not found in nested `start` block

[via RT]

# New Ticket Created by  Sam S. 
# Please include the string:  [perl #129263]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=129263 >


    ➜  my $*a = 42;  await start { say $*a }
    42

    ➜  my $*a = 42;  await start { await start { say $*a } }
    Dynamic variable $*foo not found

IRC discussion (rearranged for clarity):

    <smls>  Are threads supposed to see dynamic variables declared in the
            mainline prior to starting the thread?

    <jnthn> A start block will go the extra mile to make that happen
    <jnthn> It just takes the CALLER:: of whatever calls Promise.start iirc

    <jnthn> But if you work directly with threads then every one has its
            own fresh dynamic scope

    ...

    <smls>  Should that still work, when it's 2 levels deep into `start`?

    <jnthn> Umm...I guess it'd be nice if it worked. 
    <jnthn> Can RT it; I don't see why we can't fix that.