From @masak

<masak> rakudo​: role A[​::T?] {}; class B does A[] {}; say "alive"
<p6eval> rakudo 7b0031​: OUTPUT«===SORRY!===␤Unable to parse
def_module_name, couldn't find final ']' at line 22␤»
* masak submits rakudobug
<masak> the Lion roars again!
<TimToady> std​: role A[​::T?] {}; class B does A[] {}; say "alive"
<p6eval> std 32075​: OUTPUT«�[31m===�[0mSORRY!�[31m===�[0m␤Unable to
parse generic role [...]
<masak> ...or not.
<TimToady> I don't think that syntax is legal
<masak> I'm starting to suspect you're right...
<TimToady> std​: role A[​::T $?] {}; class B does A[] {}; say "alive"
<p6eval> std 32075​: OUTPUT«ok 00​:01 119m␤»
<masak> oh right.
<TimToady> you can't put ? on a type constraint, which :​:T is parsed as
<masak> makes sense.
<masak> rakudo​: role A[​::T $?] {}; class B does A[] {}; say "alive"
<p6eval> rakudo 7b0031​: OUTPUT«===SORRY!===␤In signature parameter,
'$?', it is illegal to use '?' twigil [...]
* masak submits this other bug instead :)
<TimToady> heh, STD's twigils require a following \w
<masak> rakudo​: role A[​::T $?] {}
<p6eval> rakudo 7b0031​: OUTPUT«===SORRY!===␤In signature parameter,
'$?', it is illegal to use '?' twigil [...]
<masak> rakudo​: sub foo(​::T $?) {}
<p6eval> rakudo 7b0031​: OUTPUT«===SORRY!===␤In signature parameter,
'$?', it is illegal to use '?' twigil [...]
<TimToady> std​: role A[​::T $ ?] {}; class B does A[] {}; say "alive"
<masak> I agree; it's not a twigil unless there's something coming after it :)

From @coke

No change on original error in a recent-vintage nom.
--
Will "Coke" Coleda

@coke - Status changed from 'new' to 'open'

From @coke

Removing testneeded tag - this is still erroring.

From @usev6

This looks good to me now​:

$ perl6-m -e 'sub foo(​::T $?) {}; say "alive"'
alive

$ perl6-m -e 'role A[​::T $?] {}; class B does A[] {}; say "alive"'
alive

The following dies, but that's okay (from the IRC log above​: "<TimToady> you can't put ? on a type constraint, which :​:T is parsed as").

$ perl6-m -e 'role A[​::T?] {}; class B does A[] {}; say "alive"'
===SORRY!=== Error while compiling -e
Unable to parse expression in generic role; couldn't find final ']'
at -e​:1
------> role A[​::T⏏?] {}; class B does A[] {}; say "alive"
  expecting any of​:
  statement list
  prefix or term
  prefix or meta-prefix
  generic role
  formal parameter
  constraint

I'll add those three as tests and if nobody objects I'll close this ticket.

From @usev6

The tests are in S06-signature/optional.t and S14-roles/parameterized-basic.t, respectively. They were added with the following commit​: Raku/roast@2b3bee5223

@usev6 - Status changed from 'open' to 'resolved'