From @jdv

[jdv@​wieldy ~]$ cat test_n_threads.p6
use v6;

await map { start {
  my $foo = "barbaz";
  $foo ~~ s/.+/{ <a b c>.roll($/.chars).join }/;
} }, ^100;
[jdv@​wieldy ~]$ perl6 test_n_threads.p6
Use of Nil in string context in block at test_n_threads.p6 line 5
Use of Nil in string context in block at test_n_threads.p6 line 5
[jdv@​wieldy ~]$ perl6 test_n_threads.p6
Use of Nil in string contextUse of Nil in string contextUse of Nil in
string context in block at test_n_threads.p6 line 5
  in block at test_n_threads.p6 line 5
  in block at test_n_threads.p6 line 5
Type check failed in binding to <anon>; expected Match but got Nil
(Nil)
  in block <unit> at test_n_threads.p6 line 3

[jdv@​wieldy ~]$ perl6 test_n_threads.p6
Use of Nil in string contextUse of Nil in string context in block at
test_n_threads.p6 line 5
Use of Nil in string context in block at test_n_threads.p6 line 5
  in block at test_n_threads.p6 line 5
Use of Nil in string context in block at test_n_threads.p6 line 5
Use of Nil in string context in block at test_n_threads.p6 line 5
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$ cat test_1_thread.p6
use v6;

PROCESS​::<$SCHEDULER>
  = ThreadPoolScheduler.new(initial_threads => 0, max_threads => 1);
await map { start {
  my $foo = "barbaz";
  $foo ~~ s/.+/{ &lt;a b c&gt;.roll($/.chars).join }/;
} }, ^100;
[jdv@​wieldy ~]$ cat test_1_thread.p6
use v6;

PROCESS​::<$SCHEDULER>
  = ThreadPoolScheduler.new(initial_threads => 0, max_threads => 1);
await map { start {
  my $foo = "barbaz";
  $foo ~~ s/.+/{ &lt;a b c&gt;.roll($/.chars).join }/;
} }, ^100;
[jdv@​wieldy ~]$ perl6 test_1_thread.p6
[jdv@​wieldy ~]$ perl6 test_1_thread.p6
[jdv@​wieldy ~]$ perl6 test_1_thread.p6
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$ cat test_no_async.p6
use v6;

map {
  my $foo = "barbaz";
  $foo ~~ s/.+/{ &lt;a b c&gt;.roll($/.chars).join }/;
}, ^100;
[jdv@​wieldy ~]$ perl6 test_no_async.p6
[jdv@​wieldy ~]$ perl6 test_no_async.p6
[jdv@​wieldy ~]$ perl6 test_no_async.p6
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$ perl6 -v
This is Rakudo version 2016.07.1-102-ge411e5d built on MoarVM version
2016.07-11-g11e02fe
implementing Perl 6.c.
[jdv@​wieldy ~]$

From @jnthn

On Mon Aug 01 20​:51​:12 2016, jdv79 wrote​:

[jdv@​wieldy ~]$ cat test_n_threads.p6
use v6;

await map { start {
my $foo = "barbaz";
$foo ~~ s/.+/{ &lt;a b c&gt;.roll($/.chars).join }/;
} }, ^100;
[jdv@​wieldy ~]$ perl6 test_n_threads.p6
Use of Nil in string context in block at test_n_threads.p6 line 5
Use of Nil in string context in block at test_n_threads.p6 line 5
[jdv@​wieldy ~]$ perl6 test_n_threads.p6
Use of Nil in string contextUse of Nil in string contextUse of Nil in
string context in block at test_n_threads.p6 line 5
in block at test_n_threads.p6 line 5
in block at test_n_threads.p6 line 5
Type check failed in binding to <anon>; expected Match but got Nil
(Nil)
in block <unit> at test_n_threads.p6 line 3

[jdv@​wieldy ~]$ perl6 test_n_threads.p6
Use of Nil in string contextUse of Nil in string context in block at
test_n_threads.p6 line 5
Use of Nil in string context in block at test_n_threads.p6 line 5
in block at test_n_threads.p6 line 5
Use of Nil in string context in block at test_n_threads.p6 line 5
Use of Nil in string context in block at test_n_threads.p6 line 5
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$ cat test_1_thread.p6
use v6;

PROCESS​::<$SCHEDULER>
= ThreadPoolScheduler.new(initial_threads => 0, max_threads => 1);
await map { start {
my $foo = "barbaz";
$foo ~~ s/.+/{ &lt;a b c&gt;.roll($/.chars).join }/;
} }, ^100;
[jdv@​wieldy ~]$ cat test_1_thread.p6
use v6;

PROCESS​::<$SCHEDULER>
= ThreadPoolScheduler.new(initial_threads => 0, max_threads => 1);
await map { start {
my $foo = "barbaz";
$foo ~~ s/.+/{ &lt;a b c&gt;.roll($/.chars).join }/;
} }, ^100;
[jdv@​wieldy ~]$ perl6 test_1_thread.p6
[jdv@​wieldy ~]$ perl6 test_1_thread.p6
[jdv@​wieldy ~]$ perl6 test_1_thread.p6
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$ cat test_no_async.p6
use v6;

map {
my $foo = "barbaz";
$foo ~~ s/.+/{ &lt;a b c&gt;.roll($/.chars).join }/;
}, ^100;
[jdv@​wieldy ~]$ perl6 test_no_async.p6
[jdv@​wieldy ~]$ perl6 test_no_async.p6
[jdv@​wieldy ~]$ perl6 test_no_async.p6
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$
[jdv@​wieldy ~]$ perl6 -v
This is Rakudo version 2016.07.1-102-ge411e5d built on MoarVM version
2016.07-11-g11e02fe
implementing Perl 6.c.
[jdv@​wieldy ~]$

Fixed by 739d1a3; test needed.

The RT System itself - Status changed from 'new' to 'open'

From @zoffixznet

Tests added in Raku/roast@16d333d4b3

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