From @bbkr

$ perl6 -e 'sub MAIN ( $x = 1|2 ) { }'

Following oneliner will hang forever on Rakudo 2018.01.
Error exists for all type of Junctions.
Doesn't matter if they are built by infix "1|2" or by method "any(1,2)".

From @zoffixznet

On Wed, 31 Jan 2018 07​:26​:24 -0800, pawel.pabian@​getresponse.com wrote​:

$ perl6 -e 'sub MAIN ( $x = 1|2 ) { }'

Following oneliner will hang forever on Rakudo 2018.01.
Error exists for all type of Junctions.
Doesn't matter if they are built by infix "1|2" or by method "any(1,2)".

We can probably improve that behaviour with an error message (it applies to any routine, not just MAIN).

The problem is you're declaring an Any parameter, but your default value is a Junction, so when the default is used, it's trying to autothread the Junction and I'm guessing it keeps looping there in the guts somewhere.

Looking at your use, I'm suspecting you meant to use a `where` clause instead of the default value​:

  `perl6 -e 'sub MAIN ( $x where 1|2 ) { }'

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

From @zoffixznet

On Wed, 31 Jan 2018 07​:56​:31 -0800, cpan@​zoffix.com wrote​:

On Wed, 31 Jan 2018 07​:26​:24 -0800, pawel.pabian@​getresponse.com
wrote​:

$ perl6 -e 'sub MAIN ( $x = 1|2 ) { }'

Following oneliner will hang forever on Rakudo 2018.01.
Error exists for all type of Junctions.
Doesn't matter if they are built by infix "1|2" or by method
"any(1,2)".

We can probably improve that behaviour with an error message (it
applies to any routine, not just MAIN).

The problem is you're declaring an Any parameter, but your default
value is a Junction, so when the default is used, it's trying to
autothread the Junction and I'm guessing it keeps looping there in the
guts somewhere.

Looking at your use, I'm suspecting you meant to use a `where` clause
instead of the default value​:

`perl6 -e 'sub MAIN ( $x where 1|2 ) { }'

I started with this, but likely won't have time to finish it this week. In case someone else wants
to give it a go, some notes​:

1) jnthn++ agreed[^1] that this should throw
2) This code doesn't go through `check_param_default_type`[^2] in Actions. I tried passing the
  thunked[^3] defaults through the routine, but compilation fails
  with `Cannot unbox a type object (Str) to a str.`
3) The infiniloop is in the BOOTSTRAP[^4]. It basically keeps autothreading itself with no
  params over and over.

[1] https://irclog.perlgeek.de/perl6/2018-01-31#i_15761475
[2] https://github.com/rakudo/rakudo/blob/72948e8477fdb92801a59a6e101b29c2da2f844e/src/Perl6/Actions.nqp#L5050-L5058
[3] https://github.com/rakudo/rakudo/blob/72948e8477fdb92801a59a6e101b29c2da2f844e/src/Perl6/Actions.nqp#L5061
[4] https://github.com/rakudo/rakudo/blob/72948e8477fdb92801a59a6e101b29c2da2f844e/src/Perl6/Metamodel/BOOTSTRAP.nqp#L3336-L3362