[perl #118063] [BUG] comma (wrongly) required between parameter with default value and returns-arrow ('-->') in Rakudo

[Carl Mäsak]

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<lizmat> r: sub a ( $a=1, --> Hash ) { say $a; my %h }; say a(2)
<camelia> rakudo 8d2ec9: OUTPUT«2␤().hash␤»
<lizmat> r: sub a ( $a=1 --> Hash ) { say $a; my %h }; say a(2)
<camelia> rakudo 8d2ec9: OUTPUT«===SORRY!===␤Missing block␤at
/tmp/NxD226NWlT:1␤------> sub a ( $a=1 --> Hash ⏏) { say $a; my %h };
say a(2)␤ expecting any of:␤ postfix␤ infix stopper␤
infix or meta-infix␤ prefix or term␤ …
<lizmat> for some reason, if we have a default, we need a comma there
<lizmat> r: sub a ( $a --> Hash ) { say $a; my %h }; say a(2)
<camelia> rakudo 8d2ec9: OUTPUT«2␤().hash␤»
* masak submits rakudobug for the required comma

I have a feeling I know what's up. The default puts the parser in EXPR
mode. The '-->' should be a stopper, but it isn't, so it gets parsed
as '- ->', binary minus and a pointy. The Hash gets gobbled up as a
parameter, and then the parser expects a block, not ')'. This is
consistent with the error message.

[Christian Bartolomaeus via RT]

This works now without the comma:

$ perl6-m -e 'sub a ( $a=1 --> Hash ) { say $a; my %h }; say a(2)'
2

^^ empty string here ;-)

I added a test to S06-signature/defaults.t with the following commit: https://github.com/perl6/roast/commit/4485db4547