[perl #78276] [BUG] Null PMC access when calling a multi sub with a parameter narrowed by a subtype that does a regex match in Rakudo

[Carl Mäsak]

# New Ticket Created by  "Carl Mäsak" 
# Please include the string:  [perl #78276]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=78276 >


<masak> rakudo: subset Greeting of Str where { /:i ^oh \s+ \w+ '!'?$/
}; subset LolGreeting of Str where { .words[1].lc eq 'hai' }; multi
detect(Str) { "not a greeting" }; multi detect(Greeting) { "regular
greeting" }; multi detect(LolGreeting) { "lol-greeting" }; say detect
"OH HAI"
<p6eval> rakudo e9e7fc: OUTPUT«Null PMC access in isa_pmc() [....]
* masak submits rakudobug
<ash_> rakudo: say 'foo' ~~ /:i foo/;
<p6eval> rakudo e9e7fc: OUTPUT«foo␤»
<masak> ash_: it's to do with multies, and subtypes.
<ash_> got ya
<masak> rakudo: subset G of Str where { /O/ }; sub detect(G) {}; detect "O"
<p6eval> rakudo e9e7fc: OUTPUT«Method 'match' not found for invocant
of class ' [...]
<masak> rakudo: subset G of Str where { /O/ }; multi detect(G) {}; detect "O"
<p6eval> rakudo e9e7fc: OUTPUT«Null PMC access in isa_pmc()␤  in
'&infix:<=>' at line 1␤  in 'Regex::Bool' at line 5970:CORE.setting␤
in 'detect' [...]
<masak> rakudo: subset G of Str where { .chars > 0 }; multi detect(G)
{}; detect "O"; say "alive"
<p6eval> rakudo e9e7fc: OUTPUT«alive␤»