Signature specifiers on Callables do not consider multi candidates

[zoffixznet]

What's the purpose of specifying something like &foo:($ --> Int) as a parameter in signatures? My understanding is so that I can specify that I only take a particular kind of routines, this way if I write &foo:($ --> Int), I know I can invoke the routine given to me as an argument with a single argument and use the result as an Int.

However, such purpose is currently not served completely. If you pass a multi routine as a Callable, even if there is a candidate that matches the specified signature, the constraint still fails:

Zoffix | m: multi foo ($) {}; multi foo () {}; -> &:() { }( &foo )
camelia | rakudo-moar  08a54212e: OUTPUT: «Constraint type check failed in binding to  parameter '<anon>'; 
expected anonymous constraint to be met but  got Sub (proto sub foo (;; Mu ...)␤ in block <unit> at <tmp>  line 1␤␤»

[zoffixznet]

Oh, nm, I just realized why it's not implemented this way:

m: multi foo (Int) { "fail" }; multi foo ($ --> Int) {}; multi foo () {}; -> &bar:($ --> Int) { say "{bar 42} is an Int?" }( &foo )

Above, the multi would get accepted because there is a matched sig, but there also exists an unmatched candidate and THAT candidate would actually get called inside my block, and give me a Str instead of an Int I was expecting, making the constraint pointless.

And if one does want to accept a multi with any matching candidate, a simple where .candidates».signature.any ~~ :(&bar:($ --> Int)) would do the job.