From @dakkar

This code​::

  role R[$a,$b] {}
  class C does R[1] {}

  C.new;

Produces the error message​::

  ===SORRY!===
  No appropriate parametric role variant available for 'R'

It would be nice to know a line number, and the signatures involved,
like we get for subs.

--
  Dakkar - <Mobilis in mobile>
  GPG public key fingerprint = A071 E618 DD2C 5901 9574
  6FE2 40EA 9883 7519 3F88
  key id = 0x75193F88

  As a math atheist, I think I should be excused from this.
  --- Calvin, to Hobbes

Could be resolved together with #4513.

$ cat >gh_old_4514.raku
 role R[$a,$b] {};
 class C does R[1] {};
 C.new;
$ ./rakudo-m gh_old_4514.raku 
===SORRY!=== Error while compiling /path/to/gh_old_4514.raku
No appropriate parametric role variant available for 'R':
    Cannot resolve caller (C, Int:D); none of these signatures match:
        (::$?CLASS ::::?CLASS Mu, Mu $a, Mu $b)
at /path/to/gh_old_4514.raku:2