[perl #125997] LTA error message when no parametric role candidate found

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