Documentation for trait is DEPRECATED assembled from the following pages:

Class: Routine §

(Routine) trait is DEPRECATED §

multi sub trait_mod:<is>(Routine:D $r, :$DEPRECATED!)

Marks a routine as deprecated, optionally with a message what to use instead.

This code

sub f() is DEPRECATED('the literal 42') { 42 }
say f();

produces this output:

42
Saw 1 occurrence of deprecated code.
================================================================================
Sub f (from GLOBAL) seen at:
  deprecated.p6, line 2
Please use the literal 42 instead.
--------------------------------------------------------------------------------
Please contact the author to have these occurrences of deprecated code
adapted, so that this message will disappear!