use strict;
use warnings;

# selfcontained simulation of feature pragma
  package my_feature;
  use Carp;
  sub import {
    my $pkg = (caller)[0];
    if ( grep {$_ eq "try"} @_ ) {
      for my $func (qw/try catch finally/) {
        carp "Warning: ${pkg}::$func() will be shadowed by feature 'tr
+y'"
          if exists &{"${pkg}::$func"};
      }
    }
  }
  1;

  BEGIN {  $INC{"my_feature.pm"} = "DEMO from " . __FILE__ }
# end simulation

package Foo;
use Try::Tiny;
use my_feature "try";
[download]

-->

perl /home/lanx/perl/pm/check_stash_sub.pl
Warning: Foo::try() will be shadowed by feature 'try' at /home/lanx/pe
+rl/pm/check_stash_sub.pl line 23.
Warning: Foo::catch() will be shadowed by feature 'try' at /home/lanx/
+perl/pm/check_stash_sub.pl line 23.
Warning: Foo::finally() will be shadowed by feature 'try' at /home/lan
+x/perl/pm/check_stash_sub.pl line 23.
[download]

NB: The warnings are emitted before any code following the use feature is compiled.