UNIVERSAL::can(__PACKAGE__, 'myfunc')

##</code><code>##

UNIVERSAL::can($pkg, 'myfunc')

##</code><code>##

sub check_for_func {
   my ($func_name) = @_;

   my @pkgs_with_func;
   my $helper;  # Don't combine this line with the assignement.

   $helper = sub {
      my ($pkg_name) = @_;

      my $pkg = do { no strict 'refs'; \%{$pkg_name.'::'} };

      push(@pkgs_with_func, $pkg_name)
         if   $pkg->{$func_name}
         && *{$pkg->{$func_name}}{CODE};

      my $pkg_name_ = ($pkg_name eq 'main'
         ? ''
         : $pkg_name.'::'
      );

      /^(.*)::$/ && $1 ne 'main' && &$helper($pkg_name_.$1)
         foreach (keys(%$pkg));
   };

   &$helper('main');
   return @pkgs_with_func;
}

print(join(', ', check_for_func('test')), $/);