You can get that warning from the following even before 5.14:

use strict;
use warnings;

sub foo {
   my ($x) = @_;
   return sub { eval 'print "$x\n";' };
}

sub bar {
   my ($x) = @_;
   return sub { $x if 0; eval 'print "$x\n";' };
}

foo("foo")->();
bar("bar")->();
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(Note: The if 0 just avoids a void context warning. Removing it doesn't change the outcome.)

That you also get it in 5.14 under some circumstances involving illegal code (my ... if ...;) is not a problem.