If you want warnings to stop your debugger if it's running, but not to actually die, this seems to work:

$SIG{'__WARN__'} = sub { warn $_[0]; $DB::single = $DB::single; $DB::s
+ingle = 1; };
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It automatically slams the debugger into single-step mode every time there's a warning. (The $DB::single = $DB::single is just to keep -w happy.)

stephen