Haha, this happens in both 5.14.1 and 5.12.2, funny

$ perl -Tle " package SNOT; print(fileno(shift @ARGV)) ; use Data::Dum
+per(); END{ warn Data::Dumper::Dumper(\%SNOT::);}" -
Insecure dependency in require while running with -T switch at -e line
+ 1.
BEGIN failed--compilation aborted.
$VAR1 = {
          'BEGIN' => *SNOT::BEGIN,
          'END' => *SNOT::END
        };

$ perl -Tle " package SNOT; print(fileno(shift @ARGV)) ; use Data::Dum
+per(); END{ warn Data::Dumper::Dumper(\%SNOT::);}" +
Insecure dependency in require while running with -T switch at -e line
+ 1.
BEGIN failed--compilation aborted.
$VAR1 = {
          'BEGIN' => *SNOT::BEGIN,
          'END' => *SNOT::END
        };

$ perl -Tle " package SNOT; print(fileno(shift @ARGV)) ; use Data::Dum
+per(); END{ warn Data::Dumper::Dumper(\%SNOT::);}" !

$VAR1 = {
          'BEGIN' => *SNOT::BEGIN,
          'END' => *SNOT::END
        };
[download]

Comment in PP(pp_fileno) even funnier

 731     if (!io || !(fp = IoIFP(io))) {
 732         /* Can't do this because people seem to do things like
 733            defined(fileno($foo)) to check whether $foo is a valid
+ fh.
 734 
 735            report_evil_fh(gv);
 736             */
 737         RETPUSHUNDEF;
 738     }
[download]

I don't know what this means :)