Hi folks,

I recently stumbled upon a weird behaviour of the perl debugger that regularly causes me a hard time debugging because it stops with a DB prompt somewhere in the vague depth. Tried perl versions 5.14.2 and 5.18.2, both versions are affected. Destilled the behaviour to the following tiny script:

#!perl -d
use strict;

package Obj;
use overload q{""} => 'string';

sub new { bless { string => pop }, shift }
sub dostuff () {}
sub string {
     dostuff; # These naughty lines (in a real module
     dostuff; # they'd do probably something useful) simply
     dostuff; # want to waste your time when debugging!
     dostuff; # There is no exit, is one?
     dostuff; # Thought there is a difference between
     dostuff; # "n test" and "s test"? - Nope!
     dostuff; # Try to "r"eturn, too - turns out it
     dostuff; # takes you further than you intended.
     dostuff; # Here comes "c 20" to your sole rescue:
     dostuff; # It will graciously take you up to
     shift->{string} # this line. Counting lines is fun, you know!
}
sub reply {
     print "Hi lonely one!\n";
}


package main;

sub test {
     my $o = Obj->new("World");
     print "Hello $o!\n";
     $o->reply();
}

test; # ... this by debugger command "s", then "s test" and/or "n test
+"

__END__
[download]

Here is my debugging session:

$ perl debugtest.pl

Loading DB routines from perl5db.pl version 1.39_10
Editor support available.

Enter h or 'h h' for help, or 'man perldebug' for more help.

main::(debugtest.pl:35):        test; # ... this by debugger command "
+s", then "s test" and/or "n test"
  DB<1> s
main::test(debugtest.pl:30):         my $o = Obj->new("World");
  DB<1> n
main::test(debugtest.pl:31):         print "Hello $o!\n";
  DB<1> 
Hello World!
main::test(debugtest.pl:32):         $o->reply();
  DB<1> 
Hi lonely one!
Debugged program terminated.  Use q to quit or R to restart,
use o inhibit_exit to avoid stopping after program termination,
h q, h R or h o to get additional info.
  DB<1> R
Warning: some settings and command-line options may be lost!

Loading DB routines from perl5db.pl version 1.39_10
Editor support available.

Enter h or 'h h' for help, or 'man perldebug' for more help.

main::(debugtest.pl:35):        test; # ... this by debugger command "
+s", then "s test" and/or "n test"
  DB<0> s test
main::((eval 5)[/usr/share/perl5/core_perl/perl5db.pl:732]:3):
3:      test;
  DB<<1>> s
main::test(debugtest.pl:30):         my $o = Obj->new("World");
  DB<<1>> n
main::test(debugtest.pl:31):         print "Hello $o!\n";
  DB<<1>> 
main::test(debugtest.pl:10):         dostuff; # These naughty lines (i
+n a real module
  DB<<1>> 
main::test(debugtest.pl:11):         dostuff; # they'd do probably som
+ething useful) simply
  DB<<1>> 
main::test(debugtest.pl:12):         dostuff; # want to waste your tim
+e when debugging!
  DB<<1>> 
main::test(debugtest.pl:13):         dostuff; # There is no exit, is o
+ne?
  DB<<1>> 
main::test(debugtest.pl:14):         dostuff; # Thought there is a dif
+ference between
  DB<<1>> 
main::test(debugtest.pl:15):         dostuff; # "n test" and "s test"?
+ - Nope!
  DB<<1>> 
main::test(debugtest.pl:16):         dostuff; # Try to "r"eturn, too -
+ turns out it
  DB<<1>> 
main::test(debugtest.pl:17):         dostuff; # takes you further than
+ you intended.
  DB<<1>> 
main::test(debugtest.pl:18):         dostuff; # Here comes "c 20" to y
+our sole rescue:
  DB<<1>> 
main::test(debugtest.pl:19):         dostuff; # It will graciously tak
+e you up to
  DB<<1>> 
main::test(debugtest.pl:20):         shift->{string} # this line. Coun
+ting lines is fun, you know!
  DB<<1>> 
Hello World!
main::test(debugtest.pl:32):         $o->reply();
  DB<<1>> 
Hi lonely one!

  DB<1> 
Hello World!
Hi lonely one!
Debugged program terminated.  Use q to quit or R to restart,
use o inhibit_exit to avoid stopping after program termination,
h q, h R or h o to get additional info.
  DB<1> R
Warning: some settings and command-line options may be lost!

Loading DB routines from perl5db.pl version 1.39_10
Editor support available.

Enter h or 'h h' for help, or 'man perldebug' for more help.

main::(debugtest.pl:35):        test; # ... this by debugger command "
+s", then "s test" and/or "n test"
  DB<1> n test
main::((eval 5)[/usr/share/perl5/core_perl/perl5db.pl:732]:3):
3:      test;
  DB<<2>> s
main::test(debugtest.pl:30):         my $o = Obj->new("World");
  DB<<2>> n
main::test(debugtest.pl:31):         print "Hello $o!\n";
  DB<<2>> 
main::test(debugtest.pl:10):         dostuff; # These naughty lines (i
+n a real module
  DB<<2>> q
[download]

The respective string method in my real project is even stepped into from a dunno-how related Moose object accessor. To find myself thrown into that method every once in a while makes debugging tedious, so I would like to work around it. It seems to be a bug in the debugger, in overload pragma perhaps (forgotten $DB::single assignment?), in them both or just in my thinking.

What do you think and why, I appreciate your advice!

-- flowdy