[perl #134312] wrong line number reported for sort subroutine?(Argument "a" isn't numeric in numeric comparison (<=>) at ... line ...)

# New Ticket Created by  "Ulrich Windl" 
# Please include the string:  [perl #134312]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=134312 >


Hi!

I think this is a bug in perl 5.18.2 (as shipped in SLES12 SP4):

Debugging a sort routine I wrote myself I get an error that I don't understand, most likely because the line number reported (maybe even the whole error message) is wrong:

First the effect (generic_sort is my sorting routine):

  DB<1> x generic_sort('', 'a')
'','a'
Argument "" isn't numeric in sort at sapgw-log-condenser.pl line 132.
 at sapgw-log-condenser.pl line 132.
        main::generic_sort('', 'a') called at (eval 7)[/usr/lib/perl5/5.18.2/perl5db.pl:732] line 2
        eval 'no strict; ($@, $!, $^E, $,, $/, $\\, $^W) = @DB::saved;package main; $^D = $^D | $DB::db_stop;
  generic_sort(\'\', \'a\');
' called at /usr/lib/perl5/5.18.2/perl5db.pl line 732
        DB::eval called at /usr/lib/perl5/5.18.2/perl5db.pl line 3096
        DB::DB called at sapgw-log-condenser.pl line 15
0  ''
1  'a'
  DB<2> l 132
132:            print "'$a','$b'\n";


Then, even more confusing, I wrote a simpler test caser of my routine, named "_sort" where I deliberately forced an error:

  DB<3> x _sort('', 'a')
'','a'
Argument "a" isn't numeric in numeric comparison (<=>) at sapgw-log-condenser.pl line 178.
 at sapgw-log-condenser.pl line 178.
        main::_sort('', 'a') called at (eval 8)[/usr/lib/perl5/5.18.2/perl5db.pl:732] line 2
        eval 'no strict; ($@, $!, $^E, $,, $/, $\\, $^W) = @DB::saved;package main; $^D = $^D | $DB::db_stop;
  _sort(\'\', \'a\');
' called at /usr/lib/perl5/5.18.2/perl5db.pl line 732
        DB::eval called at /usr/lib/perl5/5.18.2/perl5db.pl line 3096
        DB::DB called at sapgw-log-condenser.pl line 15
Argument "" isn't numeric in numeric comparison (<=>) at sapgw-log-condenser.pl line 178.
 at sapgw-log-condenser.pl line 178.
        main::_sort('', 'a') called at (eval 8)[/usr/lib/perl5/5.18.2/perl5db.pl:732] line 2
        eval 'no strict; ($@, $!, $^E, $,, $/, $\\, $^W) = @DB::saved;package main; $^D = $^D | $DB::db_stop;
  _sort(\'\', \'a\');
' called at /usr/lib/perl5/5.18.2/perl5db.pl line 732
        DB::eval called at /usr/lib/perl5/5.18.2/perl5db.pl line 3096
        DB::DB called at sapgw-log-condenser.pl line 15
0  ''
1  'a'
  DB<4> l 178
178:                return $a <=> $b;
  DB<5>

So what you see is that in the first case the line reported cannot trigger the error; even the lines around it can't.
In contrast the second example reports the correct line.

Here are the relevant lines from the source (prefixed by the line numbers):


   15   require 5.018_000;
   16   use strict;
   17   use English;

  129   sub generic_sort(@)
  130   {
  131       return sort {
  132           print "'$a','$b'\n";
  133           if ($a eq $b) {                 # trivial case
  134               return 0;
  135           } else {
  136               my ($c, $d) = ($a, $b);
  137
  138               while ($c && $d) {
... the only occurrence of a numeric comparison is this, protected by some regular expression matches:
  151                               if ((my $result = $cm <=> $dm) != 0) {
  152                                   return $result;
...
  166               }
  167           }
  168       } @_;
  169   }

  171   sub _sort(@)
  172   {
  173       return sort {
  174           print "'$a','$b'\n";
  175           if ($a eq $b) {                 # trivial case
  176               return 0;
  177           } else {
  178               return $a <=> $b;           # force an error
  179           }
  180       } @_;
  181   }

The print in line 132 was added AFTER I had observed the error. Before adding line 132, the error line reported also was 132.
Also I had added a print statement that should output before <=> is ever reached, but the print never happens.

More obscure when I set a breakpoint at line 132, and then step through:
main::(sapgw-log-condenser.pl:15):      require 5.018_000;
  DB<1> b 133
  DB<2> x generic_sort('', 'a')
initial: '','a'
main::generic_sort(sapgw-log-condenser.pl:133):
133:            if ($a eq $b) {                 # trivial case
  DB<<3>> n
main::generic_sort(sapgw-log-condenser.pl:136):
136:                my ($c, $d) = ($a, $b);
  DB<<3>> n
main::generic_sort(sapgw-log-condenser.pl:138):
138:                while ($c && $d) {
  DB<<3>> n
Argument "" isn't numeric in sort at sapgw-log-condenser.pl line 132.
...

P.S.: I did not post my sorting routine, as the code is probably not correct yet, but still the bug described does not make it easier for me to debug and fix.

> perl -V
Summary of my perl5 (revision 5 version 18 subversion 2) configuration:

  Platform:
    osname=linux, osvers=3.12.61-52.141-default, archname=x86_64-linux-thread-multi
    uname='linux sheep08 3.12.61-52.141-default #1 smp tue aug 14 07:09:09 utc 2018 (b9c454e) x86_64 x86_64 x86_64 gnulinux '
    config_args='-ds -e -Dprefix=/usr -Dvendorprefix=/usr -Dinstallusrbinperl -Dusethreads -Di_db -Di_dbm -Di_ndbm -Di_gdbm -Dd_dbm_open -Duseshrplib=true -Doptimize=-fmessage-length=0 -grecord-gcc-switches -fstack-protector -O2 -Wall -D_FORTIFY_SOURCE=2 -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection -g -Wall -pipe -Accflags=-DPERL_USE_SAFE_PUTENV -Dotherlibdirs=/usr/lib/perl5/site_perl -Dinc_version_list=5.18.0/x86_64-linux-thread-multi 5.18.0 5.18.1/x86_64-linux-thread-multi 5.18.1'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DPERL_USE_SAFE_PUTENV -fno-strict-aliasing -pipe -fstack-protector -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-fmessage-length=0 -grecord-gcc-switches -fstack-protector -O2 -Wall -D_FORTIFY_SOURCE=2 -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection -g -Wall -pipe',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DPERL_USE_SAFE_PUTENV -fno-strict-aliasing -pipe -fstack-protector'
    ccversion='', gccversion='4.8.5', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib64 -fstack-protector'
    libpth=/lib64 /usr/lib64 /usr/local/lib64
    libs=-lm -ldl -lcrypt -lpthread
    perllibs=-lm -ldl -lcrypt -lpthread
    libc=/lib64/libc-2.19.so, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.19'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E -Wl,-rpath,/usr/lib/perl5/5.18.2/x86_64-linux-thread-multi/CORE'
    cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib64 -fstack-protector'


Characteristics of this binary (from libperl):
  Compile-time options: HAS_TIMES MULTIPLICITY PERLIO_LAYERS
                        PERL_DONT_CREATE_GVSV
                        PERL_HASH_FUNC_ONE_AT_A_TIME_HARD
                        PERL_IMPLICIT_CONTEXT PERL_MALLOC_WRAP
                        PERL_PRESERVE_IVUV PERL_SAWAMPERSAND
                        PERL_USE_SAFE_PUTENV USE_64_BIT_ALL USE_64_BIT_INT
                        USE_ITHREADS USE_LARGE_FILES USE_LOCALE
                        USE_LOCALE_COLLATE USE_LOCALE_CTYPE
                        USE_LOCALE_NUMERIC USE_PERLIO USE_PERL_ATOF
                        USE_REENTRANT_API
  Built under linux
  Compiled at Aug 17 2018 14:16:32
  @INC:
    /usr/lib/perl5/site_perl/5.18.2/x86_64-linux-thread-multi
    /usr/lib/perl5/site_perl/5.18.2
    /usr/lib/perl5/vendor_perl/5.18.2/x86_64-linux-thread-multi
    /usr/lib/perl5/vendor_perl/5.18.2
    /usr/lib/perl5/5.18.2/x86_64-linux-thread-multi
    /usr/lib/perl5/5.18.2
    /usr/lib/perl5/site_perl
    .

• [perl #134312] wrong line number reported for sort subroutine?(Argument "a" isn't numeric in numeric comparison (<=>) at ... line ...) by " Ulrich Windl "