Perl's caller() function returning incorrect line number

perl

Solution

$ perl -MO=Concise a.pl
j  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 6 a.pl:5) v:*,&,{,x*,x&,x$,$ ->3
5     <2> sassign vKS/2 ->6
3        <$> const[IV 0] s ->4
4        <0> padsv[$x:3,5] sRM*/LVINTRO ->5
6     <0> unstack v* ->7
i     <2> leaveloop vK/2 ->j
7        <{> enterloop(next->b last->i redo->8) v ->e
-        <1> null vK/1 ->i
h           <|> and(other->8) vK/1 ->i
g              <2> lt sK/2 ->h
e                 <0> padsv[$x:3,5] s ->f
f                 <$> const[IV 1] s ->g
-              <@> lineseq vK ->-
-                 <@> scope vK ->b                       <---
-                    <0> ex-nextstate v ->8              <---
a                    <1> entersub[t5] vKS/TARG,2 ->b
-                       <1> ex-list K ->a
8                          <0> pushmark s ->9
-                          <1> ex-rv2cv sK/2 ->-
9                             <#> gv[*print_line] s/EARLYCV ->a
c                 <1> preinc[t2] vK/1 ->d
b                    <0> padsv[$x:3,5] sRM ->c
d                 <0> unstack v ->e
a.pl syntax OK

There's some optimization going on. The `scope` was deemed unnecessary and optimized away. (Notice the "`-`" meaning it's never reached.)

But at the same time, that removed the `nextstate` op, which is what sets the line number for warnings and for `caller`.

So, it's a bug that results from an improper optimization.

Problem

I've got the following script running on Perl 5.10.1: ``` #!/usr/bin/perl use strict; use warnings; foreach( my $x =0 ; $x < 1; $x++) { # Line 5 print_line(); # Line 6 } sub print_line { print "Function call from line: " . [caller(0)]->[2] . "\n"; } ``` Despite the call to the subroutine coming from line 6, the script outputs the line number of the start of the C-style for statement: ``` Function call from line: 5 ``` What's really weird is if I throw a random statement into one of the blank line in the C-style for loop, `caller` returns the correct line number: ``` #!/usr/bin/perl use strict; use warnings; foreach( my $x =0 ; $x < 1; $x++) { my $x = 3; print_line(); # Line 7 } sub print_line { print "Function call from line: " . [caller(0)]->[2] . "\n"; } ``` The above script correctly outputs: ``` Function call from line: 7 ``` Is this some kind of bug or is there something I can do to get `caller` to accurately report the line number?

Original source