[perl #119487] local $/ = <STDIN> broken

On Di. 27. Aug. 2013, 14:39:39, sprout wrote:
> 
> A readline optimisation is causing the order of evaluation to change,
> making the ‘local $/’ get executed too soon:
> 
> Notice how the LVINTRO line is number 3 while readline is number 5:
> 
> $ ./perl -Ilib -MO=Concise -e ' local $/ = <foo> '
> 6  <@> leave[1 ref] vKP/REFC ->(end)
> 1     <0> enter ->2
> 2     <;> nextstate(main 1 -e:1) v:{ ->3
> -     <1> null vKS/2 ->6
> -        <1> ex-rv2sv sKRM*/129 ->4
> 3           <#> gvsv[*/] s/LVINTRO ->4
> 5        <1> readline[t3] sKS/1 ->6
> 4           <#> gv[*foo] s ->5
> -e syntax OK
> 
> Here the numbers are 5 and 4, so the execution order is different:
> 
> $ ./perl -Ilib -MO=Concise -e ' local $/ = do { <foo> } '
> 7  <@> leave[1 ref] vKP/REFC ->(end)
> 1     <0> enter ->2
> 2     <;> nextstate(main 2 -e:1) v:{ ->3
> 6     <2> sassign vKS/2 ->7
> -        <1> null sK*/1 ->5
> -           <@> scope sK ->-
> -              <0> ex-nextstate v ->3
> 4              <1> readline[t3] sK/1 ->5
> 3                 <#> gv[*foo] s ->4
> -        <1> ex-rv2sv sKRM*/129 ->6
> 5           <#> gvsv[*/] s/LVINTRO ->6
> -e syntax OK
> 

That optimization seems to be blatantly invalid. :-)

% cat try.pl
#!/usr/bin/perl
use strict;
use warnings;

{
    package Ohai;

    sub TIEHANDLE {
        my $class = shift;
        bless {@_}, $class
    }

    sub READLINE {
        my $self = shift;
        $self->{readline}()
    }
}

our $xy = 42;

tie *HDL, 'Ohai', (
    readline => sub {
        print "the value of \$xy is [$xy]\n";
        qw(a b c)
    },
);

{ local $xy = do { <HDL> }; }
{ local $xy = <HDL>; }
__END__

% perl try.pl
the value of $xy is [42]
Use of uninitialized value $xy in concatenation (.) or string at try.pl
line 23.
the value of $xy is []




---
via perlbug:  queue: perl5 status: open
https://rt.perl.org:443/rt3/Ticket/Display.html?id=119487

• [perl #119487] local $/ = <STDIN> broken by Father Chrysostomos via RT
• [perl #119487] local $/ = <STDIN> broken by l.mai@web.de via RT
• [perl #119487] local $/ = <STDIN> broken by l . mai @ web . de