From bwarnock@capita.com

Local variables declared in a conditional expression of a
conditional block are not restored at the end of scope.

$a = 10;
if (local $a = 1){
}
print $a; # Should be 10, not 1

Applies to local variables declared in 'if (expr)', 'unless(expr)',
and 'elsif (expr)'. Lexical variables are okay, as are local
variables in the conditional expression of a loop block.

Occurs in 5.005_03 through 5.7.2.

Flags​:
  category=core
  severity=low

Site configuration information for perl v5.6.1​:

Configured by bryan at Sat Jun 9 11​:24​:22 EDT 2001.

Summary of my perl5 (revision 5.0 version 6 subversion 1) configuration​:
  Platform​:
  osname=linux, osvers=2.4.3-20mdk, archname=i686-linux-64all-ld
  uname='linux wakko.idiocity.nut 2.4.3-20mdk #1 sun apr 15 23​:03​:10 cest
2001 i686 unknown '
  config_args=''
  hint=recommended, useposix=true, d_sigaction=define
  usethreads=undef use5005threads=undef useithreads=undef
usemultiplicity=undef
  useperlio=undef d_sfio=undef uselargefiles=define usesocks=undef
  use64bitint=define use64bitall=define uselongdouble=define
  Compiler​:
  cc='gcc', ccflags ='-DDEBUGGING -fno-strict-aliasing -D_LARGEFILE_SOURCE
-D_FILE_OFFSET_BITS=64',
  optimize='-g',
  cppflags='-DDEBUGGING -fno-strict-aliasing'
  ccversion='', gccversion='2.96 20000731 (Linux-Mandrake 8.0
2.96-0.48mdk)', gccosandvers=''
  intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=12345678
  d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
  ivtype='long long', ivsize=8, nvtype='long double', nvsize=12,
Off_t='off_t', lseeksize=8
  alignbytes=4, usemymalloc=n, prototype=define
  Linker and Libraries​:
  ld='gcc', ldflags =' -L/usr/local/lib'
  libpth=/usr/local/lib /lib /usr/lib
  libs=-lnsl -ldb -ldl -lm -lc -lcrypt -lutil
  perllibs=-lnsl -ldl -lm -lc -lcrypt -lutil
  libc=/lib/libc-2.2.2.so, so=so, useshrplib=false, libperl=libperl.a
  Dynamic Linking​:
  dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
  cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'

Locally applied patches​:

@​INC for perl v5.6.1​:
  /usr/local/lib/perl5/5.6.1/i686-linux-64all-ld
  /usr/local/lib/perl5/5.6.1
  /usr/local/lib/perl5/site_perl/5.6.1/i686-linux-64all-ld
  /usr/local/lib/perl5/site_perl/5.6.1
  /usr/local/lib/perl5/site_perl
  .

Environment for perl v5.6.1​:
  HOME=/home/bryan
  LANG=en
  LANGUAGE=en_US​:en
  LC_COLLATE=en_US
  LC_CTYPE=en_US
  LC_MESSAGES=en_US
  LC_MONETARY=en_US
  LC_NUMERIC=en_US
  LC_TIME=en_US
  LD_LIBRARY_PATH=/usr/lib
  LOGDIR (unset)

PATH=.​:/home/bryan/bin​:/usr/local/bin​:/bin​:/usr/bin​:/usr/X11R6/bin​:/sbin​:/us
r/sbin PERL_BADLANG (unset)
  SHELL=/bin/tcsh
�

From @smpeters

[bwarnock@​capita.com - Mon Sep 03 10​:43​:30 2001]​:

-----------------------------------------------------------------
Local variables declared in a conditional expression of a
conditional block are not restored at the end of scope.

$a = 10;
if (local $a = 1){
}
print $a; # Should be 10, not 1

Applies to local variables declared in 'if (expr)', 'unless(expr)',
and 'elsif (expr)'. Lexical variables are okay, as are local
variables in the conditional expression of a loop block.

This behavior has been fixed in bleadperl by not allowing it.

./perl rt_7615.pl
Can't localize lexical variable $a at rt_7615.pl line 4.

@smpeters - Status changed from 'open' to 'resolved'

From @tamias

On Fri, Aug 26, 2005 at 09​:06​:50AM -0700, Steve Peters via RT wrote​:

[bwarnock@​capita.com - Mon Sep 03 10​:43​:30 2001]​:

-----------------------------------------------------------------
Local variables declared in a conditional expression of a
conditional block are not restored at the end of scope.

$a = 10;
if (local $a = 1){
}
print $a; # Should be 10, not 1

Applies to local variables declared in 'if (expr)', 'unless(expr)',
and 'elsif (expr)'. Lexical variables are okay, as are local
variables in the conditional expression of a loop block.

This behavior has been fixed in bleadperl by not allowing it.

./perl rt_7615.pl
Can't localize lexical variable $a at rt_7615.pl line 4.

$a isn't a lexical variable in the example, so that doesn't fix it.

Ronald

From mjtg@cam.ac.uk

Steve Peters wrote

This behavior has been fixed in bleadperl by not allowing it.

./perl rt_7615.pl
Can't localize lexical variable $a at rt_7615.pl line 4.

No it hasn't. I suspect you did the wrong test - what's that
"lexical" doing in the error message?

When I try

perl5.8.6 -w
$a = 10;
if (local $a = 1){
}
print $a; # Should be 10, not 1
__END__
Found = in conditional, should be == at - line 2.
1

the bug is still present.

I presume this is another manifestation of the fact that a conditional
involves *two* scopes, one including the condition and one not.
Perl conflates them, with unfortunate results.

I presume the resaon for conflating them is efficiency.

Mike Guy

@smpeters - Status changed from 'resolved' to 'open'

From @smpeters

[mjtg@​cam.ac.uk - Fri Aug 26 09​:47​:17 2005]​:

Steve Peters wrote

This behavior has been fixed in bleadperl by not allowing it.

./perl rt_7615.pl
Can't localize lexical variable $a at rt_7615.pl line 4.

No it hasn't. I suspect you did the wrong test - what's that
"lexical" doing in the error message?

When I try

perl5.8.6 -w
$a = 10;
if (local $a = 1){
}
print $a; # Should be 10, not 1
__END__
Found = in conditional, should be == at - line 2.
1

the bug is still present.

I presume this is another manifestation of the fact that a conditional
involves *two* scopes, one including the condition and one not.
Perl conflates them, with unfortunate results.

I presume the resaon for conflating them is efficiency.

Sorry, a C<my> crept into my code I was using for testing. So, it
appears at least lexical globals are fixed in blead, although
non-lexicals are still as broken as before. Ticket re-opened.

@smpeters - Status changed from 'open' to 'resolved'

@smpeters - Status changed from 'resolved' to 'open'

From @schwern

On Fri, Aug 26, 2005 at 09​:06​:50AM -0700, Steve Peters via RT wrote​:

$a = 10;
if (local $a = 1){
}
print $a; # Should be 10, not 1

Still busted in 5.8.6 and blead.

$ bleadperl -wle '$a = 10; if( local $a = 1 ) {} print $a'
Found = in conditional, should be == at -e line 1.
1
$ bleadperl -wle '$a = 10; if( my $a = 1 ) {} print $a'
Found = in conditional, should be == at -e line 1.
10

--
Michael G Schwern schwern@​pobox.com http​://www.pobox.com/~schwern
'All anyone gets in a mirror is themselves,' she said. 'But what you
gets in a good gumbo is everything.'
  -- "Witches Abroad" by Terry Prachett

From @jkeenan

On Sat Sep 10 14​:08​:31 2005, schwern wrote​:

On Fri, Aug 26, 2005 at 09​:06​:50AM -0700, Steve Peters via RT wrote​:

$a = 10;
if (local $a = 1){
}
print $a; # Should be 10, not 1

Still busted in 5.8.6 and blead.

$ bleadperl -wle '$a = 10; if( local $a = 1 ) {} print $a'
Found = in conditional, should be == at -e line 1.
1
$ bleadperl -wle '$a = 10; if( my $a = 1 ) {} print $a'
Found = in conditional, should be == at -e line 1.
10

And still busted in 5.16.0.

From @iabyn

On Sat, May 26, 2012 at 06​:10​:39PM -0700, James E Keenan via RT wrote​:

On Sat Sep 10 14​:08​:31 2005, schwern wrote​:

On Fri, Aug 26, 2005 at 09​:06​:50AM -0700, Steve Peters via RT wrote​:

$a = 10;
if (local $a = 1){
}
print $a; # Should be 10, not 1

Still busted in 5.8.6 and blead.

$ bleadperl -wle '$a = 10; if( local $a = 1 ) {} print $a'
Found = in conditional, should be == at -e line 1.
1
$ bleadperl -wle '$a = 10; if( my $a = 1 ) {} print $a'
Found = in conditional, should be == at -e line 1.
10

And still busted in 5.16.0.

The comparison to lexical vars is slightly misleading; its actually
lexical vars which are the more broken​: the scope of the visibility of the
'my' declaration doesn't match the scope of when the lexical is actually
freed​:

  sub DESTROY { warn "DESTROY(@​_)\n" }

  {
  $x = 1;
  if (my $x = bless []) {
  warn "in IF block​: $x\n";
  }
  warn "exited IF block​: $x\n";
  }
  warn "exited outer block​: $x\n";

  warn "----\n";

  {
  $a = 1;

  if (local $a = 2) {
  warn "in IF block​: $a\n";
  }
  warn "exited IF block​: $a\n";
  }
  warn "exited outer block​: $a\n";

which outputs​:

  in IF block​: main=ARRAY(0x235bde8)
  exited IF block​: 1
  DESTROY(main=ARRAY(0x235bde8))
  exited outer block​: 1
  ----
  in IF block​: 2
  exited IF block​: 2
  exited outer block​: 1

Here, the scope of when the lexical is freed and when the 'local' is
undone, is consistently at the end of the enclosing block, which could
arguably be viewed as correct; however the visibility of the lexical
*declaration* is only for the inner block.

--
"Do not dabble in paradox, Edward, it puts you in danger of fortuitous wit."
  -- Lady Croom, "Arcadia"

From @doy

On Sun, May 27, 2012 at 11​:22​:45PM +0100, Dave Mitchell wrote​:

On Sat, May 26, 2012 at 06​:10​:39PM -0700, James E Keenan via RT wrote​:

On Sat Sep 10 14​:08​:31 2005, schwern wrote​:

On Fri, Aug 26, 2005 at 09​:06​:50AM -0700, Steve Peters via RT wrote​:

$a = 10;
if (local $a = 1){
}
print $a; # Should be 10, not 1

Still busted in 5.8.6 and blead.

$ bleadperl -wle '$a = 10; if( local $a = 1 ) {} print $a'
Found = in conditional, should be == at -e line 1.
1
$ bleadperl -wle '$a = 10; if( my $a = 1 ) {} print $a'
Found = in conditional, should be == at -e line 1.
10

And still busted in 5.16.0.

The comparison to lexical vars is slightly misleading; its actually
lexical vars which are the more broken​: the scope of the visibility of the
'my' declaration doesn't match the scope of when the lexical is actually
freed​:

sub DESTROY \{ warn "DESTROY\(@​\_\)\\n" \}

\{
$x = 1;
if \(my $x = bless \[\]\) \{
    warn "in IF block​: $x\\n";
\}
warn "exited IF block​: $x\\n";
\}
warn "exited outer block​: $x\\n";

warn "\-\-\-\-\\n";

\{
$a = 1;

if \(local $a = 2\) \{
    warn "in IF block​: $a\\n";
\}
warn "exited IF block​: $a\\n";
\}
warn "exited outer block​: $a\\n";

which outputs​:

in IF block​: main=ARRAY\(0x235bde8\)
exited IF block​: 1
DESTROY\(main=ARRAY\(0x235bde8\)\)
exited outer block​: 1
\-\-\-\-
in IF block​: 2
exited IF block​: 2
exited outer block​: 1

Here, the scope of when the lexical is freed and when the 'local' is
undone, is consistently at the end of the enclosing block, which could
arguably be viewed as correct; however the visibility of the lexical
*declaration* is only for the inner block.

I've run into this several times in my own code, in the form of​:

  if (my $foo = something()) {
  # use $foo
  }
  elsif (my $foo = something_else()) {
  # use $foo
  }

which gives a '"my" variable $foo masks earlier declaration in same scope'
warning under "use warnings". It is somewhat irritating.

-doy

This ticket was erroneously migrated in a closed state

I'm not convinced doy's thing is actually the same problem - the contents of the psuedoscope for the if condition should persist further on, given e.g.

sub foo { (1, 2) }
if (4 < (my @foo = foo())) { meh() } else { \@foo }

being perfectly reasonable code - the question of whether the elsif condition should regard itself as a direct continuation of the if condition's pseudoscope (in which case the warning is correct) or as a new pseudoscope deriving itself from the if condition's pseudoscope (in which case the code doy provides should be warning free) seems arguable either way but separate to the late-destroy problem AFAICT.

I believe the current behavior is the correct one in the bigger picture, even if I understand why the behavior proposed here is more intuitive at first