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[perl #118983] keys()/values() autovivify dereferenced undefined scalar

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From:
Anand Galama
Date:
July 23, 2013 10:18
Subject:
[perl #118983] keys()/values() autovivify dereferenced undefined scalar
Message ID:
rt-3.6.HEAD-2552-1374574676-390.118983-75-0@perl.org
# New Ticket Created by  Anand Galama 
# Please include the string:  [perl #118983]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org:443/rt3/Ticket/Display.html?id=118983 >


This is a bug report for perl from galama@mailfish.de,
generated with the help of perlbug 1.39 running under perl 5.14.4.


-----------------------------------------------------------------
[Please describe your issue here]


When called with a dereferenced undefined scalar variable, keys()
and values() create a reference to an empty hash:

$ perl -MData::Dumper -e 'print Dumper($h); keys %$h; print Dumper($h)'
$VAR1 = undef;
$VAR1 = {};
$ perl -MData::Dumper -e 'print Dumper($h); values %$h; print Dumper($h)'
$VAR1 = undef;
$VAR1 = {};
$

The documentation says: "As a side effect, calling keys()/values()
resets the internal interator of the HASH or ARRAY (see "each")."

I am not sure if this is meant to imply that $h should point to a newly
created empty hash afterwards in the above case. If so, this should be
stated explicitly. I found this very surprising.


[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
    category=core
    severity=low
---
This perlbug was built using Perl 5.14.4 in the Fedora build system.
It is being executed now by Perl 5.14.4 - Thu Apr 11 12:56:04 UTC 2013.

Site configuration information for perl 5.14.4:

Configured by Red Hat, Inc. at Thu Apr 11 12:56:04 UTC 2013.

Summary of my perl5 (revision 5 version 14 subversion 4) configuration:

  Platform:
    osname=linux, osvers=2.6.32-358.2.1.el6.x86_64,
archname=x86_64-linux-thread-multi
    uname='linux buildvm-11.phx2.fedoraproject.org
2.6.32-358.2.1.el6.x86_64 #1 smp wed feb 20 12:17:37 est 2013 x86_64
x86_64 x86_64 gnulinux '
    config_args='-des -Doptimize=-O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4  -m64 -mtune=generic
-Dccdlflags=-Wl,--enable-new-dtags -Dlddlflags=-shared -O2 -g -pipe
-Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4  -m64 -mtune=generic -Wl,-z,relro
-DDEBUGGING=-g -Dversion=5.14.4 -Dmyhostname=localhost
-Dperladmin=root@localhost -Dcc=gcc -Dcf_by=Red Hat, Inc. -Dprefix=/usr
-Dvendorprefix=/usr -Dsiteprefix=/usr/local
-Dsitelib=/usr/local/share/perl5 -Dsitearch=/usr/local/lib64/perl5
-Dprivlib=/usr/share/perl5 -Dvendorlib=/usr/share/perl5/vendor_perl
-Darchlib=/usr/lib64/perl5 -Dvendorarch=/usr/lib64/perl5/vendor_perl
-Darchname=x86_64-linux-thread-multi -Dlibpth=/usr/local/lib64 /lib64
/usr/lib64 -Duseshrplib -Dusethreads -Duseithreads
-Dusedtrace=/usr/bin/dtrace -Duselargefiles -Dd_semctl_semun -Di_db
-Ui_ndbm -Di_gdbm -Di_shadow -Di_syslog -Dman3ext=3pm -Duseperlio
-Dinstallusrbinperl=n -Ubincompat5005 -Uversiononly
-Dpager=/usr/bin/less -isr -Dd_gethostent_r_proto -Ud_endhostent_r_proto
-Ud_sethostent_r_proto -Ud_endprotoent_r_proto -Ud_setprotoent_r_proto
-Ud_endservent_r_proto -Ud_setservent_r_proto -Dscriptdir=/usr/bin'
    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='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing
-pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE
-D_FILE_OFFSET_BITS=64',
    optimize='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions
-fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe
-fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.7.2 20120921 (Red Hat 4.7.2-2)',
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='gcc', ldflags =' -fstack-protector'
    libpth=/usr/local/lib64 /lib64 /usr/lib64
    libs=-lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread
-lc -lgdbm_compat
    perllibs=-lresolv -lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    libc=, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.15'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef,
ccdlflags='-Wl,--enable-new-dtags -Wl,-rpath,/usr/lib64/perl5/CORE'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -g -pipe -Wall
-Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m64 -mtune=generic -Wl,-z,relro '

Locally applied patches:


---
@INC for perl 5.14.4:
    /home/xxx/src/perl
    /usr/local/lib64/perl5
    /usr/local/share/perl5
    /usr/lib64/perl5/vendor_perl
    /usr/share/perl5/vendor_perl
    /usr/lib64/perl5
    /usr/share/perl5
    .

---
Environment for perl 5.14.4:
    HOME=/home/xxx
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LC_MEASUREMENT=de_DE.utf8
    LC_MONETARY=de_DE.utf8
    LC_NUMERIC=de_DE.utf8
    LC_TIME=de_DE.utf8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)

PATH=/usr/lib64/qt-3.3/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/home/xxx/.local/bin:/home/xxx/bin
    PERL5LIB=/home/xxx/src/perl
    PERL_BADLANG (unset)
    SHELL=/bin/bash


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