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[perl #129177] No autovivification, for loop aliasing,

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From:
Leszek Dubiel
Date:
September 2, 2016 21:44
Subject:
[perl #129177] No autovivification, for loop aliasing,
Message ID:
rt-4.0.24-14079-1472849664-741.129177-75-0@perl.org
# New Ticket Created by  Leszek Dubiel 
# Please include the string:  [perl #129177]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=129177 >



This is a bug report for perl from leszek@dubiel.pl,
generated with the help of perlbug 1.40 running under perl 5.20.2.


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


This is after the discussion here:  http://www.perlmonks.org/?node_id=1171041

Data structure:

my $n = {
     a => [1, 2 ],
     b => [3, 4],
};

This throws exception:

@{$$n{'x'}};

And this doesn't:

for my $e (@{$$n{'x'}}) {
}

Maybe it is somehow connected with autovivification.




Here is program:

#!/usr/bin/perl -CSDA

use utf8;
use strict;
use warnings;
no warnings qw{uninitialized numeric};
no autovivification; #  qw{fetch exists delete store};
use Data::Dumper;

print "\n\ninitialize data structures, no autovivification\n";
my $n = {
     a => [1, 2 ],
     b => [3, 4],
};
$$n{'x'}{'y'}{'z'} and die;
$$n{'x'}{'y'}[0] and die;
$$n{'x'}{'y'} and die;
$$n{'x'} and die;
print "so far, so good, no 'x' autovivified:\n";
print Dumper $n;

# "Can't use an undefined value as an ARRAY reference":
# @{$$n{'x'}} and die;

print "\n\nnow the same but in loop:\n";
for my $e (@{$$n{'x'}}) {
}
print "why 'x' autovivified?\n";
print Dumper $n;

print "\n\nnow the same but in loop:\n";
for my $e (@{[ $$n{'y'} ]}) {
}
print "why 'y' NOT autovivified?\n";
print Dumper $n;







[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
     category=core
     severity=low
---
Site configuration information for perl 5.20.2:

Configured by Debian Project at Sun Jul 24 19:46:25 UTC 2016.

Summary of my perl5 (revision 5 version 20 subversion 2) configuration:
    
   Platform:
     osname=linux, osvers=3.16.0-4-amd64, archname=i586-linux-gnu-thread-multi-64int
     uname='linux x86-csail-01 3.16.0-4-amd64 #1 smp debian 3.16.7-ckt25-2+deb8u3 (2016-07-02) i686 gnulinux '
     config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -D_FORTIFY_SOURCE=2 -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -Dldflags= -Wl,-z,relro -Dlddlflags=-shared -Wl,-z,relro -Dcccdlflags=-fPIC -Darchname=i586-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.20 -Darchlib=/usr/lib/i386-linux-gnu/perl/5.20 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/i386-linux-gnu/perl5/5.20 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.20.2 -Dsitearch=/usr/local/lib/i386-linux-gnu/perl/5.20.2 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Dusesitecustomize -Duse64bitint -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -Ui_libutil -Uversiononly -DDEBUGGING=-g -Doptimize=-O2 -Duseshrplib -Dlibperl=libperl.so.5.20.2 -des'
     hint=recommended, useposix=true, d_sigaction=define
     useithreads=define, usemultiplicity=define
     use64bitint=define, use64bitall=undef, uselongdouble=undef
     usemymalloc=n, bincompat5005=undef
   Compiler:
     cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fwrapv -fno-strict-aliasing -pipe -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
     optimize='-O2 -g',
     cppflags='-D_REENTRANT -D_GNU_SOURCE -DDEBIAN -fwrapv -fno-strict-aliasing -pipe -I/usr/local/include'
     ccversion='', gccversion='4.9.2', 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='double', nvsize=8, Off_t='off_t', lseeksize=8
     alignbytes=4, prototype=define
   Linker and Libraries:
     ld='cc', ldflags =' -fstack-protector -L/usr/local/lib'
     libpth=/usr/local/lib /usr/lib/gcc/i586-linux-gnu/4.9/include-fixed /usr/include/i386-linux-gnu /usr/lib /lib/i386-linux-gnu /lib/../lib /usr/lib/i386-linux-gnu /usr/lib/../lib /lib
     libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
     perllibs=-ldl -lm -lpthread -lc -lcrypt
     libc=libc-2.19.so, so=so, useshrplib=true, libperl=libperl.so.5.20
     gnulibc_version='2.19'
   Dynamic Linking:
     dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
     cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib -fstack-protector'

Locally applied patches:
     DEBPKG:debian/cpan_definstalldirs - Provide a sensible INSTALLDIRS default for modules installed from CPAN.
     DEBPKG:debian/db_file_ver - http://bugs.debian.org/340047 Remove overly restrictive DB_File version check.
     DEBPKG:debian/doc_info - Replace generic man(1) instructions with Debian-specific information.
     DEBPKG:debian/enc2xs_inc - http://bugs.debian.org/290336 Tweak enc2xs to follow symlinks and ignore missing @INC directories.
     DEBPKG:debian/errno_ver - http://bugs.debian.org/343351 Remove Errno version check due to upgrade problems with long-running processes.
     DEBPKG:debian/libperl_embed_doc - http://bugs.debian.org/186778 Note that libperl-dev package is required for embedded linking
     DEBPKG:fixes/respect_umask - Respect umask during installation
     DEBPKG:debian/writable_site_dirs - Set umask approproately for site install directories
     DEBPKG:debian/extutils_set_libperl_path - EU:MM: set location of libperl.a under /usr/lib
     DEBPKG:debian/no_packlist_perllocal - Don't install .packlist or perllocal.pod for perl or vendor
     DEBPKG:debian/prefix_changes - Fiddle with *PREFIX and variables written to the makefile
     DEBPKG:debian/fakeroot - Postpone LD_LIBRARY_PATH evaluation to the binary targets.
     DEBPKG:debian/instmodsh_doc - Debian policy doesn't install .packlist files for core or vendor.
     DEBPKG:debian/ld_run_path - Remove standard libs from LD_RUN_PATH as per Debian policy.
     DEBPKG:debian/libnet_config_path - Set location of libnet.cfg to /etc/perl/Net as /usr may not be writable.
     DEBPKG:debian/mod_paths - Tweak @INC ordering for Debian
     DEBPKG:debian/module_build_man_extensions - http://bugs.debian.org/479460 Adjust Module::Build manual page extensions for the Debian Perl policy
     DEBPKG:debian/prune_libs - http://bugs.debian.org/128355 Prune the list of libraries wanted to what we actually need.
     DEBPKG:fixes/net_smtp_docs - [rt.cpan.org #36038] http://bugs.debian.org/100195 Document the Net::SMTP 'Port' option
     DEBPKG:debian/perlivp - http://bugs.debian.org/510895 Make perlivp skip include directories in /usr/local
     DEBPKG:debian/deprecate-with-apt - http://bugs.debian.org/747628 Point users to Debian packages of deprecated core modules
     DEBPKG:debian/squelch-locale-warnings - http://bugs.debian.org/508764 Squelch locale warnings in Debian package maintainer scripts
     DEBPKG:debian/skip-upstream-git-tests - Skip tests specific to the upstream Git repository
     DEBPKG:debian/patchlevel - http://bugs.debian.org/567489 List packaged patches for 5.20.2-3+deb8u6 in patchlevel.h
     DEBPKG:debian/skip-kfreebsd-crash - http://bugs.debian.org/628493 [perl #96272] Skip a crashing test case in t/op/threads.t on GNU/kFreeBSD
     DEBPKG:fixes/document_makemaker_ccflags - http://bugs.debian.org/628522 [rt.cpan.org #68613] Document that CCFLAGS should include $Config{ccflags}
     DEBPKG:debian/find_html2text - http://bugs.debian.org/640479 Configure CPAN::Distribution with correct name of html2text
     DEBPKG:debian/perl5db-x-terminal-emulator.patch - http://bugs.debian.org/668490 Invoke x-terminal-emulator rather than xterm in perl5db.pl
     DEBPKG:debian/cpan-missing-site-dirs - http://bugs.debian.org/688842 Fix CPAN::FirstTime defaults with nonexisting site dirs if a parent is writable
     DEBPKG:fixes/memoize_storable_nstore - [rt.cpan.org #77790] http://bugs.debian.org/587650 Memoize::Storable: respect 'nstore' option not respected
     DEBPKG:debian/regen-skip - Skip a regeneration check in unrelated git repositories
     DEBPKG:fixes/regcomp-mips-optim - [perl #122817] http://bugs.debian.org/754054 Downgrade the optimization of regcomp.c on mips and mipsel due to a gcc-4.9 bug
     DEBPKG:debian/makemaker-pasthru - http://bugs.debian.org/758471 Pass LD settings through to subdirectories
     DEBPKG:fixes/perldoc-less-R - [rt.cpan.org #98636] http://bugs.debian.org/758689 Tell the 'less' pager to allow terminal escape sequences
     DEBPKG:fixes/pod_man_reproducible_date - http://bugs.debian.org/759405 Support POD_MAN_DATE in Pod::Man for the left-hand footer
     DEBPKG:fixes/io_uncompress_gunzip_inmemory - http://bugs.debian.org/747363 [rt.cpan.org #95494] Fix gunzip to in-memory file handle
     DEBPKG:fixes/socket_test_recv_fix - http://bugs.debian.org/758718 [perl #122657] Compare recv return value to peername in socket test
     DEBPKG:fixes/hurd_socket_recv_todo - http://bugs.debian.org/758718 [perl #122657] TODO checking the result of recv() on hurd
     DEBPKG:fixes/regexp-performance - [0fa70a0] http://bugs.debian.org/777556 [perl #123743] simpify and speed up /.*.../ handling
     DEBPKG:fixes/failed_require_diagnostics - http://bugs.debian.org/781120 [perl #123270] Report inaccesible file on failed require
     DEBPKG:fixes/array-cloning - http://bugs.debian.org/779357 [perl #124127] [902d169] fix cloning arrays with unused elements
     DEBPKG:fixes/perldb-threads - http://bugs.debian.org/779357 [perl #124127] [41ef2c6] lib/perl5db.pl: Restore noop lock prototype
     DEBPKG:fixes/CVE-2015-8607_file_spec_taint_fix - ensure File::Spec::canonpath() preserves taint
     DEBPKG:fixes/encode-unicode-bom - http://bugs.debian.org/798727 [rt.cpan.org #107043] Address https://rt.cpan.org/Public/Bug/Display.html?id=107043
     DEBPKG:debian/encode-unicode-bom-doc - http://bugs.debian.org/798727 Document Debian backport of Encode::Unicode fix
     DEBPKG:debian/kfreebsd-softupdates - http://bugs.debian.org/796798 Work around Debian Bug#796798
     DEBPKG:fixes/CVE-2016-2381_duplicate_env - remove duplicate environment variables from environ
     DEBPKG:debian/debugperl-compat-fix - [perl #127212] http://bugs.debian.org/810326 Disable PERL_TRACK_MEMPOOL for debugging builds
     DEBPKG:fixes/CVE-2015-8853_regexp_hang - http://bugs.debian.org/821848 [perl #123562] PATCH [perl #123562] Regexp-matching "hangs"
     DEBPKG:fixes/utf8_regexp_crash - http://bugs.debian.org/820328 [perl #124109] save_re_context(): do "local $n" with no PL_curpm
     DEBPKG:fixes/regcomp_whitespace_fix - http://bugs.debian.org/820328 [perl #124109] Perl_save_re_context(): re-indent after last commit
     DEBPKG:fixes/5.20.3/eval_label_crash - http://bugs.debian.org/822336 [perl #123652] eval {label:} crash
     DEBPKG:fixes/5.20.3/preserve_record_separator - http://bugs.debian.org/822336 [perl #123218] "preserve" $/ if set to a bad value
     DEBPKG:fixes/5.20.3/test_count_base_rs - http://bugs.debian.org/822336 Fix test count in t/base/rs.t
     DEBPKG:fixes/5.20.3/remove_get_magic - http://bugs.debian.org/822336 [perl #123739] Remove get-magic from $/
     DEBPKG:fixes/5.20.3/speed_up_scalar_g - http://bugs.debian.org/822336 [perl #123202] speed up scalar //g against tainted strings
     DEBPKG:fixes/5.20.3/accidental_all_features - http://bugs.debian.org/822336 Stop $^H |= 0x1c020000 from enabling all features
     DEBPKG:fixes/5.20.3/multidimensional_arrays_utf8 - http://bugs.debian.org/822336 [perl #124113] Make check for multi-dimensional arrays be UTF8-aware
     DEBPKG:fixes/5.20.3/unquoted_utf8_heredoc_terminators - http://bugs.debian.org/822336 Allow unquoted UTF-8 HERE-document terminators
     DEBPKG:fixes/5.20.3/parentheses_ambiguous_warning_utf8_functions - http://bugs.debian.org/822336 Fix "...without parentheses is ambuguous" warning for UTF-8 function names
     DEBPKG:fixes/5.20.3/leak_namepv_copy - http://bugs.debian.org/822336 [perl #123786] don't leak the temp utf8 copy of namepv
     DEBPKG:fixes/5.20.3/h2ph_hex_constants - http://bugs.debian.org/822336 h2ph: correct handling of hex constants for the preamble
     DEBPKG:fixes/5.20.3/leftbracket_XTERMORDORDOR - http://bugs.debian.org/822336 [perl #123711] Fix crash with 0-5x-l{0}
     DEBPKG:fixes/5.20.3/fatalize_warnings_unwinding - http://bugs.debian.org/822336 [perl #123398] don't fatalize warnings during unwinding (#123398)
     DEBPKG:fixes/5.20.3/setpgrp - http://bugs.debian.org/822336 =?UTF-8?q?Don=E2=80=99t=20treat=20setpgrp($nonzero)=20as=20setpgr?= =?UTF-8?q?p(1)?=
     DEBPKG:fixes/5.20.3/death_unwinding_crash - http://bugs.debian.org/822336 [perl #124156] RT #124156: death during unwinding causes crash
     DEBPKG:fixes/5.20.3/stashpvn_crash - http://bugs.debian.org/822336 [perl #125541] Fix crash with %::=(); J->${\"::"}
     DEBPKG:fixes/5.20.3/possessive_quantifier - http://bugs.debian.org/822336 [perl #125825] PATCH: [perl 125825] {n}+ possessive quantifier broken
     DEBPKG:fixes/5.20.3/quoted_code_crash - http://bugs.debian.org/822336 [perl #123712] Fix /$a[/ parsing
     DEBPKG:fixes/5.20.3/checking_sub_inwhat - http://bugs.debian.org/822336 [perl #123712] Don't check sub_inwhat
     DEBPKG:fixes/5.20.3/yylex_loop - http://bugs.debian.org/822336 Fix hang with "@{"
     DEBPKG:fixes/5.20.3/docs/op - http://bugs.debian.org/822336 Fix apidocs for OP_TYPE_IS(_OR_WAS) - arguments separated by |, not ,.
     DEBPKG:fixes/5.20.3/docs/encoding - http://bugs.debian.org/822336 perlpodspec: Corrections/adds to detecting =encoding
     DEBPKG:fixes/5.20.3/docs/SvPV_set - http://bugs.debian.org/822336 improve SvPV_set's docs, it really shouldn't be public API
     DEBPKG:fixes/5.20.3/docs/autodie - http://bugs.debian.org/822336 Fix warning message regarding "use autodie" and "use open".
     DEBPKG:fixes/5.20.3/docs/autodie_2_26 - http://bugs.debian.org/822336 perlunicook: Note that autodie >= 2.26 should be okay with "use open".
     DEBPKG:fixes/5.20.3/docs/setenv - http://bugs.debian.org/822336 Fix setenv() replacement documentation in perlclib
     DEBPKG:fixes/5.20.3/docs/clib_caution - http://bugs.debian.org/822336 perlhacktips: Add caution about clib ptr returns to static memory
     DEBPKG:fixes/5.20.3/docs/perlunicook_typos - http://bugs.debian.org/822336 Fix minor code typos in perlunicook
     DEBPKG:fixes/5.20.3/docs/ook_example - http://bugs.debian.org/822336 [perl #122322] Update OOK example in perlguts
     DEBPKG:fixes/5.20.3/docs/study_noop - http://bugs.debian.org/822336 perlfunc: mention that study() is currently a noop
     DEBPKG:fixes/CVE-2016-1238/remove-dot-when-loading - [perl #127834] (perl #127834) remove . from the end of @INC if complex modules are loaded
     DEBPKG:fixes/CVE-2016-1238/remove-dot-in-padwalker - [perl #127834] perl5db.pl: ensure PadWalker is loaded from standard paths
     DEBPKG:fixes/CVE-2016-1238/remove-dot-in-dist - [perl #127834] dist/: remove . from @INC when loading optional modules
     DEBPKG:fixes/CVE-2016-1238/remove-dot-in-cpan - [perl #127834] cpan/: remove . from @INC when loading optional modules
     DEBPKG:fixes/CVE-2016-1238/customized-encode - Update customized.dat for cpan/Encode/Encode.pm
     DEBPKG:debian/CVE-2016-1238/test-suite-without-dot - [perl #127810] Patch unit tests to explicitly insert "." into @INC when needed.
     DEBPKG:debian/CVE-2016-1238/eumm-without-dot - [perl #127810] Add PERL_USE_UNSAFE_INC support to EU::MM for fortify_inc support.
     DEBPKG:debian/CVE-2016-1238/cpan-without-dot - [perl #127810] Set PERL_USE_UNSAFE_INC for cpan usage
     DEBPKG:debian/CVE-2016-1238/mb-without-dot - Make Module::Build set PERL_USE_UNSAFE_INC
     DEBPKG:debian/CVE-2016-1238/sitecustomize-in-etc - Look for sitecustomize.pl in /etc/perl rather than sitelib on Debian systems
     DEBPKG:fixes/xsloader-eval - [rt.cpan.org #115808] http://bugs.debian.org/829578 =?UTF-8?q?Don=E2=80=99t=20let=20XSLoader=20load=20relative=20path?= =?UTF-8?q?s?=

---
@INC for perl 5.20.2:
     /etc/perl
     /usr/local/lib/i386-linux-gnu/perl/5.20.2
     /usr/local/share/perl/5.20.2
     /usr/lib/i386-linux-gnu/perl5/5.20
     /usr/share/perl5
     /usr/lib/i386-linux-gnu/perl/5.20
     /usr/share/perl/5.20
     /usr/local/lib/site_perl

---
Environment for perl 5.20.2:
     HOME=/root
     LANG=pl_PL.UTF-8
     LANGUAGE (unset)
     LC_ADDRESS=pl_PL.UTF-8
     LC_IDENTIFICATION=pl_PL.UTF-8
     LC_MEASUREMENT=pl_PL.UTF-8
     LC_MONETARY=pl_PL.UTF-8
     LC_NAME=pl_PL.UTF-8
     LC_NUMERIC=pl_PL.UTF-8
     LC_PAPER=pl_PL.UTF-8
     LC_TELEPHONE=pl_PL.UTF-8
     LC_TIME=pl_PL.UTF-8
     LD_LIBRARY_PATH (unset)
     LOGDIR (unset)
     PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/bin/X11
     PERL_BADLANG (unset)
     SHELL=/bin/bash





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