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each @{ [qw/a b c/] } loops forever #18557

Closed jimav closed 3 years ago

jimav commented 3 years ago

This is a bug report for perl from jima.avera@gmail.com, generated with the help of perlbug 1.41 running under perl 5.30.0.

'each' on anonymous array always returns element [0], looping forever

#!/usr/bin/perl
use strict; use warnings; use v5.20;

my @a = (qw/a b c/);

while (my($ix,$val) = each @a) { say "$ix $val"; } #ok

while (my($ix,$val) = each @{ \@a }) { say "$ix $val"; } #ok

while (my($ix,$val) = each @{ [ @a ] }) { say "$ix $val"; } #infinite loop

while (my($ix,$val) = each @{ [qw/a b c/] }) { say "$ix $val"; } #infinite loop

Flags: category=core severity=medium

Site configuration information for perl 5.30.0:

Configured by Ubuntu at Mon Oct 19 10:56:54 UTC 2020.

Summary of my perl5 (revision 5 version 30 subversion 0) configuration:

Platform: osname=linux osvers=4.19.0 archname=x86_64-linux-gnu-thread-multi uname='linux localhost 4.19.0 #1 smp debian 4.19.0 x86_64 gnulinux ' config_args='-Dmksymlinks -Dusethreads -Duselargefiles -Dcc=x86_64-linux-gnu-gcc -Dcpp=x86_64-linux-gnu-cpp -Dld=x86_64-linux-gnu-gcc -Dccflags=-DDEBIAN -Wdate-time -D_FORTIFY_SOURCE=2 -g -O2 -fdebug-prefix-map=/build/perl-Wfb2Cd/perl-5.30.0=. -fstack-protector-strong -Wformat -Werror=format-security -Dldflags= -Wl,-Bsymbolic-functions -Wl,-z,relro -Dlddlflags=-shared -Wl,-Bsymbolic-functions -Wl,-z,relro -Dcccdlflags=-fPIC -Darchname=x86_64-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.30 -Darchlib=/usr/lib/x86_64-linux-gnu/perl/5.30 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/x86_64-linux-gnu/perl5/5.30 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.30.0 -Dsitearch=/usr/local/lib/x86_64-linux-gnu/perl/5.30.0 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/man/man3 -Duse64bitint -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -Ui_libutil -Ui_xlocale -Uversiononly -DDEBUGGING=-g -Doptimize=-O2 -dEs -Duseshrplib -Dlibperl=libperl.so.5.30.0' hint=recommended useposix=true d_sigaction=define useithreads=define usemultiplicity=define use64bitint=define use64bitall=define uselongdouble=undef usemymalloc=n default_inc_excludes_dot=define bincompat5005=undef Compiler: cc='x86_64-linux-gnu-gcc' 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='9.3.0' gccosandvers='' intsize=4 longsize=8 ptrsize=8 doublesize=8 byteorder=12345678 doublekind=3 d_longlong=define longlongsize=8 d_longdbl=define longdblsize=16 longdblkind=3 ivtype='long' ivsize=8 nvtype='double' nvsize=8 Off_t='off_t' lseeksize=8 alignbytes=8 prototype=define Linker and Libraries: ld='x86_64-linux-gnu-gcc' ldflags =' -fstack-protector-strong -L/usr/local/lib' libpth=/usr/local/lib /usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib /usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt perllibs=-ldl -lm -lpthread -lc -lcrypt libc=libc-2.31.so so=so useshrplib=true libperl=libperl.so.5.30 gnulibc_version='2.31' Dynamic Linking: dlsrc=dl_dlopen.xs dlext=so d_dlsymun=undef ccdlflags='-Wl,-E' cccdlflags='-fPIC' lddlflags='-shared -L/usr/local/lib -fstack-protector-strong'

Locally applied patches: DEBPKG:debian/cpan_definstalldirs - Provide a sensible INSTALLDIRS default for modules installed from CPAN. DEBPKG:debian/db_file_ver - https://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 - https://bugs.debian.org/290336 Tweak enc2xs to follow symlinks and ignore missing @INC directories. DEBPKG:debian/errno_ver - https://bugs.debian.org/343351 Remove Errno version check due to upgrade problems with long-running processes. DEBPKG:debian/libperl_embed_doc - https://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/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/perlivp - https://bugs.debian.org/510895 Make perlivp skip include directories in /usr/local DEBPKG:debian/squelch-locale-warnings - https://bugs.debian.org/508764 Squelch locale warnings in Debian package maintainer scripts DEBPKG:debian/patchlevel - https://bugs.debian.org/567489 List packaged patches for 5.30.0-9ubuntu0.2 in patchlevel.h DEBPKG:fixes/document_makemaker_ccflags - https://bugs.debian.org/628522 [rt.cpan.org #68613] Document that CCFLAGS should include $Config{ccflags} DEBPKG:debian/find_html2text - https://bugs.debian.org/640479 Configure CPAN::Distribution with correct name of html2text DEBPKG:debian/perl5db-x-terminal-emulator.patch - https://bugs.debian.org/668490 Invoke x-terminal-emulator rather than xterm in perl5db.pl DEBPKG:debian/cpan-missing-site-dirs - https://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] https://bugs.debian.org/587650 Memoize::Storable: respect 'nstore' option not respected DEBPKG:debian/makemaker-pasthru - https://bugs.debian.org/758471 Pass LD settings through to subdirectories DEBPKG:debian/makemaker-manext - https://bugs.debian.org/247370 Make EU::MakeMaker honour MANnEXT settings in generated manpage headers DEBPKG:debian/kfreebsd-softupdates - https://bugs.debian.org/796798 Work around Debian Bug#796798 DEBPKG:fixes/autodie-scope - https://bugs.debian.org/798096 Fix a scoping issue with "no autodie" and the "system" sub DEBPKG:fixes/memoize-pod - [rt.cpan.org #89441] Fix POD errors in Memoize DEBPKG:debian/hurd-softupdates - https://bugs.debian.org/822735 Fix t/op/stat.t failures on hurd DEBPKG:fixes/math_complex_doc_great_circle - https://bugs.debian.org/697567 [rt.cpan.org #114104] Math::Trig: clarify definition of great_circle_midpoint DEBPKG:fixes/math_complex_doc_see_also - https://bugs.debian.org/697568 [rt.cpan.org #114105] Math::Trig: add missing SEE ALSO DEBPKG:fixes/math_complex_doc_angle_units - https://bugs.debian.org/731505 [rt.cpan.org #114106] Math::Trig: document angle units DEBPKG:fixes/cpan_web_link - https://bugs.debian.org/367291 CPAN: Add link to main CPAN web site DEBPKG:debian/hppa_op_optimize_workaround - https://bugs.debian.org/838613 Temporarily lower the optimization of op.c on hppa due to gcc-6 problems DEBPKG:debian/installman-utf8 - https://bugs.debian.org/840211 Generate man pages with UTF-8 characters DEBPKG:fixes/getopt-long-4 - https://bugs.debian.org/864544 [rt.cpan.org #122068] Fix issue #122068. DEBPKG:debian/hppa_opmini_optimize_workaround - https://bugs.debian.org/869122 Lower the optimization level of opmini.c on hppa DEBPKG:debian/sh4_op_optimize_workaround - https://bugs.debian.org/869373 Also lower the optimization level of op.c and opmini.c on sh4 DEBPKG:debian/perldoc-pager - https://bugs.debian.org/870340 [rt.cpan.org #120229] Fix perldoc terminal escapes when sensible-pager is less DEBPKG:debian/prune_libs - https://bugs.debian.org/128355 Prune the list of libraries wanted to what we actually need. DEBPKG:debian/mod_paths - Tweak @INC ordering for Debian DEBPKG:debian/configure-regen - https://bugs.debian.org/762638 Regenerate Configure et al. after probe unit changes DEBPKG:debian/deprecate-with-apt - https://bugs.debian.org/747628 Point users to Debian packages of deprecated core modules DEBPKG:debian/disable-stack-check - https://bugs.debian.org/902779 [perl #133327] Disable debugperl stack extension checks for binary compatibility with perl DEBPKG:fixes/eumm-usrmerge - https://bugs.debian.org/913637 Avoid mangling /bin non-perl shebangs on merged-/usr systems DEBPKG:debian/perlbug-editor - https://bugs.debian.org/922609 Use "editor" as the default perlbug editor, as per Debian policy DEBPKG:fixes/gid-parsing - [79e302e] https://bugs.debian.org/941985 [perl #134169] (perl #134169) mg.c reset endptr after use DEBPKG:fixes/CVE-2020-10543.patch - [PATCH v530 1/4] regcomp.c: Prevent integer overflow from nested regex quantifiers. DEBPKG:fixes/CVE-2020-10878-1.patch - [PATCH v530 2/4] study_chunk: extract rck_elide_nothing DEBPKG:fixes/CVE-2020-10878-2.patch - [PATCH v530 3/4] regcomp: use long jumps if there is any possibility of overflow DEBPKG:fixes/CVE-2020-12723.patch - [PATCH v530 4/4] study_chunk: avoid mutating regexp program within GOSUB

@INC for perl 5.30.0: /home/jima/lib/perl /home/jima/perl5/lib/perl5/x86_64-linux-gnu-thread-multi /home/jima/perl5/lib/perl5/5.30.0/x86_64-linux-gnu-thread-multi /home/jima/perl5/lib/perl5/5.30.0 /home/jima/perl5/lib/perl5/x86_64-linux-gnu-thread-multi /home/jima/perl5/lib/perl5 /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.30.0 /usr/local/share/perl/5.30.0 /usr/lib/x86_64-linux-gnu/perl5/5.30 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.30 /usr/share/perl/5.30 /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base

Environment for perl 5.30.0: HOME=/home/jima LANG=en_US.UTF-8 LANGUAGE (unset) LC_COLLATE=C LD_LIBRARY_PATH=/home/jima/local/lib:/opt/lib LOGDIR (unset) PATH=/home/jima/.local/bin:/home/jima/perl5/bin:/home/jima/bin:/home/jima/local/bin:/home/jima/jima_tools/x86_64/bin:/home/jima/jima_tools/bin:/home/jima/Qt/5.14.1/gcc_64/bin:/home/jima/Qt/Tools/QtCreator/bin:/opt/Qt/5.14.1/gcc_64/bin:/opt/Qt/Tools/QtCreator/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/bin/X11:/usr/local/bin:/usr/local/sbin:/usr/games:/usr/local/games:/snap/bin:. PERL5LIB=/home/jima/lib/perl:/home/jima/perl5/lib/perl5/x86_64-linux-gnu-thread-multi:/home/jima/perl5/lib/perl5 PERL_BADLANG (unset) PERL_LOCAL_LIB_ROOT=/home/jima/perl5 PERL_MB_OPT=--install_base /home/jima/perl5 PERL_MM_OPT=INSTALL_BASE=/home/jima/perl5 SHELL=/bin/bash

Grinnz commented 3 years ago

This is expected behavior. [] creates a new anonymous array (which subsequently has fresh iterator pointers) and while conditions are run on each iteration of the loop.

Grinnz commented 3 years ago

I would even say relying on your example of while (my($ix,$val) = each @{ \@a }) { say "$ix $val"; } is a bad idea. There are several operations that reset the variable-stored iterator used by each, some of which are non-obvious like using a hash in list context. Best to avoid each, and failing that, keep your each expression and loop as simple as possible, not referencing the variable in question at any other point in the iteration.

jimav commented 3 years ago

On 2/11/21 12:17 PM, Dan Book wrote:

I would even say relying on your example of |while (my($ix,$val) = each @{ \@a }) { say "$ix $val"; }| is a bad idea. There are several operations that reset the variable-stored iterator used by |each|, some of which are non-obvious like using a hash in list context. Best to avoid |each|, and failing that, keep your |each| expression and loop as simple as possible, not referencing the variable in question at any other point in the iteration.

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Ok, I see now the problem with the anon array.  Sorry for that.

tonycoz commented 3 years ago

As this is documented behaviour, closing.