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[perl #133240] Parsing lvalue subs returning a reference to a scalar

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From:
Philip R Brenan
Date:
June 4, 2018 13:25
Subject:
[perl #133240] Parsing lvalue subs returning a reference to a scalar
Message ID:
rt-4.0.24-14890-1527900448-838.133240-75-0@perl.org
# New Ticket Created by  Philip R Brenan 
# Please include the string:  [perl #133240]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=133240 >


Reply-To: philiprbrenan@gmail.com
To: perlbug@perl.org
Subject: Parsing lvalue subs returning a reference to a scalar
Message-Id: <5.22.1_20124_1527899987@pousadouros>
From: philiprbrenan@gmail.com

This is a bug report for perl generated with the help of perlbug 1.40
running
under perl 5.22.1.

#!/usr/bin/perl
require v5.16;

=pod

Lvalue subs returning a reference to a scalar are not always recognized in
the
same way that a scalar would be in a similar syntactic context.

=cut

my $aaa;                # Scalar - all OK
$aaa   = undef;
$aaa  += 0;
$aaa //= undef;

sub aaa:lvalue {\my $r} # Scalar returned via Lvalue sub
aaa   = undef;
aaa  += 0;              # Syntax error near "+="
aaa //= undef;          # Can't modify pattern match (m//) in scalar
assignment
---
Flags:
    category=library
    severity=none
    module=
---
Site configuration information for perl 5.22.1:

Configured by Debian Project at Thu Apr  5 12:48:47 UTC 2018.

Summary of my perl5 (revision 5 version 22 subversion 1) configuration:

  Platform:
    osname=linux, osvers=3.16.0, archname=x86_64-linux-gnu-thread-multi
    uname='linux localhost 3.16.0 #1 smp debian 3.16.0 x86_64 gnulinux '
    config_args='-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 -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/5.22
-Darchlib=/usr/lib/x86_64-linux-gnu/perl/5.22 -Dvendorprefix=/usr
-Dvendorlib=/usr/share/perl5
-Dvendorarch=/usr/lib/x86_64-linux-gnu/perl5/5.22 -Dsiteprefix=/usr/local
-Dsitelib=/usr/local/share/perl/5.22.1
-Dsitearch=/usr/local/lib/x86_64-linux-gnu/perl/5.22.1
-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 -Uversiononly
-DDEBUGGING=-g -Doptimize=-O2 -dEs -Duseshrplib -Dlibperl=libperl.so.5.22.1'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, 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='5.4.0 20160609', 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/lib/gcc/x86_64-linux-gnu/5/include-fixed
/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-2.23.so, so=so, useshrplib=true, libperl=libperl.so.5.22
    gnulibc_version='2.23'
  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 - 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/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/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 5.22.1-9ubuntu0.3 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:debian/makemaker-pasthru - http://bugs.debian.org/758471 Pass LD
settings through to subdirectories
    DEBPKG:fixes/pod_man_reproducible_date - http://bugs.debian.org/759405
Support POD_MAN_DATE in Pod::Man for the left-hand footer
    DEBPKG:debian/locale-robustness - http://bugs.debian.org/782068 [perl
#124310] Make t/run/locale.t survive missing locales masked by LC_ALL
    DEBPKG:fixes/podman-utc - http://bugs.debian.org/780259 Make the
embedded date from Pod::Man reproducible
    DEBPKG:fixes/podman-utc-docs - http://bugs.debian.org/780259
Documentation and test suite updates for UTC fix
    DEBPKG:fixes/podman-empty-date - http://bugs.debian.org/780259 Support
an empty POD_MAN_DATE environment variable
    DEBPKG:fixes/podman-pipe - http://bugs.debian.org/777405 Better errors
for man pages from standard input
    DEBPKG:debian/pod2man-customized - Update porting/customized.dat for
pod2man modifications
    DEBPKG:debian/makemaker-manext - http://bugs.debian.org/247370 Make
EU::MakeMaker honour MANnEXT settings in generated manpage headers
    DEBPKG:debian/makemaker_customized - Update t/porting/customized.dat
for files patched in Debian
    DEBPKG:debian/do-not-record-build-date - [6baa8db]
http://bugs.debian.org/774422 [perl #125830] Allow overriding the compile
time in "perl -V" output
    DEBPKG:fixes/podman-source-date-epoch - http://bugs.debian.org/801621
Make Pod::Man honor the SOURCE_DATE_EPOCH environment variable
    DEBPKG:fixes/podman-source-date-epoch-cleanups -
http://bugs.debian.org/801621 Coding style and documentation for
SOURCE_EPOCH_DATE
    DEBPKG:fixes/podman-source-date-epoch-testfix -
http://bugs.debian.org/807086 Guard for building with SOURCE_DATE_EPOCH or
POD_MAN_DATE set
    DEBPKG:debian/devel-ppport-reproducibility -
http://bugs.debian.org/801523 Sort the list of XS code files when
generating RealPPPort.xs
    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/autodie-scope - http://bugs.debian.org/798096 Fix a
scoping issue with "no autodie" and the "system" sub
    DEBPKG:debian/debugperl-compat-fix - [perl #127212]
http://bugs.debian.org/810326 Disable PERL_TRACK_MEMPOOL for debugging
builds
    DEBPKG:fixes/CVE-2015-8607_file_spec_taint_fix -
http://bugs.debian.org/810719 [perl #126862] ensure File::Spec::canonpath()
preserves taint
    DEBPKG:fixes/mkstemp-umask - http://bugs.debian.org/810924 [perl
#127322] [e57270b] Fix umask for mkstemp(3) calls
    DEBPKG:fixes/crosscompile-no-targethost - [perl #127234] Fix the
Configure escape with usecrosscompile but no targethost
    DEBPKG:fixes/podlators-no-encode - [rt.cpan.org #111156] Degrade
gracefully if utf8 is requested but Encode is not available
    DEBPKG:debian/cross-time-hires - [rt.cpan.org #111391] Add an
environment variable to skip running configuration probes
    DEBPKG:fixes/encode-unicode-pod - Unicode.pm: Fix POD error
    DEBPKG:fixes/memoize-pod - [rt.cpan.org #89441] Fix POD errors in
Memoize
    DEBPKG:fixes/ok-pod - Added encoding for pod.
    DEBPKG:fixes/CVE-2016-2381_duplicate_env - remove duplicate environment
variables from environ
    DEBPKG:fixes/CVE-2017-12837.patch - [PATCH] regcomp [perl #131582]
    DEBPKG:fixes/CVE-2017-12883.patch - [PATCH] PATCH: [perl #131598]
    DEBPKG:fixes/CVE-2016-6185.patch - [PATCH]
=?utf8?q?Don=E2=80=99t=20let=20XSLoader=20load=20relative?=
=?utf8?q?=20paths?=
    DEBPKG:fixes/CVE-2017-6512-pre.patch - [PATCH] Correct the order of
tests of chmod(). (#294)
    DEBPKG:fixes/CVE-2017-6512.patch - http://bugs.debian.org/863870 [
rt.cpan.org #121951] Prevent directory chmod race attack.
    DEBPKG:fixes/CVE-2018-6797.patch - (perl #132227) restart a node if we
change to uni rules within the node and encounter a sharp S
    DEBPKG:fixes/CVE-2018-6798-1.patch - [perl #132063]: Heap buffer
overflow
    DEBPKG:fixes/CVE-2018-6798-2.patch - v5.24.3: fix TRIE_READ_CHAR and
DECL_TRIE_TYPE to account for non-utf8 target
    DEBPKG:fixes/CVE-2018-6798-3.patch - (perl #132063) we should no longer
warn for this code
    DEBPKG:fixes/CVE-2018-6913.patch - (perl #131844) fix various space
calculation issues in pp_pack.c

---
@INC for perl 5.22.1:
    /etc/perl
    /usr/local/lib/x86_64-linux-gnu/perl/5.22.1
    /usr/local/share/perl/5.22.1
    /usr/lib/x86_64-linux-gnu/perl5/5.22
    /usr/share/perl5
    /usr/lib/x86_64-linux-gnu/perl/5.22
    /usr/share/perl/5.22
    /usr/local/lib/site_perl
    /usr/lib/x86_64-linux-gnu/perl-base
    .

---
Environment for perl 5.22.1:
    HOME=/home/phil
    LANG=en_US.UTF-8
    LANGUAGE=en_US
    LC_ADDRESS=en_US.UTF-8
    LC_ALL=en_US.UTF-8
    LC_CTYPE=en_US.UTF-8
    LC_IDENTIFICATION=en_US.UTF-8
    LC_MEASUREMENT=en_US.UTF-8
    LC_MONETARY=en_US.UTF-8
    LC_NAME=en_US.UTF-8
    LC_NUMERIC=en_US.UTF-8
    LC_PAPER=en_US.UTF-8
    LC_TELEPHONE=en_US.UTF-8
    LC_TIME=en_US.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/phil/Android/sdk/tools/:/home/phil/Android/sdk/platform-tools/:/home/phil/.local/bin:/home/phil/Android/sdk/tools/:/home/phil/Android/sdk/platform-tools/:/home/phil/.local/bin
    PERL_BADLANG (unset)
    SHELL=/bin/bash


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