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Parsing lvalue subs returning a reference to a scalar #16575

Open p5pRT opened 6 years ago

p5pRT commented 6 years ago

Migrated from rt.perl.org#133240 (status was 'open')

Searchable as RT133240$

p5pRT commented 6 years ago

From @philiprbrenan

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

p5pRT commented 6 years ago

From @cpansprout

On Fri\, 01 Jun 2018 17​:47​:28 -0700\, philiprbrenan@​gmail.com wrote​:

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

I think you want to drop the backslash.

aaa = undef; aaa += 0; # Syntax error near "+=" aaa //= undef; # Can't modify pattern match (m//) in scalar assignment

Although\, conceivably these should do aliasing\, just like \$r = \....

--

Father Chrysostomos

p5pRT commented 6 years ago

The RT System itself - Status changed from 'new' to 'open'

p5pRT commented 6 years ago

From @cpansprout

On Fri\, 01 Jun 2018 17​:47​:28 -0700\, philiprbrenan@​gmail.com wrote​:

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

I’ve just looked at it more closely. You are getting those syntax errors because aaa() has list precedence. If you declare it like this​:

sub aaa()​:lvalue {\my $r}

there is no output\, so it compiles without incident. But that it runs without incident I think is a bug. It looks like a side effect of refaliasing.

This​:

use experimental 'refaliasing'; our $r; sub aaa()​:lvalue {\$r} aaa = \our $s; warn \$r; warn \$s;

gives me​:

SCALAR(0x7fc64a82b768) at - line 4. SCALAR(0x7fc64a82b858) at - line 5.

which shows that the assignment did nothing. It should probably have produced this​:

SCALAR(0x7fc64a82b858) at - line 4. SCALAR(0x7fc64a82b858) at - line 5.

--

Father Chrysostomos