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Shouldn't Perl warn about «my $foo => "bar" || "baz";» ? #16792

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p5pRT opened this issue Dec 22, 2018 · 4 comments
Open

Shouldn't Perl warn about «my $foo => "bar" || "baz";» ? #16792

p5pRT opened this issue Dec 22, 2018 · 4 comments
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type-core

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@p5pRT
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p5pRT commented Dec 22, 2018

Migrated from rt.perl.org#133735 (status was 'open')

Searchable as RT133735$
@p5pRT
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p5pRT commented Dec 22, 2018

From @dod38fr

Created by @dod38fr

Hello

Shouldn't the following 2 lines issue a warning ?

$ perl -w -E 'my $foo => "bar" // "baz";'
$ perl -w -E 'my $foo => "bar" || "baz";'

The second part of the statement is useless. A similar line without //
or || does produce a warning​:

$ perl -w -E 'my $foo => "bar" ;'
Useless use of a constant ("bar") in void context at -e line 1.

I'd think Perl should be able to warn in the 2 first cases.

All the best

Perl Info 

Flags:
    category=core
    severity=low

Site configuration information for perl 5.28.1:

Configured by Debian at Fri Dec  7 13:23:05 UTC 2018.

Summary of my perl5 (revision 5 version 28 subversion 1) configuration:
   
  Platform:
    osname=linux
    osvers=4.9.0
    archname=x86_64-linux-gnu-thread-multi
    uname='linux localhost 4.9.0 #1 smp debian 4.9.0 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 -fdebug-prefix-map=/build/perl-znrsWe/perl-5.28.1=. -fstack-protector-strong -Wformat -Werror=format-security -Dldflags= -Wl,-z,relro -Dlddlflags=-shared -Wl,-z,relro -Dcccdlflags=-fPIC -Darchname=x86_64-linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.28 -Darchlib=/usr/lib/x86_64-linux-gnu/perl/5.28 -Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/x86_64-linux-gnu/perl5/5.28 -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl/5.28.1 -Dsitearch=/usr/local/lib/x86_64-linux-gnu/perl/5.28.1 -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 -Ui_xlocale -Uversiononly -DDEBUGGING=-g -Doptimize=-O2 -dEs -Duseshrplib -Dlibperl=libperl.so.5.28.1'
    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='8.2.0'
    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/lib/gcc/x86_64-linux-gnu/8/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-2.28.so
    so=so
    useshrplib=true
    libperl=libperl.so.5.28
    gnulibc_version='2.28'
  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 5.28.1-3 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:debian/gdbm-fatal - [perl #133295] https://bugs.debian.org/904005 Temporarily skip GDBM_File fatal.t for gdbm >= 1.15 compatibility
    DEBPKG:fixes/storable-recursion - https://bugs.debian.org/912900 [perl #133326] [120060c] (perl #133326) fix and clarify handling of recurs_sv.
    DEBPKG:fixes/caretx-fallback - https://bugs.debian.org/913347 [perl #133573] [03b94aa] RT#133573: $^X fallback when platform-specific technique fails
    DEBPKG:fixes/eumm-usrmerge - https://bugs.debian.org/913637 Avoid mangling /bin non-perl shebangs on merged-/usr systems
    DEBPKG:fixes/errno-include-path - [6c5080f] [perl #133662] https://bugs.debian.org/875921 Make Errno_pm.PL compatible with /usr/include/<ARCH>/errno.h
    DEBPKG:fixes/kfreebsd-renameat - [a3c63a9] https://bugs.debian.org/912521 [perl #133668] Also work around renameat() kernel bug on GNU/kFreeBSD
    DEBPKG:fixes/time-local-2020 - https://bugs.debian.org/915209 [rt.cpan.org #124787] Fix Time::Local tests
    DEBPKG:fixes/storable-prereq - [3f4cad1] Storable: fix for strawberry build failures:
    DEBPKG:fixes/storable-crosscompile - [perl #133411] [edf639f] (perl #133411) don't try to load Storable with -Dusecrosscompile
    DEBPKG:debian/storable-disable-probing - https://bugs.debian.org/914133 [perl #133708] Disable Storable stacksize probing when PERL_STORABLE_DONT_PROBE is set
    DEBPKG:fixes/inplace-editing-bugfix/part1 - https://bugs.debian.org/914651 (perl #133659) move argvout cleanup to a new function
    DEBPKG:fixes/inplace-editing-bugfix/part2 - https://bugs.debian.org/914651 (perl #133659) tests for global destruction handling of inplace editing
    DEBPKG:fixes/inplace-editing-bugfix/part3 - https://bugs.debian.org/914651 (perl #133659) make an in-place edit successful if the exit status is zero
    DEBPKG:fixes/fix-manifest-failures - https://bugs.debian.org/914962 Fix t/porting/manifest.t failures when run in a foreign git checkout


@INC for perl 5.28.1:
    /home/domi/private/perlDev/config-model-input-validation/lib
    /etc/perl
    /usr/local/lib/x86_64-linux-gnu/perl/5.28.1
    /usr/local/share/perl/5.28.1
    /usr/lib/x86_64-linux-gnu/perl5/5.28
    /usr/share/perl5
    /usr/lib/x86_64-linux-gnu/perl/5.28
    /usr/share/perl/5.28
    /usr/local/lib/site_perl
    /usr/lib/x86_64-linux-gnu/perl-base


Environment for perl 5.28.1:
    HOME=/home/domi
    LANG=en_GB.UTF-8
    LANGUAGE=en_US:en
    LC_MEASUREMENT=fr_FR.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/domi/perl5/perlbrew/bin:/home/domi/.local/bin:/home/domi/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games:/home/domi/hpcwp/node/bin
    PERL5LIB=:/home/domi/private/perlDev/config-model-input-validation/lib
    PERLBREW_BASHRC_VERSION=0.42
    PERLBREW_HOME=/home/domi/.perlbrew
    PERLBREW_PATH=/home/domi/perl5/perlbrew/bin
    PERLBREW_ROOT=/home/domi/perl5/perlbrew
    PERLBREW_VERSION=0.78
    PERL_BADLANG (unset)
    SHELL=/bin/bash

@p5pRT
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p5pRT commented Dec 23, 2018

From @jkeenan

On Sat, 22 Dec 2018 15​:47​:18 GMT, domi.dumont@​free.fr wrote​:

This is a bug report for perl from domi.dumont@​free.fr,
generated with the help of perlbug 1.41 running under perl 5.28.1.

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

Hello

Shouldn't the following 2 lines issue a warning ?

$ perl -w -E 'my $foo => "bar" // "baz";'
$ perl -w -E 'my $foo => "bar" || "baz";'

The second part of the statement is useless. A similar line without //
or || does produce a warning​:

$ perl -w -E 'my $foo => "bar" ;'
Useless use of a constant ("bar") in void context at -e line 1.

I'd think Perl should be able to warn in the 2 first cases.

I'm inclined to agree, particularly as using the lower-precedence 'or' operator instead of '||' throws a warning​:

#####
$ perl -w -E 'my $foo => "bar" or "baz";'
Useless use of a constant ("baz") in void context at -e line 1.
#####

--
James E Keenan (jkeenan@​cpan.org)

@p5pRT
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p5pRT commented Dec 23, 2018

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

@p5pRT
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p5pRT commented Dec 25, 2018

From @iabyn

On Sat, Dec 22, 2018 at 04​:53​:25PM -0800, James E Keenan via RT wrote​:

Shouldn't the following 2 lines issue a warning ?

$ perl -w -E 'my $foo => "bar" // "baz";'
$ perl -w -E 'my $foo => "bar" || "baz";'

I think its intentional.

This is intended *not* to warn​:

  perl -we'use constant SILENT => 1; SILENT || print'

When the LHS of || is a compile-time true value, the RHS part of the
optree is thrown away, so the expression becomes just the constant
1, and whereas a constant in void context would normally warn, in
this case the warning is suppressed.

--
Spock (or Data) is fired from his high-ranking position for not being able
to understand the most basic nuances of about one in three sentences that
anyone says to him.
  -- Things That Never Happen in "Star Trek" #19

@xenu xenu removed the affects-5.28 label Nov 19, 2021
@xenu xenu removed the Severity Low label Dec 29, 2021
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