Better error message for push onto assignment #14703

p5pRT · 2015-05-13T12:52:32Z

Migrated from rt.perl.org#125174 (status was 'rejected')

Searchable as RT125174$

p5pRT · 2015-05-13T12:52:32Z

From @epa

Created by @epa

This program has a typo in the last line:

use warnings;
use strict;
use 5.018;
my @a;
push @a = 5, 6;

The error message from perl is

Not an ARRAY reference at t line 5.

This must be because of the new feature whereby you can
C<push $r, ...> directly if $r is an array reference. In older perls
you had to say C<push @$r, ...>.

But still it's an unhappy series of events. Could anything be done to
make the error message more helpful?

Of course, this works

my @a;
@a = 5;
push @a, 6;

but this doesn't:

push((@a = 5), 6);

In fact, even what looks like a definite list assignment somehow gets
turned into something else when used with push:

my @a, @b;
push((@a = @b), 5);

(This seems inconsistent with the general principle that you can use assignment
as a part of a larger expression, even one that modifies, which is fine with scalars:
($x = $y) ++;
This sort of thing never quite works with arrays but it is usually not obvious why.)

Is it possible to just forbid assignments as the target of push?

Perl Info


Flags:
    category=core
    severity=wishlist

Site configuration information for perl 5.18.4:

Configured by Red Hat, Inc. at Thu Apr  2 16:17:20 UTC 2015.

Summary of my perl5 (revision 5 version 18 subversion 4) configuration:
   
  Platform:
    osname=linux, osvers=3.19.1-201.fc21.x86_64, archname=x86_64-linux-thread-multi
    uname='linux buildvm-23.phx2.fedoraproject.org 3.19.1-201.fc21.x86_64 #1 smp wed mar 18 04:29:24 utc 2015 x86_64 x86_64 x86_64 gnulinux '
    config_args='-des -Doptimize=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches  -m64 -mtune=generic -Dccdlflags=-Wl,--enable-new-dtags -Dlddlflags=-shared -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches  -m64 -mtune=generic -Wl,-z,relro  -Dshrpdir=/usr/lib64 -DDEBUGGING=-g -Dversion=5.18.4 -Dmyhostname=localhost -Dperladmin=root@localhost -Dcc=gcc -Dcf_by=Red Hat, Inc. -Dprefix=/usr -Dvendorprefix=/usr -Dsiteprefix=/usr/local -Dsitelib=/usr/local/share/perl5 -Dsitearch=/usr/local/lib64/perl5 -Dprivlib=/usr/share/perl5 -Dvendorlib=/usr/share/perl5/vendor_perl -Darchlib=/usr/lib64/perl5 -Dvendorarch=/usr/lib64/perl5/vendor_perl -Darchname=x86_64-linux-thread-multi -Dlibpth=/usr/local/lib64 /lib64 /usr/lib64 -Duseshrplib -Dusethreads -Duseithreads -Dusedtrace=/usr/bin/dtrace -Duselargefiles -Dd_semctl_semun -Di_db -Ui_ndbm -Di_gdbm -Di_shadow -Di_syslog -Dman3ext=3pm -Duseperlio -Dinstallusrbinperl=n -Ubincompat5005 -Uversiononly -Dpager=/usr/bin/less -isr -Dd_gethostent_r_proto -Ud_endhostent_r_proto -Ud_sethostent_r_proto -Ud_endprotoent_r_proto -Ud_setprotoent_r_proto -Ud_endservent_r_proto -Ud_setservent_r_proto -Dscriptdir=/usr/bin -Dusesitecustomize'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.8.3 20140911 (Red Hat 4.8.3-7)', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='gcc', ldflags =' -fstack-protector'
    libpth=/usr/local/lib64 /lib64 /usr/lib64
    libs=-lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread -lc -lgdbm_compat
    perllibs=-lresolv -lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    libc=, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.18'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,--enable-new-dtags'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -Wl,-z,relro '

Locally applied patches:
    Fedora Patch1: Removes date check, Fedora/RHEL specific
    Fedora Patch3: support for libdir64
    Fedora Patch4: use libresolv instead of libbind
    Fedora Patch5: USE_MM_LD_RUN_PATH
    Fedora Patch6: Skip hostname tests, due to builders not being network capable
    Fedora Patch7: Dont run one io test due to random builder failures
    Fedora Patch9: Fix find2perl to translate ? glob properly (RT#113054)
    Fedora Patch10: Update h2ph(1) documentation (RT#117647)
    Fedora Patch11: Update pod2html(1) documentation (RT#117623)
    Fedora Patch12: Disable ornaments on perl5db AutoTrace tests (RT#118817)
    Fedora Patch14: Do not use system Term::ReadLine::Gnu in tests (RT#118821)
    Fedora Patch15: Define SONAME for libperl.so
    Fedora Patch16: Install libperl.so to -Dshrpdir value
    Fedora Patch18: Fix crash with \\&$glob_copy (RT#119051)
    Fedora Patch19: Fix coreamp.t rand test (RT#118237)
    Fedora Patch20: Reap child in case where exception has been thrown (RT#114722)
    Fedora Patch21: Fix using regular expressions containing multiple code blocks (RT#117917)
    Fedora Patch22: Create site paths by cpan for the first time (CPAN RT#99905)
    Fedora Patch200: Link XS modules to libperl.so with EU::CBuilder on Linux
    Fedora Patch201: Link XS modules to libperl.so with EU::MM on Linux


@INC for perl 5.18.4:
    /home/eda/lib/perl5/
    /home/eda/lib64/perl5/
    /usr/local/lib64/perl5
    /usr/local/share/perl5
    /usr/lib64/perl5/vendor_perl
    /usr/share/perl5/vendor_perl
    /usr/lib64/perl5
    /usr/share/perl5
    .


Environment for perl 5.18.4:
    HOME=/home/eda
    LANG=en_GB.UTF-8
    LANGUAGE (unset)
    LC_COLLATE=C
    LC_CTYPE=en_GB.UTF-8
    LC_MESSAGES=en_GB.UTF-8
    LC_MONETARY=en_GB.UTF-8
    LC_NUMERIC=en_GB.UTF-8
    LC_TIME=en_GB.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/eda/bin:/home/eda/bin:/usr/local/bin:/usr/bin:/sbin:/usr/sbin:/sbin:/usr/sbin
    PERL5LIB=/home/eda/lib/perl5/:/home/eda/lib64/perl5/
    PERL_BADLANG (unset)
    SHELL=/bin/bash

-- 
Ed Avis <eda@waniasset.com>
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p5pRT · 2015-08-02T00:52:54Z

From @jkeenan

On Wed May 13 05:52:32 2015, eda@waniasset.com wrote:

This is a bug report for perl from eda@waniasset.com,
generated with the help of perlbug 1.39 running under perl 5.18.4.

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

This program has a typo in the last line:

use warnings;
use strict;
use 5.018;
my @a;
push @a = 5, 6;

The error message from perl is

Not an ARRAY reference at t line 5.

This must be because of the new feature whereby you can
C<push $r, ...> directly if $r is an array reference. In older perls
you had to say C<push @$r, ...>.

But still it's an unhappy series of events. Could anything be done to
make the error message more helpful?

When I run that code with 'use warnings' -- as you have typed it -- I am duly forewarned:

#####
$ perl 125174-push-assign.pl
push on reference is experimental at 125174-push-assign.pl line 5.
Not an ARRAY reference at 125174-push-assign.pl line 5.
#####

--
James E Keenan (jkeenan@cpan.org)

p5pRT · 2015-08-02T00:52:54Z

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

p5pRT · 2015-08-02T19:27:13Z

From @epa

Thanks for trying to reproduce this. I didn't see any warning with 5.18.
Since then I believe that auto-deref, as C<push $ref, 0>, has been marked as
deprecated - or experimental, whatever the distinction between the two terms
may be. So a better warning appears in later perl versions unless you have
chosen to disable experimental warnings.

If auto-deref one day goes back to happening without warning, this bug will
need to be revisited.

p5pRT · 2017-06-09T16:01:21Z

From @epa

Since auto-deref was removed in 5.24, I think this bug has been superseded.

p5pRT · 2017-06-09T18:33:55Z

From @jkeenan

On Fri, 09 Jun 2017 16:01:21 GMT, ed wrote:

Since auto-deref was removed in 5.24, I think this bug has been superseded.

Indeed.

#####
$ cat 125174-push-assignment.pl
use 5.26.0;
use warnings;

{
my @a;
eval { push @a = 5,6; };
}

{
my @a;
eval { push((@a = 5), 6); };
}

{
my (@a, @b);
eval { push((@a = @b), 5); };
}

$ perl 125174-push-assignment.pl
Experimental push on scalar is now forbidden at 125174-push-assignment.pl line 6, near "6;"
Experimental push on scalar is now forbidden at 125174-push-assignment.pl line 11, near "6)"
Experimental push on scalar is now forbidden at 125174-push-assignment.pl line 16, near "5)"
Execution of 125174-push-assignment.pl aborted due to compilation errors.
#####

Thanks for following up on this.

--
James E Keenan (jkeenan@cpan.org)

p5pRT · 2017-06-09T18:33:56Z

@jkeenan - Status changed from 'open' to 'rejected'

p5pRT closed this as completed Jun 9, 2017

p5pRT added Wishlist affects-5.18 distro-Linux type-core labels Oct 19, 2019

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Better error message for push onto assignment #14703

Better error message for push onto assignment #14703

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Better error message for push onto assignment #14703

Better error message for push onto assignment #14703

Comments

p5pRT commented May 13, 2015

p5pRT commented May 13, 2015

From @epa

Created by @epa

p5pRT commented Aug 2, 2015

From @jkeenan

p5pRT commented Aug 2, 2015

p5pRT commented Aug 2, 2015

From @epa

p5pRT commented Jun 9, 2017

From @epa

p5pRT commented Jun 9, 2017

From @jkeenan

p5pRT commented Jun 9, 2017