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'Exiting eval via next' when explicit label given #16612

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p5pRT opened this issue Jul 6, 2018 · 4 comments
Open

'Exiting eval via next' when explicit label given #16612

p5pRT opened this issue Jul 6, 2018 · 4 comments

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@p5pRT
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@p5pRT p5pRT commented Jul 6, 2018

Migrated from rt.perl.org#133339 (status was 'open')

Searchable as RT133339$

@p5pRT
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@p5pRT p5pRT commented Jul 6, 2018

From @epa

Created by @epa

I think I understand the rationale for this warning​:

% perl -wE 'foreach (1) { eval { next } }'
Exiting eval via next at -e line 1.

However, when the loop label is explicitly given, I don't believe it should warn

% perl -wE 'LOOP​: foreach (1) { eval { next LOOP } }'
Exiting eval via next at -e line 1.

The programmer has specified exactly which control flow structure the
next (or break or redo) should affect, so there is no need for a
warning about possible confusion with whether or not the 'eval' block
counts as a control flow structure.

In my opinion the whole warning about 'Exiting eval via next' is a
little dubious, but the scope of this bug report is only in the
specific case when a loop label is provided. It should be turned off
in that case. Changing it in general would be a different bug.

I guess though it could still warn when the labelled block *is* an eval!

% perl -wE 'FOO​: eval { redo FOO }'

Perl Info

Flags:
    category=core
    severity=low

Site configuration information for perl 5.22.2:

Configured by Red Hat, Inc. at Fri Nov  4 14:35:02 UTC 2016.

Summary of my perl5 (revision 5 version 22 subversion 2) configuration:
   
  Platform:
    osname=linux, osvers=4.7.9-200.fc24.x86_64, archname=x86_64-linux-thread-multi
    uname='linux buildvm-12.phx2.fedoraproject.org 4.7.9-200.fc24.x86_64 #1 smp thu oct 20 14:26:16 utc 2016 x86_64 x86_64 x86_64 gnulinux '
    config_args='-des -Doptimize=none -Dccflags=-O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches  -m64 -mtune=generic -Dldflags=-Wl,-z,relro  -Dccdlflags=-Wl,--enable-new-dtags -Wl,-z,relro  -Dlddlflags=-shared -Wl,-z,relro  -Dshrpdir=/usr/lib64 -DDEBUGGING=-g -Dversion=5.22.2 -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
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fwrapv -fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='  -g',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fwrapv -fno-strict-aliasing -I/usr/local/include'
    ccversion='', gccversion='5.3.1 20160406 (Red Hat 5.3.1-6)', 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='gcc', ldflags ='-Wl,-z,relro  -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib64 /lib64 /usr/lib64 /usr/local/lib /usr/lib /lib/../lib64 /usr/lib/../lib64 /lib
    libs=-lpthread -lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lpthread -lresolv -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.22.so, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.22'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,--enable-new-dtags -Wl,-z,relro '
    cccdlflags='-fPIC', lddlflags='-shared -Wl,-z,relro  -L/usr/local/lib -fstack-protector-strong'

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 Patch15: Define SONAME for libperl.so
    Fedora Patch16: Install libperl.so to -Dshrpdir value
    Fedora Patch22: Document Math::BigInt::CalcEmu requires Math::BigInt (CPAN RT#85015)
    Fedora Patch26: Make *DBM_File desctructors thread-safe (RT#61912)
    Fedora Patch27: Make PadlistNAMES() lvalue again (CPAN RT#101063)
    Fedora Patch28: Make magic vtable writable as a work-around for Coro (CPAN RT#101063)
    Fedora Patch29: Fix duplicating PerlIO::encoding when spawning threads (RT#31923)
    Fedora Patch30: Do not let XSLoader load relative paths (CVE-2016-6185)
    Fedora Patch31: Avoid loading optional modules from default . (CVE-2016-1238)
    Fedora Patch32: Fix a crash in lexical scope warnings (RT#128597)
    Fedora Patch33: Do not mangle errno from failed socket calls (RT#128316)
    Fedora Patch34: Fix crash in "evalbytes S" (RT#129196)
    Fedora Patch35: Fix crash in "evalbytes S" (RT#129196)
    Fedora Patch36: Fix crash in "evalbytes S" (RT#129196)
    Fedora Patch37: Fix crash in splice (RT#129164, RT#129166, RT#129167)
    Fedora Patch38: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
    Fedora Patch39: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
    Fedora Patch40: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
    Fedora Patch41: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
    Fedora Patch42: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
    Fedora Patch43: Fix crash when matching UTF-8 string with non-UTF-8 substrings (RT#129350)
    Fedora Patch44: Fix parsing perl options in shell bang line (RT#129336)
    Fedora Patch45: Fix firstchar bitmap under UTF-8 with prefix optimization (RT#129950)
    Fedora Patch46: Avoid infinite loop in h2xs tool if enum and type have the same name (RT130001)
    Fedora Patch47: Fix stack handling when calling chdir without an argument (RT#129130)
    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 5.22.2:
    /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 5.22.2:
    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/lib64/perl5/
    PERL_BADLANG (unset)
    SHELL=/bin/bash

@p5pRT
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@p5pRT p5pRT commented Aug 25, 2018

From @xsawyerx

I disagree with this. I believe "next" should work in an eval, no matter
how you use with - with labels or not.

On 07/06/2018 07​:57 PM, Ed Avis (via RT) wrote​:

# New Ticket Created by "Ed Avis"
# Please include the string​: [perl #133339]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=133339 >

This is a bug report for perl from eda@​waniasset.com,
generated with the help of perlbug 1.40 running under perl 5.22.2.

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

I think I understand the rationale for this warning​:

% perl -wE 'foreach (1) { eval { next } }'
Exiting eval via next at -e line 1.

However, when the loop label is explicitly given, I don't believe it should warn

% perl -wE 'LOOP​: foreach (1) { eval { next LOOP } }'
Exiting eval via next at -e line 1.

The programmer has specified exactly which control flow structure the
next (or break or redo) should affect, so there is no need for a
warning about possible confusion with whether or not the 'eval' block
counts as a control flow structure.

In my opinion the whole warning about 'Exiting eval via next' is a
little dubious, but the scope of this bug report is only in the
specific case when a loop label is provided. It should be turned off
in that case. Changing it in general would be a different bug.

I guess though it could still warn when the labelled block *is* an eval!

% perl -wE 'FOO​: eval { redo FOO }'

[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags​:
category=core
severity=low
---
Site configuration information for perl 5.22.2​:

Configured by Red Hat, Inc. at Fri Nov 4 14​:35​:02 UTC 2016.

Summary of my perl5 (revision 5 version 22 subversion 2) configuration​:

Platform​:
osname=linux, osvers=4.7.9-200.fc24.x86_64, archname=x86_64-linux-thread-multi
uname='linux buildvm-12.phx2.fedoraproject.org 4.7.9-200.fc24.x86_64 #1 smp thu oct 20 14​:26​:16 utc 2016 x86_64 x86_64 x86_64 gnulinux '
config_args='-des -Doptimize=none -Dccflags=-O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -Dldflags=-Wl,-z,relro -Dccdlflags=-Wl,--enable-new-dtags -Wl,-z,relro -Dlddlflags=-shared -Wl,-z,relro -Dshrpdir=/usr/lib64 -DDEBUGGING=-g -Dversion=5.22.2 -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 -Dinstallu
srbinperl=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
use64bitint=define, use64bitall=define, uselongdouble=undef
usemymalloc=n, bincompat5005=undef
Compiler​:
cc='gcc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fwrapv -fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
optimize=' -g',
cppflags='-D_REENTRANT -D_GNU_SOURCE -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fwrapv -fno-strict-aliasing -I/usr/local/include'
ccversion='', gccversion='5.3.1 20160406 (Red Hat 5.3.1-6)', 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='gcc', ldflags ='-Wl,-z,relro -fstack-protector-strong -L/usr/local/lib'
libpth=/usr/local/lib64 /lib64 /usr/lib64 /usr/local/lib /usr/lib /lib/../lib64 /usr/lib/../lib64 /lib
libs=-lpthread -lresolv -lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
perllibs=-lpthread -lresolv -lnsl -ldl -lm -lcrypt -lutil -lc
libc=libc-2.22.so, so=so, useshrplib=true, libperl=libperl.so
gnulibc_version='2.22'
Dynamic Linking​:
dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,--enable-new-dtags -Wl,-z,relro '
cccdlflags='-fPIC', lddlflags='-shared -Wl,-z,relro -L/usr/local/lib -fstack-protector-strong'

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 Patch15​: Define SONAME for libperl.so
Fedora Patch16​: Install libperl.so to -Dshrpdir value
Fedora Patch22​: Document Math​::BigInt​::CalcEmu requires Math​::BigInt (CPAN RT#85015)
Fedora Patch26​: Make *DBM_File desctructors thread-safe (RT#61912)
Fedora Patch27​: Make PadlistNAMES() lvalue again (CPAN RT#101063)
Fedora Patch28​: Make magic vtable writable as a work-around for Coro (CPAN RT#101063)
Fedora Patch29​: Fix duplicating PerlIO​::encoding when spawning threads (RT#31923)
Fedora Patch30​: Do not let XSLoader load relative paths (CVE-2016-6185)
Fedora Patch31​: Avoid loading optional modules from default . (CVE-2016-1238)
Fedora Patch32​: Fix a crash in lexical scope warnings (RT#128597)
Fedora Patch33​: Do not mangle errno from failed socket calls (RT#128316)
Fedora Patch34​: Fix crash in "evalbytes S" (RT#129196)
Fedora Patch35​: Fix crash in "evalbytes S" (RT#129196)
Fedora Patch36​: Fix crash in "evalbytes S" (RT#129196)
Fedora Patch37​: Fix crash in splice (RT#129164, RT#129166, RT#129167)
Fedora Patch38​: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
Fedora Patch39​: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
Fedora Patch40​: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
Fedora Patch41​: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
Fedora Patch42​: Fix string overrun in Perl_gv_fetchmethod_pvn_flags (RT#129267)
Fedora Patch43​: Fix crash when matching UTF-8 string with non-UTF-8 substrings (RT#129350)
Fedora Patch44​: Fix parsing perl options in shell bang line (RT#129336)
Fedora Patch45​: Fix firstchar bitmap under UTF-8 with prefix optimization (RT#129950)
Fedora Patch46​: Avoid infinite loop in h2xs tool if enum and type have the same name (RT130001)
Fedora Patch47​: Fix stack handling when calling chdir without an argument (RT#129130)
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 5.22.2​:
/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 5.22.2​:
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/lib64/perl5/
PERL_BADLANG (unset)
SHELL=/bin/bash

@p5pRT
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@p5pRT p5pRT commented Aug 25, 2018

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

@p5pRT
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@p5pRT p5pRT commented Aug 25, 2018

From @epa

On Sat, 25 Aug 2018 02​:03​:10 -0700, xsawyerx@​gmail.com wrote​:

I disagree with this. I believe "next" should work in an eval, no
matter how you use with - with labels or not.

Have I misunderstood? It appears you are agreeing with the bug report, not disagreeing.

The bug is to stop issuing a warning in some cases when 'next' is given inside 'eval'. Of course, it should continue working as it does now, just more quietly.

To keep the scope of the bug as small as possible I filed it just for the specific case of a loop label being given. However, if the perl5-porters think the warning should disappear in all cases, that would be even better.

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