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state stub doesn't get init-once behaviour #16221

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p5pRT opened this issue Nov 4, 2017 · 2 comments
Open

state stub doesn't get init-once behaviour #16221

p5pRT opened this issue Nov 4, 2017 · 2 comments

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@p5pRT
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p5pRT commented Nov 4, 2017

Migrated from rt.perl.org#132394 (status was 'new')

Searchable as RT132394$

@p5pRT
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p5pRT commented Nov 4, 2017

From zefram@fysh.org

Created by zefram@fysh.org

$ perl -Mfeature=state -lwe '$i = 0; sub f { state() = $i++; 1; } f(); f(); print $i'
2

"state()" is a state variable declaration of a list of no variables.
It is correctly parsed as a list, causing the assignment to be a list
assignment. List assignment to a "state" expression is supposed to be
forbidden currently, as a temporary arrangement until we're sure which
expressions should qualify for initialisation semantics (which we now
are) and pending implementation of those semantics. So it is a mistake
that assignment to "state()" is accepted.

But worse than it being accepted, it's accepted with the wrong semantics.
Since "state()" is a "state" expression at its top level, assignment to it
should get one-time-initialisation semantics. But as you see above, the
rhs of the assignment is evaluated each time the assignment is reached.

What's going on is that "state()" yields a bare "stub" op, with no flag
or other clue of its "state" nature. Note that "(state())" yields an
identical stub, but should not get initialisation semantics because its
"state" isn't at top level. Assignment to "(state())" is therefore
currently mistakenly accepted, but gets the correct behaviour, so isn't
a problem.

Perl Info

Flags:
    category=core
    severity=low

Site configuration information for perl 5.27.5:

Configured by zefram at Fri Oct 20 23:24:00 BST 2017.

Summary of my perl5 (revision 5 version 27 subversion 5) configuration:
   
  Platform:
    osname=linux
    osvers=3.16.0-4-amd64
    archname=x86_64-linux-thread-multi
    uname='linux barba.rous.org 3.16.0-4-amd64 #1 smp debian 3.16.43-2+deb8u2 (2017-06-26) x86_64 gnulinux '
    config_args='-des -Dprefix=/home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52 -Duselargefiles -Dusethreads -Uafs -Ud_csh -Uusesfio -Uusenm -Duseshrplib -Dusedevel -Uversiononly -Ui_db'
    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='cc'
    ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
    optimize='-O2'
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='4.9.2'
    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='cc'
    ldflags =' -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/gcc/x86_64-linux-gnu/4.9/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=-lpthread -lnsl -ldb -ldl -lm -lcrypt -lutil -lc
    perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=libc-2.19.so
    so=so
    useshrplib=true
    libperl=libperl.so
    gnulibc_version='2.19'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E -Wl,-rpath,/home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/5.27.5/x86_64-linux-thread-multi/CORE'
    cccdlflags='-fPIC'
    lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'



@INC for perl 5.27.5:
    /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/site_perl/5.27.5/x86_64-linux-thread-multi
    /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/site_perl/5.27.5
    /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/5.27.5/x86_64-linux-thread-multi
    /home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/lib/5.27.5


Environment for perl 5.27.5:
    HOME=/home/zefram
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/zefram/usr/perl/perl_install/perl-5.27.5-i64-f52/bin:/home/zefram/usr/perl/util:/home/zefram/pub/x86_64-unknown-linux-gnu/bin:/home/zefram/pub/common/bin:/usr/bin:/bin:/usr/local/bin:/usr/games
    PERLDOC=-oman
    PERL_BADLANG (unset)
    SHELL=/usr/bin/zsh

@p5pRT
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p5pRT commented Nov 4, 2017

From zefram@fysh.org

Additional​: the same thing happens with "state(undef)", "state(undef,
undef)", etc.​:

$ perl -Mfeature=state -lwe '$i = 0; sub f { state(undef) = $i++; 1; } f(); f(); print $i'
2

"state(undef)" compiles to an "undef" op, just like "(undef)".
"state(undef, undef)" compiles to a "list" op containing two "undef"
ops, just like "(undef, undef)".

-zefram

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