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$a.="$b" doesn't stringify $b #16398

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p5pRT opened this issue Jan 31, 2018 · 4 comments
Closed

$a.="$b" doesn't stringify $b #16398

p5pRT opened this issue Jan 31, 2018 · 4 comments

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@p5pRT
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@p5pRT p5pRT commented Jan 31, 2018

Migrated from rt.perl.org#132793 (status was 'resolved')

Searchable as RT132793$

@p5pRT
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@p5pRT p5pRT commented Jan 31, 2018

From zefram@fysh.org

Created by zefram@fysh.org

Another multiconcat bug​:

$ perl5.27.5 -lwe 'package Lhs { use overload ".=" => sub { warn ref(\$_[1]); "foo"; }; } package Rhs { use overload "\"\"" => sub { warn "stringified"; "bar" }; } my $a = bless({}, "Lhs"); my $b = bless({}, "Rhs"); $a .= "$b"'
stringified at -e line 1.
SCALAR at -e line 1.
$ perl5.27.8 -lwe 'package Lhs { use overload ".=" => sub { warn ref(\$_[1]); "foo"; }; } package Rhs { use overload "\"\"" => sub { warn "stringified"; "bar" }; } my $a = bless({}, "Lhs"); my $b = bless({}, "Rhs"); $a .= "$b"'
REF at -e line 1.

Passing the rhs reference through to the lhs overload method would be
correct if the expression were '$a .= $b', and indeed both perl versions
do pass it through in that case. But explicit stringification must
be honoured.

Found this while testing around [perl #132783].

Perl Info

Flags:
    category=core
    severity=medium

Site configuration information for perl 5.27.8:

Configured by zefram at Sat Jan 20 03:46:58 GMT 2018.

Summary of my perl5 (revision 5 version 27 subversion 8) 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-5.27.8-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 -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    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-5.27.8-i64-f52/lib/5.27.8/x86_64-linux-thread-multi/CORE'
    cccdlflags='-fPIC'
    lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'



@INC for perl 5.27.8:
    /home/zefram/usr/perl/perl_install/perl-5.27.8-i64-f52/lib/site_perl/5.27.8/x86_64-linux-thread-multi
    /home/zefram/usr/perl/perl_install/perl-5.27.8-i64-f52/lib/site_perl/5.27.8
    /home/zefram/usr/perl/perl_install/perl-5.27.8-i64-f52/lib/5.27.8/x86_64-linux-thread-multi
    /home/zefram/usr/perl/perl_install/perl-5.27.8-i64-f52/lib/5.27.8


Environment for perl 5.27.8:
    HOME=/home/zefram
    LANG (unset)
    LANGUAGE (unset)
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/zefram/usr/perl/perl_install/perl-5.27.8-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
    PERL_BADLANG (unset)
    SHELL=/usr/bin/zsh

@p5pRT
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@p5pRT p5pRT commented Feb 20, 2018

From @iabyn

On Wed, Jan 31, 2018 at 05​:17​:18AM -0800, Zefram wrote​:

Another multiconcat bug​:

$ perl5.27.5 -lwe 'package Lhs { use overload ".=" => sub { warn ref(\$_[1]); "foo"; }; } package Rhs { use overload "\"\"" => sub { warn "stringified"; "bar" }; } my $a = bless({}, "Lhs"); my $b = bless({}, "Rhs"); $a .= "$b"'
stringified at -e line 1.
SCALAR at -e line 1.
$ perl5.27.8 -lwe 'package Lhs { use overload ".=" => sub { warn ref(\$_[1]); "foo"; }; } package Rhs { use overload "\"\"" => sub { warn "stringified"; "bar" }; } my $a = bless({}, "Lhs"); my $b = bless({}, "Rhs"); $a .= "$b"'
REF at -e line 1.

Passing the rhs reference through to the lhs overload method would be
correct if the expression were '$a .= $b', and indeed both perl versions
do pass it through in that case. But explicit stringification must
be honoured.

Found this while testing around [perl #132783].

Now fixed with the following commit. Note that it merely restores the
existing buggy and inconsistent 5.26.0 and earlier behaviour. I'll
look into whether to rationalise such behaviour post 5.28.0 release.

commit 55b62de
Author​: David Mitchell <davem@​iabyn.com>
AuthorDate​: Mon Feb 19 11​:59​:03 2018 +0000
Commit​: David Mitchell <davem@​iabyn.com>
CommitDate​: Mon Feb 19 22​:06​:49 2018 +0000

  pp_multiconcat​: correctly honour stringify
 
  RT #132793, RT #132801
 
  In something like $x .= "$overloaded", the $overloaded stringify method
  wasn't being called.
 
  However, it turns that the existing (pre-multiconcat) behaviour is also
  buggy and inconsistent. That behaviour has been restored as-is.
  At some future time, these bugs might be addressed.
 
  Here are some comments from the new tests added to overload.t​:
 
  Since 5.000, any OP_STRINGIFY immediately following an OP_CONCAT
  is optimised away, on the assumption that since concat will always
  return a valid string anyway, it doesn't need stringifying.
  So in "$x", the stringify is needed, but on "$x$y" it isn't.
  This assumption is flawed once overloading has been introduced, since
  concat might return an overloaded object which still needs stringifying.
  However, this flawed behaviour is apparently needed by at least one
  module, and is tested for in opbasic/concat.t​: see RT #124160.
 
  There is also a wart with the OPpTARGET_MY optimisation​: specifically,
  in $lex = "...", if $lex is a lexical var, then a chain of 2 or more
  concats *doesn't* optimise away OP_STRINGIFY​:
 
  $lex = "$x"; # stringifies
  $lex = "$x$y"; # doesn't stringify
  $lex = "$x$y$z..."; # stringifies

--
More than any other time in history, mankind faces a crossroads. One path
leads to despair and utter hopelessness. The other, to total extinction.
Let us pray we have the wisdom to choose correctly.
  -- Woody Allen

@p5pRT
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@p5pRT p5pRT commented Feb 20, 2018

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

@p5pRT
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@p5pRT p5pRT commented Feb 20, 2018

@iabyn - Status changed from 'open' to 'resolved'

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