reset() silently fails to reset some variables like $1, $^W

[mauke]

Description
reset() works with some core variables (e.g. $0, $^X), but not others (e.g. $|, $1, $^W).

Steps to Reproduce

$ perl -wE '$| = 1; reset "|"; say $|'
1
$ perl -wE '"hello" =~ /(.*)/; reset "0-9"; say $0, $1'
Use of uninitialized value $0 in say at -e line 1.
hello
$ perl -wE 'reset "\x01-\x1f"; say $^X, $^W'
Use of uninitialized value $^X in say at -e line 1.
1

Expected behavior
I would've expected all of these variables to be reset to undef, or if that's not possible (eyeing $| in particular), an error or warning to be generated.

Perl configuration

Summary of my perl5 (revision 5 version 36 subversion 0) configuration:
   
  Platform:
    osname=linux
    osvers=5.15.0-53-generic
    archname=x86_64-linux
    uname='linux luum 5.15.0-53-generic #59-ubuntu smp mon oct 17 18:53:30 utc 2022 x86_64 x86_64 x86_64 gnulinux '
    config_args='-de -Dprefix=/home/mauke/perl5/perlbrew/perls/perl-5.36.0 -Duseshrplib -Aeval:scriptdir=/home/mauke/perl5/perlbrew/perls/perl-5.36.0/bin'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=undef
    usemultiplicity=undef
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
  Compiler:
    cc='cc'
    ccflags ='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
    optimize='-O2'
    cppflags='-fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include'
    ccversion=''
    gccversion='11.3.0'
    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='cc'
    ldflags =' -fstack-protector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /usr/lib/x86_64-linux-gnu /usr/lib /usr/lib64
    libs=-lpthread -lnsl -ldb -ldl -lm -lcrypt -lutil -lc
    perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
    libc=/lib/x86_64-linux-gnu/libc.so.6
    so=so
    useshrplib=true
    libperl=libperl.so
    gnulibc_version='2.35'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E -Wl,-rpath,/home/mauke/perl5/perlbrew/perls/perl-5.36.0/lib/5.36.0/x86_64-linux/CORE'
    cccdlflags='-fPIC'
    lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'


Characteristics of this binary (from libperl): 
  Compile-time options:
    HAS_TIMES
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
  Built under linux
  Compiled at Nov 21 2022 09:12:40
  %ENV:
    PERLBREW_BASHRC_VERSION="0.74"
    PERLBREW_HOME="/home/mauke/.perlbrew"
    PERLBREW_MANPATH="/home/mauke/perl5/perlbrew/perls/perl-5.36.0/man"
    PERLBREW_PATH="/home/mauke/perl5/perlbrew/bin:/home/mauke/perl5/perlbrew/perls/perl-5.36.0/bin"
    PERLBREW_PERL="perl-5.36.0"
    PERLBREW_ROOT="/home/mauke/perl5/perlbrew"
    PERLBREW_VERSION="0.94"
    PERLDOC="-oterm"
  @INC:
    /home/mauke/perl5/perlbrew/perls/perl-5.36.0/lib/site_perl/5.36.0/x86_64-linux
    /home/mauke/perl5/perlbrew/perls/perl-5.36.0/lib/site_perl/5.36.0
    /home/mauke/perl5/perlbrew/perls/perl-5.36.0/lib/5.36.0/x86_64-linux
    /home/mauke/perl5/perlbrew/perls/perl-5.36.0/lib/5.36.0

[Leont]

Yeah, those are variables that are lazily initialized (in gv_magicalize), so they will get reinitialized after reset.

[demerphq]

I wouldn't expect reset to change $1 and other regex vars, they aren't writable, so arguably there is nothing to reset. We don't have a variable that represent PL_curpm currently, and the regexp vars are essentially ties that expose the state of PL_curpm.

[tonycoz]

The problem with $1 and $^W isn't that they're gv_magicalized after the reset, but that set magic isn't called.

gv_magicalize() is called for each of the names during compilation before the reset is called, e.g, from debugging the $^W test case:

Breakpoint 2, S_gv_magicalize (gv=0x555555c14690, stash=0x555555bf0648, 
    name=0x555555c1b281 "\027", len=1, sv_type=SVt_PV) at gv.c:2068
2068    {
(gdb) bt
#0  S_gv_magicalize (gv=0x555555c14690, stash=0x555555bf0648, 
    name=0x555555c1b281 "\027", len=1, sv_type=SVt_PV) at gv.c:2068
#1  0x0000555555610c0e in Perl_gv_fetchpvn_flags (
    nambeg=0x555555c1b281 "\027", full_len=1, flags=1, sv_type=SVt_PV)
    at gv.c:2693
#2  0x0000555555656f8c in S_pending_ident () at toke.c:9973
#3  0x000055555565511d in Perl_yylex () at toke.c:9592
...
(gdb) c
Continuing.

Breakpoint 1, Perl_sv_resetpvn (s=0x555555c1d0b0 "\001-\037", len=3, 
    stash=0x555555bf0648) at sv.c:10065
10065   {
(gdb) c

If I modify sv_resetpvn() to call set magic, we get more reasonable (if noisy) results:

tony@venus:.../git/perl6$ ./perl -Ilib -wE 'reset "0-9"; say $0, $1'
Modification of a read-only value attempted at -e line 1.
tony@venus:.../git/perl6$ ./perl -Ilib -wE 'reset "\x01-\x1f"; say $^X, $^W'
Use of uninitialized value in symbol reset at -e line 1.
Use of uninitialized value in symbol reset at -e line 1.
0

Note that $1 etc aren't marked read only, the error there is thrown by the magic handling. If $1 was marked read only sv_resetpvn() would skip trying to modify it.

Similarly with the uninitialized value warnings: one for $^H and another for $^W since it was "summoned" during compilation.