require__before hook interacts weirdly with mortals?

[dakkar]

Description

Setting ${^HOOK}{require__before} to any coderef (even just sub{}), then calling require(some_non_constant_function()), produces a Use of uninitialized value in require warning.

Steps to Reproduce

Two files:

One.pm:

package One;
use v5.42;

sub path_for($f) { $f =~ s{::}{/}g; "${f}.pm" }

sub import {
    my ($class,$name)=@_;
    require(path_for($name));
}

then:

perl -I . -E '${^HOOK}{require__before} = sub {}; require One;One->import(shift)' Carp

will print:

Use of uninitialized value in require at One.pm line 8.

Furthermore:

• not all package names produce the warning (I can't find a pattern)
  • these warn: Carp, Cwd, open, Test, Test2
  • these don't: FindBin, charnames, Data::Dumper
  • a non-existed package will cause the "uninitialized" warning to be printed before the Can't locate … error
• replacing the require line with require(my $p=path_for($name)) makes the warning go away (this is why I mentioned mortals in the title)

Expected behavior

No warnings.

Perl configuration

Summary of my perl5 (revision 5 version 42 subversion 1) configuration:
   
  Platform:
    osname=linux
    osvers=6.18.12-gentoo-x86_64
    archname=x86_64-linux-thread-multi
    uname='linux exelion 6.18.12-gentoo-x86_64 #6 smp preempt_dynamic tue mar 10 14:00:33 gmt 2026 x86_64 11th gen intel(r) core(tm) i7-1185g7 @ 3.00ghz genuineintel gnulinux '
    config_args='-de -Dprefix=/home/dakkar/perl5/perlbrew/perls/perl-5.42.1 -Dusethreads -Aeval:scriptdir=/home/dakkar/perl5/perlbrew/perls/perl-5.42.1/bin'
    hint=recommended
    useposix=true
    d_sigaction=define
    useithreads=define
    usemultiplicity=define
    use64bitint=define
    use64bitall=define
    uselongdouble=undef
    usemymalloc=n
    default_inc_excludes_dot=define
  Compiler:
    cc='cc'
    ccflags ='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64'
    optimize='-O2'
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong'
    ccversion=''
    gccversion='15.2.1 20260214'
    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/lib /usr/local/lib /lib64 /usr/lib64 /lib /usr/local/lib64
    libs=-lpthread -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lpthread -ldl -lm -lcrypt -lutil -lc
    libc=/lib/../lib64/libc.so.6
    so=so
    useshrplib=false
    libperl=libperl.a
    gnulibc_version='2.42'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs
    dlext=so
    d_dlsymun=undef
    ccdlflags='-Wl,-E'
    cccdlflags='-fPIC'
    lddlflags='-shared -O2 -L/usr/local/lib -fstack-protector-strong'


Characteristics of this binary (from libperl): 
  Compile-time options:
    HAS_LONG_DOUBLE
    HAS_STRTOLD
    HAS_TIMES
    MULTIPLICITY
    PERLIO_LAYERS
    PERL_COPY_ON_WRITE
    PERL_DONT_CREATE_GVSV
    PERL_HASH_FUNC_SIPHASH13
    PERL_HASH_USE_SBOX32
    PERL_MALLOC_WRAP
    PERL_OP_PARENT
    PERL_PRESERVE_IVUV
    PERL_USE_SAFE_PUTENV
    USE_64_BIT_ALL
    USE_64_BIT_INT
    USE_ITHREADS
    USE_LARGE_FILES
    USE_LOCALE
    USE_LOCALE_COLLATE
    USE_LOCALE_CTYPE
    USE_LOCALE_NUMERIC
    USE_LOCALE_TIME
    USE_PERLIO
    USE_PERL_ATOF
    USE_REENTRANT_API
    USE_THREAD_SAFE_LOCALE
  Built under linux
  Compiled at Mar 19 2026 13:59:22
  %ENV:
    PERLBREW_HOME="/home/dakkar/.perlbrew"
    PERLBREW_MANPATH="/home/dakkar/perl5/perlbrew/perls/perl-5.42.1/man"
    PERLBREW_PATH="/home/dakkar/perl5/perlbrew/bin:/home/dakkar/perl5/perlbrew/perls/perl-5.42.1/bin"
    PERLBREW_PERL="perl-5.42.1"
    PERLBREW_ROOT="/home/dakkar/perl5/perlbrew"
    PERLBREW_SHELLRC_VERSION="0.88"
    PERLBREW_VERSION="1.02"
    PERLDOC="-MPod::Text::Color::Delight"
  @INC:
    /home/dakkar/perl5/perlbrew/perls/perl-5.42.1/lib/site_perl/5.42.1/x86_64-linux-thread-multi
    /home/dakkar/perl5/perlbrew/perls/perl-5.42.1/lib/site_perl/5.42.1
    /home/dakkar/perl5/perlbrew/perls/perl-5.42.1/lib/5.42.1/x86_64-linux-thread-multi
    /home/dakkar/perl5/perlbrew/perls/perl-5.42.1/lib/5.42.1

[leonerd]

Uh; interesting. I tried to reproduce this on older perls. I removed the use v5.42 and adjusted the code to not use signatures. If I do that I get warnings from 5.38 onwards:

  --- perl5.38.3 --- 
Use of uninitialized value in require at One.pm line 9.

  --- perl5.40.1 --- 
Use of uninitialized value in require at One.pm line 9.

  --- perl5.42.0 --- 
Use of uninitialized value in require at One.pm line 9.

  --- perl --- 
Use of uninitialized value in require at One.pm line 9.

which makes sense as that was when the %{^HOOK} mechanism was added. I think we can safely say this is not a new regression in blead.