This module enables all features and sets strict and warnings on by default with experimental warnings off. WARNING: this is not the definitive list of what will be in perl 7 but provides a way to test what might break in perl 7 but on 5.30.0

compat-perl5.pm

package compat::perl5;

# This helps hint to perl 7+ what level of compatibility this code has with future versions of perl.
# use compat::perl5 should be the first thing in your code. Especially before use strict, warnings, v5.XXX, or feature.

BEGIN {
    $] <= 8 or die("This code is incompatible with Perl 8. Please see XXX for more information.");
    if ( $] > 6 ) {
        warn_quietly_once("This code is being run using Perl $]. It should be updated or may break in Perl 8. See YYY for more information.");
    }
}

sub import {

    # no warnings;
    ${^WARNING_BITS} = undef;

    # perl  -e'my $h; BEGIN {  $h = $^H } printf("\$^H = 0x%08X\n", $h); '
    $^H = 0x0;

    %^H = ();
}

1;

compat-perl7.pm

package compat::perl7;

# use compat::perl7 enables perl 5 code to function in a perl 7-ish way as much as possible compared to the version you are running.
# it also is a hint to both tools and the compiler what the level of compatibility is with future versions of the language.

BEGIN {
    # This code is a proof of concept provided against 5.30. In order for this code to work on other versions of perl
    # we would need to generate it via p7.pm.PL as part of shipping it to CPAN.
    $] >= 5.030 && $] < 5.031 or die("Perl 5.30 is required to use this module.");
}

sub import {

    # use warnings; no warnings qw/experimental/;
    # perl -e'use warnings; no warnings qw/experimental/;  my $w; BEGIN {$w = ${^WARNING_BITS} } print unpack("H*", $w) . "\n"'
    ${^WARNING_BITS} = pack( "H*", "55555555555555555555555515000440050454" );

    # use strict; use utf8;
    # perl  -MData::Dumper -e'my $h; use strict; use utf8; use feature (qw/bitwise current_sub declared_refs evalbytes fc postderef_qq refaliasing say signatures state switch unicode_eval unicode_strings/); BEGIN {  $h = $^H } printf("\$^H = 0x%08X\n", $h); print Dumper \%^H; '
    $^H = 0x1C820FE2;

    %^H = (
        'feature___SUB__'      => 1,
        'feature_bitwise'      => 1,
        'feature_evalbytes'    => 1,
        'feature_fc'           => 1,
        'feature_myref'        => 1,
        'feature_postderef_qq' => 1,
        'feature_refaliasing'  => 1,
        'feature_say'          => 1,
        'feature_signatures'   => 1,
        'feature_state'        => 1,
        'feature_switch'       => 1,
        'feature_unicode'      => 1,
        'feature_unieval'      => 1
    );
}

1;

note older versions don't understand newer "use v5.44" and get very angry if you use them.

Will this ever be non-secret? I was thinking about doing something similar.

I don't think I realized it was secret.

fixed.

note that https://github.com/Perl/perl5/blob/core-p7/regen/pX.pl provides a way to generate these two files

you can view the generated files here:

• p7: https://github.com/Perl/perl5/blob/core-p7/lib/p7.pm
• p5: https://github.com/Perl/perl5/blob/core-p7/lib/p5.pm

We should close this gist and move the discussion to the repo itself.