=head1 NAME

Canary::Stability - canary to check perl compatibility for schmorp's modules

=head1 SYNOPSIS

 # in Makefile.PL
 use Canary::Stability DISTNAME => 2001, MINIMUM_PERL_VERSION;

=head1 DESCRIPTION

This module is used by Schmorp's modules during configuration stage to
test the installed perl for compatibility with his modules.

It's not, at this stage, meant as a tool for other module authors,
although in principle nothing prevents them from subscribing to the same
ideas.

See the F<Makefile.PL> in L<Coro> or L<AnyEvent> for usage examples.

=cut

package Canary::Stability;

BEGIN {
   $VERSION = 2012;
}

sub sgr {
   # we just assume ANSI almost everywhere
   # red 31, yellow 33, green 32
   local $| = 1;

   $ENV{PERL_CANARY_STABILITY_COLOUR} ne 0
   and ((-t STDOUT and length $ENV{TERM}) or $ENV{PERL_CANARY_STABILITY_COLOUR})
   and print "\e[$_[0]m";
}

sub import {
   my (undef, $distname, $minvers, $minperl) = @_;

   $ENV{PERL_CANARY_STABILITY_DISABLE}
      and return;

   $minperl ||= 5.008002;

   print <<EOF;

***
*** Canary::Stability COMPATIBILITY AND SUPPORT CHECK
*** =================================================
***
*** Hi!
***
*** I do my best to provide predictable and reliable software.
***
*** However, in recent releases, P5P (who maintain perl) have been
*** introducing regressions that are sometimes subtle and at other times
*** catastrophic, often for personal preferences with little or no concern
*** for existing code, most notably CPAN.
***
*** For this reason, it has become very hard for me to maintain the level
*** of reliability and support I have committed myself to in the past, at
*** least with some perl versions: I simply can't keep up working around new
*** bugs or gratituous incompatibilities, and in turn you might suffer from
*** unanticipated problems.
***
*** Therefore I have introduced a support and compatibility check, the results
*** of which follow below, together with a FAQ and some recommendations.
***
*** This check is just to let you know that there might be a risk, so you can
*** make judgement calls on how to proceed - it will not keep the module from
*** installing or working.
***
EOF

   if ($minvers > $VERSION) {
      sgr 33;
      print <<EOF;
*** The stability canary says: (nothing, it died of old age).
***
*** Your Canary::Stability module (used by $distname) is too old.
*** This is not a fatal problem - while you might want to upgrade to version
*** $minvers (currently installed version: $VERSION) to get better support
*** status testing, you might also not want to care at all, and all will
*** be well as long $distname works well enough for you, as the stability
*** canary is only used when installing the distribution.
EOF
   } elsif ($] < $minperl) {

      sgr 33;
      print <<EOF;
*** The stability canary says: chirp (it seems concerned about something).
***
*** Your perl version ($]) is older than the $distname distribution
*** likes ($minperl). This is not a fatal problem - the module might work
*** well with your version of perl, but it does mean the author likely
*** won't do anything to make it work if it breaks.
EOF
   } elsif (defined $Internals::StabilityBranchVersion) {
      # note to people studying this modules sources:
      # the above test is not considered a clean or stable way to
      # test for the stability branch.

      sgr 32;
      print <<EOF;
*** The stability canary says: chirp! chirp! (it seems to be quite excited)
***
*** It seems you are running schmorp's stability branch of perl.
*** All should be well, and if it isn't, you should report this as a bug
*** to the $distname author.
EOF
   } elsif ($] < 5.021) {
      #sgr 32;
      print <<EOF;
*** The stability canary says: chirp! chirp! (it seems to be quite happy)
***
*** Your version of perl ($]) is quite supported by $distname, nothing
*** else to be said, hope it comes in handy.
EOF
   } else {
      sgr 31;
      print <<EOF;
*** The stability canary says: (nothing, it was driven away by harsh weather)
***
*** It seems you are running perl version $], likely the "official" or
*** "standard" version. While there is nothing wrong with doing that,
*** standard perl versions 5.022 and up are not supported by $distname.
*** While this might be fatal, it might also be all right - if you run into
*** problems, you might want to downgrade your perl or switch to the
*** stability branch.
***
*** If everything works fine, you can ignore this message.
EOF
      sgr 0;
      print <<EOF;
***
*** Stability canary mini-FAQ:
***
*** Do I need to do anything?
***    With luck, no. While some distributions are known to fail
***    already, most should probably work. This message is here
***    to alert you that your perl is not supported by $distname,
***    and if things go wrong, you either need to downgrade, or
***    sidegrade to the stability variant of your perl version,
***    or simply live with the consequences.
***
*** What is this canary thing?
***    It's purpose is to check support status of $distname with
***    respect to your perl version.
***
*** What is this "stability branch"?
***    It's a branch or fork of the official perl, by schmorp, to
***    improve stability and compatibility with existing modules.
***
*** How can I skip this prompt on automated installs?
***    Set PERL_CANARY_STABILITY_NOPROMPT=1 in your environment.
***    More info is in the Canary::Stability manpage.
***
*** Long version of this FAQ: http://stableperl.schmorp.de/faq.html
*** Stability Branch homepage: http://stableperl.schmorp.de/
***

EOF

      unless ($ENV{PERL_CANARY_STABILITY_NOPROMPT}) {
         require ExtUtils::MakeMaker;

         ExtUtils::MakeMaker::prompt ("Continue anyways? ", "y") =~ /^y/i
            or die "FATAL: User aborted configuration of $distname.\n";
      }
   }

   sgr 0;
}

=head1 ENVIRONMENT VARIABLES

=over 4

=item C<PERL_CANARY_STABILITY_NOPROMPT=1>

Do not prompt the user on alert messages.

=item C<PERL_CANARY_STABILITY_COLOUR=0>

Disable use of colour.

=item C<PERL_CANARY_STABILITY_COLOUR=1>

Force use of colour.

=item C<PERL_CANARY_STABILITY_DISABLE=1>

Disable this modules functionality completely.

=back

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://software.schmorp.de/pkg/Canary-Stability.html

=cut

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