# PODNAME: Alien::Build::Manual::FAQ
# ABSTRACT: Frequently Asked Questions about Alien::Build
# VERSION

__END__

=pod

=encoding UTF-8

=head1 NAME

Alien::Build::Manual::FAQ - Frequently Asked Questions about Alien::Build

=head1 VERSION

version 1.95_01

=head1 SYNOPSIS

 perldoc Alien::Build::Manual::FAQ

=head1 DESCRIPTION

This document serves to answer the most frequently asked questions made by developers
creating L<Alien> modules using L<Alien::Build>.

=head1 QUESTIONS

=head2 What is Alien, Alien::Base and Alien::Build?

Alien in a Perl namespace for defining dependencies in CPAN for libraries and tools which
are not "native" to CPAN.  For a manifesto style description of the Why, and How see
L<Alien>.  L<Alien::Base> is a base class for the L<Alien> runtime.  L<Alien::Build> is
a tool for probing the operating system for existing libraries and tools, and downloading, building
and installing packages.  L<alienfile> is a recipe format for describing how to probe,
download, build and install a package.

=head2 How do I build a package that uses I<build system>

=head3 autoconf

Use the autoconf plugin (L<Alien::Build::Plugin::Build::Autoconf>).  If your package
provides a pkg-config C<.pc> file, then you can also use the PkgConfig plugin
(L<Alien::Build::Plugin::PkgConfig::Negotiate>).

 use alienfile
 plugin PkgConfig => 'libfoo';
 share {
   start_url => 'http://example.org/dist';
   plugin Download => (
     version => qr/libfoo-([0-9\.])\.tar\.gz$/,
   );
   plugin Extract => 'tar.gz';
   plugin 'Build::Autoconf';
 };

If you need to provide custom flags to configure, you can do that too:

 share {
   plugin 'Build::Autoconf';
   build [
     '%{configure} --disable-shared --enable-foo',
     '%{make}',
     '%{make} install',
   ];
 };

If your package requires GNU Make, use C<%{gmake}> instead of C<%{make}>.

=head3 autoconf-like

If you see an error like this:

 Unknown option "--with-pic".

It is because the autoconf plugin uses the C<--with-pic> option by default, since
it makes sense most of the time, and autoconf usually ignores options that it does
not recognize.  Some autoconf style build systems fail when they see an option that
they do not recognize.  You can turn this behavior off for these packages:

 plugin 'Build::Autoconf' => (
   with_pic => 0,
 );

Another thing about the autoconf plugin is that it uses C<DESTDIR> to do a double
staged install.  If you see an error like "nothing was installed into destdir", that
means that your package does not support C<DESTDIR>.  You should instead use the
MSYS plugin and use a command sequence to do the build like this:

 share {
   plugin 'Build::MSYS';
   build [
     # explicitly running configure with "sh" will make sure that
     # it works on windows as well as UNIX.
     'sh configure --prefix=%{.install.prefix} --disable-shared',
     '%{make}',
     '%{make} install',
   ];
 };

=head3 CMake

There is an alien L<Alien::cmake3> that provides C<cmake> 3.x or better (It is preferred to the
older L<Alien::CMake>).  Though it is recommended that you use the C<cmake> 
(L<Alien::Build::Plugin::Build::CMake>) plugin instead of using L<Alien::cmake3>.

 use alienfile;
 
 share {
   plugin 'Build::CMake';
   build [
     # this is the default build step, if you do not specify one.
     [ '%{cmake}',
         @{ meta->prop->{plugin_build_cmake}->{args} },
         # ... put extra cmake args here ...
         '.'
     ],
     '%{make}',
     '%{make} install',
   ];
 };

=head3 vanilla Makefiles

L<Alien::Build> provides a helper (C<%{make}>) for the C<make> that is used by Perl and
L<ExtUtils::MakeMaker> (EUMM).  Unfortunately the C<make> supported by Perl and EUMM on
Windows (C<nmake> and C<dmake>) are not widely supported by most open source projects.
(Thankfully recent perls and EUMM support GNU Make on windows now).

You can use the C<make> plugin (L<Alien::Build::Plugin::Build::Make>) to tell the
L<Alien::Build> system know which make the project that you are alienizing requires.

 plugin 'Build::Make' => 'umake';
 # umake makes %{make} either GNU Make or BSD Make on Unix and GNU Make on Windows.
 build {
   build [
     # You can use the Perl config compiler and cflags using the %{perl.config...} helper
     [ '%{make}', 'CC=%{perl.config.cc}', 'CFLAGS=%{perl.config.cccdlflags} %{perl.config.optimize}' ],
     [ '%{make}', 'install', 'PREFIX=%{.install.prefix}' ],
   ],
 };

Some open source projects require GNU Make, and you can specify that, and L<Alien::gmake>
will be pulled in on platforms that do not already have it.

 plugin 'Build::Make' => 'gmake';
 ...

=head2 How do I probe for a package that uses pkg-config

Use the C<pkg-config> plugin (L<Alien::Build::Plugin::PkgConfig::Negotiate>):

 use alienfile;
 plugin 'PkgConfig' => (
   pkg_name => 'libfoo',
 );

It will probe for a system version of the library.  It will also add the appropriate C<version>
C<cflags> and C<libs> properties on either a C<system> or C<share> install.

=head2 How do I specify a minimum or exact version requirement for packages that use pkg-config?

The various pkg-config plugins all support atleast_version, exact_version and maximum_version
fields, which have the same meaning as the C<pkg-config> command line interface:

 use alienfile;
 
 plugin 'PkgConfig', pkg_name => foo, atleast_version => '1.2.3';

or

 use alienfile;
 
 plugin 'PkgConfig', pkg_name => foo, exact_version => '1.2.3';

=head2 How to create an Alien module for a packages that do not support pkg-config?

=head3 Packages that provide a configuration script

Many packages provide a command that you can use to get the appropriate version, compiler
and linker flags.  For those packages you can just use the commands in your L<alienfile>.
Something like this:

 use alienfile;
 
 probe [ 'foo-config --version' ];
 
 share {
   ...
 
   build [
     '%{make} PREFIX=%{.runtime.prefix}',
     '%{amek} install PREFIX=%{.runtime.prefix}',
   ];
 };
 
 gather [
   [ 'foo-config', '--version', \'%{.runtime.version}' ],
   [ 'foo-config', '--cflags',  \'%{.runtime.cflags}'  ],
   [ 'foo-config', '--libs',    \'%{.runtime.libs}'    ],
 ];

=head3 Packages that require a compile test

Some packages just expect you do know that C<-lfoo> will work.  For those you can use
the C<cbuilder> plugin (L<Alien::Build::Plugin::Probe::CBuilder>.

 use alienfile;
 plugin 'Probe::CBuilder' => (
   cflags => '-I/opt/libfoo/include',
   libs   => '-L/opt/libfoo/lib -lfoo',
 );
 
 share {
   ...
   gather sub {
     my($build) = @_;
     my $prefix = $build->runtime_prop->{prefix};
     $build->runtime_prop->{cflags} = "-I$prefix/include ";
     $build->runtime_prop->{libs}   = "-L$prefix/lib -lfoo ";
   };
 }

This plugin will build a small program with these flags and test that it works.  (There
are also options to provide a program that can make simple tests to ensure the library
works).  If the probe works, it will set the compiler and linker flags.  (There are also
options for extracting the version from the test program).  If you do a share install
you will need to set the compiler and linker flags yourself in the gather step, if you
aren't using a build plugin that will do that for you.

=head2 Can/Should I write a tool oriented Alien module?

Certainly.  The original intent was to provide libraries, but tools are also quite doable using
the L<Alien::Build> toolset.  A good example of how to do this is L<Alien::nasm>.  You will want
to use the 'Probe::CommandLine':

 use alienfile;
 
 plugin 'Probe::CommandLine' => (
   command => 'gzip',
 );

=head2 How do I test my package once it is built (before it is installed)?

Use L<Test::Alien>.  It has extensive documentation, and integrates nicely with L<Alien::Base>.

=head2 How do I patch packages that need alterations?

If you have a diff file you can use patch:

 use alienfile;
 
 probe sub { 'share' }; # replace with appropriate probe
 
 share {
   ...
   patch [ '%{patch} -p1 < %{.install.patch}/mypatch.diff' ];
   build [ ... ] ;
 }
 
 ...

You can also patch using Perl if that is easier:

 use alienfile;
 
 probe sub { 'share' };
 
 share {
   ...
   patch sub {
     my($build) = @_;
     # make changes to source prior to build
   };
   build [ ... ];
 };

=head2 The flags that a plugin produces are wrong!

Sometimes, the compiler or linker flags that the PkgConfig plugin comes up with are not quite
right.  (Frequently this is actually because a package maintainer is providing a broken
C<.pc> file).  (Other plugins may also have problems).  You could replace the plugin's C<gather> step
but a better way is to provide a subroutine callback to be called after the gather stage
is complete.  You can do this with the L<alienfile> C<after> directive:

 use alienfile;
 
 plugin 'PlgConfig' => 'libfoo';
 
 share {
   ...
   after 'gather' => sub {
     my($build) = @_;
     $build->runtime_prop->{libs}        .= " -lbar";        # libfoo also requires libbar
     $build->runtime_prop->{libs_static} .= " -lbar -lbaz";  # libfoo also requires libbaz under static linkage
   };
 };

Sometimes you only need to do this on certain platforms.  You can adjust the logic based on C<$^O>
appropriately.

 use alienfile;
 
 plugin 'PlgConfig' => 'libfoo';
 
 share {
   ...
   after 'gather' => sub {
     my($build) = @_;
     if($^O eq 'MSWin32') {
       $build->runtime_prop->{libs} .= " -lpsapi";
     }
   };
 };

=head2 599 Internal Exception errors downloading packages from the internet

 Alien::Build::Plugin::Fetch::HTTPTiny> 599 Internal Exception fetching http://dist.libuv.org/dist/v1.15.0
 Alien::Build::Plugin::Fetch::HTTPTiny> exception: IO::Socket::SSL 1.42 must be installed for https support
 Alien::Build::Plugin::Fetch::HTTPTiny> exception: Net::SSLeay 1.49 must be installed for https support
 Alien::Build::Plugin::Fetch::HTTPTiny> An attempt at a SSL URL https was made, but your HTTP::Tiny does not appear to be able to use https.
 Alien::Build::Plugin::Fetch::HTTPTiny> Please see: https://metacpan.org/pod/Alien::Build::Manual::FAQ#599-Internal-Exception-errors-downloading-packages-from-the-internet
 error fetching http://dist.libuv.org/dist/v1.15.0: 599 Internal Exception at /Users/ollisg/.perlbrew/libs/perl-5.26.0@test1/lib/perl5/Alien/Build/Plugin/Fetch/HTTPTiny.pm line 68.

(Older versions of L<Alien::Build> produced a less verbose more confusing version of this diagnostic).

TL;DR, instead of this:

 share {
   start_url => 'http://example.org/dist';
   ...
 };

do this:

 share {
   start_url => 'https://example.org/dist';
 };

If the website is going to redirect to a secure URL anyway.

The "599 Internal Exception" indicates an "internal" exception from L<HTTP::Tiny> and is not a real
HTTP status code or error.  This could mean a number of different problems, but most frequently
indicates that a SSL request was made without the required modules (L<Net::SSLeay> and
L<IO::Socket::SSL>).  Normally the L<Alien::Build::Plugin::Download::Negotiate>
and L<Alien::Build::Plugin::Fetch::HTTPTiny> will make sure that the appropriate modules are added
to your prerequisites for you if you specify a C<https> URL.  Some websites allow an initial request
from C<http> but then redirect to C<https>.  If you can it is better to specify C<https>, if you
cannot, then you can instead use the C<ssl> property on either of those two plugins.

=head2 Network fetch is turned off

If you get an error like this:

 Alien::Build> install type share requested or detected, but network fetch is turned off
 Alien::Build> see see https://metacpan.org/pod/Alien::Build::Manual::FAQ#Network-fetch-is-turned-off

This is because your environment is setup not to install aliens that require the network.  You
can turn network fetch back on by setting C<ALIEN_INSTALL_NETWORK> to true, or by unsetting it.
This environment variable is designed for environments that don't ever want to install aliens that
require downloading source packages over the internet.

=head2 I would really prefer you not download stuff off the internet

The idea of L<Alien> is to download missing packages and build them automatically to make installing
easier.  Some people may not like this, or may even have security requirements that they not download
random package over the internet (caveat, downloading random stuff off of CPAN may not be any safer,
so make sure you audit all of the open source software that you use appropriately).  Another reason
you may not want to download from the internet is if you are packaging up an alien for an operating
system vendor, which will always want to use the system version of a library.  In that situation you
don't want L<Alien::Build> to go off and download something from the internet because the probe failed
for some reason.

This is easy to take care of, simply set C<ALIEN_INSTALL_TYPE> to C<system> and a build from source
code will never be attempted.  On systems that do not provide system versions of the library or tool
you will get an error, allowing you to install the library, and retry the alien install.  You can
also set the environment variable on just some aliens.

 % export ALIEN_INSTALL_TYPE=system  # for everyone
 
 % env ALIEN_INSTALL_TYPE=system cpanm -v Alien::libfoo

=head2 For testing I would like to test both system and share installs!

You can use the C<ALIEN_INSTALL_TYPE> environment variable.  It will force either a C<share> or
C<system> install depending on how it is set.  For travis you can do something like this:

 env:
   matrix:
     - ALIEN_INSTALL_TYPE=share
     - ALIEN_INSTALL_TYPE=system

=head2 How do I use Alien::Build from Dist::Zilla?

For creating L<Alien::Base> and L<Alien::Build> based dist from L<Dist::Zilla> you can use the
dzil plugin L<Dist::Zilla::Plugin::AlienBuild>.

=head2 Cannot find either a share directory or a ConfigData module

If you see an error like this:

 Cannot find either a share directory or a ConfigData module for Alien::libfoo.
 (Alien::libfoo loaded from lib/Alien/libfoo.pm)
 Please see https://metacpan.org/pod/distribution/Alien-Build/lib/Alien/Build/Manual/FAQ.pod#Cannot-find-either-a-share-directory-or-a-ConfigData-module
 Can't locate Alien/libfoo/ConfigData.pm in @INC (you may need to install the Alien::libfoo::ConfigData module) (@INC contains: ...)

it means you are trying to use an Alien that hasn't been properly installed.  An L<Alien::Base>
based Alien needs to have either the share directory build during the install process or for
older legacy L<Alien::Base::ModuleBuild> based Aliens, a ConfigData module generated by
L<Module::Build>.

This usually happens if you try to use an Alien module from the lib directory as part of the
Alien's distribution.  You need to build the alien and use C<blib/lib> instead of C<lib> or
install the alien and use the installed path.

It is also possible that your Alien installer is not set up correctly.  Make sure your
C<Makefile.PL> is using L<Alien::Build::MM> correctly.

=head2 I have a question not listed here!

There are a number of forums available to people working on L<Alien>, L<Alien::Base> and
L<Alien::Build> modules:

=over 4

=item C<#native> on irc.perl.org

This is intended for native interfaces in general so is a good place for questions about L<Alien>
generally or L<Alien::Base> and L<Alien::Build> specifically.

=item mailing list

The C<perl5-alien> google group is intended for L<Alien> issues generally, including L<Alien::Base>
and L<Alien::Build>.

L<https://groups.google.com/forum/#!forum/perl5-alien>

=item Open a support ticket

If you have an issue with L<Alie::Build> itself, then please open a support ticket on the project's GitHub issue 
tracker.

L<https://github.com/plicease/Alien-Build/issues>

=back

=head1 SEE ALSO

L<Alien::Build>, L<Alien::Build::MM>, L<Alien::Build::Plugin>, L<alienfile>

=head1 AUTHOR

Author: Graham Ollis E<lt>plicease@cpan.orgE<gt>

Contributors:

Diab Jerius (DJERIUS)

Roy Storey (KIWIROY)

Ilya Pavlov

David Mertens (run4flat)

Mark Nunberg (mordy, mnunberg)

Christian Walde (Mithaldu)

Brian Wightman (MidLifeXis)

Zaki Mughal (zmughal)

mohawk (mohawk2, ETJ)

Vikas N Kumar (vikasnkumar)

Flavio Poletti (polettix)

Salvador Fandiño (salva)

Gianni Ceccarelli (dakkar)

Pavel Shaydo (zwon, trinitum)

Kang-min Liu (劉康民, gugod)

Nicholas Shipp (nshp)

Juan Julián Merelo Guervós (JJ)

Joel Berger (JBERGER)

Petr Pisar (ppisar)

Lance Wicks (LANCEW)

Ahmad Fatoum (a3f, ATHREEF)

José Joaquín Atria (JJATRIA)

Duke Leto (LETO)

Shoichi Kaji (SKAJI)

Shawn Laffan (SLAFFAN)

Paul Evans (leonerd, PEVANS)

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2011-2020 by Graham Ollis.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut
