=head1 NAME

Alien::Base::ModuleBuild::FAQ - Frequently Asked Questions about Alien::Base::ModuleBuild

=head1 SYNOPSIS

 perldoc Alien::Base::FAQ

=head1 DESCRIPTION

This document serves to answer the most frequently asked questions made by L<Alien::Base> authors.

=head2 What is Alien and Alien::Base?

Alien is 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 and framework for creating Alien distributions.  The idea is to address as many of the common challenges
to developing Alien modules in the base class to simplify the process.

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

The C<alien_version_check> attribute to L<Alien::Base::ModuleBuild> will be executed to determine if
the library is provided by the operating system.  The default for this is C<%{pkg_config} --modversion %n>
which simply checks to see if any version of that package is available, and prints the version
number.  You can use the C<--atleast-version>, C<--exact-version> options to require a specific range of versions,
but these flags do not work with the C<--modversion> flag, so be sure to invoke separately.

 use Alien::Base::ModuleBuild;
 Alien::Base::ModuleBuild->new(
   dist_name           => 'Alien::Foo',
   alien_name          => 'foo',
   configure_requires  => { 'Alien::Base::ModuleBuild' => '0.022' }, # required for %{pkg_config}
   alien_version_check => '%{pkg_config} --atleast-version 1.2.3 %n && %{pkg_config} --modversion %n',
   ...
 )->create_build_script;

It is better to use the built in C<%{pkg_config}> helper as it will use the system provided pkg-config
if it is available and fallback on the pure perl L<PkgConfig> if not.

You can also use C<--exact-version> to specify an exact version.

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

Although L<Alien::Base> and L<Alien::Base::ModuleBuild> assume packages come with a C<pkg-config>
C<.pc> file to determine compiler and linker flags by default, you can implement an Alien module
for packages that do use C<pkg-config> by following these tasks:

=over 4

=item subclass L<Alien::Base::ModuleBuild> and implement C<alien_check_installed_version>

Create a subclass of L<Alien::Base::ModuleBuild> and put it in the C<inc> directory of your distribution so
that it can be used during install but won't I<be installed>.

 # inc/My/ModuleBuild.pm
 package My::ModuleBuild;
 
 use parent 'Alien::Base::ModuleBuild';
 
 sub alien_check_installed_version {
   my($class) = @_;
   
   # determine if your library is already provided by the system
   my $version = ...;
   
   # return false if the library is NOT provided by the system
   return unless defined $version;
   
   # otherwise return the version detected
   # (if you cannot determine the version it
   #  is usually sufficient to return a true value)
   return $version;
 }

There are number of methods you can use to determine if the system provides your library.  From Perl
methods include L<Devel::CheckLib>, L<ExtUtils::CBuilder>, L<ExtUtls::CChecker>, L<Config::AutoConf>,
L<FFI::CheckLib> among others.  It is also frequently possible to determine if a library is installed
using a C<-config> suffixed program.  For example C<libxml2> comes with xml2-config which provides the
existence, compiler and linker flags it needs.  In my experience, however, most packages that provide a
C<-config> suffixed program also provide a C<pkg-config> interface as well.

=item implement C<alien_check_built_version> in your L<Alien::Base::ModuleBuild> subclass

You should also implement C<alien_check_build_version> which will be executed from the package build
root once the package is successfully built.

 # inc/My/ModuleBuild.pm
 package My::ModuleBuild;
 
 ...
 
 sub alien_check_built_version {
   my($self) = @_;
   
   my $version = ...
   
   # (Again, if you cannot determine the version,
   #  it is usually sufficent to return a true value)
   return $version;
 }

=item set C<alien_provides_cflags> and C<alien_provides_libs> in C<Build.PL>.

Add something like this to your C<Build.PL>:

 # Build.PL
 use lib 'inc';
 use My::ModuleBuild;
 
 My::ModuleBuild->new(
   ...
   alien_provides_cflags => '-I/usr/include/foo',
   alien_provides_libs   => '-L/usr/lib/foo -lfoo',
   ...
 );

Note that it is frequently sufficient to provide C<alien_provides_libs> and the appropriate C<-l> flag.
These flags will be used in the event that the system package can be found.  It is a good idea to verify
that these flags do indeed work in C<alien_check_installed_version> above.

=back

For a fully implemented example, see L<Alien::Libbz2>.

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

There are many ways to test Alien modules before (or after) they are installed, but instead
of rolling your own, consider using L<Test::Alien> which is light on dependencies and will
test your module very closely to the way that it will actaully be used.  That is to say by
building a mini XS or FFI extension and using it.  It even has tests for tool oriented Alien
distributions (like L<Alien::gmake> and L<Alien::patch>).  Here is a short example, there
are many others included with the L<Test::Alien> documentation:

 use Test2::V0;
 use Test::Alien 0.05;
 use Alien::Editline;
 
 alien_ok 'Alien::Editline';
 my $xs = do { local $/; <DATA> };
 xs_ok $xs, with_subtest {
   my($module) = @_;
   ok $module->version;
 };
 
 done_testing;
 
 __DATA__
 
 #include "EXTERN.h"
 #include "perl.h"
 #include "XSUB.h"
 #include <editline/readline.h>
 
 /* having a string parameter that we ignore
    allows us to call this as a class method */
 const char *
 version(const char *class)
 {
   return rl_library_version;
 }
 
 MODULE = TA_MODULE PACKAGE = TA_MODULE
 
 const char *version(class);
     const char *class;

=head2 How do I patch packages that need minor (or major) alterations?

One approach is to create a unified diff for patches that you want to apply and simply run patch on them.  The
L<Alien::patch> and the C<%{patch}> helper can be used like this:

 # Build.PL
 use Alien::Base::ModuleBuild;
 
 Alien::Base::ModuleBuild->new(
   ...
   alien_bin_requires => {
     'Alien::patch' => 0.06, # needed for %{patch} helper
   },
   alien_build_commands => [
     '%{patch} -p1 < ../../patch/mypackage.patch',
     ...
   ],
   ...
 )->create_build_script;

Create a folder in your distribution root called C<patch> and place the C<mypackage.patch> file in there.  Since 
the C<patch> command will be executed in the package root instead of the distribution root, you need to use a 
relative path prefixed by C<../..>.  Here we use L<Alien::patch> to provide patch even in environments where it
is not provided.

A more powerful approach to patching is to write a perl subroutine to modify the source after it has been 
extracted.  One way to do this is to create a module in your distribution's inc directory that does the 
patching (modules in inc can be used during build/test but won't be installed):

 # inc/My/AlienPatch.pm
 package My::AlienPatch;
 
 # add this sub to the main namespace
 # so we don't need to quote or escape
 # anything below
 sub main::alien_patch {
   # is executed in the package root,
   # make what ever changes you need to
   # to the source here.
 }
 
 1;

 # Build.PL
 use Alien::Base::ModuleBuild;
 
 Alien::Base::ModuleBuild->new(
   ...
   alien_build_commands => [
     # %x will be replaced by path for calling Perl
     # from the command line
     "%x -I../../inc -MMy::AlienPatch -e alien_patch",
     ...
   ],
   ...
 )->create_build_script;

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

=head3 autoconf

By default L<Alien::Base::ModuleBuild> assumes a package with an autoconf style C<configure> script.  The 
default is
 
 # Build.PL
 use Alien::Base::ModuleBuild;
 Alien::Base::ModuleBuild->new(
   ...
   alien_build_commands => [
     '%c --prefix=%s',
     'make',
   ],
   alien_install_commands => [
     'make install',
   ],
   ...
 )->create_build_script;

There are a couple of short cuts here, C<%c> indicates the platform independent method for executing the 
C<configure> script, plus any normal autoconf flags that are appropriate for Perl Alien libraries. The C<%c> 
also tells L<Alien::Base::ModuleBuild> to use L<Alien::MSYS> on Windows platforms and to add that as a 
dependency.  The C<%s> is a placeholder for the location to which the package will be installed.  This is 
normally in a share directory specific to your distribution.

=head3 autoconf-like

If you see an error like this:

 Unknown option "--with-pic".

It may be because your package provides a C<configure> script that provides an autoconf-style interface, but is 
not actually autoconf.  L<Alien::Base::ModuleBuild> is aggressive in using the C<--with-pic> option because when 
supported by autoconf it produces position independent code (important for reliably building XS extensions), and 
when not supported autoconf simply ignores the option. Unfortunately some autoconf-style C<configure> scripts 
consider it an error when they see options that they do not recognize.  You can tell L<Alien::Base::ModuleBuild> 
to not use the C<--with-pic> option via the C<alien_autoconf_with_pic> property:

 # Build.PL
 use Alien::Base::ModuleBuild;
 Alien::Base::ModuleBuild->new(
   ...
   alien_autoconf_with_pic => 0,
   ...
 )->create_build_script;

=head3 CMAKE

You probably cannot count on CMake being available on most platforms.  Fortunately, there is an alien 
distribution L<Alien::CMake> which will either use the CMake provided by the operating system, or download and 
install it for you.  You can use this from your C<Build.PL> with the C<alien_bin_requires> property:

 # Build.PL
 use Alien::Base::ModuleBuild;
 use Config;
 Alien::Base::ModuleBuild->new(
   ...
   alien_bin_requires => {
     'Alien::CMake' => 0.07,
   },
   alien_build_commands => [
     # acutal required arguments may vary
     "cmake -G 'Unix Makefiles' -DCMAKE_MAKE_PROGRAM=$Config{make} -DCMAKE_INSTALL_PREFIX:PATH=%s",
     "$Config{make}",
   ],
   alien_install_commands => [
     "$Config{make} install",
   ],
   ...
 )->create_build_script;


=head3 vanilla Makefiles?

If you want to use the same C<make> as Perl, you can use L<Config>:

 # Build.PL
 use Alien::Base::ModuleBuild;
 use Config;
 Alien::Base::ModuleBuild->new(
   ...
   alien_build_commands => [
     "$Config{make}",
   ],
   alien_install_commands => [
     "$Config{make} install",
   ],
   ...
 )->create_build_script;

=head3 Gnu Makefiles?

Some packages require GNU Make's unique syntax.  Perl's L<Config> provides an entry for C<gmake>, but it is 
frequently wrong.  Do not depend on it.  Instead you can ues L<Alien::gmake> to provide a real GNU Make (either 
from the operating system, or built from source):

 # Build.PL
 use Alien::Base::ModuleBuild;
 
 Alien::Base::ModuleBuild->new(
   ...
   alien_bin_requires => {
     'Alien::gmake' => 0.11, # needed for %{gmake} helper
   },
   alien_build_commands => [
     "%{gmake}",
   ],
   alien_install_commands => [
     "%{gmake} install",
   ],
   ...
 )->create_build_script;

=head2 When debugging my package build, I get different results!

If you get results from running the commands in your shell different to what happens when your C<Alien::> 
distribution attempts to build, it may be because your environment is different than the one that your 
distribution is using.  For example, if you use L<Alien::CMake> or L<Alien::gmake> to build with specific tools 
that are provided by your operating system, L<Alien::Build::ModuleBuild> will adjust the path before executing 
build and install commands.

In the alien build directory (usually C<_alien>) you will find environment files that you can source
into your shell (C<env.csh> for tcsh and C<env.sh> for bourne based shells), which should provide the 
identical environment used by the build process in order to troubleshoot the build manually.

 % source _alien/env.sh

=head2 Can/Should I write a tool oriented Alien module using C<Alien::Base> that provides executables instead of a library?

Certainly.  The original intent was to provide libraries, but tools are also quite doable using the 
C<Alien::Base> toolset.  A simple minded example of this which is fairly easy to replicate is L<Alien::m4>.

In general, this means specifying a subclass in your C<Build.PL> and bundling it in your distribution C<inc> directory.

C<Build.PL>:

 ...
 use lib 'inc';
 use My::ModuleBuild;
 
 My::ModuleBuild->new(
   ...
 )->create_build_script;

C<inc/My/ModuleBuild.pm>:

 package My::ModuleBuild;
 
 use strict;
 use warnings;
 use parent 'Alien::Base::ModuleBuild';
 use Capture::Tiny qw( capture );
 
 sub alien_check_installed_version
 {
   # see Alien::Base::ModuleBuild#alien_check_installed_version for details
   
   my($self) = @_;
   my($stdout, $stderr) = capture { system 'mytool', '--version' };
   
   # return empty list if the tool is unavailable on the system,
   # or unacceptable.
   return if $! || ...;

   # parse from stdout or stderr
   my $version = ...;
   return $version;
 }
 
 sub alien_check_built_version
 {
   # see Alien::Base::ModuleBuild#alien_check_built_version for details
   
   # return empty list if the tool version cannot be found, or if it
   # is unacceptable.  Note that this will cause a failure, so "unknown"
   # may be reasonable if the tool version cannot be determined.
   return if ...;
   
   # determine from the tool itself, or the current directory.
   my $version = ...;
   return $version;
 }
 
 1;

As usual your C<Alien::MyTool> class will simply be a subclass of L<Alien::Base>.
If you tool is installed in a C<bin> directory, you are done, the default C<bin_dir>
implementation should work for you.  Otherwise you may need to provide an alternate
implementation:

 package Alien::MyTool;
 
 use strict;
 use warnings;
 use parent 'Alien::Base';
 use File::Spec;
 
 sub bin_dir
 {
   # see Alien::Base#bin_dir for details
   # You only need to override the default implementation if your tool
   # does not install into the standard "bin" directory.

   my($class) = @_;
   
   # normally for system installs the tool should already be in your
   # PATH, so return an empty list.
   return if $class->install_type eq 'system';
   
   # install_type = share
   my $dist_dir = $class->dist_dir;
   return ("$dist_dir/some/bin", "$dist_dir/some/other/bin");
 }
 
 1;

Now once your tool based Alien is installed you can use the C<bin_dir> method to
update the C<PATH> as necessary:

 use Alien::MyTool;
 use Env qw( @PATH );
 
 unshift @PATH, Alien::MyTool->bin_dir;
 system 'mytool';

=back
 
=head2 How do I use C<Alien::Base> from C<Dist::Zilla>

For creating L<Alien::Base> based dists from L<Dist::Zilla> you can use the plugin 
L<Dist::Zilla::Plugin::Alien>.

=head2 How do I check the built version if my library doesn't provide a C<.pc> file.

The default implementation of C<alien_check_built_version> uses several heuristics,
but leans heavily on C<pkg-config> style C<.pc> files, so if your library or tool
does not provide a C<.pc>, the version may not be detected and your build may fail.

A lot of libraries are bundled as tarballs with the version in the directory name
that they are extracted into, and the current directory when C<alien_check_built_version>
is called is the build root, so you can use C<File::chdir> as an easy way to determine
the version number:

 package My::ModuleBuild;
 
 use strict;
 use warnings;
 use parent 'Alien::Base::ModuleBuild';
 use File::chdir; # provides @CWD
 
 sub alien_check_built_version
 {
   my $dir_name = $CWD[-1];
   
   if($dir_name =~ /^libfoo-([0-9\.]+)$/) {
     return $1;
   } else {
     # Note that this will trigger a build failure
     return;
   }
 }
 
 1;

Using L<File::chdir> and C<@CWD> is a common idiom in L<Alien::Base>, because L<File::chdir>
is already a dependency of L<Alien::Base>.  For packages that do not provide a version number
in the extracted directory, you may require some creativity.

=head2 I have question not listed here!

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

=over 4

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

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

=item mailing list

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

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

=item Open a support ticket

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

L<https://github.com/Perl5-Alien/Alien-Base-ModuleBuild/issues>

=back
 
=head1 SEE ALSO

=over

=item * 

L<Alien::Base>

=item *

L<Alien::Base::ModuleBuild>

=item *

L<Alien::Base::ModuleBuild::API>

=back

=head1 AUTHOR

Original author: Joel Berger, E<lt>joel.a.berger@gmail.comE<gt>

Current maintainer: Graham Ollis E<lt>plicease@cpan.orgE<gt> and the L<Alien::Base> team

=head1 COPYRIGHT AND LICENSE

Copyright (C) 2012-2017 by Joel Berger

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

=cut
