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

=head2 "cannot open shared object file" trying to load XS

The error looks something like this:

 t/acme_alien_dontpanic2.t ....... 1/?
 # Failed test 'xs'
 # at t/acme_alien_dontpanic2.t line 13.
 #   XSLoader failed
 #     Can't load '/home/cip/.cpanm/work/1581635869.456/Acme-Alien-DontPanic2-2.0401/_alien/tmp/test-alien-lyiQNX/auto/Test/Alien/XS/Mod0/Mod0.so' for module Test::Alien::XS::Mod0: libdontpanic.so.0: cannot open shared object file: No such file or di...
 #  at /home/cip/perl5/lib/perl5/Test/Alien.pm line 414.
 # Compilation failed in require at /home/cip/perl5/lib/perl5/Test/Alien.pm line 414.
 # BEGIN failed--compilation aborted at /home/cip/perl5/lib/perl5/Test/Alien.pm line 414.
 t/acme_alien_dontpanic2.t ....... Dubious, test returned 1 (wstat 256, 0x100)
 Failed 1/6 subtests
 t/acme_alien_dontpanic2__ffi.t .. ok

This error happened at test time for the Alien, but depending on your environment and Alien it might
happen later and the actual diagnostic wording might vary.

This is usually because your XS or Alien tries to use dynamic libraries instead of static ones.
Please consult the section about dynamic vs. static libraries in L<Alien::Build::Manual::AlienAuthor>.
The TL;DR is that L<Alien::Build::Plugin::Gather::IsolateDynamic> might help.
If you are the Alien author and the package you are alienizing doesn't have a static option you can
use L<Alien::Role::Dino>, but please note the extended set of caveats!

=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 Does not detect system package even though it is installed

This could just be because the alien requires a more recent package that what is provided by your