perl/Git/LoadCPAN.pm

   1 package Git::LoadCPAN;
   2 use 5.008;
   3 use strict;
   4 use warnings;
   5
   6 =head1 NAME
   7
   8 Git::LoadCPAN - Wrapper for loading modules from the CPAN (OS) or Git's own copy
   9
  10 =head1 DESCRIPTION
  11
  12 The Perl code in Git depends on some modules from the CPAN, but we
  13 don't want to make those a hard requirement for anyone building from
  14 source.
  15
  16 Therefore the L<Git::LoadCPAN> namespace shipped with Git contains
  17 wrapper modules like C<Git::LoadCPAN::Module::Name> that will first
  18 attempt to load C<Module::Name> from the OS, and if that doesn't work
  19 will fall back on C<FromCPAN::Module::Name> shipped with Git itself.
  20
  21 Usually distributors will not ship with Git's Git::FromCPAN tree at
  22 all via the C<NO_PERL_CPAN_FALLBACKS> option, preferring to use their
  23 own packaging of CPAN modules instead.
  24
  25 This module is only intended to be used for code shipping in the
  26 C<git.git> repository. Use it for anything else at your peril!
  27
  28 =cut
  29
  30 # NO_PERL_CPAN_FALLBACKS_STR evades the sed search-replace from the
  31 # Makefile, and allows for detecting whether the module is loaded from
  32 # perl/Git as opposed to perl/build/Git, which is useful for one-off
  33 # testing without having Error.pm et al installed.
  34 use constant NO_PERL_CPAN_FALLBACKS_STR => '@@' . 'NO_PERL_CPAN_FALLBACKS' . '@@';
  35 use constant NO_PERL_CPAN_FALLBACKS => (
  36         q[@@NO_PERL_CPAN_FALLBACKS@@] ne ''
  37         and
  38         q[@@NO_PERL_CPAN_FALLBACKS@@] ne NO_PERL_CPAN_FALLBACKS_STR
  39 );
  40
  41 sub import {
  42         shift;
  43         my $caller = caller;
  44         my %args = @_;
  45         my $module = exists $args{module} ? delete $args{module} : die "BUG: Expected 'module' parameter!";
  46         my $import = exists $args{import} ? delete $args{import} : die "BUG: Expected 'import' parameter!";
  47         die "BUG: Too many arguments!" if keys %args;
  48
  49         # Foo::Bar to Foo/Bar.pm
  50         my $package_pm = $module;
  51         $package_pm =~ s[::][/]g;
  52         $package_pm .= '.pm';
  53
  54         eval {
  55                 require $package_pm;
  56                 1;
  57         } or do {
  58                 my $error = $@ || "Zombie Error";
  59
  60                 if (NO_PERL_CPAN_FALLBACKS) {
  61                         chomp(my $error = sprintf <<'THEY_PROMISED', $module);
  62 BUG: The '%s' module is not here, but NO_PERL_CPAN_FALLBACKS was set!
  63
  64 Git needs this Perl module from the CPAN, and will by default ship
  65 with a copy of it. This Git was built with NO_PERL_CPAN_FALLBACKS,
  66 meaning that whoever built it promised to provide this module.
  67
  68 You're seeing this error because they broke that promise, and we can't
  69 load our fallback version, since we were asked not to install it.
  70
  71 If you're seeing this error and didn't package Git yourself the
  72 package you're using is broken, or your system is broken. This error
  73 won't appear if Git is built without NO_PERL_CPAN_FALLBACKS (instead
  74 we'll use our fallback version of the module).
  75 THEY_PROMISED
  76                         die $error;
  77                 }
  78
  79                 my $Git_LoadCPAN_pm_path = $INC{"Git/LoadCPAN.pm"} || die "BUG: Should have our own path from %INC!";
  80
  81                 require File::Basename;
  82                 my $Git_LoadCPAN_pm_root = File::Basename::dirname($Git_LoadCPAN_pm_path) || die "BUG: Can't figure out lib/Git dirname from '$Git_LoadCPAN_pm_path'!";
  83
  84                 require File::Spec;
  85                 my $Git_pm_FromCPAN_root = File::Spec->catdir($Git_LoadCPAN_pm_root, '..', 'FromCPAN');
  86                 die "BUG: '$Git_pm_FromCPAN_root' should be a directory!" unless -d $Git_pm_FromCPAN_root;
  87
  88                 local @INC = ($Git_pm_FromCPAN_root, @INC);
  89                 require $package_pm;
  90         };
  91
  92         if ($import) {
  93                 no strict 'refs';
  94                 *{"${caller}::import"} = sub {
  95                         shift;
  96                         use strict 'refs';
  97                         unshift @_, $module;
  98                         goto &{"${module}::import"};
  99                 };
 100                 use strict 'refs';
 101         }
 102 }
 103
 104 1;