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+package Git::LoadCPAN;
+use 5.008;
+use strict;
+use warnings;
+
+=head1 NAME
+
+Git::LoadCPAN - Wrapper for loading modules from the CPAN (OS) or Git's own copy
+
+=head1 DESCRIPTION
+
+The Perl code in Git depends on some modules from the CPAN, but we
+don't want to make those a hard requirement for anyone building from
+source.
+
+Therefore the L<Git::LoadCPAN> namespace shipped with Git contains
+wrapper modules like C<Git::LoadCPAN::Module::Name> that will first
+attempt to load C<Module::Name> from the OS, and if that doesn't work
+will fall back on C<FromCPAN::Module::Name> shipped with Git itself.
+
+Usually distributors will not ship with Git's Git::FromCPAN tree at
+all via the C<NO_PERL_CPAN_FALLBACKS> option, preferring to use their
+own packaging of CPAN modules instead.
+
+This module is only intended to be used for code shipping in the
+C<git.git> repository. Use it for anything else at your peril!
+
+=cut
+
+# NO_PERL_CPAN_FALLBACKS_STR evades the sed search-replace from the
+# Makefile, and allows for detecting whether the module is loaded from
+# perl/Git as opposed to perl/build/Git, which is useful for one-off
+# testing without having Error.pm et al installed.
+use constant NO_PERL_CPAN_FALLBACKS_STR => '@@' . 'NO_PERL_CPAN_FALLBACKS' . '@@';
+use constant NO_PERL_CPAN_FALLBACKS => (
+ q[@@NO_PERL_CPAN_FALLBACKS@@] ne ''
+ and
+ q[@@NO_PERL_CPAN_FALLBACKS@@] ne NO_PERL_CPAN_FALLBACKS_STR
+);
+
+sub import {
+ shift;
+ my $caller = caller;
+ my %args = @_;
+ my $module = exists $args{module} ? delete $args{module} : die "BUG: Expected 'module' parameter!";
+ my $import = exists $args{import} ? delete $args{import} : die "BUG: Expected 'import' parameter!";
+ die "BUG: Too many arguments!" if keys %args;
+
+ # Foo::Bar to Foo/Bar.pm
+ my $package_pm = $module;
+ $package_pm =~ s[::][/]g;
+ $package_pm .= '.pm';
+
+ eval {
+ require $package_pm;
+ 1;
+ } or do {
+ my $error = $@ || "Zombie Error";
+
+ if (NO_PERL_CPAN_FALLBACKS) {
+ chomp(my $error = sprintf <<'THEY_PROMISED', $module);
+BUG: The '%s' module is not here, but NO_PERL_CPAN_FALLBACKS was set!
+
+Git needs this Perl module from the CPAN, and will by default ship
+with a copy of it. This Git was built with NO_PERL_CPAN_FALLBACKS,
+meaning that whoever built it promised to provide this module.
+
+You're seeing this error because they broke that promise, and we can't
+load our fallback version, since we were asked not to install it.
+
+If you're seeing this error and didn't package Git yourself the
+package you're using is broken, or your system is broken. This error
+won't appear if Git is built without NO_PERL_CPAN_FALLBACKS (instead
+we'll use our fallback version of the module).
+THEY_PROMISED
+ die $error;
+ }
+
+ my $Git_LoadCPAN_pm_path = $INC{"Git/LoadCPAN.pm"} || die "BUG: Should have our own path from %INC!";
+
+ require File::Basename;
+ 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'!";
+
+ require File::Spec;
+ my $Git_pm_FromCPAN_root = File::Spec->catdir($Git_LoadCPAN_pm_root, '..', 'FromCPAN');
+ die "BUG: '$Git_pm_FromCPAN_root' should be a directory!" unless -d $Git_pm_FromCPAN_root;
+
+ local @INC = ($Git_pm_FromCPAN_root, @INC);
+ require $package_pm;
+ };
+
+ if ($import) {
+ no strict 'refs';
+ *{"${caller}::import"} = sub {
+ shift;
+ use strict 'refs';
+ unshift @_, $module;
+ goto &{"${module}::import"};
+ };
+ use strict 'refs';
+ }
+}
+
+1;