Make life easier for packagers with BUILDING_AS_PACKAGE

Also README.packaging and bundled/README.

Changes

@@ -7,6 +7,12 @@
     * my::bundle::copy_bundles() will only load File::Copy::Recursive if
       it needs it, allowing vendors packaging MakeMaker to just delete
       bundled/*
+    * Bundling can be overridden by setting the BUILDING_AS_PACKAGE
+      environment variable.  This makes life easier for vendor packagers.
+
+    Docs
+    * README.packaging explains how to package MakeMaker
+    * bundled/README explains what the bundled directory is about.
 
 
 6.63_01  Sun Oct 23 16:57:24 PDT 2011

Makefile.PL

@@ -18,6 +18,8 @@ use lib qw(lib);    # build ourself with ourself
 use File::Spec;
 use ExtUtils::MakeMaker 6.50;
 
+my $BUILDING_AS_PACKAGE = $ENV{BUILDING_AS_PACKAGE};
+
 BEGIN {
     die "You have File::Spec version $File::Spec::VERSION\n" . "ExtUtils::MakeMaker requires File::Spec >= 0.8 to build at all.\n"
       if $File::Spec::VERSION < 0.8;
@@ -46,19 +48,42 @@ CHANGE_WARN
 # Test::Harnesses prior to 2.00 shoved all of @INC onto the command line
 # when a test had -T.  This made it too long.  So we need a Test::Harness
 # > 2.00 on VMS for t/testlib.t
-my %prereq = ();
-$prereq{'Test::Harness'} = 2.00 if $^O eq 'VMS';
+my %Extra_Prereqs = ();
+$Extra_Prereqs{'Test::Harness'} = 2.00 if $^O eq 'VMS';
 
 check_environment();
 
-my::bundles::copy_bundles("bundled", "inc");
+# Special case for MakeMaker being built as a vendor package
+if( $BUILDING_AS_PACKAGE ) {
+    # Some of these are lower than what we bundle.  That's ok, we
+    # bundle the latest because we might as well, but we don't want to
+    # burden vendors with having to update everything.
+    %Extra_Prereqs = (
+        'CPAN::Meta'            => '2.112580',
+        'CPAN::Meta::YAML'      => '0.002',
+        'ExtUtils::Command'     => '1.16',
+        'ExtUtils::Install'     => '1.52',
+        'ExtUtils::Manifest'    => '1.58',
+        'File::Temp'            => '0.22',
+        'JSON::PP'              => '2.27103',
+        'Parse::CPAN::Meta'     => '1.4400',
+        'Scalar::Util'          => '1.13',
+        'version'               => '0.82',
+        'Version::Requirements' => '0.101020',
+    );
+
+    $Extra_Prereqs{'JSON::PP::Compat5006'} = '1.09' if $] < 5.008;
+}
+else {
+    my::bundles::copy_bundles("bundled", "inc");
+}
 
 my $MM = WriteMakefile(
     NAME         => $PACKAGE,
     VERSION_FROM => "lib/$PACKAGE_FILE.pm",    # finds $VERSION
 
     PREREQ_PM => {
-        %prereq,
+        %Extra_Prereqs,
         'File::Spec'     => 0.8,               # splitpath(), rel2abs()
         'Pod::Man'       => 0,                 # manifypods needs Pod::Man
         'File::Basename' => 0,

README.packaging

@@ -0,0 +1,23 @@
+If you wish to package MakeMaker in a binary package, here's some tips.
+
+tl;dr version:
+
+1a) Set the BUILDING_AS_PACKAGE environment variable to a true value.
+OR
+1b) Set the $BUILDING_AS_PACKAGE variable in the Makefile.PL to true.
+2)  Package normally, but watch out for dependency loops.
+
+MakeMaker cannot have any dependencies, everything depends on it and
+that would be a dependency loop.  It instead bundles pre-built copies
+of all its non-core dependencies in the bundled/ directory.  It adds
+them to itself if they're not already installed.
+
+This can confuse packagers, it makes it look like MakeMaker contains a
+lot more modules than it really does and causes conflicts.
+
+You can tell MakeMaker not to use it's bundles and instead declare the
+dependencies normally.  This is done either by setting the
+BUILDING_AS_PACKAGE environment variable to true or by patching the
+Makefile.PL and setting $BUILDING_AS_PACKAGE to true.  On the down
+side, there will be dependency loops which your packaging system will
+have to resolve.

bundled/README

@@ -0,0 +1,5 @@
+This directory contains CPAN modules which ExtUtils-MakeMaker depends on.
+They are bundled with ExtUtils-MakeMaker to avoid dependency loops.
+
+Vendor packages will want to disable this bundling.  See README.packaging in the top
+level directory for details.

my/bundles.pm

@@ -3,6 +3,8 @@ package my::bundles;
 use strict;
 use warnings;
 
+use File::Path;
+
 
 =head1 NAME
 
@@ -28,11 +30,8 @@ inc/ as a flattened module directory that MakeMaker can install.
 
 =cut
 
-require lib;
 my $bundle_dir = "bundled";
 
-use File::Path;
-
 my %special_dist = (
     "Scalar-List-Utils" => sub {
         # Special case for Scalar::Util, never override the XS version with a
@@ -47,16 +46,23 @@ my %special_dist = (
 );
 
 
-sub import {
+sub add_bundles_to_inc {
     opendir my $dh, $bundle_dir or die "Can't open bundles directory: $!";
     my @bundles = map { "$bundle_dir/$_" } grep !/^\./, readdir $dh;
+
+    require lib;
     lib->import(@bundles);
+
+    return;
 }
 
 
 sub copy_bundles {
     my($src, $dest) = @_;
 
+    # So we can use them to copy them.
+    add_bundles_to_inc();
+
     rmtree $dest;
     mkpath $dest;