Use a buildcustomize.pl to set @INC in miniperl when building extensions.

With the build tools now shipped in various subdirectories of cpan/ and dist/
we need to add several paths to @INC when invoking MakeMaker (etc) to build
extensions.

The previous approach of using $ENV{PERL5LIB} was fragile, because:
a: It was hitting the length limit for %ENV variables on VMS
b: It was running the risk of race conditions in a parallel build -
   ExtUtils::Makemaker "knows" to add -I../..lib, which puts lib at the *front*
   of @INC, but if one parallel process happens to copy a module into lib/
   whilst another is searching for it, the second may get a partial read
c: Overwriting $ENV{PERL5LIB} breaks any system where any of the installed
   build tools are actually implemented in Perl, if they are relying on
   $ENV{PERL5LIB} for setup

This approach

a: Doesn't have %ENV length limits
b: Ensures that lib/ is last, so copy targets are always shadowing copy
   sources
c: Only affects miniperl, and doesn't touch $ENV{PERL5LIB}

Approaches that turned out to have fatal flaws:

1: Using $ENV{PERL5OPT} with a module fails because ExtUtils::MakeMaker
   searches for the build perl without setting lib, and treats the error
   caused by a failed -M as "not a valid perl 5 binary"
2: Refactoring ExtUtils::MakeMaker to *not* use -I for lib, and instead rely
   on $ENV{PERL5LIB} [which includes "../../lib"] fails because:
   some extensions have subdirectories, and on these EU::MM correctly uses
   -I../../../lib, where as $ENV{PERL5LIB} only has space for relative paths,
   and only with two levels.

This approach actually takes advantage of ExtUtils::MakeMaker setting an -I
option correct for the depth of directory being built.

1 files changed, 3 insertions, 35 deletions

diff --git a/make_ext.pl b/make_ext.pl
index b780ec9dab..13a15b4601 100644
--- a/make_ext.pl
+++ b/make_ext.pl
@@ -4,11 +4,9 @@ use warnings;
 use Config;
 BEGIN {
     if ($^O eq 'MSWin32') {
-	unshift @INC, ('../dist/Cwd', '../dist/Cwd/lib');
-	require File::Spec::Functions;
+	unshift @INC, '../dist/Cwd';
 	require FindExt;
-    }
-    else {
+    } else {
 	unshift @INC, 'dist/Cwd';
     }
 }
@@ -18,27 +16,6 @@ my $is_Win32 = $^O eq 'MSWin32';
 my $is_VMS = $^O eq 'VMS';
 my $is_Unix = !$is_Win32 && !$is_VMS;
 
-# To clarify, this isn't the entire suite of modules considered "toolchain"
-# It's not even all modules needed to build ext/
-# It's just the source paths of the (minimum complete set of) modules in ext/
-# needed to build the nonxs modules
-# After which, all nonxs modules are in lib, which was always sufficient to
-# allow miniperl to build everything else.
-
-# This list cannot get any longer without overflowing the length limit for
-# environment variables on VMS
-my @toolchain = qw(cpan/AutoLoader/lib
-		   dist/Cwd dist/Cwd/lib
-		   dist/ExtUtils-Command/lib
-		   dist/ExtUtils-Install/lib
-		   cpan/ExtUtils-MakeMaker/lib
-		   dist/ExtUtils-Manifest/lib
-		   cpan/File-Path/lib
-		   );
-
-# Used only in ExtUtils::Liblist::Kid::_win32_ext()
-push @toolchain, 'cpan/Text-ParseWords/lib' if $is_Win32;
-
 my @ext_dirs = qw(cpan dist ext);
 my $ext_dirs_re = '(?:' . join('|', @ext_dirs) . ')';
 
@@ -296,16 +273,7 @@ sub build_extension {
     $perl ||= "$up/miniperl";
     my $return_dir = $up;
     my $lib_dir = "$up/lib";
-    # $lib_dir must be last, as we're copying files into it, and in a parallel
-    # make there's a race condition if one process tries to open a module that
-    # another process has half-written.
-    my @new_inc = ((map {"$up/$_"} @toolchain), $lib_dir);
-    if ($is_Win32) {
-	@new_inc = map {File::Spec::Functions::rel2abs($_)} @new_inc;
-    }
-    $ENV{PERL5LIB} = join $Config{path_sep}, @new_inc;
     $ENV{PERL_CORE} = 1;
-    # warn $ENV{PERL5LIB};
 
     my $makefile;
     if ($is_VMS) {
@@ -421,7 +389,7 @@ EOM
 	    @cross = '-MCross';
 	}
 	    
-	my @args = (@cross, 'Makefile.PL');
+	my @args = ("-I$lib_dir", @cross, 'Makefile.PL');
 	if ($is_VMS) {
 	    my $libd = VMS::Filespec::vmspath($lib_dir);
 	    push @args, "INST_LIB=$libd", "INST_ARCHLIB=$libd";