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, 6 insertions, 2 deletions

diff --git a/vms/descrip_mms.template b/vms/descrip_mms.template
index 82fddde428..846afa49c8 100644
--- a/vms/descrip_mms.template
+++ b/vms/descrip_mms.template
@@ -361,7 +361,7 @@ CRTLOPTS =,$(CRTL)/Options
 unidatadirs = lib/unicore/To lib/unicore/lib
 
 # Modules which must be installed before we can build extensions
-LIBPREREQ = $(ARCHDIR)Config.pm $(ARCHDIR)Config_heavy.pl [.lib.VMS]Filespec.pm $(ARCHDIR)vmspipe.com [.lib]re.pm
+LIBPREREQ = $(ARCHDIR)Config.pm $(ARCHDIR)Config_heavy.pl [.lib.VMS]Filespec.pm $(ARCHDIR)vmspipe.com [.lib]re.pm [.lib]buildcustomize.pl
 
 utils1 = [.lib.pods]perldoc.com [.lib.ExtUtils]Miniperl.pm [.utils]c2ph.com [.utils]h2ph.com 
 utils2 = [.utils]h2xs.com [.utils]libnetcfg.com [.lib]perlbug.com [.utils]dprofpp.com  [.utils]json_pp.com
@@ -460,6 +460,9 @@ archcorefiles : $(ac) $(ARCHAUTO)time.stamp
 [.lib]re.pm  : [.ext.re]re.pm
 	Copy/NoConfirm/Log $(MMS$SOURCE) [.lib]
 
+[.lib]buildcustomize.pl : write_buildcustomize.pl $(MINIPERL_EXE)
+       $(MINIPERL) write_buildcustomize.pl > [.lib]buildcustomize.pl
+
 vmspipe.com : [.vms]vmspipe.com
 	Copy/NoConfirm/Log $(MMS$SOURCE) []
 
@@ -566,7 +569,7 @@ unidatafiles.ts : $(MINIPERL_EXE) [.lib]Config.pm [.lib.unicore]mktables nonxsex
 	@ If F$Search("$(MMS$TARGET)").nes."" Then Delete/NoLog/NoConfirm $(MMS$TARGET);*
 	@ Copy/NoConfirm _NLA0: $(MMS$TARGET)
  
-DynaLoader$(O) : $(ARCHDIR)Config.pm $(MINIPERL_EXE) [.lib.VMS]Filespec.pm 
+DynaLoader$(O) : [.lib]buildcustomize.pl $(ARCHDIR)Config.pm $(MINIPERL_EXE) [.lib.VMS]Filespec.pm 
 	$(MINIPERL) make_ext.pl "MAKE=$(MMS)" "DynaLoader"
 
 dynext : $(LIBPREREQ) $(DBG)perlshr$(E) unidatafiles.ts DynaLoader$(O) preplibrary makeppport $(MINIPERL_EXE)
@@ -1896,6 +1899,7 @@ tidy : cleanlis
 	- If F$Search("[.utils]*.com;-1").nes."" Then Purge/NoConfirm/Log [.utils]*.com
 	- If F$Search("[.x2p]*.com;-1").nes."" Then Purge/NoConfirm/Log [.x2p]*.com
 	- If F$Search("[.lib.pods]*.com;-1").nes."" Then Purge/NoConfirm/Log [.lib.pods]*.com
+	- If F$Search("[.lib]buildcustomize.pl;-1").nes."" Then Purge/NoConfirm/Log [.lib]buildcustomize.pl
 
 clean : tidy cleantest
       	- $(MINIPERL) make_ext.pl "MAKE=$(MMS)" "--all" "--target=clean"