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, 8 insertions, 5 deletions

diff --git a/Cross/Makefile-cross-SH b/Cross/Makefile-cross-SH
index 2ea58f5a9d..d1d2cbf7a1 100644
--- a/Cross/Makefile-cross-SH
+++ b/Cross/Makefile-cross-SH
@@ -324,7 +324,7 @@ $spitshell >>$Makefile <<'!NO!SUBS!'
 
 CONFIGPM = xlib/$(CROSS_NAME)/Config.pm
 
-private = preplibrary $(CONFIGPM) $(CROSS_LIB)/Config.pod
+private = preplibrary $(CONFIGPM) $(CROSS_LIB)/Config.pod lib/buildcustomize.pl
 
 shextract = Makefile cflags config.h makedepend \
 	makedir myconfig writemain pod/Makefile
@@ -738,6 +738,9 @@ lib/lib.pm:	miniperl $(CONFIGPM)
 	@-rm -f $@
 	$(LDLIBPTH) ./miniperl -Ilib -MCross lib/lib_pm.PL
 
+lib/buildcustomize.pl: $(MINIPERL_EXE) write_buildcustomize.pl
+	$(MINIPERL) write_buildcustomize.pl >lib/buildcustomize.pl
+
 unidatafiles $(unidatafiles): uni.data
 
 uni.data: miniperl$(EXE_EXT) $(CONFIGPM) lib/unicore/mktables
@@ -904,16 +907,16 @@ manicheck:	FORCE
 
 
 
-$(DYNALOADER):	preplibrary FORCE
+$(DYNALOADER): lib/buildcustomize.pl preplibrary FORCE
 	@$(LDLIBPTH) $(RUN) ./miniperl$(EXE_EXT) -Ilib make_ext.pl --cross $@ MAKE=$(MAKE) LIBPERL_A=$(LIBPERL) LINKTYPE=static $(STATIC_LDFLAGS)
 
-d_dummy $(dynamic_ext):	miniperl$(EXE_EXT) preplibrary makeppport $(DYNALOADER) FORCE
+d_dummy $(dynamic_ext):	miniperl$(EXE_EXT) lib/buildcustomize.pl preplibrary makeppport $(DYNALOADER) FORCE
 	@$(LDLIBPTH) $(RUN) ./miniperl$(EXE_EXT) -Ilib make_ext.pl --cross $@ MAKE=$(MAKE) LIBPERL_A=$(LIBPERL) LINKTYPE=dynamic
 
-s_dummy $(static_ext):	miniperl$(EXE_EXT) preplibrary makeppport $(DYNALOADER) FORCE
+s_dummy $(static_ext):	miniperl$(EXE_EXT) lib/buildcustomize.pl preplibrary makeppport $(DYNALOADER) FORCE
 	@$(LDLIBPTH) $(RUN) ./miniperl$(EXE_EXT) -Ilib make_ext.pl --cross $@ MAKE=$(MAKE) LIBPERL_A=$(LIBPERL) LINKTYPE=static $(STATIC_LDFLAGS)
 
-n_dummy $(nonxs_ext):	miniperl$(EXE_EXT) preplibrary $(DYNALOADER) FORCE
+n_dummy $(nonxs_ext):	miniperl$(EXE_EXT) lib/buildcustomize.pl preplibrary $(DYNALOADER) FORCE
 	@$(LDLIBPTH) $(RUN) ./miniperl$(EXE_EXT) -Ilib make_ext.pl --cross $@ MAKE=$(MAKE) LIBPERL_A=$(LIBPERL)
 !NO!SUBS!