add supporting target and options to generate patches for ExternalProjects

also add the support for the convention that a patch filename
encode the -p value if it end with .[0-9]
for instance foo.patch.2 indicate a -p2 patch

usage:

generate a 'reference' copy of the expanded and patched file structure
$> make clucene.clean
$> patches=t make clucene

go to the module
$> cd clucene

edit files in $WORKDIR/UnpackedTarball/clucene

force a rebuild of things that depend on that UnpackedTarball
$> make clucene.rebuild


create a -p1 patch named clucene.new.patch.1 in the module's directory
$> make clucene.genpatch

you can then rename it, place it where appropriate in the module
hierarchy, update the UnpackedTarball_lucene.mk to apply it.

rinse and repeat from the top (yes the make lucene.clean is needed
to regenerate a 'reference' expanded and patched tarball)

Change-Id: I419c54a5981cffa385521596ba5016d2ca7ef52a
Reviewed-on: https://gerrit.libreoffice.org/712Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>

solenv/gbuild/TargetLocations.mk

@@ -171,6 +171,7 @@ gb_UnoApiHeadersTarget_get_comprehensive_target = $(WORKDIR)/UnoApiHeadersTarget
 gb_UnoApiHeadersTarget_get_target = $(WORKDIR)/UnoApiHeadersTarget/$(1)/normal.done
 gb_UnoApiPartTarget_get_target = $(WORKDIR)/UnoApiPartTarget/$(1)
 gb_UnpackedTarball_get_dir = $(WORKDIR)/UnpackedTarball/$(1)
+gb_UnpackedTarball_get_pristine_dir = $(WORKDIR)/UnpackedTarball/$(1).org
 gb_UnpackedTarball_get_final_target = $(WORKDIR)/UnpackedTarball/$(1).update
 gb_UnpackedTarball_get_target = $(WORKDIR)/UnpackedTarball/$(1).done
 gb_UnpackedTarball_get_preparation_target = $(WORKDIR)/UnpackedTarball/$(1).prepare

solenv/gbuild/UnpackedTarball.mk

@@ -131,7 +131,9 @@ $(call gb_Helper_abbreviate_dirs,\
 		$(foreach file,$(UNPACKED_FIX_EOL),$(call gb_UnpackedTarball_CONVERTTOUNIX,$(file)) && ) \
 		$(if $(UNPACKED_PATCHES),\
 			for p in $(UNPACKED_PATCHES); do \
-				$(GNUPATCH) -s -p$(UNPACKED_PATCHLEVEL) < "$$p" || exit 1;\
+				pl=$(UNPACKED_PATCHLEVEL); \
+				s=$${p##*.}; case "$$s" in [0-9]$(CLOSE_PAREN) pl="$$s"; ;; esac ; \
+				$(GNUPATCH) -s -p$$pl < "$$p" || exit 1;\
 			done && \
 		) \
 		$(foreach file,$(UNPACKED_FIX_EOL),$(call gb_UnpackedTarball_CONVERTTODOS,$(file)) && ) \
@@ -145,6 +147,10 @@ $(call gb_Helper_abbreviate_dirs,\
 		$(if $(UNPACKED_POST_ACTION),\
 			$(UNPACKED_POST_ACTION) && \
 		) \
+	    $(if $(gb_KEEP_PRISTINE), \
+			rm -fr $(call gb_UnpackedTarball_get_pristine_dir,$(2)) && \
+			cp -r $(call gb_UnpackedTarball_get_dir,$(2)) $(call gb_UnpackedTarball_get_pristine_dir,$(2)) && \
+		) \
 		touch $(1) \
 	) || \
 	( \
@@ -174,6 +180,7 @@ $(call gb_UnpackedTarball_get_clean_target,%) :
 			$(call gb_UnpackedTarball_get_target,$*) \
 			$(call gb_UnpackedTarball_get_preparation_target,$*) \
 			$(call gb_UnpackedTarball_get_dir,$*) \
+			$(call gb_UnpackedTarball_get_pristine_dir,$*) \
 			$(foreach subdir,$(UNPACKED_SUBDIRS),$(gb_EXTERNAL_HEADERS_DIR)/$(subdir)) \
 	)
 
@@ -365,4 +372,26 @@ $(foreach file,$(2),$(call gb_UnpackedTarball_mark_output_file,$(1),$(file)))
 
 endef
 
+# force the rebuild of an external target
+# this only works when running as partial build.
+#
+%.rebuild :
+	if [ -f $(call gb_UnpackedTarball_get_target,$*) ] ; then \
+		touch $(call gb_UnpackedTarball_get_target,$*) ; \
+		make ;\
+	fi
+
+%.genpatch :
+	if [ -d $(call gb_UnpackedTarball_get_dir,$*) -a -d  $(call gb_UnpackedTarball_get_pristine_dir,$*) ] ; then \
+		( \
+		    patch_file=$$(pwd)/$*.new.patch.1; \
+			cd $(call gb_UnpackedTarball_get_dir,) ; \
+			diff -ur $*.org $* > $$patch_file; \
+		    echo "Patch $$patch_file generated" ; \
+		); \
+	else \
+		echo "Error: No pristine tarball avaialable for $*" 1>&2 ; \
+	fi
+
+
 # vim: set noet sw=4 ts=4:

solenv/gbuild/gbuild.mk

@@ -71,6 +71,8 @@ endef
 
 COMMA :=,
 
+CLOSE_PAREN :=)
+
 # optional extensions that should never be essential
 ifneq ($(wildcard $(GBUILDDIR)/extensions/pre_*.mk),)
 include $(wildcard $(GBUILDDIR)/extensions/pre_*.mk)
@@ -145,6 +147,12 @@ gb_FULLDEPS := $(true)
 endif
 endif
 
+ifneq ($(strip $(patches)$(PATCHES)),)
+gb_KEEP_PRISTINE := $(true)
+else
+gb_KEEP_PRISTINE := $(false)
+endif
+
 # save user-supplied flags for latter use
 # TODO remove after the old build system is abolished
 ifneq ($(strip $(ENVCFLAGS)),)