[PATCH 18/36] build: only generate version.h when needed

[Luc Van Oostenryck <luc.vanoostenryck@gmail.com>]

From: Uwe Kleine-König <uwe@kleine-koenig.org>

This way version.h isn't generated when running $(make clean) but only
when lib.c is about to be compiled.

This simplifies packaging for Debian because the package building programs
abort when there are additional files after $(make clean).

Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 Makefile | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/Makefile b/Makefile
index 460a261f1..ea3ce89a4 100644
--- a/Makefile
+++ b/Makefile
@@ -1,13 +1,5 @@
 VERSION=0.5.1
 
-# Generating file version.h if current version has changed
-SPARSE_VERSION:=$(shell git describe 2>/dev/null || echo '$(VERSION)')
-VERSION_H := $(shell cat version.h 2>/dev/null)
-ifneq ($(lastword $(VERSION_H)),"$(SPARSE_VERSION)")
-$(info $(shell echo '     GEN      'version.h))
-$(shell echo '#define SPARSE_VERSION "$(SPARSE_VERSION)"' > version.h)
-endif
-
 OS = linux
 
 
@@ -199,6 +191,18 @@ cflags   += $($(*)_CFLAGS) $(CPPFLAGS) $(CFLAGS)
 selfcheck: $(OBJS:.o=.sc)
 
 
+SPARSE_VERSION:=$(shell git describe 2>/dev/null || echo '$(VERSION)')
+lib.o: version.h
+version.h: FORCE
+	@echo '#define SPARSE_VERSION "$(SPARSE_VERSION)"' > version.h.tmp
+	@if cmp -s version.h version.h.tmp; then \
+		rm version.h.tmp; \
+	else \
+		echo    '     GEN      '$@; \
+		mv version.h.tmp version.h; \
+	fi
+
+
 clean: clean-check
 	rm -f *.[oa] .*.d *.so $(PROGRAMS) $(SLIB_FILE) pre-process.h version.h
 
@@ -220,3 +224,5 @@ clean-check:
 	                 -o -name "*.c.error.got" \
 	                 -o -name "*.c.error.diff" \
 	                 \) -exec rm {} \;
+
+.PHONY: FORCE
-- 
2.14.0