[sb2] Avoid rebuilds when configure.ac changes but not it's output

When configure.ac or config.mak.in change but not their output their
will be repeated rebuilds as the timestamp their output files such as
config.mak stay older than their dependency.

The timestamp file's timestamp will always update after the targets
dependency changed.

Signed-off-by: Björn Bidar <[email protected]>

.gitignore

@@ -7,6 +7,8 @@
 config.log
 include/config.h
 include/config.h.in
+stamp-h
+stamp-h.in
 configure
 config.guess
 config.status
@@ -17,6 +19,8 @@ autom4te.cache
 aclocal.*
 *.a
 config.mak
+stamp-mak
+stamp-mak.in
 preload/exported.h
 preload/ldexportlist
 preload/wrappers.c

Makefile

@@ -75,15 +75,23 @@ do-all: $(targets)
 # Don't erase these files if make is interrupted while refreshing them.
 .PRECIOUS: $(OBJDIR)/config.status
 .NOTPARALLEL: $(DIST_FILES)
-$(DIST_FILES): $(SRCDIR)/configure $(SRCDIR)/config.mak.in
+# Use a proxy timestamp file here since config.mak and config.h
+# don't update unless their contents change when the dependencies
+# that generate them change, avoid repeated rebuilds after changing
+# files such as configure.ac e.g. after checking out a new branch
+$(DIST_FILES): $(OBJDIR)/stamp-mak
+$(OBJDIR)/stamp-mak: $(SRCDIR)/configure $(SRCDIR)/config.mak.in
 	$(OBJDIR)/config.status --recheck
+	echo > $(OBJDIR)/stamp-mak
 
 $(SRCDIR)/configure: $(SRCDIR)/configure.ac
 	cd $(SRCDIR); \
 	./autogen.sh
 
-$(OBJDIR)/include/config.h: $(SRCDIR)/include/config.h.in $(OBJDIR)/config.status
-	$(OBJDIR)/config.status config.h
+$(OBJDDIR)/include/config.h: $(OBJDIR)/stamp-h
+$(OBJDIR)/stamp-h: $(SRCDIR)/include/config.h.in $(OBJDIR)/config.status
+	$(OBJDIR)/config.status include/config.h
+	echo > $(OBJDIR)/stamp-h
 
 $(OBJDIR)/include/scratchbox2_version.h: $(OBJDIR)/config.mak
 	mkdir -p $(OBJDIR)/include
@@ -209,9 +217,11 @@ ifeq ($(OS),Linux)
 endif
 
 CLEAN_FILES += $(targets) \
+				$(SRCDIR)/stamp-h \
 				$(OBJDIR)/include/config.h \
 				$(OBJDIR)/include/scratchbox2_version.h
 DISTCLEAN_FILES +=	$(DIST_FILES) \
+					$(OBJDIR)/stamp-mak \
 					$(OBJDIR)/config.log \
 					$(SRCDIR)/configure \
 					$(SRCDIR)/include/config.h.in

autogen.sh

@@ -4,3 +4,6 @@
 
 rm -rf configure autom4te.cache
 autoreconf --verbose --force --install
+
+echo > stamp-h.in
+echo > stamp-mak.in

configure.ac

@@ -15,6 +15,9 @@ AC_CONFIG_AUX_DIR([build-aux])
 #AC_CONFIG_SRCDIR([src/libfakechroot.c])
 AC_CONFIG_HEADERS([include/config.h])
 AC_CONFIG_FILES([config.mak])
+dnl Generate timestamp so that configure output files timestamps are in sync
+AC_CONFIG_FILES([stamp-h], [echo timestamp > stamp-h])
+AC_CONFIG_FILES([stamp-mak], [echo timestamp > stamp-mak])
 AC_PROG_CC
 AC_PROG_CXX