[PATCH v3 1/3] build: write version.stamp file containing $(VERSION) string

[Tomi Ollila <tomi.ollila@iki.fi>]

This version file will be as prerequisite to the target files
that use the version info for some purpose, like printing
it for the user to examine. The contents of the version.stamp
file is seldom read by the build system itself as the $(VERSION)
variable has the same information.

Thanks to Trevor, David and Mark for their contributions.
---
 .gitignore     |  1 +
 Makefile.local | 14 +++++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/.gitignore b/.gitignore
index ef4f074..1fb3a71 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 .first-build-message
 Makefile.config
+version.stamp
 TAGS
 tags
 *cscope*
diff --git a/Makefile.local b/Makefile.local
index 174506c..3a56c06 100644
--- a/Makefile.local
+++ b/Makefile.local
@@ -22,6 +22,11 @@ VERSION:=$(shell cat ${srcdir}/version)
 ifeq ($(filter release release-message pre-release update-versions,$(MAKECMDGOALS)),)
 ifeq ($(IS_GIT),yes)
 VERSION:=$(shell git describe --match '[0-9.]*'|sed -e s/_/~/ -e s/-/+/ -e s/-/~/)
+# Write the file 'version.stamp' in case its contents differ from $(VERSION)
+FILE_VERSION:=$(shell test -f version.stamp && read vs < version.stamp || vs=; echo $$vs)
+ifneq ($(FILE_VERSION),$(VERSION))
+       $(shell echo "$(VERSION)" > version.stamp)
+endif
 endif
 endif
 
@@ -69,6 +74,11 @@ ifeq ($(shell cat .first-build-message 2>/dev/null),)
 endif
 endif
 
+# Depend (also) on the file 'version'. In case of ifeq ($(IS_GIT),yes)
+# this file may already have been updated.
+version.stamp: version
+	echo $(VERSION) > $@
+
 $(TAR_FILE):
 	if git tag -v $(VERSION) >/dev/null 2>&1; then \
            ref=$(VERSION); \
@@ -280,6 +290,8 @@ notmuch_client_srcs =		\
 
 notmuch_client_modules = $(notmuch_client_srcs:.c=.o)
 
+notmuch.o: version.stamp
+
 notmuch: $(notmuch_client_modules) lib/libnotmuch.a util/libutil.a parse-time-string/libparse-time-string.a
 	$(call quiet,CXX $(CFLAGS)) $^ $(FINAL_LIBNOTMUCH_LDFLAGS) -o $@
 
@@ -318,7 +330,7 @@ install-desktop:
 	desktop-file-install --mode 0644 --dir "$(DESTDIR)$(desktop_dir)" notmuch.desktop
 
 SRCS  := $(SRCS) $(notmuch_client_srcs)
-CLEAN := $(CLEAN) notmuch notmuch-shared $(notmuch_client_modules) notmuch.elc
+CLEAN := $(CLEAN) notmuch notmuch-shared $(notmuch_client_modules) version.stamp
 
 DISTCLEAN := $(DISTCLEAN) .first-build-message Makefile.config
 
-- 
1.8.0