emacs: Avoid rebuilding .eldeps even when there's nothing to do

[notmuch] / emacs / Makefile.local

diff --git a/emacs/Makefile.local b/emacs/Makefile.local
index 42bfbd96c78dee4a4e06cc5bb50208861c692edc..6a39b32d2fab386252faddcd228072b2735215b6 100644 (file)
--- a/emacs/Makefile.local
+++ b/emacs/Makefile.local
@@ -33,10 +33,19 @@ ifeq ($(HAVE_EMACS),1)
 $(dir)/.eldeps: $(dir)/Makefile.local $(dir)/make-deps.el $(emacs_sources)
        $(call quiet,EMACS) --directory emacs -batch -l make-deps.el \
                -f batch-make-deps $(emacs_sources) > $@.tmp && \
 $(dir)/.eldeps: $(dir)/Makefile.local $(dir)/make-deps.el $(emacs_sources)
        $(call quiet,EMACS) --directory emacs -batch -l make-deps.el \
                -f batch-make-deps $(emacs_sources) > $@.tmp && \

-               (cmp -s $@.tmp $@ || mv $@.tmp $@)
--include $(dir)/.eldeps
+               mv $@.tmp $@
+# We could include .eldeps directly, but that would cause a make
+# restart whenever any .el file was modified, even if dependencies
+# didn't change, because the mtime of .eldeps will change.  Instead,
+# we include a second file, .eldeps.x, which we ensure always has the
+# same content as .eldeps, but its mtime only changes when dependency
+# information changes, in which case a make restart is necessary
+# anyway.
+$(dir)/.eldeps.x: $(dir)/.eldeps
+       @cmp -s $^ $@ || cp $^ $@
+-include $(dir)/.eldeps.x

 endif
 endif

-CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp
+CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp $(dir)/.eldeps.x

 
 ifeq ($(HAVE_EMACS),1)
 %.elc: %.el $(global_deps)
 
 ifeq ($(HAVE_EMACS),1)
 %.elc: %.el $(global_deps)