Quoth Tomi Ollila on Feb 13 at 9:26 am: > On Thu, Feb 13 2014, Austin Clements <amdragon@MIT.EDU> wrote: > > > Quoth Tomi Ollila on Jan 25 at 12:21 pm: > >> So that the target is newer than its prerequisites. > >> --- > >> emacs/Makefile.local | 3 +-- > >> 1 file changed, 1 insertion(+), 2 deletions(-) > >> > >> diff --git a/emacs/Makefile.local b/emacs/Makefile.local > >> index 42bfbd9..d5d402e 100644 > >> --- a/emacs/Makefile.local > >> +++ b/emacs/Makefile.local > >> @@ -32,8 +32,7 @@ emacs_bytecode = $(emacs_sources:.el=.elc) > >> ifeq ($(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 && \ > >> - (cmp -s $@.tmp $@ || mv $@.tmp $@) > >> + -f batch-make-deps $(emacs_sources) > $@.tmp && mv $@.tmp $@ > >> -include $(dir)/.eldeps > >> endif > >> CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp > > > > Is this just so the rule doesn't get run again on the next make > > invocation (unless, of course, a dependent changed)? > > Basically yes. I did multiple builds in rapid succession when developing > something and this thing confused me quite a lot in the beginning... > > > Interestingly, if any of the dependents have changed, but in ways that > > don't affect .eldeps, this change will make the build more expensive > > because it will trigger a make restart after .eldeps is updated. > > I wondered what was the reason for the recipe you've chosen here, has > it something to do with inodes or something ;) (and were going to ask > an alternative to touch (or even : > $@) the target... > > ... but now I understand. E.g. change in notmuch-lib.el will cause *all* > .el files to be re-bytecompiled after this change. This is unrelated to the cmp in the recipe. A change in notmuch-lib.el *must* cause almost all .el files to be recompiled because they almost all require it and may use macros from it. If you touch, e.g., notmuch-hello.el, you'll see that very little is rebuilt (with or without this patch). > An alternative to this patch would be adding a message to the rule > which informs user to touch .eldeps to avoid re-doing .eldeps if > that irritates one :D > > something like: > > (cmp -s $@.tmp $@ && \ > echo "touch $@ to avoid redoing this target" || mv $@.tmp $@) I think this patch is good as it is; I was just pointing out that the change also has a performance drawback in some situations. (Knowing make, there's probably *some* way to get the best of both worlds and it's probably really ugly.) > Thanks, > > Tomi