On Thu, Feb 13 2014, Austin Clements <amdragon@MIT.EDU> wrote: > 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.) Ah, now I understand, because emacs/Makefile.local includes emacs/.eldeps when it notices mtime of emacs/.eldeps changes it restarts itself... ... to compare with current behaviour: $ make ... $ touch emacs/notmuch.el $ make ... $ make Use "make V=1" to see the verbose compile lines. EMACS emacs/.eldeps make: Nothing to be done for `all'. $ make Use "make V=1" to see the verbose compile lines. EMACS emacs/.eldeps make: Nothing to be done for `all'. $ make Use "make V=1" to see the verbose compile lines. EMACS emacs/.eldeps make: Nothing to be done for `all'. It will rerun emacs -L emacs -batch -l make-deps.el -f batch-make-deps ... over and over again... I thought I figured out a solution involving .eldeps.stamp file but that turned out to be no-go... (circular dependency netween .eldeps.stamp and Makefile.local). So, with this if one edits emacs/* files and keeps building byte-compiled versions often, make will both run EMACS emacs/.eldeps and restarting -- and when moving to edit other files both of the above stops. Without this change after editing emacs/* files EMACS emacs/.eldeps will be executed until it is touched or make clean executed (I wonder how make handles rebuilding emacs/.eldeps while doing make clean ;) Tomi