Quoth myself on Feb 14 at 4:58 pm: > Quoth Tomi Ollila on Feb 14 at 9:24 pm: > > 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 > > Here's a way that works, but it's more complicated than your patch and > doesn't seem to perform any better: > > diff --git a/emacs/Makefile.local b/emacs/Makefile.local > index 42bfbd9..8a1f1c2 100644 > --- a/emacs/Makefile.local > +++ b/emacs/Makefile.local > @@ -29,14 +29,28 @@ emacs_bytecode = $(emacs_sources:.el=.elc) > # the byte compiler may load an old .elc file when processing a > # "require" or we may fail to rebuild a .elc that depended on a macro > # from an updated file. > +# > +# We do this in two rules. .eldeps is the "real" dependencies file > +# and will be rebuilt if and only if a .el source file changes. We > +# could include this directly, but then whenever a .el file changed > +# (and .eldeps's mtime changed), make would restart immediately after > +# the include below. To avoid this, we create a second file, > +# .eldeps.x, that we only update when its *contents* differ from > +# .eldeps. .eldeps will often have an mtime older than .eldeps.x (any > +# .el file change that does not change dependencies will cause this), > +# so the .eldeps.x rule will often run, but it executes quickly and > +# quietly and will not trigger a make restart unless the dependencies > +# actually change. Here's a version of this comment that gets to the point directly: # We could include .eldeps directly, but that would cause a make # restart whenever any .el file was modified, even if dependencies # didn't change, because the mtime of .eldeps will change. Instead, # we include a second file, .eldeps.x, which we ensure always has the # same content as .eldeps, but its mtime only changes when dependency # information changes, in which case a make restart is necessary # anyway. > ifeq ($(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 $@) > --include $(dir)/.eldeps > + mv $@.tmp $@ > +$(dir)/.eldeps.x: $(dir)/.eldeps > + @cmp -s $^ $@ || cp $^ $@ > +-include $(dir)/.eldeps.x > endif > -CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp > +CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp $(dir)/.eldeps.x > > ifeq ($(HAVE_EMACS),1) > %.elc: %.el $(global_deps)