Re: [PATCH 1/1] emacs: always write emacs/.eldeps when the target is remade

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+From: Tomi Ollila <tomi.ollila@iki.fi>\r
+To: Austin Clements <amdragon@MIT.EDU>\r
+Subject: Re: [PATCH 1/1] emacs: always write emacs/.eldeps when the target is\r
+       remade\r
+In-Reply-To: <20140213074944.GY4375@mit.edu>\r
+References: <1390645309-2326-1-git-send-email-tomi.ollila@iki.fi>\r
+       <20140213071026.GX4375@mit.edu> <m2sirn1nik.fsf@guru.guru-group.fi>\r
+       <20140213074944.GY4375@mit.edu>\r
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+Date: Fri, 14 Feb 2014 21:24:15 +0200\r
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+\r
+On Thu, Feb 13 2014, Austin Clements <amdragon@MIT.EDU> wrote:\r
+\r
+> Quoth Tomi Ollila on Feb 13 at  9:26 am:\r
+>> On Thu, Feb 13 2014, Austin Clements <amdragon@MIT.EDU> wrote:\r
+>> \r
+>> > Quoth Tomi Ollila on Jan 25 at 12:21 pm:\r
+>> >> So that the target is newer than its prerequisites.\r
+>> >> ---\r
+>> >>  emacs/Makefile.local | 3 +--\r
+>> >>  1 file changed, 1 insertion(+), 2 deletions(-)\r
+>> >> \r
+>> >> diff --git a/emacs/Makefile.local b/emacs/Makefile.local\r
+>> >> index 42bfbd9..d5d402e 100644\r
+>> >> --- a/emacs/Makefile.local\r
+>> >> +++ b/emacs/Makefile.local\r
+>> >> @@ -32,8 +32,7 @@ emacs_bytecode = $(emacs_sources:.el=.elc)\r
+>> >>  ifeq ($(HAVE_EMACS),1)\r
+>> >>  $(dir)/.eldeps: $(dir)/Makefile.local $(dir)/make-deps.el $(emacs_sources)\r
+>> >>          $(call quiet,EMACS) --directory emacs -batch -l make-deps.el \\r
+>> >> -                -f batch-make-deps $(emacs_sources) > $@.tmp && \\r
+>> >> -                (cmp -s $@.tmp $@ || mv $@.tmp $@)\r
+>> >> +                -f batch-make-deps $(emacs_sources) > $@.tmp && mv $@.tmp $@\r
+>> >>  -include $(dir)/.eldeps\r
+>> >>  endif\r
+>> >>  CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp\r
+>> >\r
+>> > Is this just so the rule doesn't get run again on the next make\r
+>> > invocation (unless, of course, a dependent changed)?\r
+>> \r
+>> Basically yes. I did multiple builds in rapid succession when developing\r
+>> something and this thing confused me quite a lot in the beginning...\r
+>> \r
+>> > Interestingly, if any of the dependents have changed, but in ways that\r
+>> > don't affect .eldeps, this change will make the build more expensive\r
+>> > because it will trigger a make restart after .eldeps is updated.\r
+>> \r
+>> I wondered what was the reason for the recipe you've chosen here, has\r
+>> it something to do with inodes or something ;) (and were going to ask\r
+>> an alternative to touch (or even : > $@) the target...\r
+>> \r
+>> ... but now I understand. E.g. change in notmuch-lib.el will cause *all* \r
+>> .el files to be re-bytecompiled after this change. \r
+>\r
+> This is unrelated to the cmp in the recipe.  A change in\r
+> notmuch-lib.el *must* cause almost all .el files to be recompiled\r
+> because they almost all require it and may use macros from it.  If you\r
+> touch, e.g., notmuch-hello.el, you'll see that very little is rebuilt\r
+> (with or without this patch).\r
+>\r
+>> An alternative to this patch would be adding a message to the rule\r
+>> which informs user to touch .eldeps to avoid re-doing .eldeps if\r
+>> that irritates one :D\r
+>> \r
+>> something like:\r
+>> \r
+>> (cmp -s $@.tmp $@ && \\r
+>>      echo "touch $@ to avoid redoing this target" || mv $@.tmp $@)\r
+>\r
+> I think this patch is good as it is; I was just pointing out that the\r
+> change also has a performance drawback in some situations.  (Knowing\r
+> make, there's probably *some* way to get the best of both worlds and\r
+> it's probably really ugly.)\r
+\r
+Ah, now I understand, because emacs/Makefile.local includes emacs/.eldeps\r
+when it notices mtime of emacs/.eldeps changes it restarts itself...\r
+\r
+... to compare with current behaviour:\r
+\r
+$ make\r
+...\r
+$ touch emacs/notmuch.el\r
+$ make\r
+...\r
+$ make\r
+Use "make V=1" to see the verbose compile lines.\r
+EMACS emacs/.eldeps\r
+make: Nothing to be done for `all'.\r
+$ make\r
+Use "make V=1" to see the verbose compile lines.\r
+EMACS emacs/.eldeps\r
+make: Nothing to be done for `all'.\r
+$ make\r
+Use "make V=1" to see the verbose compile lines.\r
+EMACS emacs/.eldeps\r
+make: Nothing to be done for `all'.\r
+\r
+It will rerun emacs -L emacs -batch -l make-deps.el -f batch-make-deps ...\r
+over and over again...\r
+\r
+I thought I figured out a solution involving .eldeps.stamp file but\r
+that turned out to be no-go... (circular dependency netween .eldeps.stamp\r
+and Makefile.local).\r
+\r
+So, with this if one edits emacs/* files and keeps building byte-compiled\r
+versions often, make will both run EMACS emacs/.eldeps and restarting\r
+-- and when moving to edit other files both of the above stops. Without\r
+this change after editing emacs/* files EMACS emacs/.eldeps will be\r
+executed until it is touched or make clean executed (I wonder how make\r
+handles rebuilding emacs/.eldeps while doing make clean ;)\r
+\r
+\r
+Tomi\r