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+ Wed, 19 Feb 2014 22:47:50 +0200 (EET)\r
+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: <20140219195457.GD13537@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
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+ <20140214215736.GD4375@mit.edu> <20140219195457.GD13537@mit.edu>\r
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+Date: Wed, 19 Feb 2014 22:47:49 +0200\r
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+\r
+On Wed, Feb 19 2014, Austin Clements <amdragon@MIT.EDU> wrote:\r
+\r
+> Quoth myself on Feb 14 at 4:58 pm:\r
+>> Quoth Tomi Ollila on Feb 14 at 9:24 pm:\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
+>> \r
+>> Here's a way that works, but it's more complicated than your patch and\r
+>> doesn't seem to perform any better:\r
+>> \r
+>> diff --git a/emacs/Makefile.local b/emacs/Makefile.local\r
+>> index 42bfbd9..8a1f1c2 100644\r
+>> --- a/emacs/Makefile.local\r
+>> +++ b/emacs/Makefile.local\r
+>> @@ -29,14 +29,28 @@ emacs_bytecode = $(emacs_sources:.el=.elc)\r
+>> # the byte compiler may load an old .elc file when processing a\r
+>> # "require" or we may fail to rebuild a .elc that depended on a macro\r
+>> # from an updated file.\r
+>> +#\r
+>> +# We do this in two rules. .eldeps is the "real" dependencies file\r
+>> +# and will be rebuilt if and only if a .el source file changes. We\r
+>> +# could include this directly, but then whenever a .el file changed\r
+>> +# (and .eldeps's mtime changed), make would restart immediately after\r
+>> +# the include below. To avoid this, we create a second file,\r
+>> +# .eldeps.x, that we only update when its *contents* differ from\r
+>> +# .eldeps. .eldeps will often have an mtime older than .eldeps.x (any\r
+>> +# .el file change that does not change dependencies will cause this),\r
+>> +# so the .eldeps.x rule will often run, but it executes quickly and\r
+>> +# quietly and will not trigger a make restart unless the dependencies\r
+>> +# actually change.\r
+>\r
+> Here's a version of this comment that gets to the point directly:\r
+>\r
+> # We could include .eldeps directly, but that would cause a make\r
+> # restart whenever any .el file was modified, even if dependencies\r
+> # didn't change, because the mtime of .eldeps will change. Instead,\r
+> # we include a second file, .eldeps.x, which we ensure always has the\r
+> # same content as .eldeps, but its mtime only changes when dependency\r
+> # information changes, in which case a make restart is necessary\r
+> # anyway.\r
+\r
+I think this behaviour is tolerable: instead of verbosely re-run emacs to\r
+re-create .eldeps every time just to see the new .eldeps is not going to be\r
+used we just silently re-run only lightweight cmp.\r
+\r
+Tomi\r
+\r
+>\r
+>> ifeq ($(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
+>> --include $(dir)/.eldeps\r
+>> + mv $@.tmp $@\r
+>> +$(dir)/.eldeps.x: $(dir)/.eldeps\r
+>> + @cmp -s $^ $@ || cp $^ $@\r
+>> +-include $(dir)/.eldeps.x\r
+>> endif\r
+>> -CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp\r
+>> +CLEAN+=$(dir)/.eldeps $(dir)/.eldeps.tmp $(dir)/.eldeps.x\r
+>> \r
+>> ifeq ($(HAVE_EMACS),1)\r
+>> %.elc: %.el $(global_deps)\r
+> _______________________________________________\r
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