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+ id 1WEQlr-0007tC-LY; Fri, 14 Feb 2014 16:58:09 -0500\r
+Date: Fri, 14 Feb 2014 16:58:07 -0500\r
+From: Austin Clements <amdragon@MIT.EDU>\r
+To: Tomi Ollila <tomi.ollila@iki.fi>\r
+Subject: Re: [PATCH 1/1] emacs: always write emacs/.eldeps when the target is\r
+ remade\r
+Message-ID: <20140214215736.GD4375@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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+\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 = $(emacs_sources:.el=.elc)\r
+ # the byte compiler may load an old .elc file when processing a\r
+ # "require" or we may fail to rebuild a .elc that depended on a macro\r
+ # from an updated file.\r
++#\r
++# We do this in two rules. .eldeps is the "real" dependencies file\r
++# and will be rebuilt if and only if a .el source file changes. We\r
++# could include this directly, but then whenever a .el file changed\r
++# (and .eldeps's mtime changed), make would restart immediately after\r
++# the include below. To avoid this, we create a second file,\r
++# .eldeps.x, that we only update when its *contents* differ from\r
++# .eldeps. .eldeps will often have an mtime older than .eldeps.x (any\r
++# .el file change that does not change dependencies will cause this),\r
++# so the .eldeps.x rule will often run, but it executes quickly and\r
++# quietly and will not trigger a make restart unless the dependencies\r
++# actually change.\r
+ ifeq ($(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
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