[PATCH 1/1] emacs: always write emacs/.eldeps when the target is remade
Tomi Ollila
tomi.ollila at iki.fi
Fri Feb 14 11:24:15 PST 2014
On Thu, Feb 13 2014, Austin Clements <amdragon at MIT.EDU> wrote:
> Quoth Tomi Ollila on Feb 13 at 9:26 am:
>> On Thu, Feb 13 2014, Austin Clements <amdragon at 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
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