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

[Tomi Ollila]

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. 

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 $@)

Thanks, 

Tomi