Re: dpkg-buildflags

[Goswin von Brederlow <goswin-v-b@web.de>]

Pierre Habouzit <madcoder@madism.org> writes:

> On Thu, Jul 01, 2010 at 10:04:02AM +0200, Goswin von Brederlow wrote:
>> Pierre Habouzit <madcoder@madism.org> writes:
>> 
>> > On Wed, Jun 30, 2010 at 03:05:10PM +0200, Goswin von Brederlow wrote:
>> >> mrvn@book:~% cat Makefile
>> >> $(eval $(shell echo FOO=1; echo BAR=2))
>> >> $(info FOO=$(FOO))
>> >> $(info BAR=$(BAR))
>> >> all:
>> >> 
>> >> mrvn@book:~% make
>> >> FOO=1 BAR=2
>> >> BAR=
>> >> make: Nothing to be done for `all'.
>> >> 
>> >> 
>> >> How do you get make to honor line breaks in $(eval ...)?
>> >
>> > gah, make is annoying. Well there is always the possibility:
>> >
>> > -include dpkg-buildflags.mk
>> > dpkg-buildflags.mk:
>> > 	$(shell dpkg-buildflags --export=make) > $@
>> >
>> > Which is probably a hell of a lot simpler.
>> > Stupid make....
>> 
>> Indeed.
>> 
>> > (for those not very comfortable with make, the -include
>> > dpkg-buildflags.mk will check if the file exist, if not won't complain
>> > but will find if there is a target named 'dpkg-buildflags.mk', if yes
>> > will do its rules and retry to include the file.
>> >
>> > Which in the end does what is meant.
>> 
>> Except it won't make the file ever again even if the dpkg-buildflags
>> output changes. So if you want to preserve timestamps unless the output
>> changes you need something like this. If the timestamp doesn't matter
>> you just need the .PHONY.
>> 
>> -include dpkg-buildflags.mk
>> dpkg-buildflags.mk:
>>  	$(shell dpkg-buildflags --export=make) > $@.new
>>         @if ! cmp 2>/dev/null --quiet $@.new $@; then \
>>           echo Updating $@; \
>>           mv $@.new $@; \
>>         else \
>>           rm $@.new; \
>>         fi
>
> You don't need to protect the regeneration with your
> update-only-if-changed trick because no rule will ever depend upon the
> dpkg-buildflags.mk freshness, so the sole need you have is to mark the
> rule PHONY if you need such a thing.

Since the file should be removed in clean it probably doesn't need to be
PHONY. If any of the flags are changed you need to remove all object
files anyway so debian/rules clean would be in order then.

MfG
        Goswin