Re: [PATCH v2] Makefile: make the "sparse" target non-.PHONY

From: Ramsay Jones <ramsay@ramsayjones.plus.com>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: Junio C Hamano <gitster@pobox.com>, Jeff King <peff@peff.net>,
	git@vger.kernel.org, Denton Liu <liu.denton@gmail.com>
Subject: Re: [PATCH v2] Makefile: make the "sparse" target non-.PHONY
Date: Fri, 24 Sep 2021 17:38:48 +0100	[thread overview]
Message-ID: <7673e7aa-9737-a9eb-74ff-e11f071356e2@ramsayjones.plus.com> (raw)
In-Reply-To: <87a6k24vdc.fsf@evledraar.gmail.com>

On 24/09/2021 02:16, Ævar Arnfjörð Bjarmason wrote:
> 
> On Fri, Sep 24 2021, Ramsay Jones wrote:
> 
>> On 23/09/2021 18:39, Junio C Hamano wrote:
>>> Jeff King <peff@peff.net> writes:
>>>
>>>> On Thu, Sep 23, 2021 at 02:07:16AM +0200, Ævar Arnfjörð Bjarmason wrote:
>>>>
>>>>> We ensure that the recursive dependencies are correct by depending on
>>>>> the *.o file, which in turn will have correct dependencies by either
>>>>> depending on all header files, or under
>>>>> "COMPUTE_HEADER_DEPENDENCIES=yes" the headers it needs.
>>>>>
>>>>> This means that a plain "make sparse" is much slower, as we'll now
>>>>> need to make the *.o files just to create the *.sp files, but
>>>>> incrementally creating the *.sp files is *much* faster and less
>>>>> verbose, it thus becomes viable to run "sparse" along with "all" as
>>>>> e.g. "git rebase --exec 'make all sparse'".
>>>>
>>>> OK. I think this solves the dependency issues sufficiently. It is a
>>>> tradeoff that you must do the normal build in order to do the sparse
>>>> check now. That is certainly fine for my workflow (I am building Git all
>>>> the time, and only occasionally run "make sparse"). I don't know if
>>>> others would like it less (e.g., if Ramsay is frequently running sparse
>>>> checks without having just built).
>>>>
>>>> (I'd say "I do not care that much either way", but then I do not care
>>>> all that much either way about incremental sparse checks either, so I'm
>>>> not sure my opinion really matters).
>>>
>>> My build procedure runs "make sparse" before the primary build,
>>> simply because the former tends to be much faster to fail when there
>>> is an issue in the code.  I can understand that depending on .o is a
>>> cheap way to piggyback on the dependencies it has, but my latency
>>> will get much slower if this goes in _and_ I keep trying to pick up
>>> potentially problematic patches from the list.
>>
>>
>> I always run 'make sparse -k >sp-out 2>&1' after having done the main
>> build, so that is not an issue for me. Note that I always send all
>> output from each build step (for master, next and seen) to a series of
>> (branch keyed) files, so that I can easily diff from branch to branch.
>> Also, as above, I use '-k' on the 'sparse' and 'hdr-check' targets to
>> collect all errors/warnings in one go.
>>
>> So, this evening, with the v2 version of Ævar's patch having landed in
>> the 'seen' branch, we see this (abridged) diff between next and seen:
>>
>>   $ diff nsp-out ssp-out
>>   77a78
>>   >     SP hook.c
>>   289a291
>>   >     SP builtin/hook.c
>>   417a420
>>   >     SP t/helper/test-reftable.c
>>   449a453,478
>>   >     SP reftable/basics.c
>> ...
>>   >     SP reftable/tree_test.c
>>   452a482,483
>>   >     CC contrib/scalar/scalar.o
>>   >     SP contrib/scalar/scalar.c
>>   $ 
>>
>> So, this almost looks normal, except for the 'CC' line! Having discovered
>> some leftover cruft from old builds yesterday:
>>
>>   $ git ls-files | grep contrib/scalar
>>   contrib/scalar/.gitignore
>>   contrib/scalar/Makefile
>>   contrib/scalar/scalar.c
>>   contrib/scalar/scalar.txt
>>   contrib/scalar/t/Makefile
>>   contrib/scalar/t/t9099-scalar.sh
>>   $ ls contrib/scalar
>>   Makefile  scalar.c  scalar.o  scalar.sp  scalar.txt  t/
>>   $ rm contrib/scalar/scalar.{o,sp}
>>   $ make
>>       SUBDIR git-gui
>>       SUBDIR gitk-git
>>       SUBDIR templates
>>   $ make sparse
>>       CC contrib/scalar/scalar.o
>>       SP contrib/scalar/scalar.c
>>   $ 
>>
>> Hmm, interesting, but not relevant here. So, lets play a bit:
>>
>>   $ make sparse  
>>   $ make git.sp
>>   $ make git.sp
>>   $ touch git.sp
>>   $ make git.sp
>>   $ touch git.c
>>   $ make git.sp
>>       CC git.o
>>       SP git.c
>>   $ touch git.o
>>   $ make git.sp
>>       SP git.c
>>   $ 
>>
>> Hmm, so I think it is working as designed. However, I find it to be
>> more than a little irritating (curmudgeon alert!).
> 
> Specifically that there's now "SP" lines in the output, that *.sp files
> are created at all, that they're created where they are, or some
> combination of those thigs?

Heh, just ignore me.

Although I haven't done much testing, I believe your patch correctly
implements what you intended.

ATB,
Ramsay Jones