Re: [PATCH 8/8] hook-list.h: add a generated list of hooks, like config-list.h

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Nov 15, 2021, 22:49 UTC
Message-ID: <211115.86bl2lqbbt.gmgdl@evledraar.gmail.com>
In-Reply-To: <20211115224015.vzfevpvptysxzpaa@glandium.org>

On Tue, Nov 16 2021, Mike Hommey wrote:

Show 29 quoted lines

> On Mon, Nov 15, 2021 at 11:26:36PM +0100, Ævar Arnfjörð Bjarmason wrote:
>> 
>> On Tue, Nov 16 2021, Mike Hommey wrote:
>> 
>> > On Thu, Sep 23, 2021 at 12:30:03PM +0200, Ævar Arnfjörð Bjarmason wrote:
>> >> -builtin/help.sp builtin/help.s builtin/help.o: config-list.h GIT-PREFIX
>> >> +hook.sp hook.s hook.o: hook-list.h
>> >> +
>> >> +builtin/help.sp builtin/help.s builtin/help.o: config-list.h hook-list.h GIT-PREFIX
>> >
>> > hook-list.h is only included from buitin/bugreport.c, so
>> > builtin/bugreport.o should be the one with the hook-list.h dependency,
>> > shouldn't it?
>> 
>> Well spotted, yes. This is a mistake. I think from some earlier WIP
>> version of the series.
>> 
>> In practice we don't really miss dependencies due to these sorts of
>> mistakes since we use the .depends files, i.e. GCC & Clang figure this
>> out for us:
>> 
>>     $ grep hook-list .depend/* */.depend/*
>>     builtin/.depend/bugreport.o.d: compat/compiler.h git-compat-util.h hook.h hook-list.h
>>     builtin/.depend/bugreport.o.d:hook-list.h:
>
> But aren't those .depends files are only created when compiling object
> files, such that builtin/.depend/bugreport.o.d wouldn't exist until
> bugreport.c is compiled, which would fail if hook-list.h wasn't created
> before that?

Fail how?

I don't think it could fail, because the purpose of these dependency relationships is to avoid needless *re*builds. So if you're building for the first time it doesn't matter, your compiler will find the relevant things to include for you. It doesn't need what's in the Makefile to do that.

See [1], what I said about LIB_H there applies more generally for the .depends files.

It will only fail in the sense that it over-depends, i.e. if you do:

    git clean -dxf; make builtin/help.o

We'll generate the hook list, as opposed to for buildin/add.o or whatever, but I'd say that generally doesn't matter all that much, what matters is that we don't miss dependency relationships.

Anyway, I'll try to loop around to fixing this, just wanted to gather some interest in the more general set of fixes I've got. I've got some fixes queued up after that that fix/improve the *.sp and *.s parts of the line you quoted (and other similar lines). I'd prefer just to fix this along with those so the two don't textually conflict.

1. https://lore.kernel.org/git/211110.86h7cki0uo.gmgdl@evledraar.gmail.com/