Re: [PATCH 3/4] Makefile: use the sha1collisiondetection submodule by default

[Junio C Hamano <gitster@pobox.com>]

Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:

> Change the build process so that instead of needing to supply
> DC_SHA1_SUBMODULE=YesPlease to use the sha1collisiondetection
> submodule instead of the copy of the same code shipped in the sha1dc
> directory, it uses the submodule by default unless
> NO_DC_SHA1_SUBMODULE=UnfortunatelyYes is supplied.
> ...
> This change removes the "auto" logic Junio added in
> cac87dc01d ("sha1collisiondetection: automatically enable when
> submodule is populated", 2017-07-01), I feel that automatically
> falling back to using sha1dc would defeat the point, which is to smoke
> out any remaining users of git.git who have issues cloning the
> submodule for whatever reason.

I think it makes sense to drop 'auto' if we were to go this route.
I do not think the right value for NO_DC_SHA1_SUBMODULE should be
"unfortunately yes"; it should be spelled NoThanks or something.
It's not like an external reason "unfortunately" prevents you from
using the code from the submodule---the person sets it deliberately
and by choice.

>     Makefile:1031: *** The sha1collisiondetection submodule is not
>     checked out. Please make it available, either by cloning with
>     --recurse-submodules, or by running "git submodule update
>     --init". If you can't use it for whatever reason you can define
>     NO_DC_SHA1_SUBMODULE=UnfortunatelyYes.  Stop.

Likewise here.