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

Ævar Arnfjörð Bjarmason  [off-list ref] 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.