Re: [PATCH v4 7/9] Makefile: document SHA-1 and SHA-256 default and selection order

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

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

> For the *_SHA1 and *_SHA256 flags we've discussed the various flags,
> but not the fact that when you define multiple flags we'll pick one.
>
> Which one we pick depends on the order they're listed in the Makefile,
> which differed from the order we discussed them in this documentation.
>
> Let's be explicit about how we select these, and re-arrange the
> listings so that they're listed in the priority order we've picked.

That makes sense.  What is not explicit enough, at least at this
stage, is that, even though we say "if you do not choose one, the
default is used" (which by the way is an awkward thing to see---that
is the definition of being the default, so the statement itself has
zero bit of useful information), we do not say what implementation
exactly is used as the default.

> This behavior makes it easier to e.g. integrate with autoconf-like
> systems, where the configuration can provide everything it can
> support, and Git is tasked with picking the first one it prefers.

Well explained.

> +# ==== Default SHA-1 backend ====
> +#
> +# If no *_SHA1 backend is picked we'll fall back on using the default.
> +#
> +# Multiple *_SHA1 backends can be selected, the first supported one
> +# listed in "Other SHA-1 implementations" will be picked.