Subject: Re: [PATCH 10/10] Enable SHA-256 by default in breaking changes mode

From: Junio C Hamano <[email-masked]>
Date: Fri, 20 Jun 2025 08:03:23 -0700

"brian m. carlson" <[email-masked]> writes:

> Our document on breaking changes indicates that we intend to default to
> SHA-256 in Git 3.0.  Since most people choose the default option, this
> is an important security upgrade to our defaults.
>
> To allow people to test this case, when WITH_BREAKING_CHANGES is set in
> the configuration, build Git with SHA-256 as the default hash.  Update
> the testsuite to reflect this configuration so that the tests pass.

Another thing that I suspect nobody wrote tests for, but we must be
absolutely certain, is that the post-3.0 Git can still interoperate
well with historical SHA-1 repositories (I am not talking about
"fetch from SHA-1 into SHA-256", but "the binary does not lose
ability to work in SHA-1 repositories or fetch/push between SHA-1
repositories, only because the default is set to SHA-256"), even in
old repositories people have been using for ages without the
core.repositoryformatversion defined.

Thanks.