Re: [PATCH] setup: default hash algo to GIT_HASH_DEFAULT

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

"brian m. carlson" <sandals@crustytoothpaste.net> writes:

> When we have no other hash algorithm to choose, we set no hash
> algorithm, which ends up with us defaulting to SHA-1.  Instead, default
> to GIT_HASH_DEFAULT.  This means that we will choose SHA-256 in breaking
> changes mode and in Git 3.0, which is what we want.
>
> Reported-by: Adam Dinwoodie <adam@dinwoodie.org>
> Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
> ---
>  setup.c         |  2 ++
>  t/t0001-init.sh | 16 ++++++++++++++++
>  2 files changed, 18 insertions(+)

With Git 3.0, we promised that SHA-1/SHA-256 interop will not have
to be ready, and that SHA-256 would become the default.  And this
patch would be a good thing to have for the second promise.

But didn't we also discuss "empty/initial repository whose hash
algorithm is undecided can take a push of either SHA-1 or SHA-256
payload and that first push can decide and freeze the hash algorithm
used in the repository" or something along that line?

I am wondering if we want to reserve 'HASH_UNKNOWN' for such a "was
just created, not quite finished initializing yet" state.

The patch looks good for the goal stated in the log message.

Thanks.




> diff --git a/setup.c b/setup.c
> index 61bcdafe82..4a0dfc8908 100644
> --- a/setup.c
> +++ b/setup.c
> @@ -2830,6 +2830,8 @@ static void repository_format_configure(struct repository_format *repo_fmt,
>  			repo_fmt->hash_algo = env_algo;
>  	} else if (cfg.hash != GIT_HASH_UNKNOWN) {
>  		repo_fmt->hash_algo = cfg.hash;
> +	} else {
> +		repo_fmt->hash_algo = GIT_HASH_DEFAULT;
>  	}
>  
>  	/*
> diff --git a/t/t0001-init.sh b/t/t0001-init.sh
> index f1d227f271..98c7562f32 100755
> --- a/t/t0001-init.sh
> +++ b/t/t0001-init.sh
> @@ -516,6 +516,22 @@ test_expect_success 're-init from a linked worktree' '
>  	)
>  '
>  
> +test_expect_success 'git init uses default object format' '
> +	test_when_finished "rm -rf repo" &&
> +	(
> +		sane_unset GIT_DEFAULT_HASH &&
> +		git init repo &&
> +		if test_have_prereq WITH_BREAKING_CHANGES
> +		then
> +			echo sha256
> +		else
> +			echo sha1
> +		fi >expect &&
> +		git -C repo rev-parse --show-object-format >actual &&
> +		test_cmp expect actual
> +	)
> +'
> +
>  test_expect_success 'init honors GIT_DEFAULT_HASH' '
>  	test_when_finished "rm -rf sha1 sha256" &&
>  	GIT_DEFAULT_HASH=sha1 git init sha1 &&