Re: [PATCH v2 1/2] setup: tweak upgrade policy to grandfather worktreeconfig

> One possible way to alert a user of this issue is to warn them when Git
> notices an extension exists, but core.repositoryFormatVersion is not a
> correct value. However,
>
>  - it requires the end-user to read, understand and execute the
>    manual upgrade
>
>  - it encourages to follow the same procedure blindly, making the
>    protection even less useful
>
> Let's instead keep failing hard without teaching how to bypass the
> repository protection, but allow upgrading even when only the
> worktreeconfig extension exists in an old repository, which is
> likely to be set by a broke version of Git that did not update the
> repository version when setting the extension.
>
> This change of behavior is made visible by testing how 'git
> sparse-checkout init' behaves to upgrade the repository format version
> even if the extension.worktreeConfig is already set. This would
> previously fail without a clear way forward.
>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
> ---
>  cache.h                            |  2 +-
>  setup.c                            | 12 ++++++++----
>  t/t1091-sparse-checkout-builtin.sh | 12 ++++++++++++
>  3 files changed, 21 insertions(+), 5 deletions(-)
>
> diff --git a/cache.h b/cache.h
> index e5885cc9ea..8ff46857f6 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -1042,8 +1042,8 @@ struct repository_format {
>  	int worktree_config;
>  	int is_bare;
>  	int hash_algo;
> -	int has_extensions;
>  	char *work_tree;
> +	int has_unallowed_extensions;
>  	struct string_list unknown_extensions;
>  };
>
> diff --git a/setup.c b/setup.c
> index eb066db6d8..65270440a9 100644
> --- a/setup.c
> +++ b/setup.c
> @@ -455,12 +455,13 @@ static int check_repo_format(const char *var, const char *value, void *vdata)
>  	if (strcmp(var, "core.repositoryformatversion") == 0)
>  		data->version = git_config_int(var, value);
>  	else if (skip_prefix(var, "extensions.", &ext)) {
> -		data->has_extensions = 1;
>  		/*
>  		 * record any known extensions here; otherwise,
>  		 * we fall through to recording it as unknown, and
>  		 * check_repository_format will complain
>  		 */
> +		int is_unallowed_extension = 1;
> +
>  		if (!strcmp(ext, "noop"))
>  			;
>  		else if (!strcmp(ext, "preciousobjects"))
> @@ -469,10 +470,13 @@ static int check_repo_format(const char *var, const char *value, void *vdata)
>  			if (!value)
>  				return config_error_nonbool(var);
>  			data->partial_clone = xstrdup(value);
> -		} else if (!strcmp(ext, "worktreeconfig"))
> +		} else if (!strcmp(ext, "worktreeconfig")) {
>  			data->worktree_config = git_config_bool(var, value);
> -		else
> +			is_unallowed_extension = 0;
> +		} else
>  			string_list_append(&data->unknown_extensions, ext);
> +
> +		data->has_unallowed_extensions |= is_unallowed_extension;
>  	}
>
>  	return read_worktree_config(var, value, vdata);
> @@ -560,7 +564,7 @@ int upgrade_repository_format(int target_version)
>  		return 0;
>
>  	if (verify_repository_format(&repo_fmt, &err) < 0 ||
> -	    (!repo_fmt.version && repo_fmt.has_extensions)) {
> +	    (!repo_fmt.version && repo_fmt.has_unallowed_extensions)) {
>  		warning("unable to upgrade repository format from %d to %d: %s",
>  			repo_fmt.version, target_version, err.buf);
>  		strbuf_release(&err);
> diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
> index 88cdde255c..6e339c7c8e 100755
> --- a/t/t1091-sparse-checkout-builtin.sh
> +++ b/t/t1091-sparse-checkout-builtin.sh
> @@ -68,6 +68,18 @@ test_expect_success 'git sparse-checkout init' '
>  	check_files repo a
>  '
>
> +test_expect_success 'git sparse-checkout works if repository format is wrong' '
> +	test_when_finished git -C repo config core.repositoryFormatVersion 1 &&
> +	git -C repo config --unset core.repositoryFormatVersion &&
> +	git -C repo sparse-checkout init &&
> +	git -C repo config core.repositoryFormatVersion >actual &&
> +	echo 1 >expect &&
> +	git -C repo config core.repositoryFormatVersion 0 &&
> +	git -C repo sparse-checkout init &&
> +	git -C repo config core.repositoryFormatVersion >actual &&
> +	test_cmp expect actual
> +'
> +
>  test_expect_success 'git sparse-checkout list after init' '
>  	git -C repo sparse-checkout list >actual &&
>  	cat >expect <<-\EOF &&
> --
> gitgitgadget
>
>