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 <redacted>
Signed-off-by: Derrick Stolee <redacted>
---
 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 &&
--

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