Partially revert c8aed5e8 (repository: stop setting SHA1 as the
default object hash, 2024-05-07), to keep end-user systems still
broken when we have gap in our test coverage but yet give them an
escape hatch to set the GIT_TEST_DEFAULT_HASH_ALGO environment
variable to "sha1" in order to revert to the previous behaviour.
Due to the way the end-user facing GIT_DEFAULT_HASH environment
variable is used in our test suite, we unfortunately cannot reuse it
for this purpose.
Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx>
---
repository.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 44 insertions(+)
diff --git a/repository.c b/repository.c
index 15c10015b0..c62e329878 100644
--- a/repository.c
+++ b/repository.c
@@ -19,6 +19,28 @@
static struct repository the_repo;
struct repository *the_repository = &the_repo;
+/*
+ * An escape hatch: if we hit a bug in the production code that fails
+ * to set an appropriate hash algorithm (most likely to happen when
+ * running outside a repository), we can tell the user who reported
+ * the crash to set the environment variable to "sha1" (all lowercase)
+ * to revert to the historical behaviour of defaulting to SHA-1.
+ */
+static void set_default_hash_algo(struct repository *repo)
+{
+ const char *hash_name;
+ int algo;
+
+ hash_name = getenv("GIT_TEST_DEFAULT_HASH_ALGO");
+ if (!hash_name)
+ return;
+ algo = hash_algo_by_name(hash_name);
+ if (algo == GIT_HASH_UNKNOWN)
+ return;
+
+ repo_set_hash_algo(repo, algo);
+}
+
void initialize_repository(struct repository *repo)
{
repo->objects = raw_object_store_new();
@@ -26,6 +48,28 @@ void initialize_repository(struct repository *repo)
repo->parsed_objects = parsed_object_pool_new();
ALLOC_ARRAY(repo->index, 1);
index_state_init(repo->index, repo);
+
+ /*
+ * When a command runs inside a repository, it learns what
+ * hash algorithm is in use from the repository, but some
+ * commands are designed to work outside a repository, yet
+ * they want to access the_hash_algo, if only for the length
+ * of the hashed value to see if their input looks like a
+ * plausible hash value.
+ *
+ * We are in the process of identifying such code paths and
+ * giving them an appropriate default individually; any
+ * unconverted code paths that try to access the_hash_algo
+ * will thus fail. The end-users however have an escape hatch
+ * to set GIT_TEST_DEFAULT_HASH_ALGO environment variable to
+ * "sha1" to get back the old behaviour of defaulting to SHA-1.
+ *
+ * This escape hatch is deliberately kept unadvertised, so
+ * that they see crashes and we can get a report before
+ * telling them about it.
+ */
+ if (repo == the_repository)
+ set_default_hash_algo(repo);
}
static void expand_base_dir(char **out, const char *in,
--
2.45.1-216-g4365c6fcf9
