[v2,05/10] object-name.c: make dependency on object_type order more obvious

Commit Message

Ævar Arnfjörð Bjarmason April 20, 2021, 1 p.m. UTC

Add an assert to make it more obvious that we were effectively
hardcoding OBJ_TAG in sort_ambiguous() as "4".

I wrote this code in 5cc044e0257 (get_short_oid: sort ambiguous
objects by type, then SHA-1, 2018-05-10), there was already a comment
about this magic, but let's make sure that someone doing a potential
reordering of "enum object_type" in the future would notice it
breaking this function (and probably a bunch of other things...).

Signed-off-by: Ævar Arnfjörð Bjarmason <[e-mail]>
---
 object-name.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Patch

diff --git a/object-name.c b/object-name.c
index 4d7f0c66cf..b6a7328b7a 100644
--- a/object-name.c
+++ b/object-name.c
@@ -408,6 +408,8 @@  static int sort_ambiguous(const void *a, const void *b, void *ctx)
 	enum object_type b_type = oid_object_info(sort_ambiguous_repo, b, NULL);
 	enum object_type a_type_sort;
 	enum object_type b_type_sort;
+	const enum object_type tag_type_offs = OBJ_TAG - OBJ_NONE;
+	assert(tag_type_offs == 4);
 
 	/*
 	 * Sorts by hash within the same object type, just as
@@ -425,8 +427,8 @@  static int sort_ambiguous(const void *a, const void *b, void *ctx)
 	 * cleverly) do that with modulus, since the enum assigns 1 to
 	 * commit, so tag becomes 0.
 	 */
-	a_type_sort = a_type % 4;
-	b_type_sort = b_type % 4;
+	a_type_sort = a_type % tag_type_offs;
+	b_type_sort = b_type % tag_type_offs;
 	return a_type_sort > b_type_sort ? 1 : -1;
 }