On 8/15/25 1:26 AM, Jeff King wrote:
> On Wed, Aug 13, 2025 at 02:19:14PM +0100, Phillip Wood wrote:
>
>> I had a quick look at the callers of describe_commit() and they all seem to
>> use an oid that they get from looking up a commit so I'm not sure under what
>> circumstances this call to lookup_commit_reference() can fail.
>
> I wonder if it would make sense for describe_commit() to just take a
> "struct commit" pointer.
Yes, a lot.
> Then it could skip the call to turn the oid
> into a commit entirely, and the compiler would make sure we always have
> a commit. :)
>
> Something like this (totally untested, and not something I'm planning to
> follow up on, but maybe inspirational):
>
> diff --git a/builtin/describe.c b/builtin/describe.c
> index 32f5bf513f..3e8691a4c4 100644
> --- a/builtin/describe.c
> +++ b/builtin/describe.c
> @@ -352,26 +352,24 @@ static void append_suffix(int depth, const struct object_id *oid, struct strbuf
> repo_find_unique_abbrev(the_repository, oid, abbrev));
> }
>
> -static void describe_commit(struct object_id *oid, struct strbuf *dst)
> +static void describe_commit(struct commit *cmit, struct strbuf *dst)
> {
> - struct commit *cmit, *gave_up_on = NULL;
> + struct commit *gave_up_on = NULL;
> struct lazy_queue queue = LAZY_QUEUE_INIT;
> struct commit_name *n;
> struct possible_tag all_matches[MAX_TAGS];
> unsigned int match_cnt = 0, annotated_cnt = 0, cur_match;
> unsigned long seen_commits = 0;
> unsigned int unannotated_cnt = 0;
>
> - cmit = lookup_commit_reference(the_repository, oid);
> -
> n = find_commit_name(&cmit->object.oid);
> if (n && (tags || all || n->prio == 2)) {
> /*
> * Exact match to an existing ref.
> */
> append_name(n, dst);
> if (n->misnamed || longformat)
> - append_suffix(0, n->tag ? get_tagged_oid(n->tag) : oid, dst);
> + append_suffix(0, n->tag ? get_tagged_oid(n->tag) : &cmit->object.oid, dst);
> if (suffix)
> strbuf_addstr(dst, suffix);
> return;
> @@ -528,7 +526,7 @@ static void describe_commit(struct object_id *oid, struct strbuf *dst)
> }
>
> struct process_commit_data {
> - struct object_id current_commit;
> + struct commit *current_commit;
> struct object_id looking_for;
> struct strbuf *dst;
> struct rev_info *revs;
> @@ -537,7 +535,7 @@ struct process_commit_data {
> static void process_commit(struct commit *commit, void *data)
> {
> struct process_commit_data *pcd = data;
> - pcd->current_commit = commit->object.oid;
> + pcd->current_commit = commit;
> }
>
> static void process_object(struct object *obj, const char *path, void *data)
> @@ -546,7 +544,7 @@ static void process_object(struct object *obj, const char *path, void *data)
>
> if (oideq(&pcd->looking_for, &obj->oid) && !pcd->dst->len) {
> reset_revision_walk();
> - describe_commit(&pcd->current_commit, pcd->dst);
> + describe_commit(pcd->current_commit, pcd->dst);
pcd->current_commit is initialized to NULL below, but
traverse_commit_list() without a filter must have set it via our
process_commit() callback before we get to the describe_commit() call.
Or are there weird repositories (e.g., just a blob, just a tag) that can
cause traverse_commit_list() to call its show_object() callback without
ever calling its show_commit() callback? I don't see how, but may be
missing some way.
> strbuf_addf(pcd->dst, ":%s", path);
> clear_prio_queue(&pcd->revs->commits);
> }
> @@ -556,7 +554,7 @@ static void describe_blob(struct object_id oid, struct strbuf *dst)
> {
> struct rev_info revs;
> struct strvec args = STRVEC_INIT;
> - struct process_commit_data pcd = { *null_oid(the_hash_algo), oid, dst, &revs};
> + struct process_commit_data pcd = { NULL, oid, dst, &revs};
>
> strvec_pushl(&args, "internal: The first arg is not parsed",
> "--objects", "--in-commit-order", "--reverse", "HEAD",
> @@ -589,7 +587,7 @@ static void describe(const char *arg, int last_one)
> cmit = lookup_commit_reference_gently(the_repository, &oid, 1);
>
> if (cmit)
> - describe_commit(&oid, &sb);
> + describe_commit(cmit, &sb);
> else if (odb_read_object_info(the_repository->objects,
> &oid, NULL) == OBJ_BLOB)
> describe_blob(oid, &sb);
