refs: introduce wrapper struct for `each_ref_fn`

The `each_ref_fn` callback function type is used across our code base
for several different functions that iterate through reference. There's
a bunch of callbacks implementing this type, which makes any changes to
the callback signature extremely noisy. An example of the required churn
is e8207717f1 (refs: add referent to each_ref_fn, 2024-08-09): adding a
single argument required us to change 48 files.

It was already proposed back then [1] that we might want to introduce a
wrapper structure to alleviate the pain going forward. While this of
course requires the same kind of global refactoring as just introducing
a new parameter, it at least allows us to more change the callback type
afterwards by just extending the wrapper structure.

One counterargument to this refactoring is that it makes the structure
more opaque. While it is obvious which callsites need to be fixed up
when we change the function type, it's not obvious anymore once we use
a structure. That being said, we only have a handful of sites that
actually need to populate this wrapper structure: our ref backends,
"refs/iterator.c" as well as very few sites that invoke the iterator
callback functions directly.

Introduce this wrapper structure so that we can adapt the iterator
interfaces more readily.

[1]: <ZmarVcF5JjsZx0dl@tanuki>

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 19 insertions, 14 deletions

diff --git a/builtin/fsck.c b/builtin/fsck.c
index 8ee95e0d67..ed4eea1680 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -530,14 +530,13 @@ static int fsck_handle_reflog(const char *logname, void *cb_data)
 	return 0;
 }
 
-static int fsck_handle_ref(const char *refname, const char *referent UNUSED, const struct object_id *oid,
-			   int flag UNUSED, void *cb_data UNUSED)
+static int fsck_handle_ref(const struct reference *ref, void *cb_data UNUSED)
 {
 	struct object *obj;
 
-	obj = parse_object(the_repository, oid);
+	obj = parse_object(the_repository, ref->oid);
 	if (!obj) {
-		if (is_promisor_object(the_repository, oid)) {
+		if (is_promisor_object(the_repository, ref->oid)) {
 			/*
 			 * Increment default_refs anyway, because this is a
 			 * valid ref.
@@ -546,19 +545,19 @@ static int fsck_handle_ref(const char *refname, const char *referent UNUSED, con
 			 return 0;
 		}
 		error(_("%s: invalid sha1 pointer %s"),
-		      refname, oid_to_hex(oid));
+		      ref->name, oid_to_hex(ref->oid));
 		errors_found |= ERROR_REACHABLE;
 		/* We'll continue with the rest despite the error.. */
 		return 0;
 	}
-	if (obj->type != OBJ_COMMIT && is_branch(refname)) {
-		error(_("%s: not a commit"), refname);
+	if (obj->type != OBJ_COMMIT && is_branch(ref->name)) {
+		error(_("%s: not a commit"), ref->name);
 		errors_found |= ERROR_REFS;
 	}
 	default_refs++;
 	obj->flags |= USED;
 	fsck_put_object_name(&fsck_walk_options,
-			     oid, "%s", refname);
+			     ref->oid, "%s", ref->name);
 	mark_object_reachable(obj);
 
 	return 0;
@@ -580,13 +579,19 @@ static void get_default_heads(void)
 	worktrees = get_worktrees();
 	for (p = worktrees; *p; p++) {
 		struct worktree *wt = *p;
-		struct strbuf ref = STRBUF_INIT;
+		struct strbuf refname = STRBUF_INIT;
 
-		strbuf_worktree_ref(wt, &ref, "HEAD");
-		fsck_head_link(ref.buf, &head_points_at, &head_oid);
-		if (head_points_at && !is_null_oid(&head_oid))
-			fsck_handle_ref(ref.buf, NULL, &head_oid, 0, NULL);
-		strbuf_release(&ref);
+		strbuf_worktree_ref(wt, &refname, "HEAD");
+		fsck_head_link(refname.buf, &head_points_at, &head_oid);
+		if (head_points_at && !is_null_oid(&head_oid)) {
+			struct reference ref = {
+				.name = refname.buf,
+				.oid = &head_oid,
+			};
+
+			fsck_handle_ref(&ref, NULL);
+		}
+		strbuf_release(&refname);
 
 		if (include_reflogs)
 			refs_for_each_reflog(get_worktree_ref_store(wt),