packfile: disentangle return value of packed_object_info()

The `packed_object_info()` function returns the type of the packed
object. While we use an `enum object_type` to store the return value,
this type is not to be confused with the actual object type. It _may_
contain the object type, but it may just as well encode that the given
packed object is stored as a delta.

We have removed the only caller that relied on this returned object type
in the preceding commit, so let's simplify semantics and return either 0
on success or a negative error code otherwise.

This unblocks a small optimization where we can skip reading the object
type altogether.

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

Author: pks-t

packfile.c

@@ -1587,6 +1587,7 @@ int packed_object_info(struct repository *r, struct packed_git *p,
 	unsigned long size;
 	off_t curpos = obj_offset;
 	enum object_type type;
+	int ret;
 
 	/*
 	 * We always get the representation type, but only convert it to
@@ -1607,12 +1608,12 @@ int packed_object_info(struct repository *r, struct packed_git *p,
 			off_t base_offset = get_delta_base(p, &w_curs, &tmp_pos,
 							   type, obj_offset);
 			if (!base_offset) {
-				type = OBJ_BAD;
+				ret = -1;
 				goto out;
 			}
 			*oi->sizep = get_size_from_delta(p, &w_curs, tmp_pos);
 			if (*oi->sizep == 0) {
-				type = OBJ_BAD;
+				ret = -1;
 				goto out;
 			}
 		} else {
@@ -1625,7 +1626,7 @@ int packed_object_info(struct repository *r, struct packed_git *p,
 		if (offset_to_pack_pos(p, obj_offset, &pos) < 0) {
 			error("could not find object at offset %"PRIuMAX" "
 			      "in pack %s", (uintmax_t)obj_offset, p->pack_name);
-			type = OBJ_BAD;
+			ret = -1;
 			goto out;
 		}
 
@@ -1639,7 +1640,7 @@ int packed_object_info(struct repository *r, struct packed_git *p,
 		if (oi->typep)
 			*oi->typep = ptot;
 		if (ptot < 0) {
-			type = OBJ_BAD;
+			ret = -1;
 			goto out;
 		}
 	}
@@ -1649,7 +1650,7 @@ int packed_object_info(struct repository *r, struct packed_git *p,
 			if (get_delta_base_oid(p, &w_curs, curpos,
 					       oi->delta_base_oid,
 					       type, obj_offset) < 0) {
-				type = OBJ_BAD;
+				ret = -1;
 				goto out;
 			}
 		} else
@@ -1672,9 +1673,11 @@ int packed_object_info(struct repository *r, struct packed_git *p,
 		break;
 	}
 
+	ret = 0;
+
 out:
 	unuse_pack(&w_curs);
-	return type;
+	return ret;
 }
 
 static void *unpack_compressed_entry(struct packed_git *p,
@@ -2152,7 +2155,7 @@ int packfile_store_read_object_info(struct packfile_store *store,
 				    unsigned flags UNUSED)
 {
 	struct pack_entry e;
-	int rtype;
+	int ret;
 
 	if (!find_pack_entry(store->odb->repo, oid, &e))
 		return 1;
@@ -2164,8 +2167,8 @@ int packfile_store_read_object_info(struct packfile_store *store,
 	if (!oi)
 		return 0;
 
-	rtype = packed_object_info(store->odb->repo, e.p, e.offset, oi);
-	if (rtype < 0) {
+	ret = packed_object_info(store->odb->repo, e.p, e.offset, oi);
+	if (ret < 0) {
 		mark_bad_packed_object(e.p, oid);
 		return -1;
 	}

packfile.h

@@ -378,6 +378,10 @@ void release_pack_memory(size_t);
 /* global flag to enable extra checks when accessing packed objects */
 extern int do_check_packed_object_crc;
 
+/*
+ * Look up the object info for a specific offset in the packfile.
+ * Returns zero on success, a negative error code otherwise.
+ */
 int packed_object_info(struct repository *r,
 		       struct packed_git *pack,
 		       off_t offset, struct object_info *);