pack-objects: use object_id struct in pack-reuse code

When the pack-reuse code is dumping an OFS_DELTA entry to a client that
doesn't support it, we re-write it as a REF_DELTA. To do so, we use
nth_packed_object_sha1() to get the oid, but that function is soon going
away in favor of the more type-safe nth_packed_object_id(). Let's switch
now in preparation.

Note that this does incur an extra hash copy (from the pack idx mmap to
the object_id and then to the output, rather than straight from mmap to
the output). But this is not worth worrying about. It's probably not
measurable even when it triggers, and this is fallback code that we
expect to trigger very rarely (since everybody supports OFS_DELTA these
days anyway).

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

builtin/pack-objects.c

@@ -872,14 +872,15 @@ static void write_reused_pack_one(size_t pos, struct hashfile *out,
 		/* Convert to REF_DELTA if we must... */
 		if (!allow_ofs_delta) {
 			int base_pos = find_revindex_position(reuse_packfile, base_offset);
-			const unsigned char *base_sha1 =
-				nth_packed_object_sha1(reuse_packfile,
-						       reuse_packfile->revindex[base_pos].nr);
+			struct object_id base_oid;
+
+			nth_packed_object_id(&base_oid, reuse_packfile,
+					     reuse_packfile->revindex[base_pos].nr);
 
 			len = encode_in_pack_object_header(header, sizeof(header),
 							   OBJ_REF_DELTA, size);
 			hashwrite(out, header, len);
-			hashwrite(out, base_sha1, 20);
+			hashwrite(out, base_oid.hash, 20);
 			copy_pack_data(out, reuse_packfile, w_curs, cur, next - cur);
 			return;
 		}