builtin/pack-objects: avoid using struct object_id for pack hash

We use struct object_id for the names of objects.  It isn't intended to
be used for other hash values that don't name objects such as the pack
hash.

Because struct object_id will soon need to have its algorithm member
set, using it in this code path would mean that we didn't set that
member, only the hash member, which would result in a crash.  For both
of these reasons, switch to using an unsigned char array of size
GIT_MAX_RAWSZ.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/pack-objects.c

@@ -1030,7 +1030,7 @@ static void write_pack_file(void)
 	write_order = compute_write_order();
 
 	do {
-		struct object_id oid;
+		unsigned char hash[GIT_MAX_RAWSZ];
 		char *pack_tmp_name = NULL;
 
 		if (pack_to_stdout)
@@ -1059,13 +1059,13 @@ static void write_pack_file(void)
 		 * If so, rewrite it like in fast-import
 		 */
 		if (pack_to_stdout) {
-			finalize_hashfile(f, oid.hash, CSUM_HASH_IN_STREAM | CSUM_CLOSE);
+			finalize_hashfile(f, hash, CSUM_HASH_IN_STREAM | CSUM_CLOSE);
 		} else if (nr_written == nr_remaining) {
-			finalize_hashfile(f, oid.hash, CSUM_HASH_IN_STREAM | CSUM_FSYNC | CSUM_CLOSE);
+			finalize_hashfile(f, hash, CSUM_HASH_IN_STREAM | CSUM_FSYNC | CSUM_CLOSE);
 		} else {
-			int fd = finalize_hashfile(f, oid.hash, 0);
-			fixup_pack_header_footer(fd, oid.hash, pack_tmp_name,
-						 nr_written, oid.hash, offset);
+			int fd = finalize_hashfile(f, hash, 0);
+			fixup_pack_header_footer(fd, hash, pack_tmp_name,
+						 nr_written, hash, offset);
 			close(fd);
 			if (write_bitmap_index) {
 				if (write_bitmap_index != WRITE_BITMAP_QUIET)
@@ -1100,17 +1100,17 @@ static void write_pack_file(void)
 			strbuf_addf(&tmpname, "%s-", base_name);
 
 			if (write_bitmap_index) {
-				bitmap_writer_set_checksum(oid.hash);
+				bitmap_writer_set_checksum(hash);
 				bitmap_writer_build_type_index(
 					&to_pack, written_list, nr_written);
 			}
 
 			finish_tmp_packfile(&tmpname, pack_tmp_name,
 					    written_list, nr_written,
-					    &pack_idx_opts, oid.hash);
+					    &pack_idx_opts, hash);
 
 			if (write_bitmap_index) {
-				strbuf_addf(&tmpname, "%s.bitmap", oid_to_hex(&oid));
+				strbuf_addf(&tmpname, "%s.bitmap", hash_to_hex(hash));
 
 				stop_progress(&progress_state);
 
@@ -1124,7 +1124,7 @@ static void write_pack_file(void)
 
 			strbuf_release(&tmpname);
 			free(pack_tmp_name);
-			puts(oid_to_hex(&oid));
+			puts(hash_to_hex(hash));
 		}
 
 		/* mark written objects as written to previous pack */