t/helper/test-read-midx.c: add '--show-objects'

The 'read-midx' helper is used in places like t5319 to display basic
information about a multi-pack-index.

In the next patch, the MIDX writing machinery will learn a new way to
choose from which pack an object is selected when multiple copies of
that object exist.

To disambiguate which pack introduces an object so that this feature can
be tested, add a '--show-objects' option which displays additional
information about each object in the MIDX.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/helper/test-read-midx.c

@@ -4,7 +4,7 @@
 #include "repository.h"
 #include "object-store.h"
 
-static int read_midx_file(const char *object_dir)
+static int read_midx_file(const char *object_dir, int show_objects)
 {
 	uint32_t i;
 	struct multi_pack_index *m;
@@ -43,13 +43,29 @@ static int read_midx_file(const char *object_dir)
 
 	printf("object-dir: %s\n", m->object_dir);
 
+	if (show_objects) {
+		struct object_id oid;
+		struct pack_entry e;
+
+		for (i = 0; i < m->num_objects; i++) {
+			nth_midxed_object_oid(&oid, m, i);
+			fill_midx_entry(the_repository, &oid, &e, m);
+
+			printf("%s %"PRIu64"\t%s\n",
+			       oid_to_hex(&oid), e.offset, e.p->pack_name);
+		}
+		return 0;
+	}
+
 	return 0;
 }
 
 int cmd__read_midx(int argc, const char **argv)
 {
-	if (argc != 2)
-		usage("read-midx <object-dir>");
+	if (!(argc == 2 || argc == 3))
+		usage("read-midx [--show-objects] <object-dir>");
 
-	return read_midx_file(argv[1]);
+	if (!strcmp(argv[1], "--show-objects"))
+		return read_midx_file(argv[2], 1);
+	return read_midx_file(argv[1], 0);
 }