object_array: add a "clear" function

There's currently no easy way to free the memory associated
with an object_array (and in most cases, we simply leak the
memory in a rev_info's pending array). Let's provide a
helper to make this easier to handle.

We can make use of it in list-objects.c, which does the same
thing by hand (but fails to free the "name" field of each
entry, potentially leaking memory).
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

list-objects.c

@@ -228,11 +228,6 @@ void traverse_commit_list(struct rev_info *revs,
 		die("unknown pending object %s (%s)",
 		    sha1_to_hex(obj->sha1), name);
 	}
-	if (revs->pending.nr) {
-		free(revs->pending.objects);
-		revs->pending.nr = 0;
-		revs->pending.alloc = 0;
-		revs->pending.objects = NULL;
-	}
+	object_array_clear(&revs->pending);
 	strbuf_release(&base);
 }

object.c

@@ -383,6 +383,16 @@ void object_array_filter(struct object_array *array,
 	array->nr = dst;
 }
 
+void object_array_clear(struct object_array *array)
+{
+	int i;
+	for (i = 0; i < array->nr; i++)
+		object_array_release_entry(&array->objects[i]);
+	free(array->objects);
+	array->objects = NULL;
+	array->nr = array->alloc = 0;
+}
+
 /*
  * Return true iff array already contains an entry with name.
  */

object.h

@@ -133,6 +133,12 @@ void object_array_filter(struct object_array *array,
  */
 void object_array_remove_duplicates(struct object_array *array);
 
+/*
+ * Remove any objects from the array, freeing all used memory; afterwards
+ * the array is ready to store more objects with add_object_array().
+ */
+void object_array_clear(struct object_array *array);
+
 void clear_object_flags(unsigned flags);
 
 #endif /* OBJECT_H */