Merge branch 'sg/object-as-type-commit-graph-fix'

The commit-graph facility did not work when in-core objects that
are promoted from unknown type to commit (e.g. a commit that is
accessed via a tag that refers to it) were involved, which has been
corrected.

* sg/object-as-type-commit-graph-fix:
  object_as_type: initialize commit-graph-related fields of 'struct commit'

alloc.c

@@ -99,18 +99,23 @@ void *alloc_object_node(struct repository *r)
 	return obj;
 }
-unsigned int alloc_commit_index(struct repository *r)
+static unsigned int alloc_commit_index(struct repository *r)
 {
 	return r->parsed_objects->commit_count++;
 }
-void *alloc_commit_node(struct repository *r)
+void init_commit_node(struct repository *r, struct commit *c)
 {
-	struct commit *c = alloc_node(r->parsed_objects->commit_state, sizeof(struct commit));
 	c->object.type = OBJ_COMMIT;
 	c->index = alloc_commit_index(r);
 	c->graph_pos = COMMIT_NOT_FROM_GRAPH;
 	c->generation = GENERATION_NUMBER_INFINITY;
+}
+
+void *alloc_commit_node(struct repository *r)
+{
+	struct commit *c = alloc_node(r->parsed_objects->commit_state, sizeof(struct commit));
+	init_commit_node(r, c);
 	return c;
 }

alloc.h

@@ -9,11 +9,11 @@ struct repository;
 void *alloc_blob_node(struct repository *r);
 void *alloc_tree_node(struct repository *r);
+void init_commit_node(struct repository *r, struct commit *c);
 void *alloc_commit_node(struct repository *r);
 void *alloc_tag_node(struct repository *r);
 void *alloc_object_node(struct repository *r);
 void alloc_report(struct repository *r);
-unsigned int alloc_commit_index(struct repository *r);
 struct alloc_state *allocate_alloc_state(void);
 void clear_alloc_state(struct alloc_state *s);

object.c

@@ -164,8 +164,9 @@ void *object_as_type(struct repository *r, struct object *obj, enum object_type
 		return obj;
 	else if (obj->type == OBJ_NONE) {
 		if (type == OBJ_COMMIT)
-			((struct commit *)obj)->index = alloc_commit_index(r);
-		obj->type = type;
+			init_commit_node(r, (struct commit *) obj);
+		else
+			obj->type = type;
 		return obj;
 	}
 	else {