possible fix for commit-graph race issue

Alternative may be to fill in all trees when closing graph file.

Gross cast?

Author: peff

commit-graph.c

@@ -825,6 +825,9 @@ void close_commit_graph(struct object_database *o)
 	if (!o->commit_graph)
 		return;
 
+	/*
+	 * could fill blank maybe_tree here?
+	 */
 	clear_commit_graph_data_slab(&commit_graph_data_slab);
 	deinit_bloom_filters();
 	free_commit_graph(o->commit_graph);

commit.c

@@ -434,6 +434,27 @@ static inline void set_commit_tree(struct commit *c, struct tree *t)
 	c->maybe_tree = t;
 }
 
+static void load_tree_from_commit_contents(struct repository *r, struct commit *commit)
+{
+	enum object_type type;
+	unsigned long size;
+	char *buf;
+	const char *p;
+	struct object_id tree_oid;
+
+	buf = odb_read_object(r->objects, &commit->object.oid, &type, &size);
+	if (!buf)
+		return;
+
+	if (type == OBJ_COMMIT &&
+	    skip_prefix(buf, "tree ", &p) &&
+	    !parse_oid_hex(p, &tree_oid, &p) &&
+	    *p == '\n')
+		set_commit_tree(commit, lookup_tree(r, &tree_oid));
+
+	free(buf);
+}
+
 struct tree *repo_get_commit_tree(struct repository *r,
 				  const struct commit *commit)
 {
@@ -443,7 +464,16 @@ struct tree *repo_get_commit_tree(struct repository *r,
 	if (commit_graph_position(commit) != COMMIT_NOT_FROM_GRAPH)
 		return get_commit_tree_in_graph(r, commit);
 
-	return NULL;
+	/*
+	 * This is either a corrupt commit, or one which we partially loaded
+	 * from a graph file but then subsequently threw away the graph data.
+	 *
+	 * Optimistically assume it's the latter and try to reload from
+	 * scratch. This gives a performance penalty if it really is a corrupt
+	 * commit, but presumably that happens rarely.
+	 */
+	load_tree_from_commit_contents(r, (struct commit *)commit);
+	return commit->maybe_tree;
 }
 
 struct object_id *get_commit_tree_oid(const struct commit *commit)