--- a/rust/hg-cpython/src/exceptions.rs	Thu Jan 10 10:23:22 2019 -0500
+++ b/rust/hg-cpython/src/exceptions.rs	Sat Dec 22 11:38:03 2018 +0100
@@ -1,3 +1,15 @@
+// ancestors.rs
+//
+// Copyright 2018 Georges Racinet <gracinet@anybox.fr>
+//
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2 or any later version.
+
+//! Bindings for Rust errors
+//!
+//! [`GraphError`] exposes `hg::GraphError` as a subclass of `ValueError`
+//!
+//! [`GraphError`]: struct.GraphError.html
 use cpython::exc::ValueError;
 use cpython::{PyErr, Python};
 use hg;