improve message from broken builtin config

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

diff --git a/src/config.rs b/src/config.rs
index abdc573fd1c12d7783be7b5311e4c339c4391929..56abf1d7086e90459e458ba8d25d8a39660c733e 100644 (file)
--- a/src/config.rs
+++ b/src/config.rs
@@ -856,7 +856,8 @@ pub fn read(opts: &Opts, end: LinkEnd) -> Vec<InstanceConfig> {
     );
 
     agg.read_string(DEFAULT_CONFIG.into(),
-                    "<build-in defaults>".as_ref()).unwrap();
+                    "<build-in defaults>".as_ref())
+      .expect("builtin configuration is broken");
 
     agg.read_toplevel(&opts.config)?;
     for extra in &opts.extra_config {