display the full path to the function if no MIR is found

src/interpreter/mod.rs

@@ -282,6 +282,7 @@ pub fn trait_method(
     }
 
     fn load_mir(&self, def_id: DefId) -> CachedMir<'a, 'tcx> {
+        use rustc_trans::back::symbol_names::def_id_to_string;
         match self.tcx.map.as_local_node_id(def_id) {
             Some(node_id) => CachedMir::Ref(self.mir_map.map.get(&node_id).unwrap()),
             None => {
@@ -292,7 +293,7 @@ fn load_mir(&self, def_id: DefId) -> CachedMir<'a, 'tcx> {
 
                 let cs = &self.tcx.sess.cstore;
                 let mir = cs.maybe_get_item_mir(self.tcx, def_id).unwrap_or_else(|| {
-                    panic!("no mir for {:?}", def_id);
+                    panic!("no mir for `{}`", def_id_to_string(self.tcx, def_id));
                 });
                 let cached = Rc::new(mir);
                 mir_cache.insert(def_id, cached.clone());

src/lib.rs

@@ -12,6 +12,7 @@
 // From rustc.
 #[macro_use] extern crate rustc;
 extern crate rustc_mir;
+extern crate rustc_trans;
 extern crate syntax;
 #[macro_use] extern crate log;
 extern crate log_settings;

tests/run-fail/inception.rs

-// error-pattern:no mir for DefId
+// error-pattern:no mir for `env_logger/
 
 use std::env;
 use std::process::{Command, Output};