syntax: Do not accidentally treat multi-segment meta-items as single-segment

src/libsyntax/test.rs

@@ -438,6 +438,9 @@ fn get_test_runner(sd: &errors::Handler, krate: &ast::Crate) -> Option<ast::Path
             sd.span_fatal(test_attr.span(),
                 "#![test_runner(..)] accepts exactly 1 argument").raise()
         }
-        meta_list[0].word().as_ref().unwrap().ident.clone()
+        match meta_list[0].meta_item() {
+            Some(meta_item) if meta_item.is_word() => meta_item.ident.clone(),
+            _ => sd.span_fatal(test_attr.span, "`test_runner` argument must be a path").raise()
+        }
     })
 }