Use bug! instead of panic!

Co-authored-by: varkor <github@varkor.com>

src/librustc_typeck/astconv.rs

@@ -489,7 +489,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             "lifetime" => ParamKindOrd::Lifetime,
             "type" => ParamKindOrd::Type,
             "constant" => ParamKindOrd::Const,
-            _ => panic!(),
+            // It's more concise to match on the string representation, though it means
+            // the match is non-exhaustive.
+            _ => bug!("invalid generic parameter kind"),
         };
         let arg_ord = match arg {
             GenericArg::Lifetime(_) => ParamKindOrd::Lifetime,