Hide <...> defined here note if the source is not available

compiler/rustc_typeck/src/structured_errors/wrong_number_of_generic_args.rs

@@ -731,7 +731,11 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
     /// Builds the `type defined here` message.
     fn show_definition(&self, err: &mut DiagnosticBuilder<'_>) {
         let mut spans: MultiSpan = if let Some(def_span) = self.tcx.def_ident_span(self.def_id) {
-            def_span.into()
+            if self.tcx.sess.source_map().span_to_snippet(def_span).is_ok() {
+                def_span.into()
+            } else {
+                return;
+            }
         } else {
             return;
         };