remove expect() in unnecessary_transmutes

Author: bend-n

compiler/rustc_mir_transform/src/check_unnecessary_transmutes.rs

@@ -27,7 +27,7 @@ impl<'a, 'tcx> UnnecessaryTransmuteChecker<'a, 'tcx> {
     fn is_unnecessary_transmute(
         &self,
         function: &Operand<'tcx>,
-        arg: String,
+        arg: &str,
         span: Span,
     ) -> Option<Error> {
         let fn_sig = function.ty(self.body, self.tcx).fn_sig(self.tcx).skip_binder();
@@ -89,7 +89,7 @@ impl<'tcx> Visitor<'tcx> for UnnecessaryTransmuteChecker<'_, 'tcx> {
             && let span = self.body.source_info(location).span
             && let Some(lint) = self.is_unnecessary_transmute(
                 func,
-                self.tcx.sess.source_map().span_to_snippet(arg).expect("ok"),
+                self.tcx.sess.source_map().span_to_snippet(arg).as_deref().unwrap_or("…"),
                 span,
             )
             && let Some(hir_id) = terminator.source_info.scope.lint_root(&self.body.source_scopes)