replace old literal in expr

src/librustc_typeck/check/demand.rs

@@ -422,7 +422,12 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             let suffix_suggestion = format!(
                 "{}{}{}{}",
                 if needs_paren { "(" } else { "" },
-                src,
+                {
+                    // 42u8
+                    // ^^
+                    let lit_offset = src.len() - checked_ty.to_string().len();
+                    &src[..lit_offset]
+                },
                 expected_ty,
                 if needs_paren { ")" } else { "" },
             );