fixme added

Author: KMJ-007

compiler/rustc_session/src/options.rs

@@ -1377,7 +1377,10 @@ pub mod parse {
                 "PrintPasses" => AutoDiff::PrintPasses,
                 "LooseTypes" => AutoDiff::LooseTypes,
                 "Inline" => AutoDiff::Inline,
-                _ => return false,
+                _ => {
+                    // FIXME(ZuseZ4): print an error saying which value is not recognized
+                    return false;
+                }
             };
             slot.push(variant);
         }