error: failed to find an overloaded call trait for closure call --> $DIR/fn-fn_mut-call-ill-formed.rs:39:5 | LL | a(); | ^^^ | = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods error: failed to find an overloaded call trait for closure call --> $DIR/fn-fn_mut-call-ill-formed.rs:43:5 | LL | b(); | ^^^ | = help: make sure the `fn`/`fn_mut`/`fn_once` lang items are defined and have correctly defined `call`/`call_mut`/`call_once` methods error: aborting due to 2 previous errors