error[E0053]: method `call_once` has an incompatible type for trait --> $DIR/issue-15094.rs:11:5 | LL | fn call_once(self, _args: ()) { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected "rust-call" fn, found "Rust" fn | = note: expected signature `extern "rust-call" fn(Debuger<_>, ())` found signature `fn(Debuger<_>, ())` error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0053`.