error: implementation of `FnOnce` is not general enough --> $DIR/issue-30906.rs:18:5 | LL | test(Compose(f, |_| {})); | ^^^^ implementation of `FnOnce` is not general enough | = note: `fn(&'2 str) -> T` must implement `FnOnce<(&'1 str,)>`, for any lifetime `'1`... = note: ...but it actually implements `FnOnce<(&'2 str,)>`, for some specific lifetime `'2` error: aborting due to previous error