1 error[E0121]: the placeholder `_` is not allowed within types on item signatures for return types
2 --> $DIR/issue-98260.rs:3:27
4 LL | fn a(aa: B) -> Result<_, B> {
7 | | not allowed in type signatures
8 | help: replace with the correct return type: `Result<(), B>`
10 error: aborting due to previous error
12 For more information about this error, try `rustc --explain E0121`.