error[E0308]: mismatched types
  --> $DIR/coerce-result-return-value-2.rs:8:17
   |
LL | fn foo4(x: Result<(), A>) -> Result<(), B> {
   |                              ------------- expected `Result<(), B>` because of return type
LL |     match true {
LL |         true => x,
   |                 ^ expected `Result<(), B>`, found `Result<(), A>`
   |
   = note: expected enum `Result<_, B>`
              found enum `Result<_, A>`
help: use `?` to coerce and return an appropriate `Err`, and wrap the resulting value in `Ok` so the expression remains of type `Result`
   |
LL |         true => Ok(x?),
   |                 +++ ++

error[E0308]: mismatched types
  --> $DIR/coerce-result-return-value-2.rs:14:24
   |
LL | fn foo5(x: Result<(), A>) -> Result<(), B> {
   |                              ------------- expected `Result<(), B>` because of return type
LL |     match true {
LL |         true => return x,
   |                        ^ expected `Result<(), B>`, found `Result<(), A>`
   |
   = note: expected enum `Result<_, B>`
              found enum `Result<_, A>`
help: use `?` to coerce and return an appropriate `Err`, and wrap the resulting value in `Ok` so the expression remains of type `Result`
   |
LL |         true => return Ok(x?),
   |                        +++ ++

error[E0308]: mismatched types
  --> $DIR/coerce-result-return-value-2.rs:21:28
   |
LL |       let _: Result<(), B> = {
   |  ____________________________^
LL | |         Err(A);
LL | |     };
   | |_____^ expected `Result<(), B>`, found `()`
   |
   = note:   expected enum `Result<(), B>`
           found unit type `()`

error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0308`.