error[E0308]: mismatched types
  --> $DIR/coerce-result-return-value.rs:8:5
   |
LL | fn foo1(x: Result<(), A>) -> Result<(), B> {
   |                              ------------- expected `Result<(), B>` because of return type
LL |     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 |     Ok(x?)
   |     +++ ++

error[E0308]: mismatched types
  --> $DIR/coerce-result-return-value.rs:11:12
   |
LL | fn foo2(x: Result<(), A>) -> Result<(), B> {
   |                              ------------- expected `Result<(), B>` because of return type
LL |     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 |     return Ok(x?);
   |            +++ ++

error[E0308]: mismatched types
  --> $DIR/coerce-result-return-value.rs:15:9
   |
LL | fn foo3(x: Result<(), A>) -> Result<(), B> {
   |                              ------------- expected `Result<(), B>` because of return type
LL |     if true {
LL |         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 |         Ok(x?)
   |         +++ ++

error[E0308]: mismatched types
  --> $DIR/coerce-result-return-value.rs:17:9
   |
LL | fn foo3(x: Result<(), A>) -> Result<(), B> {
   |                              ------------- expected `Result<(), B>` because of return type
...
LL |         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 |         Ok(x?)
   |         +++ ++

error: aborting due to 4 previous errors

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