6c3879d1f1
When a method chain ending in `?` causes an E0277 because the
expression's `Result::Err` variant doesn't have a type that can be
converted to the `Result<_, E>` type parameter in the return type,
provide additional context of which parts of the chain can and can't
support the `?` operator.
```
error[E0277]: `?` couldn't convert the error to `String`
--> $DIR/question-mark-result-err-mismatch.rs:28:25
|
LL | fn bar() -> Result<(), String> {
| ------------------ expected `String` because of this
LL | let x = foo();
| ----- this can be annotated with `?` because it has type `Result<String, String>`
LL | let one = x
LL | .map(|s| ())
| ----------- this can be annotated with `?` because it has type `Result<(), String>`
LL | .map_err(|_| ())?;
| ---------------^ the trait `From<()>` is not implemented for `String`
| |
| this can't be annotated with `?` because it has type `Result<(), ()>`
|
= note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
= help: the following other types implement trait `From<T>`:
<String as From<char>>
<String as From<Box<str>>>
<String as From<Cow<'a, str>>>
<String as From<&str>>
<String as From<&mut str>>
<String as From<&String>>
= note: required for `Result<(), String>` to implement `FromResidual<Result<Infallible, ()>>`
```
Fix #72124.
26 lines
1.1 KiB
Text
26 lines
1.1 KiB
Text
error[E0277]: `?` couldn't convert the error to `()`
|
|
--> $DIR/issue-32709.rs:4:11
|
|
|
|
|
LL | fn a() -> Result<i32, ()> {
|
|
| --------------- expected `()` because of this
|
|
LL | Err(5)?;
|
|
| ------^ the trait `From<{integer}>` is not implemented for `()`
|
|
| |
|
|
| this can't be annotated with `?` because it has type `Result<_, {integer}>`
|
|
|
|
|
= note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
|
|
= help: the following other types implement trait `From<T>`:
|
|
<(T,) as From<[T; 1]>>
|
|
<(T, T) as From<[T; 2]>>
|
|
<(T, T, T) as From<[T; 3]>>
|
|
<(T, T, T, T) as From<[T; 4]>>
|
|
<(T, T, T, T, T) as From<[T; 5]>>
|
|
<(T, T, T, T, T, T) as From<[T; 6]>>
|
|
<(T, T, T, T, T, T, T) as From<[T; 7]>>
|
|
<(T, T, T, T, T, T, T, T) as From<[T; 8]>>
|
|
and 4 others
|
|
= note: required for `Result<i32, ()>` to implement `FromResidual<Result<Infallible, {integer}>>`
|
|
|
|
error: aborting due to 1 previous error
|
|
|
|
For more information about this error, try `rustc --explain E0277`.
|