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When a `?` operation requires an `Into` conversion with additional bounds (like having a concrete error but wanting to convert to a trait object), we handle it speficically and provide the same kind of information we give other `?` related errors.
```
error[E0277]: `?` couldn't convert the error: `E: std::error::Error` is not satisfied
--> $DIR/bad-question-mark-on-trait-object.rs:5:13
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LL | fn foo() -> Result<(), Box<dyn std::error::Error>> {
| -------------------------------------- required `E: std::error::Error` because of this
LL | Ok(bar()?)
| ^ the trait `std::error::Error` is not implemented for `E`
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= note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
= note: required for `Box<dyn std::error::Error>` to implement `From<E>`
```
Avoid talking about `FromResidual` when other more relevant information is being given, particularly from `rust_on_unimplemented`.
59 lines
2.1 KiB
Plaintext
59 lines
2.1 KiB
Plaintext
error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
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--> $DIR/try-operator-on-main.rs:7:31
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LL | fn main() {
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| --------- this function should return `Result` or `Option` to accept `?`
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LL | // error for a `Try` type on a non-`Try` fn
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LL | std::fs::File::open("foo")?;
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| ^ cannot use the `?` operator in a function that returns `()`
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help: consider adding return type
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LL ~ fn main() -> Result<(), Box<dyn std::error::Error>> {
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LL | // error for a `Try` type on a non-`Try` fn
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...
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LL | try_trait_generic::<()>();
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LL + Ok(())
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error[E0277]: the `?` operator can only be applied to values that implement `Try`
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--> $DIR/try-operator-on-main.rs:10:5
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LL | ()?;
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| ^^^ the `?` operator cannot be applied to type `()`
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= help: the trait `Try` is not implemented for `()`
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error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
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--> $DIR/try-operator-on-main.rs:10:7
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LL | fn main() {
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| --------- this function should return `Result` or `Option` to accept `?`
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...
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LL | ()?;
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| ^ cannot use the `?` operator in a function that returns `()`
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error[E0277]: the trait bound `(): Try` is not satisfied
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--> $DIR/try-operator-on-main.rs:14:25
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LL | try_trait_generic::<()>();
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| ^^ the trait `Try` is not implemented for `()`
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note: required by a bound in `try_trait_generic`
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--> $DIR/try-operator-on-main.rs:17:25
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LL | fn try_trait_generic<T: Try>() -> T {
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| ^^^ required by this bound in `try_trait_generic`
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error[E0277]: the `?` operator can only be applied to values that implement `Try`
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--> $DIR/try-operator-on-main.rs:19:5
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LL | ()?;
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| ^^^ the `?` operator cannot be applied to type `()`
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= help: the trait `Try` is not implemented for `()`
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error: aborting due to 5 previous errors
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For more information about this error, try `rustc --explain E0277`.
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