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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`.
22 lines
909 B
Plaintext
22 lines
909 B
Plaintext
error[E0277]: the `?` operator can only be used on `Result`s, not `Option`s, in a function that returns `Result`
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--> $DIR/try-on-option.rs:5:6
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LL | fn foo() -> Result<u32, ()> {
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| --------------------------- this function returns a `Result`
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LL | let x: Option<u32> = None;
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LL | x?;
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| ^ use `.ok_or(...)?` to provide an error compatible with `Result<u32, ()>`
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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-on-option.rs:11:6
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LL | fn bar() -> u32 {
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| --------------- this function should return `Result` or `Option` to accept `?`
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LL | let x: Option<u32> = None;
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LL | x?;
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| ^ cannot use the `?` operator in a function that returns `u32`
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error: aborting due to 2 previous errors
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For more information about this error, try `rustc --explain E0277`.
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