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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`.
111 lines
4.3 KiB
Plaintext
111 lines
4.3 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/return-from-residual-sugg-issue-125997.rs:10:44
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LL | fn test1() {
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| ---------- this function should return `Result` or `Option` to accept `?`
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LL | let mut _file = File::create("foo.txt")?;
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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 test1() -> Result<(), Box<dyn std::error::Error>> {
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LL | let mut _file = File::create("foo.txt")?;
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LL |
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LL + Ok(())
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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/return-from-residual-sugg-issue-125997.rs:15:44
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LL | fn test2() {
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| ---------- this function should return `Result` or `Option` to accept `?`
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LL | let mut _file = File::create("foo.txt")?;
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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 test2() -> Result<(), Box<dyn std::error::Error>> {
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LL | let mut _file = File::create("foo.txt")?;
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LL |
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LL | println!();
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LL + Ok(())
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error[E0277]: the `?` operator can only be used in a method that returns `Result` or `Option` (or another type that implements `FromResidual`)
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--> $DIR/return-from-residual-sugg-issue-125997.rs:34:48
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LL | fn test4(&self) {
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| --------------- this function should return `Result` or `Option` to accept `?`
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LL | let mut _file = File::create("foo.txt")?;
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| ^ cannot use the `?` operator in a method that returns `()`
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help: consider adding return type
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LL ~ fn test4(&self) -> Result<(), Box<dyn std::error::Error>> {
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LL | let mut _file = File::create("foo.txt")?;
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LL |
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LL ~ Ok(())
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LL ~ }
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error[E0277]: the `?` operator can only be used in a method that returns `Result` or `Option` (or another type that implements `FromResidual`)
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--> $DIR/return-from-residual-sugg-issue-125997.rs:39:48
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LL | fn test5(&self) {
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| --------------- this function should return `Result` or `Option` to accept `?`
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LL | let mut _file = File::create("foo.txt")?;
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| ^ cannot use the `?` operator in a method that returns `()`
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help: consider adding return type
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LL ~ fn test5(&self) -> Result<(), Box<dyn std::error::Error>> {
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LL | let mut _file = File::create("foo.txt")?;
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LL |
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LL | println!();
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LL ~ Ok(())
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LL ~ }
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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/return-from-residual-sugg-issue-125997.rs:46:44
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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 | let mut _file = File::create("foo.txt")?;
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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 | let mut _file = File::create("foo.txt")?;
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LL |
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LL | mac!();
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LL + Ok(())
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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/return-from-residual-sugg-issue-125997.rs:23:52
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LL | fn test3() {
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| ---------- this function should return `Result` or `Option` to accept `?`
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LL | let mut _file = File::create("foo.txt")?;
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| ^ cannot use the `?` operator in a function that returns `()`
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...
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LL | mac!();
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| ------ in this macro invocation
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= note: this error originates in the macro `mac` (in Nightly builds, run with -Z macro-backtrace for more info)
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help: consider adding return type
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LL ~ fn test3() -> Result<(), Box<dyn std::error::Error>> {
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LL | let mut _file = File::create("foo.txt")?;
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LL |
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LL | println!();
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LL ~ Ok(())
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LL ~ }
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error: aborting due to 6 previous errors
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For more information about this error, try `rustc --explain E0277`.
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