error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
  --> $DIR/return-from-residual-sugg-issue-125997.rs:10:44
   |
LL | fn test1() {
   | ---------- this function should return `Result` or `Option` to accept `?`
LL |     let mut _file = File::create("foo.txt")?;
   |                                            ^ cannot use the `?` operator in a function that returns `()`
   |
   = help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
help: consider adding return type
   |
LL ~ fn test1() -> Result<(), Box<dyn std::error::Error>> {
LL |     let mut _file = File::create("foo.txt")?;
LL |
LL +     Ok(())
   |

error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
  --> $DIR/return-from-residual-sugg-issue-125997.rs:15:44
   |
LL | fn test2() {
   | ---------- this function should return `Result` or `Option` to accept `?`
LL |     let mut _file = File::create("foo.txt")?;
   |                                            ^ cannot use the `?` operator in a function that returns `()`
   |
   = help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
help: consider adding return type
   |
LL ~ fn test2() -> Result<(), Box<dyn std::error::Error>> {
LL |     let mut _file = File::create("foo.txt")?;
LL |
LL |     println!();
LL +     Ok(())
   |

error[E0277]: the `?` operator can only be used in a method that returns `Result` or `Option` (or another type that implements `FromResidual`)
  --> $DIR/return-from-residual-sugg-issue-125997.rs:34:48
   |
LL |     fn test4(&self) {
   |     --------------- this function should return `Result` or `Option` to accept `?`
LL |         let mut _file = File::create("foo.txt")?;
   |                                                ^ cannot use the `?` operator in a method that returns `()`
   |
   = help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
help: consider adding return type
   |
LL ~     fn test4(&self) -> Result<(), Box<dyn std::error::Error>> {
LL |         let mut _file = File::create("foo.txt")?;
LL |
LL ~         Ok(())
LL ~     }
   |

error[E0277]: the `?` operator can only be used in a method that returns `Result` or `Option` (or another type that implements `FromResidual`)
  --> $DIR/return-from-residual-sugg-issue-125997.rs:39:48
   |
LL |     fn test5(&self) {
   |     --------------- this function should return `Result` or `Option` to accept `?`
LL |         let mut _file = File::create("foo.txt")?;
   |                                                ^ cannot use the `?` operator in a method that returns `()`
   |
   = help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
help: consider adding return type
   |
LL ~     fn test5(&self) -> Result<(), Box<dyn std::error::Error>> {
LL |         let mut _file = File::create("foo.txt")?;
LL |
LL |         println!();
LL ~         Ok(())
LL ~     }
   |

error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
  --> $DIR/return-from-residual-sugg-issue-125997.rs:46:44
   |
LL | fn main() {
   | --------- this function should return `Result` or `Option` to accept `?`
LL |     let mut _file = File::create("foo.txt")?;
   |                                            ^ cannot use the `?` operator in a function that returns `()`
   |
   = help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
help: consider adding return type
   |
LL ~ fn main() -> Result<(), Box<dyn std::error::Error>> {
LL |     let mut _file = File::create("foo.txt")?;
LL |
LL |     mac!();
LL +     Ok(())
   |

error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
  --> $DIR/return-from-residual-sugg-issue-125997.rs:23:52
   |
LL |         fn test3() {
   |         ---------- this function should return `Result` or `Option` to accept `?`
LL |             let mut _file = File::create("foo.txt")?;
   |                                                    ^ cannot use the `?` operator in a function that returns `()`
...
LL |     mac!();
   |     ------ in this macro invocation
   |
   = help: the trait `FromResidual<Result<Infallible, std::io::Error>>` is not implemented for `()`
   = note: this error originates in the macro `mac` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider adding return type
   |
LL ~         fn test3() -> Result<(), Box<dyn std::error::Error>> {
LL |             let mut _file = File::create("foo.txt")?;
LL |
LL |             println!();
LL ~             Ok(())
LL ~         }
   |

error: aborting due to 6 previous errors

For more information about this error, try `rustc --explain E0277`.