rust/tests/ui/async-await/issue-67765-async-diagnostic.rs

// edition:2018
//
// Regression test for issue #67765
// Tests that we point at the proper location when giving
// a lifetime error.
fn main() {}

async fn func<'a>() -> Result<(), &'a str> {
    let s = String::new();

    let b = &s[..];

    Err(b)?; //~ ERROR cannot return value referencing local variable `s`

    Ok(())
}
Use an 'approximate' universal upper bound when reporting region errors Fixes #67765 When reporting errors during MIR region inference, we sometimes use `universal_upper_bound` to obtain a named universal region that we can display to the user. However, this is not always possible - in a case like `fn foo<'a, 'b>() { .. }`, the only upper bound for a region containing `'a` and `'b` is `'static`. When displaying diagnostics, it's usually better to display some named region (even if there are multiple involved) rather than fall back to a generic error involving `'static`. This commit adds a new `approx_universal_upper_bound` method, which uses the lowest-numbered universal region if the only alternative is to return `'static`. 2020-06-27 13:54:56 -04:00			`// edition:2018`
			`//`
			`// Regression test for issue #67765`
			`// Tests that we point at the proper location when giving`
			`// a lifetime error.`
			`fn main() {}`

			`async fn func<'a>() -> Result<(), &'a str> {`
			`let s = String::new();`

			`let b = &s[..];`

			Err(b)?; //~ ERROR cannot return value referencing local variable `s`

			`Ok(())`
			`}`