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Dylan DPC
0740015d59
Fix suggestions for missing return type lifetime specifiers This pull request aims to fix #84592. The issue is that the current code seems to assume that there is only a single relevant span pointing to the missing lifetime, and only looks at the first one: https://github.com/rust-lang/rust/blob/e5f83d24aee866a14753a7cedbb4e301dfe5bef5/compiler/rustc_resolve/src/late/lifetimes.rs#L2959 This is incorrect, though, and leads to incorrect error messages and invalid suggestions. For instance, the example from #84592: ```rust struct TwoLifetimes<'x, 'y> { x: &'x (), y: &'y (), } fn two_lifetimes_needed(a: &(), b: &()) -> TwoLifetimes<'_, '_> { TwoLifetimes { x: &(), y: &() } } ``` currently leads to: ``` error[E0106]: missing lifetime specifiers --> src/main.rs:6:57 | 6 | fn two_lifetimes_needed(a: &(), b: &()) -> TwoLifetimes<'_, '_> { | --- --- ^^ expected 2 lifetime parameters | = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `a` or `b` help: consider introducing a named lifetime parameter | 6 | fn two_lifetimes_needed<'a>(a: &'a (), b: &'a ()) -> TwoLifetimes<'_<'a, 'a>, '_> { | ^^^^ ^^^^^^ ^^^^^^ ^^^^^^^^^^ ``` There are two problems: - The error message is wrong. There is only _one_ lifetime parameter expected at the location pointed to by the error message (and another one at a separate location). - The suggestion is incorrect and will not lead to correct code. With the changes in this PR, I get the following output: ``` error[E0106]: missing lifetime specifiers --> p.rs:6:57 | 6 | fn two_lifetimes_needed(a: &(), b: &()) -> TwoLifetimes<'_, '_> { | --- --- ^^ ^^ expected named lifetime parameter | | | expected named lifetime parameter | = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `a` or `b` help: consider introducing a named lifetime parameter | 6 | fn two_lifetimes_needed<'a>(a: &'a (), b: &'a ()) -> TwoLifetimes<'a, 'a> { | ^^^^ ^^^^^^ ^^^^^^ ^^ ^^ error: aborting due to previous error For more information about this error, try `rustc --explain E0106`. ``` Mainly, I changed `add_missing_lifetime_specifiers_label()` to receive a _vector_ of spans (and counts) instead of just one, and adjusted its body accordingly.