Ambiguous elided lifetime error claims non-elided lifetime is elided

[wthrowe]

struct Thing<'a>(&'a ());

fn func1<'a>(_arg: &'a Thing) -> &() { unimplemented!() }
fn func2<'a>(_arg: &Thing<'a>) -> &() { unimplemented!() }

gives

test.rs:3:34: 3:37 error: missing lifetime specifier [E0106]
test.rs:3 fn func1<'a>(_arg: &'a Thing) -> &() { unimplemented!() }
                                           ^~~
test.rs:3:34: 3:37 help: run `rustc --explain E0106` to see a detailed explanation
test.rs:3:34: 3:37 help: this function's return type contains a borrowed value, but the signature does not say which one of `_arg`'s 2 elided lifetimes it is borrowed from
test.rs:4:35: 4:38 error: missing lifetime specifier [E0106]
test.rs:4 fn func2<'a>(_arg: &Thing<'a>) -> &() { unimplemented!() }
                                            ^~~
test.rs:4:35: 4:38 help: run `rustc --explain E0106` to see a detailed explanation
test.rs:4:35: 4:38 help: this function's return type contains a borrowed value, but the signature does not say which one of `_arg`'s 2 elided lifetimes it is borrowed from
error: aborting due to 2 previous errors

Each time it refers to "_arg's 2 elided lifetimes", but in both cases only one of _arg's lifetimes is elided.

[arielb1]

We should just remove the "elided" - the rules work (and always worked) for all lifetimes.

[Mark-Simulacrum]

E-easy/E-mentor. The code needs to be updated here to remove elided. A few tests will then fail, probably src/test/compile-fail/issue-26638.rs, src/test/compile-fail/issue-30255.rs, and src/test/compile-fail/lifetime-elision-return-type-requires-explicit-lifetime.rs which will need to be updated to remove the word elided as well.

Let us know if you'd like to work on this, or if you have any questions; we'll be happy to help.

[stephen-lazaro]

I'd be happy to take a shot at this over the weekend if no one else is interested, doesn't look like too much of a brain teaser. :)

[Mark-Simulacrum]

Go ahead! Let us know if there's anything we can do to help you out.

./x.py test --incremental src/test/compile-fail is probably your best bet for compiling and testing in this case.

[Mark-Simulacrum]

Reopening per #42415 (comment).

[steveklabnik]

Triage: the error today:

Compiling playground v0.0.1 (/playground)
error[E0106]: missing lifetime specifier
 --> src/lib.rs:3:34
  |
3 | fn func1<'a>(_arg: &'a Thing) -> &() { unimplemented!() }
  |                                  ^ expected lifetime parameter
  |
  = help: this function's return type contains a borrowed value, but the signature does not say which one of `_arg`'s 2 lifetimes it is borrowed from

error[E0106]: missing lifetime specifier
 --> src/lib.rs:4:35
  |
4 | fn func2<'a>(_arg: &Thing<'a>) -> &() { unimplemented!() }
  |                                   ^ expected lifetime parameter
  |
  = help: this function's return type contains a borrowed value, but the signature does not say which one of `_arg`'s 2 lifetimes it is borrowed from

error: aborting due to 2 previous errors

It still does not suggest 'a, so keeping open as per @estebank 's comment.