"0 elided lifetimes" is confusing

[sanxiyn]

fn a() -> &i32 {
    panic!();
}
fn b(x: i32) -> &i32 {
    panic!();
}

test.rs:1:11: 1:15 help: this function's return type contains a borrowed value,
but there is no value for it to be borrowed from
test.rs:4:17: 4:21 help: this function's return type contains a borrowed value,
but the signature does not say which one of `x`'s 0 elided lifetimes it is borrowed from

Help for a is reasonable, but help for b is not. See also #22760.

[arielb1]

@sanxiyn

What would you prefer for an error message? Same as the previous one?

[sanxiyn]

Yes, same as the previous one would be an improvement.

[Manishearth]

Code:

rust/src/librustc_typeck/astconv.rs

Line 199 in 323781c

fn report_elision_failure(

The fix is basically to check for n == 0 in any of the elision failure cases and then show the second warning unconditionally in such a case.