[bug] -> _ inference fails for &'static str

[oriongonza]

rust-analyzer version: 2023-12-18

rustc version: 1.76

fn infer() -> _ {
    "hi"
}

Has the correct code action (3) but if we choose 2 we get

fn infer() -> &str {
    "hi"
}

which doesn't compile.

[Young-Flash]

related to add_return_type assist

[oriongonza]

similar result for

fn test<'a, 'b>(a: &'a u8, b: &'b u8) -> _ {
    b
}

However for this

struct S<'a>(&'a u8);
fn test(s: S) -> _ {
    s
}

There are two code actions:

1. Add this function return type: S<'_> (good)
2. Replace with the correct return type: S<'static> (?)

[lnicola]

"replace with the correct return type: S<'static>" is from cargo check.

[oriongonza]

Is that a rustc "error" (?) then?

[lnicola]

Try cargo check on that code and you'll see what I mean.

[oriongonza]

Yes, I know what you mean but the fact that there is a difference between cargo check and r-a should be considered a bug, right?

[lnicola]

Maybe. The rust-analyzer diagnostics and assists are completely separate from the ones in the compiler. Most of the time they're worse, but I've seen cases where the RA fixes were better than the compiler's.

In this case I suspect RA gets it right mostly by accident.