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#13354 diagnose some incorrect usages of the question mark operator creates incorrect error #13429

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DaughterOfMars opened this issue Oct 17, 2022 · 2 comments · Fixed by #13433
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#13354 diagnose some incorrect usages of the question mark operator creates incorrect error #13429

DaughterOfMars opened this issue Oct 17, 2022 · 2 comments · Fixed by #13433
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A-ty type system / type inference / traits / method resolution

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@DaughterOfMars
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DaughterOfMars commented Oct 17, 2022 •
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The changes made by #13354 cause the following incorrect error in this minimal example using axum:

use axum::{routing::get, Router, Server};

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    Server::bind(&([0, 0, 0, 0], 8080).into())
        .serve(
            Router::new()
                .route("test", get(|| async { "hello" }))
                .into_make_service(),
        )
        .await?;

    Ok(())
}
the trait `Try` is not implemented for `_`rust-analyzer[not-implemented](https://rust-analyzer.github.io/manual.html#not-implemented)

rust-analyzer version: 0.3.1248-standalone (0531aab52 2022-10-16)

rustc version: rustc 1.66.0-nightly (a37499ae6 2022-09-18)
@Veykril
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Veykril commented Oct 17, 2022

Ah dammit, the type of the {...}.await expression is <Server<AddrIncoming, IntoMakeService<Router<Body>>, Exec> as IntoFuture>::Output, that is r-a can't deduce it, so it fails to figure out that the trait is implemented for it. @flodiebold is there an easy way to check whether we fail to solve a projection so that I can skip out on emitting the diagnostic for that?

@Veykril Veykril added the A-ty type system / type inference / traits / method resolution label Oct 17, 2022
@lnicola lnicola mentioned this issue Oct 17, 2022
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@flodiebold
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Hmm yeah this is the general "preventing follow-up errors" problem. I don't think you can really tell from the type that there was a problem, since these placeholders can also occur legitimately, but looking for placeholders and error types might be the best approach for now.

@Veykril Veykril mentioned this issue Oct 18, 2022
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Revert "feat: Diagnose some incorrect usages of the question mark operator" rust-lang/rust-analyzer
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@flodiebold @Veykril @DaughterOfMars