procedural macro + anyhow macro causes type-mismatch: expected Result<{unknown}, Error>, found ()

[ivan]

Rust nightly accepts this code, but rust-analyzer is confused by the combination of a procedural macro (futures_async_stream::try_stream) and an anyhow macro:

[package]
name = "ra-proc-macro-type-issue"
version = "0.1.0"
edition = "2021"

[dependencies]
anyhow = "1.0"
futures = "0.3"
futures-async-stream = "0.2"

#![feature(
    generators,
    proc_macro_hygiene,
    stmt_expr_attributes,
)]

use anyhow::{Error, bail};
use futures::stream::BoxStream;
use futures_async_stream::try_stream;

fn minimized_try_stream() -> BoxStream<'static, Result<String, Error>> {
    Box::pin(
        #[try_stream]
        async move {
            if false {
                bail!("bye");
            }
        }
    )
}

fn main() {
    let _ = minimized_try_stream();
}

(if true does the same.)

(also available at https://github.com/ludios/ra-proc-macro-type-issue)

expected Result<{unknown}, Error>, found () rust-analyzer(type-mismatch)

rust-analyzer version: 1f709d5 2022-05-05 nightly

rustc version: rustc 1.62.0-nightly (30f386087 2022-05-05)

relevant settings: (eg. client settings, or environment variables like CARGO, RUSTUP_HOME or CARGO_HOME)

[ivan]

I have found this workaround from #11815 useful:

    "rust-analyzer.diagnostics.disabled": [
        "type-mismatch"
    ],

update: now

    "rust-analyzer.diagnostics.disabled": [
        "E0308"
    ],

[cynecx]

The attr proc-macro doesn't get expanded at all, that's what's causing the type mismatch.

[Veykril]

Ye, we only support attributes on items currently

[flodiebold]

Right, I don't think we expand attribute macros on expressions.

[gautamg795]

Rather than globally disabling the type-mismatch diagnostic, is there any sort of marker that can be placed inline at the point of macro usage to ignore this diagnostic?

[flodiebold]

No, there isn't.

[gautamg795]

Is there any plan (i.e. a GitHub issue I could follow) for expanding attribute macros on expressions? Or any other suggestions that wouldn't require globally disabling the often-useful diagnostic?

[flodiebold]

#12558

[Veykril]

Closing as duplicate of the above issue