Try blocks give false errors (`type-mismatch` false positive)

[Kixiron]

Rust Analyzer sometimes gives errors on try blocks where there shouldn't be any, e.g.

let _: Option<()> = try {
    let first_rhs = self.values.get(graph.input_source(sub.rhs()))?;

    let lhs_sub = *graph.cast_input_source::<Sub>(sub.lhs())?;
    let second_rhs = self.values.get(graph.input_source(lhs_sub.rhs()))?;

    let sum = first_rhs + second_rhs;
    let new_rhs = graph.constant(sum);
    self.values.add(new_rhs.value(), sum);

    graph.remove_inputs(sub.node());

    let value = graph.input_source(lhs_sub.lhs());
    graph.add_value_edge(value, sub.lhs());
    graph.add_value_edge(new_rhs.value(), sub.rhs());

    self.changes.inc::<"sub-sub">();
};

This code is correct (and rustc doesn't complain), but RA emits this error:

Changing it as suggested (adding a Some(()) or None to the end of the block) is incorrect and (correctly) causes both rustc and RA to emit errors

rust-analyzer version: bc08b8eff 2022-03-28 stable

rustc version: (eg. output of rustc -V)

rustc 1.60.0-nightly (777bb86bc 2022-01-20)
binary: rustc
commit-hash: 777bb86bcdbc568be7cff6eeeaaf81a89b4aa50b
commit-date: 2022-01-20
host: x86_64-pc-windows-msvc
release: 1.60.0-nightly
LLVM version: 13.0.0

relevant settings: N/A

[flodiebold]

Support for try blocks isn't implemented at all yet:
https://github.com/rust-analyzer/rust-analyzer/blob/9eb7553d5ab7cd512b7edf8d8a30b191be0dc761/crates/hir_ty/src/infer/expr.rs#L153-L157

[cjhopman]

While it's not implemented, I'm pretty sure it's a recent regression that it's now showing errors here. We've used try_blocks for quite a while and haven't had this issue.

[cjhopman]

Yeah, I see this on 0.2.993, but not on 0.2.985.

[bjorn3]

We recently started showing type mismatch errors. Before that those weren't shown at all.

[peku33]

expiriencing the same issue

[ndmitchell]

@bjorn3 - is there a way to disable type mismatch errors until this issue is resolved, e.g. with a config change for impacted users? Unfortunately this shows a large number of errors in the project I work on.

[lnicola]

They are disabled by default. Check if you've enabled experimental diagnostics or if you're on an older version.

[ndmitchell]

@lnicola I had pinned my Rust Analyzer extension due to a previous bug - removing the pin fixed the errors. Thanks!

[KapJI]

I have these errors on Windows even with experimental diagnostics disabled :(

RA version: ad6810e 2022-06-06 stable
VS Code extension: 0.3.1083

[flodiebold]

@KapJI can you show an example?

[KapJI]

@flodiebold Trivial example:

#![feature(try_blocks)]

fn test() -> bool {
    let result: Result<bool, ()> = try {
        true
    };
    result.unwrap()
}

expected Result<bool, ()>, found bool rust-analyzer[type-mismatch]

Rust toolchain: nightly-2022-04-05-x86_64-pc-windows-msvc

[flodiebold]

Hmm yeah, that's happening because we have a quick fix in this case (the "wrap in Ok" suggestion). You could disable the diagnostic completely instead.