spurious type-mismatch error in code with generics with value parameters

[fhars]

The following code (a caricature of what the fugit crate does) compiles without warnings, yet rust analyzer flags expected Rate<u32, NOM, DENOM>, found Rate<u32, _, _> [type-mismatch] in the definition of the new() method, and in the call to run()at the end:

  pub struct Rate<T, const NOM: u32, const DENOM: u32> {
    raw: T,
}

impl<const NOM: u32, const DENOM: u32> Rate<u32, NOM, DENOM> {
    fn new(raw: u32) -> Self {
        Rate { raw }
    }

    fn to_raw(&self) -> u32 {
        self.raw
    }
}

trait ExtU32 {
    fn f<const NOM: u32, const DENOM: u32>(self) -> Rate<u32, NOM, DENOM>;
}

impl ExtU32 for u32 {
    fn f<const NOM: u32, const DENOM: u32>(self) -> Rate<u32, NOM, DENOM> {
        Rate::<u32, NOM, DENOM>::new(self)
    }
}

fn run(t: Rate<u32, 1, 1>) {
    println!("Hello, {}", t.to_raw());
}

fn main() {
    run(100.f());
}

Relevant info:

 ✔ user@dev-vm:~ $ rustc --version
rustc 1.59.0 (9d1b2106e 2022-02-23)

Someone has been working on this in the last few days, but it is not fixed:

 ✔ user@dev-vm:~ $ rust-analyzer --version
rust-analyzer bc08b8eff 2022-04-02 dev
 ✔ user@dev-vm:~ $ rust-analyzer diagnostics ra-test/
processing crate: ra_test, module: /home/user/ra-test/src/main.rs
Diagnostic { code: DiagnosticCode("type-mismatch"), message: "expected Rate<u32, 1, 1>, found Rate<u32, _, _>", range: 582..589, severity: Error, unused: false, experimental: true, fixes: None }
Diagnostic { code: DiagnosticCode("type-mismatch"), message: "expected Rate<u32, NOM, DENOM>, found Rate<u32, _, _>", range: 172..184, severity: Error, unused: false, experimental: true, fixes: None }
Diagnostic { code: DiagnosticCode("type-mismatch"), message: "expected Rate<u32, NOM, DENOM>, found Rate<u32, _, _>", range: 162..190, severity: Error, unused: false, experimental: true, fixes: None }

diagnostic scan complete

[ERROR rust_analyzer] Unexpected error: diagnostic error detected
diagnostic error detected
 ✘ user@dev-vm:~ $ 

Today's nightly has one error less:

 ✔ user@dev-vm:~ $ rust-analyzer --version
rust-analyzer 2366d8e05 2022-04-06 dev
 ✔ user@dev-vm:~ $ rust-analyzer diagnostics ra-test/
processing crate: ra_test, module: /home/user/ra-test/src/main.rs
Diagnostic { code: DiagnosticCode("type-mismatch"), message: "expected Rate<u32, 1, 1>, found Rate<u32, _, _>", range: 582..589, severity: Error, unused: false, experimental: true, fixes: None }
Diagnostic { code: DiagnosticCode("type-mismatch"), message: "expected Rate<u32, NOM, DENOM>, found Rate<u32, _, _>", range: 172..184, severity: Error, unused: false, experimental: true, fixes: None }

diagnostic scan complete

[ERROR rust_analyzer] Unexpected error: diagnostic error detected
diagnostic error detected
 ✘ user@dev-vm:~ $ 

[flodiebold]

Support for const generics is still very WIP, CC #8655.