incorrect result of #![deny(unused_qualifications)] in match block

[teckick]

Summary

#![deny(unused_qualifications)] does not work in match block.

Lint Name

#![deny(unused_qualifications)]

Reproducer

I tried this code:

tree:

|- main.rs
|- status.rs

// main.rs

#![deny(unused_qualifications)]
#![allow(dead_code)]

mod status;

use status::StatusCode;

fn main() -> anyhow::Result<()> {
    let st = StatusCode::Ok;
    let resp = status::Resp{status: st};
    match resp.status() {
        status::StatusCode::Ok => {Ok(())} // lint should warn but not
        status::StatusCode::NotFound => {Ok(())}  // lint should warn but not
    }
}

// status.rs

#[derive(Clone)]
pub enum StatusCode {
    Ok,
    NotFound,
}

pub struct Resp {
    pub(crate) status: StatusCode,
}

impl Resp {
    pub fn status(&self) -> StatusCode {
        self.status.clone()
    }
}

run the following cmd:

cargo clippy

I expected to see this happen:

error: unnecessary qualification

Instead, this happened:

no error

Version

rustc 1.62.1 (e092d0b6b 2022-07-16)
binary: rustc
commit-hash: e092d0b6b43f2de967af0887873151bb1c0b18d3
commit-date: 2022-07-16
host: x86_64-apple-darwin
release: 1.62.1
LLVM version: 14.0.5

[Xuanwo]

I can't find unused-qualifications in https://rust-lang.github.io/rust-clippy/master/index.html.

I'm guessing it's a rustc lint?

There are some things need to check:

• Upgrade to 1.63 (the latest stable) to check again.
• Use cargo +nightly check to check whether this has been resolved nightly.

[giraffate]

The unused_qualifications is the rustc's lint: https://doc.rust-lang.org/stable/nightly-rustc/rustc_lint/builtin/static.UNUSED_QUALIFICATIONS.html, so it would be better that this issue is moved to rust-lang/rust.

The main.rs bring status::StatusCode in that scope, but it doesn't use status::StatusCode as it is. It uses status::StatusCode::Ok and status::StatusCode::NotFound, so the unused_qualifications lint doesn't fire.

[teckick]

@giraffate Thanks for answer! I start another issue in rust-lang/rust.