use_self still gives false positives

[imp]

Now that #6818 is fixed and the fix (#6833) has made its way to the nightly there are still cases of false positives:

Lint name: use_self

I tried this code:

#![deny(clippy::use_self)]
use serde::Deserialize;

#[derive(Debug, Deserialize)]
#[serde(untagged)]
enum Direction {
    North,
}

fn main() {
    let d = Direction::North;

    println!("{:?}", d);
}

I expected to see this happen: clippy clean - no warning/errors

Instead, this happened:

    Checking playground v0.0.1 (/playground)
error: unnecessary structure name repetition
 --> src/main.rs:6:6
  |
6 |   enum Direction {
  |  ______^
7 | |     North,
  | |____^ help: use the applicable keyword: `Self`
  |
note: the lint level is defined here
 --> src/main.rs:1:9
  |
1 | #![deny(clippy::use_self)]
  |         ^^^^^^^^^^^^^^^^
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#use_self

error: aborting due to previous error

error: could not compile `playground`

To learn more, run the command again with --verbose.

Interestingly enough it the code generated by #[serde(untagged)] that triggers this lint. If this line is commented out then clippy seems to be happy

Meta

• cargo clippy -V: clippy 0.1.52 (2021-03-13 acca818)

• rustc -Vv:

rustc 1.52.0-nightly (acca81892 2021-03-13)
binary: rustc
commit-hash: acca818928654807ed3bc1ce0e97df118f8716c8
commit-date: 2021-03-13
host: x86_64-unknown-linux-gnu
release: 1.52.0-nightly
LLVM version: 12.0.0

[Y-Nak]

This issue would be automatically fixed when rust-lang/rust#84122 is addressed.

[barafael]

For reference, here are two cases in which the same false positive occurs:

• smart-default with the SmartDefault derive macro
• num-derive with the FromPrimitive and ToPrimitive derive macros
  • This PR on num-derive proposes to stop using the type name and instead use Self in the generated code, solving the problem inside num-derive: Fix #47 rust-num/num-derive#49

[carols10cents]

This problem has now made it to the clippy that's in beta (specifically 1.61.0-beta.1 (0f231250b 2022-04-05))

Here's a reproduction, this project has 0 warnings with the clippy with Rust 1.60 but has warnings with the clippy with 1.61.0-beta.1:

Cargo.toml:

[package]
name = "foo"
version = "0.1.0"
edition = "2021"

[dependencies]
serde = { version = "1.0", features = ["derive"] }

src/lib.rs:

#![warn(clippy::use_self)]

use serde::Serialize;

#[derive(Serialize)]
pub enum Status {
    Pass,
    Fail,
}

warning:

error: unnecessary structure name repetition
 --> src/lib.rs:6:10
  |
6 | pub enum Status {
  |          ^^^^^^ help: use the applicable keyword: `Self`
  |
  = note: `-D clippy::use-self` implied by `-D warnings`
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#use_self

cargo expand shows the code serde is generating is:

#![feature(prelude_import)]
#![warn(clippy::use_self)]
#[prelude_import]
use std::prelude::rust_2021::*;
#[macro_use]
extern crate std;
use serde::Serialize;
pub enum Status {
    Pass,
    Fail,
}
#[doc(hidden)]
#[allow(non_upper_case_globals, unused_attributes, unused_qualifications)]
const _: () = {
    #[allow(unused_extern_crates, clippy::useless_attribute)]
    extern crate serde as _serde;
    #[automatically_derived]
    impl _serde::Serialize for Status {
        fn serialize<__S>(
            &self,
            __serializer: __S,
        ) -> _serde::__private::Result<__S::Ok, __S::Error>
        where
            __S: _serde::Serializer,
        {
            match *self {
                Status::Pass => {
                    _serde::Serializer::serialize_unit_variant(__serializer, "Status", 0u32, "Pass")
                }
                Status::Fail => {
                    _serde::Serializer::serialize_unit_variant(__serializer, "Status", 1u32, "Fail")
                }
            }
        }
    }
};

which does contain the repetition in the match, but I think this is still a clippy bug because clippy didn't warn about this with the previous version and it's pointing to code that definitely shouldn't use Self.

[kleinesfilmroellchen]

I can reproduce this as well. Shouldn't clippy not apply this lint (and others) on impls and functions marked as #[automatically_derived]?

[tyranron]

Now it fires on stable 😭