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 😭

[repi]

The use_self lint is fantastic and we've run it multiple times manually to fix up our code with it over the last year or so, but even as of latest 1.63 these false positives on enums that use serde Serialize/Deserialize prevent us from enabling and enforcing use of the lint. Would be great if could be solved!

[daxpedda]

I believe this should now be fixable with the help of #8694.