single_match gives bad suggestion

[VuiMuich]

Clippy gave me a solution, that lead to compiler error error[E0369]: binary operation == cannot be applied to type 'T'
Went to discord for help and bunch of guys unanimously suggested to report this as a bug.

I wrote this simple example below as minimal way to create the same lint.

I tried this code:

struct Mytype {
  some_field: i32,
  another_field: i32,
}

impl Mytype{
  pub fn new() -> Mytype {
        Mytype {
        some_field: 1,
        another_field: 2,
      }
  }
}

fn main() {
  let item: Mytype = Mytype::new();
  let some_vec: Vec<Mytype> = vec![item];

  // clippy complains about this statement
  match some_vec.iter().find(|i| i.some_field < i.another_field ) {
    None => {
      println!("Exit early.");
      return;
    }
    _ => (),
  }

  // clippy suggests this solution which will result in an [E0369]
  // if some_vec.iter().find(|i| i.some_field < i.another_field ) == None {
  // println!("Exit early:");
  // return;
  // }

  // clippy should suggest a statement like this
  if some_vec.iter().any(|i| i.some_field > i.another_field ) {
      println!("Exit early.");
      return;
  }

  println!("proper End")
}

This is the original lint to above example:

# cargo clippy --all-targets --all-features
warning: you seem to be trying to use `match` for an equality check. Consider using `if`
  --> src/main.rs:20:3
   |
20 | /   match some_vec.iter().find(|i| i.some_field < i.another_field ) {
21 | |     None => {
22 | |       println!("Exit early.");
23 | |       return;
24 | |     }
25 | |     _ => (),
26 | |   }
   | |___^
   |
   = note: `#[warn(clippy::single_match)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#single_match
help: try this
   |
20 |   if some_vec.iter().find(|i| i.some_field < i.another_field ) == None {
21 |     println!("Exit early.");
22 |     return;
23 |   }
   |

warning: 1 warning emitted

    Finished dev [unoptimized + debuginfo] target(s) in 0.01s

And the original error when you uncomment the suggested code

   Compiling report_clippy_bug v0.1.0 (/home/vuimuich/Documents/report_clippy_bug)
error[E0369]: binary operation `==` cannot be applied to type `Option<&Mytype>`
  --> src/main.rs:29:64
   |
29 |   if some_vec.iter().find(|i| i.some_field < i.another_field ) == None {
   |      --------------------------------------------------------- ^^ ---- Option<_>
   |      |
   |      Option<&Mytype>

error: aborting due to previous error

For more information about this error, try `rustc --explain E0369`.
error: could not compile `report_clippy_bug`

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

Meta

• cargo clippy -V: clippy 0.1.51 (2fd73fa 2021-03-23)
• rustc -Vv:

  rustc 1.51.0 (2fd73fabe 2021-03-23)
  binary: rustc
  commit-hash: 2fd73fabe469357a12c2c974c140f67e7cdd76d0
  commit-date: 2021-03-23
  host: x86_64-unknown-linux-gnu
  release: 1.51.0
  LLVM version: 11.0.1
  

[giraffate]

Thanks for the report!

Clippy gave me a solution, that lead to compiler error error[E0369]: binary operation == cannot be applied to type 'T'

I couldn't reproduce a compile error in the example you show. FYI I tried this: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=f1c072709e6bdc249d442ae1b812a84d

[VuiMuich]

Oh, then simplifying to a Vec was probably a bad idea.

The original error occurred with a custom type Window. Gonna try to update the example code so it breaks the same way it did originally.

[VuiMuich]

Updated original post with modified code and matching clippy lint and error with uncommented suggested code.

Apologies if this isn't the most minimal possible example, but I'm still relatively fresh to rust..