Double not incorrectly triggers `nonminimal_bool` when !v returns `bool` but v is not `bool`

[endorpersand]

Summary

When a type implements Not and outputs bool, Clippy suggests to simplify the expression !!x to just x, even though that isn't equivalent.

Lint Name

nonminimal_bool

Reproducer

I tried this code:

struct Foo(bool);
impl std::ops::Not for Foo {
    type Output = bool;

    fn not(self) -> Self::Output {
        !self.0
    }
}

fn main() {
    let _: bool = !!Foo(true);
}

I saw this happen:

warning: this boolean expression can be simplified
  --> src/report.rs:11:19
   |
11 |     let _: bool = !!Foo(true);
   |                   ^^^^^^^^^^^ help: try: `Foo(true)`
   |

I expected to see this happen:
This lint shouldn't have triggered.

Version

rustc 1.69.0 (84c898d65 2023-04-16)
binary: rustc
commit-hash: 84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc
commit-date: 2023-04-16
host: x86_64-apple-darwin
release: 1.69.0
LLVM version: 15.0.7

Additional Labels

No response

[xFrednet]

This probably only requires a type check for the inner expression and some tests. It should be a good first issue :)

@rustbot label +good-first-issue

[disco07]

@rustbot claim

[lochetti]

Maybe we can close this issue, after the PR #10845?