Wrong lint in case of to_*_mut method

[dodomorandi]

Lint name: wrong_self_convention

I tried this code:

pub enum Test<T> {
    None,
    One(T),
    Many(Vec<T>),
}

impl<T> Test<T> {
    pub fn to_many(&self) -> Option<&[T]> {
        match self {
            Self::Many(data) => Some(data),
            _ => None,
        }
    }

    pub fn to_many_mut(&mut self) -> Option<&mut [T]> {
        match self {
            Self::Many(data) => Some(data),
            _ => None,
        }
    }
}

I expected to see this happen: in order to get an optional variant of the enum, the naming convention to_* should be used, because the match statement cannot be considered free (therefore as_* is not ok). Moreover, the name to_mut (à la Cow::to_mut) cannot be used in this case, because there are two non-empty variants. Therefore using to_many_mut for the name of the method seems the right choice.

Instead, this happened: clippy says that to_* should follow the convention of taking self by reference.

My rationale is that, when a method starts with to_, it should expect a &mut self parameter if ends with _mut, otherwise &self.

Meta

• cargo clippy -V: clippy 0.0.212 (cb75ad5 2021-02-10)
• rustc -Vv:

  rustc 1.50.0 (cb75ad5db 2021-02-10)
  binary: rustc
  commit-hash: cb75ad5db02783e8b0222fee363c5f63f7e2cf5b
  commit-date: 2021-02-10
  host: x86_64-unknown-linux-gnu
  release: 1.50.0
  

[mgacek8]

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