False error for take

[tfgast]

I've been seeing this false error. I managed to reduce it down to the following code with no non std dependencies. Rust analyzer thinks it's Iterator::take, but it's actually Option::take

use std::marker::PhantomData;

pub trait SimulationType: Sized {
    type Dim: Dimension;
    type TV: Array<Dim = Self::Dim>;
    type IV: Array<Dim = Self::Dim>;
}

pub trait Array: Sized {
    type Dim: Dimension;
}

pub trait Dimension: Sized {
    type I: Iterator<Item = Self>;
}

impl<S: SimulationType> Sim<S> {
    pub fn bad_error(&mut self) {
        let _ = self.integrator.take().unwrap();
    }
}

pub struct Sim<S> {
    integrator: Option<()>,
    phantom: PhantomData<S>,
}

[jRimbault]

Hi, I believe I have the same error here, my scan method is inferred to be the one from Iterator. Before that the min and max methods here were confused with the ones from Iterator also.

[itsfarseen]

Same error when trying to take() out of Option in std::process::Child.stdin

[flodiebold]

@happycoder97 Local imports are not supported yet: #1165

[itsfarseen]

@flodiebold moving the imports fixed it. Thanks :)

[eminence]

Here's another way to reproduce the original issue:

pub fn foo<T, U>(_a: T, _b: U)
where
    T: IntoIterator<Item = ()>,
    U: IntoIterator<Item = ()>,
{
    let mut x: Option<()> = None;
    let _ = x.take();
}

Guess on my part: the problem relates to how IntoIterator and SimulationType (from the original report) both have associated types that reference other Self types (either type IntoIter: Iterator<Item = Self::Item> in the case of IntoIterator, or type TV: Array<Dim = Self::Dim> in the case of SimulationType).

(Also just adding for the record that the error issues by RA is a mismatched-arg-count error, to make it easier to search for this issue in the future)

[eminence]

After more than half a year with this error in my project, I'm starting to get motivated to do something about it 😄. But I'm not at all familiar with the code involved. Does anyone have any hints about where to start looking, or any other relevant mentoring tips?

[flodiebold]

Huh! I think that's probably a very similar if not the same issue as #9990, i.e. a Chalk problem with environment clause elaboration (rust-lang/chalk#727). It could maybe serve as a simpler example though 🤔