Generic Mul Bound Error

[pacmanmati]

I tried this code:

use cgmath::{Vector3, Point3};
use std::ops::Mul;

#[derive(Debug)]
pub struct Ray<S> {
    pub origin: Point3<S>,
    pub direction: Vector3<S>,
}

impl <S> Ray<S> {
    pub fn new(origin: Point3<S>, direction: Vector3<S>) -> Self {
	Self { origin, direction }
    }

    pub fn at(&self, t: S) -> Self {
	let aaa = self.direction * t;
	Self { origin: self.origin, direction: aaa }
    }
}

I expected to see this happen: Compiler suggests the following bound

where
    Vector3<S>: Mul<S, Output = Vector3<S>>

Instead, this happened: Compiler suggests the following bound

where
    S: Mul<Output = Vector3<S>>

the above bound doesn't constrain the generic correctly and the compiler will keep requesting you add it despite it already being present.

Meta

The bug also occurs when I use nightly.

rustc --version --verbose:

rustc 1.50.0 (cb75ad5db 2021-02-10)
binary: rustc
commit-hash: cb75ad5db02783e8b0222fee363c5f63f7e2cf5b
commit-date: 2021-02-10
host: aarch64-apple-darwin
release: 1.50.0

[moxian]

This has been fixed in #94034

minimization

mod cgmath {
    pub trait BaseNum {}
    pub struct Vector3<S>(S);

    impl<S: BaseNum> std::ops::Mul<S> for Vector3<S>
    {
        type Output = Self;
        fn mul(self, other: S) -> Self {
            todo!()
        }
    }
}

use cgmath::Vector3;

pub struct Ray<S> {
    pub direction: Vector3<S>,
}

impl<S> Ray<S>
where
    S: std::ops::Mul<Output = S>,
{
    pub fn at(&self, t: S) -> Self {
        let aaa = self.direction * t;
        Self { direction: aaa }
    }
}

nightly-2022-04-26 output:

error[E0369]: cannot multiply `Vector3<S>` by `S`
  --> src\lib.rs:25:34
   |
25 |         let aaa = self.direction * t;
   |                   -------------- ^ - S
   |                   |
   |                   Vector3<S>
   |
help: consider further restricting this bound
   |
22 |     S: std::ops::Mul<Output = S> + std::ops::Mul<Output = S>,
   |                                  +++++++++++++++++++++++++++

For more information about this error, try `rustc --explain E0369`.

nightly-2022-04-27 output:

error[E0369]: cannot multiply `Vector3<S>` by `S`
  --> src\lib.rs:25:34
   |
25 |         let aaa = self.direction * t;
   |                   -------------- ^ - S
   |                   |
   |                   Vector3<S>
   |
help: consider further restricting this bound
   |
22 |     S: std::ops::Mul<Output = S> + cgmath::BaseNum,
   |                                  +++++++++++++++++

For more information about this error, try `rustc --explain E0369`.

@rustbot label: -E-needs-mcve +S-has-bisection