I published a crate on crates.io recently and when I tried using it my code no longer compiles, reverting to the local version through crate = { path = "/path/to/crate/" } fixes compilation. The source code in both versions is the same, I am using the latest version of the crate in both.

The actual error is this:

In this impl

impl<'a, V, E, F> WaveFrontCompatible<'a> for HalfMesh<V, E, F>
where
    V: PrimitiveContainer,
    E: PrimitiveContainer,
    F: PrimitiveContainer,
    V::PrimitiveData: VertDataGetters,
    F::PrimitiveData: FaceDataGetters<
        Normal = <<V as PrimitiveContainer>::PrimitiveData as VertDataGetters>::V3,
        Uv = <<V as PrimitiveContainer>::PrimitiveData as VertDataGetters>::V2,
    >,
{
    type Index = usize;
    type Scalar = <<V as PrimitiveContainer>::PrimitiveData as VertDataGetters>::Scalar;
    type Vert2D = <<V as PrimitiveContainer>::PrimitiveData as VertDataGetters>::V2;
    type Vert3D = <<V as PrimitiveContainer>::PrimitiveData as VertDataGetters>::V3;
}

error[E0277]: cannot multiply `<<V as traits::PrimitiveContainer>::PrimitiveData as geometry_traits::VertDataGetters>::Scalar` by `<<V as traits::PrimitiveContainer>::PrimitiveData as geometry_traits::VertDataGetters>::V2`
  --> src/wavefront.rs:19:19
   |
19 |     type Vert2D = <<V as PrimitiveContainer>::PrimitiveData as VertDataGetters>::V2;
   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no implementation for `<<V as traits::PrimitiveContainer>::PrimitiveData as geometry_traits::VertDataGetters>::Scalar * <<V as traits::PrimitiveContainer>::PrimitiveData as geometry_traits::VertDataGetters>::V2`

i.e. the compiler claims that Scalar and V2 cannot be multiplied together.

If we look at the definition of that trait we see this:

pub trait VertDataGetters
{
    type Scalar: ScalarLike;
    type V2: VectorLike<Scalar = Self::Scalar>;
    type V3: VectorLike<Scalar = Self::Scalar>;
    fn position(&self) -> Self::V3;
    fn normal(&self) -> Self::V3;
    fn uv(&self) -> Self::V2;
}

If we then look at the definition of VectorLike we see this:

pub trait VectorLike:
    LinAlg<Self::Scalar>
    + Index<usize, Output = Self::Scalar>
    + IndexMut<usize, Output = Self::Scalar>
    + Default
{
    type Scalar: ScalarLike + Mul<Self, Output = Self>;
}

And finally, the defintion of LinAlg

pub trait LinAlg<S>:
    Mul<S, Output = Self>
    + Add<Output = Self>
    + AddAssign<Self>
    + Sub<Output = Self>
    + Div<S, Output = Self>
    + Neg
    + Copy // Consider removing this one and only requiring clone.
    + Sized
where S: ScalarLike + Mul<Self, Output = Self>,
{
}

So LinAlg<S> requires that the type implements multiplication with S in both diretions.

Then VectorLike forwards that restriction to VectorLike::Scalar.

So VertDataGetters guarantees that all of V2 * Scalar, V3 * Scalar, Scalar * V2 and V3 * Scalar are valid operations via:

    type V2: VectorLike<Scalar = Self::Scalar>;
    type V3: VectorLike<Scalar = Self::Scalar>;

So this error:

no implementation for `<<V as traits::PrimitiveContainer>::PrimitiveData as geometry_traits::VertDataGetters>::Scalar * <<V as traits::PrimitiveContainer>::PrimitiveData as geometry_traits::VertDataGetters>::V2`

Should be impossible since that product exists due to the trait bounds specified on the type. Why am I seeing this?