`Methods from Deref<Target=[T]>` doesnt appear for type aliases

[drewcassidy]

I have a type alias for a type that implements Deref<Target=[T], but Rustdoc doesnt generate the corresponding section in the sidebar like it does for the concrete type I'm aliasing

#[derive(Copy, Clone, Eq, PartialEq, Debug)]
pub struct Col<T: Copy, const N: usize> {
    data: [T; N],
}

pub type Mat<T, const H: usize, const W: usize> = Col<Col<T, W>, H>;

// snip

impl<T: Copy, const N: usize> Deref for Col<T, N> {
    type Target = [T];

    fn deref(&self) -> &Self::Target {
        &self.data
    }
}

rustdoc 1.82.0 (f6e511e 2024-10-15) on macOS 15.2

[camelid]

This is because rustdoc injects impls for type aliases using JS (to avoid doc size ballooning). The Deref impl is shown, just not the specialized Methods from Deref section. I suppose we'd just need to add special support for this to the code that generates the JS, as well as to the JS itself? cc @notriddle

[notriddle]

Yes, that sounds like a reasonable idea.

The discussion I've been putting off is whether Deref should, in general, work this way. There's not really any particular difference from type aliases: most crates use it sparingly, but a few of them (for example, gtk) make extensive use of it.