Cross-crate intra-doc links broken for functions when there's a doc(hidden) full-crate reexport involved

[Manishearth]

Discovered in rust-lang/futures-rs#2177 (comment)

// crate main:
pub use dependency::future::{ready, Ready};

// crate dependency:

#[doc(hidden)]
pub mod __reexport {
    pub use crate::*;
}

pub mod future {
    mod ready {

        /// Link to [`ready`](function@ready)
        pub struct Ready;
        pub fn ready() {}

    }
    pub use self::ready::{ready, Ready};

}

The link to ready does not work.

[Manishearth]

The reason is that the access_levels check fails because the item is not in the map at all.

I suspect the checks for hidden are breaking things. If a mod is hidden I think we should be skipping the module entirely.

[Manishearth]

It's unclear to me why this only happens for functions, and not structs.

[Manishearth]

Ah, this is basically a variant of #31948 , and the fix for that (#33002) explicitly only handled types and mods.

[Manishearth]

Fix is in #73365

@jyn514 would you be able to include that commit in your branch and a test based on the example above?