rustdoc: Downstream implementors are not linked to

[camelid]

Rustdoc doesn't link to implementors of a trait where the implementors are in a downstream crate; e.g., rustc_middle::mir::visit::Visitor:

I would think this is a limitation related to #74481, but the implementors are listed, they just aren't linked to, so I'm not sure what the cause is.

[jyn514]

I think this is a duplicate of #76736.

[jyn514]

If you can reproduce outside of rustc, that's a bug though.

[camelid]

I can reproduce it in a private project, but I'd rather not share the sources. I'll see if I can get an MCVE.

[camelid]

MCVE: https://github.com/camelid/rust-issue-78615

[jyn514]

The code from that repo:

// crate a
pub trait MyTrait {}

pub struct MyLocalStruct;

impl MyTrait for MyLocalStruct {}

// crate b
use crate_a::MyTrait;

pub struct MyStruct;

impl MyTrait for MyStruct {}

[camelid]

Yeah, I just wanted to provide a repo that you can just clone and build to reproduce :)

[camelid]

Weirdly, the issue seems to be spurious: Sometimes I see impl MyTrait for MyStruct in the "Implementors" list, sometimes I see nothing.

EDIT: Never mind, I was sometimes running with --document-private-items. I'll make MyStruct public to fix this.

[camelid]

The output for camelid/rust-issue-78615@3dfc5ea:

[camelid]

This partially worked as of nightly-2020-04-08:

Note that MyTrait is linked to for the MyStruct impl, but not for the MyLocalStruct impl. Also note that there is only a source link for MyLocalStruct.