rustdoc intra-doc links: false positive on trait impls from other crates

[QuietMisdreavus]

In crate inner:

/// this is a trait
pub trait SomeTrait {
    /// this is a method for [SomeTrait]
    fn qwop();
}

/// this is an impl for [SomeTrait].
impl<T> SomeTrait for T {
    fn qwop() {}
}

Crate outer only needs to link against inner, and since my testbed is set to 2018 it's just the following:

#[doc(no_inline)]
pub use inner;

Building docs for outer will generate false positives for the items in inner: (My testbed uses asdf for outer and qwop for inner, but the message should be the same)

$ cargo +nightly doc
 Documenting asdf v0.1.0 (/home/misdreavus/git/asdf)
warning: `[SomeTrait]` cannot be resolved, ignoring it...
 --> /home/misdreavus/git/asdf/qwop/src/lib.rs:7:26
  |
7 | /// this is an impl for [SomeTrait].
  |                          ^^^^^^^^^ cannot be resolved, ignoring
  |
  = note: #[warn(intra_doc_link_resolution_failure)] on by default
  = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`

warning: `[SomeTrait]` cannot be resolved, ignoring it...
 --> /home/misdreavus/git/asdf/qwop/src/lib.rs:3:31
  |
3 |     /// this is a method for [SomeTrait]
  |                               ^^^^^^^^^ cannot be resolved, ignoring
  |
  = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`

    Finished dev [unoptimized + debuginfo] target(s) in 2.74s

[dhardy]

Not sure if this is exactly the same issue, but Rand has a lot of false positive "cannot be resolved" warnings (e.g. here).

[najamelan]

Seeing false positives in futures-rs as well:

warning: `[AsyncSeekExt::seek]` cannot be resolved, ignoring it...
 --> futures-util/src/io/seek.rs:7:29
  |
7 | /// Future for the [`seek`](AsyncSeekExt::seek) method.
  |                             ^^^^^^^^^^^^^^^^^^ cannot be resolved, ignoring
  |
  = help: to escape `[` and `]` characters, just add '\' before them like `\[` or `\]`

This will generate a correct link, but still warn. Anything else I tried fails to generate a correct link:

::futures::io::AsyncSeekExt::seek
::futures_util::io::AsyncSeekExt::seek
super::AsyncSeekExt::seek <- note that this one does NOT warn but does NOT generate correct link
crate::io::AsyncSeekExt::seek
self::super::AsyncSeekExt::seek

[jyn514]

This no longer warns on the latest nightly, I expect it's a special case of #65983.