How to link to other fns/structs/enums/traits in rustdoc?

As of Rust 1.48, you can now rely on RFC 1946. This adds the concept of intra-documentation links. This allows using Rust paths as the URL of a link:

1. [Iterator](std::iter::Iterator)
2. [Iterator][iter], and somewhere else in the document: [iter]: std::iter::Iterator
3. [Iterator], and somewhere else in the document: [Iterator]: std::iter::Iterator

The RFC also introduces “Implied Shortcut Reference Links”. This allows leaving out the link reference, which is then inferred automatically.

1. [std::iter::Iterator], without having a link reference definition for Iterator anywhere else in the document
2. [`std::iter::Iterator`], without having a link reference definition for Iterator anywhere else in the document (same as previous style but with back ticks to format link as inline code)

As a concrete example, this source code:

//! Check out [ExampleStruct], especially [this
//! method](ExampleStruct::foo), but [the trait method][trait] is also
//! cool. There is also [an enum variant you can
//! use](nested::ExampleEnum::Beta).
//!
//! [trait]: ExampleTrait::bar

pub struct ExampleStruct;

impl ExampleStruct {
    pub fn foo(&self) {}
}

pub trait ExampleTrait {
    fn bar();
}

pub mod nested {
    pub enum ExampleEnum {
        Alpha,
        Beta,
    }
}

Produces this documentation:

Specifically, this HTML is generated:

<p>Check out <a href="../doc_link_example/struct.ExampleStruct.html" title="ExampleStruct">ExampleStruct</a>, especially <a href="../doc_link_example/struct.ExampleStruct.html#method.foo">this method</a>, but <a href="../doc_link_example/trait.ExampleTrait.html#tymethod.bar">the trait method</a> is also cool. There is also <a href="../doc_link_example/nested/enum.ExampleEnum.html#Beta.v">an enum variant you can use</a>.</p>