The tracking issue for this feature is: #45040

The doc_spotlight feature allows the use of the spotlight parameter to the #[doc] attribute, to "spotlight" a specific trait on the return values of functions. Adding a #[doc(spotlight)] attribute to a trait definition will make rustdoc print extra information for functions which return a type that implements that trait. This attribute is applied to the Iterator, io::Read, and io::Write traits in the standard library.

You can do this on your own traits, like this:

#![feature(doc_spotlight)]

#[doc(spotlight)]
pub trait MyTrait {}

pub struct MyStruct;
impl MyTrait for MyStruct {}

/// The docs for this function will have an extra line about `MyStruct` implementing `MyTrait`,
/// without having to write that yourself!
pub fn my_fn() -> MyStruct { MyStruct }

This feature was originally implemented in PR #45039.