rust/tests/rustdoc-ui/error-in-impl-trait
..
async.rs
closure.rs
const-generics.rs
generic-argument.rs
impl-keyword-closure.rs
impl-keyword.rs
infinite-recursive-type-2.rs
infinite-recursive-type-impl-trait-return.rs
infinite-recursive-type-impl-trait-return.stderr
infinite-recursive-type.rs
README.md
realistic-async.rs
trait-alias-closure.rs
trait-alias.rs

Each of these needs to be in a separate file, because the delay_span_bug ICE in rustdoc won't be triggerred if even a single other error was emitted.

However, conceptually they are all testing basically the same thing. See https://github.com/rust-lang/rust/pull/73566#issuecomment-653689128 for more details.