A documentation comment that doesn't document anything was found.
Erroneous code example:
```compile_fail,E0585
fn main() {
// The following doc comment will fail:
/// This is a useless doc comment!
}
```
Documentation comments need to be followed by items, including functions,
types, modules, etc. Examples:
```
/// I'm documenting the following struct:
struct Foo;
/// I'm documenting the following function:
fn foo() {}
```