Suggest use ... as _ if the type is used for traits calls only

[nyurik]

What it does

If a specific trait is brought into the scope just because it extends some type, but not used directly, alias it as an anonymous _. I have frequently seen it with the common for std::io::Write:

use std::io::Write as _;  // <-- don't introduce the "Write" trait into the scope

fn main() {
    std::io::stdout().write_all(b"Hello, world!").unwrap();
}

Lint Name

use_non_polluting_alias_for_traits

Category

No response

Advantage

• does not introduce (directly) unused traits into the scope

Drawbacks

No response

Example

For trait methods like

mod ext {
    pub trait Foo {
        fn foo(&self) {
            println!("foo");
        }
    }

    impl Foo for i32 {}
}

This example

fn main() {
    use crate::ext::Foo;  // <- no aliasing, polluting
    42.foo();
}

Could be written as:

fn main() {
    use crate::ext::Foo as _; // non-polluting aliasing
    42.foo();
}

[Alexendoo]

Duplicate of #9021