Lint against non-idiomatic use paths

What it does

Warn users about importing item other than modules, types, traits and derive macros.

Categories (optional)

• Kind: clippy::style.

What is the advantage of the recommended code over the original code

From https://doc.rust-lang.org/book/ch07-04-bringing-paths-into-scope-with-the-use-keyword.html#creating-idiomatic-use-paths:

Specifying the parent module when calling the function makes it clear that the function isn’t locally defined while still minimizing repetition of the full path.

when bringing in structs, enums, and other items with use, it’s idiomatic to specify the full path.

The book does not say about how to import macros. Personally, I suggest that warn about importing:

• functions,
• function-like and attribute-like macros,
• consts,
• statics,

while allowing importing:

• derive macros,
• modules,
• traits,
• types.

Drawbacks

This style might not be suitable for everyone, and should not be enforced by default.

Example

mod front_of_house {
    pub mod hosting {
        pub fn add_to_waitlist() {}
    }
}

use self::front_of_house::hosting::add_to_waitlist;

pub fn eat_at_restaurant() {
    add_to_waitlist();
    add_to_waitlist();
    add_to_waitlist();
}

Could be written as:

mod front_of_house {
    pub mod hosting {
        pub fn add_to_waitlist() {}
    }
}

use self::front_of_house::hosting;

pub fn eat_at_restaurant() {
    hosting::add_to_waitlist();
    hosting::add_to_waitlist();
    hosting::add_to_waitlist();
}

Start from the issue's examples and the linked Rust Book section on creating idiomatic use paths. Define the lint behavior for functions, function-like and attribute-like macros, consts, and statics, while allowing derive macros, modules, traits, and types. Done means the proposed non-default style lint consistently distinguishes these item categories.