Why is this an issue?

Importing every public name from a module using a wildcard (use _::*) is a bad idea because:

• It could lead to conflicts between names defined locally and the ones imported.
• It reduces code readability as developers will have a hard time knowing where names come from.
• It clutters the local namespace, which makes debugging more difficult.

Remember that imported names can change when you update your dependencies. A wildcard import that works today might be broken tomorrow.

Exceptions

No issue will be raised for modules that their name contains prelude . Many crates, including the standard library, provide modules named prelude that are specifically designed for wildcard import.

No issue will be raised in test modules. This is defined as any module with test in the name.

How to fix it

There are two ways to avoid a wildcard import:

• Replace it with use mymodule; and access module members as mymodule::myfunction. If the module name is too long, alias it to a shorter name. Example: use std::collections as col;
• List every imported name. If necessary, import statements can be split on multiple lines using parentheses (preferred solution) or backslashes.

Code examples

Noncompliant code example

use std::collections::*; // Noncompliant
fn main() {
    let mut map = HashMap::new();
    map.insert(1, 2);
}

Compliant solution

use std::collections::HashMap;
fn main() {
    let mut map = HashMap::new();
    map.insert(1, 2);
}

Or

use std::collections::HashMap as HM;
fn main() {
    let mut map = HM::new();
    map.insert(1, 2);
}

Resources

Documentation

• Clippy Lints - https://rust-lang.github.io/rust-clippy/master/index.html#wildcard_imports