How to quiet a warning for a single statement in Rust?

Question

Say there is a single warning such as path_statements, unused_variables. Is there a way to ignore a single instant of this, without isolating them

Answer 1

To silence warnings you have to add the allow(warning_type) attribute to the affected expression or any of its parents. If you only want to silence the warning on one specific expression, you can add the attribute to that expression/statement:

fn main() {
    #[allow(unused_variables)]
    let not_used = 27;

    #[allow(path_statements)]
    std::io::stdin;

    println!("hi!");
}

However, the feature of adding attributes to statements/expressions (as opposed to items, like functions) is still a bit broken. In particular, in the above code, the std::io::stdin line still triggers a warning. You can read the ongoing discussion about this feature here.

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Often it is not necessary to use an attribute though. Many warnings (like unused_variables and unused_must_use) can be silenced by using let _ = as the left side of your statement. In general, any variable that starts with an underscore won't trigger unused-warnings.

Answer 2

If you want to silence all warnings of a kind in a module, write e.g. #![allow(dead_code)] (note the exclamation mark) at the top of the module. This will disable all warnings of this kind in the whole module. You can also call rustc with e.g. -A dead_code.

You can disable all warnings by writing #![allow(warnings)] at the top of the module.

You can insert a module (as described in the Rust book) where the specific warnings are ignored.

As Lukas said, you can also write e.g. #[allow(dead_code)] on a statement or an expression.