rust/tests/ui/lint/unused/unused-result.rs

#![allow(dead_code)]
#![deny(unused_results, unused_must_use)]
//~^ NOTE: the lint level is defined here
//~| NOTE: the lint level is defined here

#[must_use]
enum MustUse { Test }

#[must_use = "some message"]
enum MustUseMsg { Test2 }

fn foo<T>() -> T { panic!() }

fn bar() -> isize { return foo::<isize>(); }
fn baz() -> MustUse { return foo::<MustUse>(); }
fn qux() -> MustUseMsg { return foo::<MustUseMsg>(); }

#[allow(unused_results)]
fn test() {
    foo::<isize>();
    foo::<MustUse>(); //~ ERROR: unused `MustUse` that must be used
    foo::<MustUseMsg>(); //~ ERROR: unused `MustUseMsg` that must be used
    //~^ NOTE: some message
}

#[allow(unused_results, unused_must_use)]
fn test2() {
    foo::<isize>();
    foo::<MustUse>();
    foo::<MustUseMsg>();
}

fn main() {
    foo::<isize>(); //~ ERROR: unused result of type `isize`
    foo::<MustUse>(); //~ ERROR: unused `MustUse` that must be used
    foo::<MustUseMsg>(); //~ ERROR: unused `MustUseMsg` that must be used
    //~^ NOTE: some message

    let _ = foo::<isize>();
    let _ = foo::<MustUse>();
    let _ = foo::<MustUseMsg>();
}