src/test/ui/lint/unused/unused-closure.rs

   1 // Test that closures and generators are "must use" types.
   2 // edition:2018
   3
   4 #![feature(async_closure)]
   5 #![feature(generators)]
   6 #![deny(unused_must_use)]
   7
   8 fn unused() {
   9     || { //~ ERROR unused closure that must be used
  10         println!("Hello!");
  11     };
  12
  13     async {};    //~ ERROR unused implementer of `Future` that must be used
  14     || async {}; //~ ERROR unused closure that must be used
  15     async || {}; //~ ERROR unused closure that must be used
  16
  17
  18     [Box::new([|| {}; 10]); 1]; //~ ERROR unused array of boxed arrays of closures that must be used
  19
  20     vec![|| "a"].pop().unwrap(); //~ ERROR unused closure that must be used
  21
  22     let b = false;
  23         || true; //~ ERROR unused closure that must be used
  24     println!("{}", b);
  25 }
  26
  27 fn ignored() {
  28     let _ = || {};
  29     let _ = || yield 42;
  30 }
  31
  32 fn main() {
  33     unused();
  34     ignored();
  35 }