Tour of WGSL

@must_use

A function with a return type may be marked with the @must_use attribute, which makes it a compile time error if there a statement that is just a call to that function.

In other words, the value resulting from calling that function must be used for some purpose:

in a larger expression,
in an assignment or declaration, or
to manage control flow, etc.

Many of the builtin functions are marked as @must_use.

@must_use
fn a() -> i32 {
  return 10;
}

fn b() -> i32 {
  return 10;
}

fn c() {
  let d = a();  // Ok, result is used
  b();          // Ok, not marked @must_use

  if a() < 5 {  // Ok, used to manage control flow.

  }

  // a();       // Error, result not used
}