rust/tests/coverage/coroutine.coverage

   LL|       |#![feature(coroutines, coroutine_trait, stmt_expr_attributes)]
   LL|       |
   LL|       |use std::ops::{Coroutine, CoroutineState};
   LL|       |use std::pin::Pin;
   LL|       |
   LL|       |// The following implementation of a function called from a `yield` statement
   LL|       |// (apparently requiring the Result and the `String` type or constructor)
   LL|       |// creates conditions where the `coroutine::StateTransform` MIR transform will
   LL|       |// drop all `Counter` `Coverage` statements from a MIR. `simplify.rs` has logic
   LL|       |// to handle this condition, and still report dead block coverage.
   LL|      1|fn get_u32(val: bool) -> Result<u32, String> {
   LL|      1|    if val {
   LL|      1|        Ok(1)
   LL|       |    } else {
   LL|      0|        Err(String::from("some error"))
   LL|       |    }
   LL|      1|}
   LL|       |
   LL|      1|fn main() {
   LL|      1|    let is_true = std::env::args().len() == 1;
   LL|      1|    let mut coroutine = #[coroutine] || {
   LL|      1|        yield get_u32(is_true);
   LL|      1|        return "foo";
   LL|      1|    };
   LL|       |
   LL|      1|    match Pin::new(&mut coroutine).resume(()) {
   LL|      1|        CoroutineState::Yielded(Ok(1)) => {}
   LL|      0|        _ => panic!("unexpected return from resume"),
   LL|       |    }
   LL|      1|    match Pin::new(&mut coroutine).resume(()) {
   LL|      1|        CoroutineState::Complete("foo") => {}
   LL|      0|        _ => panic!("unexpected return from resume"),
   LL|       |    }
   LL|      1|}