coverage: Add test to codify existing behavior

Currently `await` is only counted towards coverage if the containing
function is suspended and resumed at least once. A future commit will
fix this and update the test to reflect the new behavior.

Author: jonathan-conder

Diff for: tests/coverage/await_ready.cov-map

@@ -0,0 +1,26 @@
+Function name: await_ready::await_ready
+Raw bytes (9): 0x[01, 01, 00, 01, 01, 0a, 01, 00, 1e]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 1
+- Code(Counter(0)) at (prev + 10, 1) to (start + 0, 30)
+
+Function name: await_ready::await_ready::{closure#0}
+Raw bytes (19): 0x[01, 01, 00, 03, 01, 0a, 1e, 02, 0c, 05, 03, 0a, 00, 0f, 09, 01, 01, 00, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 3
+- Code(Counter(0)) at (prev + 10, 30) to (start + 2, 12)
+- Code(Counter(1)) at (prev + 3, 10) to (start + 0, 15)
+- Code(Counter(2)) at (prev + 1, 1) to (start + 0, 2)
+
+Function name: await_ready::main
+Raw bytes (9): 0x[01, 01, 00, 01, 01, 10, 01, 03, 02]
+Number of files: 1
+- file 0 => global file 1
+Number of expressions: 0
+Number of file 0 mappings: 1
+- Code(Counter(0)) at (prev + 16, 1) to (start + 3, 2)
+

Diff for: tests/coverage/await_ready.coverage

@@ -0,0 +1,38 @@
+   LL|       |#![feature(coverage_attribute)]
+   LL|       |#![feature(custom_inner_attributes)] // for #![rustfmt::skip]
+   LL|       |#![feature(noop_waker)]
+   LL|       |#![rustfmt::skip]
+   LL|       |//@ edition: 2021
+   LL|       |
+   LL|       |#[coverage(off)]
+   LL|       |async fn ready() -> u8 { 1 }
+   LL|       |
+   LL|      1|async fn await_ready() -> u8 {
+   LL|      1|    // FIXME(#98712): await is only covered if the function yields
+   LL|      1|    ready()
+   LL|      0|        .await
+   LL|      1|}
+   LL|       |
+   LL|      1|fn main() {
+   LL|      1|    let mut future = Box::pin(await_ready());
+   LL|      1|    executor::block_on(future.as_mut());
+   LL|      1|}
+   LL|       |
+   LL|       |mod executor {
+   LL|       |    use core::future::Future;
+   LL|       |    use core::pin::pin;
+   LL|       |    use core::task::{Context, Poll, Waker};
+   LL|       |
+   LL|       |    #[coverage(off)]
+   LL|       |    pub fn block_on<F: Future>(mut future: F) -> F::Output {
+   LL|       |        let mut future = pin!(future);
+   LL|       |        let mut context = Context::from_waker(Waker::noop());
+   LL|       |
+   LL|       |        loop {
+   LL|       |            if let Poll::Ready(val) = future.as_mut().poll(&mut context) {
+   LL|       |                break val;
+   LL|       |            }
+   LL|       |        }
+   LL|       |    }
+   LL|       |}
+

Diff for: tests/coverage/await_ready.rs

@@ -0,0 +1,37 @@
+#![feature(coverage_attribute)]
+#![feature(custom_inner_attributes)] // for #![rustfmt::skip]
+#![feature(noop_waker)]
+#![rustfmt::skip]
+//@ edition: 2021
+
+#[coverage(off)]
+async fn ready() -> u8 { 1 }
+
+async fn await_ready() -> u8 {
+    // FIXME(#98712): await is only covered if the function yields
+    ready()
+        .await
+}
+
+fn main() {
+    let mut future = Box::pin(await_ready());
+    executor::block_on(future.as_mut());
+}
+
+mod executor {
+    use core::future::Future;
+    use core::pin::pin;
+    use core::task::{Context, Poll, Waker};
+
+    #[coverage(off)]
+    pub fn block_on<F: Future>(mut future: F) -> F::Output {
+        let mut future = pin!(future);
+        let mut context = Context::from_waker(Waker::noop());
+
+        loop {
+            if let Poll::Ready(val) = future.as_mut().poll(&mut context) {
+                break val;
+            }
+        }
+    }
+}