Auto merge of #104219 - bryangarza:async-track-caller-dup, r=eholk

Support `#[track_caller]` on async fns

Adds `#[track_caller]` to the generator that is created when we desugar the async fn.

Fixes #78840

Open questions:
- What is the performance impact of adding `#[track_caller]` to every `GenFuture`'s `poll(...)` function, even if it's unused (i.e., the parent span does not set `#[track_caller]`)? We might need to set it only conditionally, if the indirection causes overhead we don't want.

src/test/ui/async-await/track-caller/panic-track-caller.rs

@@ -0,0 +1,76 @@
+// run-pass
+// edition:2021
+// needs-unwind
+#![feature(closure_track_caller)]
+
+use std::future::Future;
+use std::panic;
+use std::sync::{Arc, Mutex};
+use std::task::{Context, Poll, Wake};
+use std::thread::{self, Thread};
+
+/// A waker that wakes up the current thread when called.
+struct ThreadWaker(Thread);
+
+impl Wake for ThreadWaker {
+    fn wake(self: Arc<Self>) {
+        self.0.unpark();
+    }
+}
+
+/// Run a future to completion on the current thread.
+fn block_on<T>(fut: impl Future<Output = T>) -> T {
+    // Pin the future so it can be polled.
+    let mut fut = Box::pin(fut);
+
+    // Create a new context to be passed to the future.
+    let t = thread::current();
+    let waker = Arc::new(ThreadWaker(t)).into();
+    let mut cx = Context::from_waker(&waker);
+
+    // Run the future to completion.
+    loop {
+        match fut.as_mut().poll(&mut cx) {
+            Poll::Ready(res) => return res,
+            Poll::Pending => thread::park(),
+        }
+    }
+}
+
+async fn bar() {
+    panic!()
+}
+
+async fn foo() {
+    bar().await
+}
+
+#[track_caller]
+async fn bar_track_caller() {
+    panic!()
+}
+
+async fn foo_track_caller() {
+    bar_track_caller().await
+}
+
+fn panicked_at(f: impl FnOnce() + panic::UnwindSafe) -> u32 {
+    let loc = Arc::new(Mutex::new(None));
+
+    let hook = panic::take_hook();
+    {
+        let loc = loc.clone();
+        panic::set_hook(Box::new(move |info| {
+            *loc.lock().unwrap() = info.location().map(|loc| loc.line())
+        }));
+    }
+    panic::catch_unwind(f).unwrap_err();
+    panic::set_hook(hook);
+    let x = loc.lock().unwrap().unwrap();
+    x
+}
+
+fn main() {
+    assert_eq!(panicked_at(|| block_on(foo())), 41);
+    assert_eq!(panicked_at(|| block_on(foo_track_caller())), 54);
+}