Rollup merge of #123349 - compiler-errors:async-closure-captures, r=oli-obk

Fix capture analysis for by-move closure bodies

The check we were doing to figure out if a coroutine was borrowing from its parent coroutine-closure was flat-out wrong -- a misunderstanding of mine of the way that `tcx.closure_captures` represents its captures.

Fixes #123251 (the miri/ui test I added should more than cover that issue)

r? `@oli-obk` -- I recognize that this PR may be underdocumented, so please ask me what I should explain further.

Author: workingjubilee

tests/pass/async-closure-captures.rs

@@ -0,0 +1,91 @@
+// Same as rustc's `tests/ui/async-await/async-closures/captures.rs`, keep in sync
+
+#![feature(async_closure, noop_waker)]
+
+use std::future::Future;
+use std::pin::pin;
+use std::task::*;
+
+pub fn block_on<T>(fut: impl Future<Output = T>) -> T {
+    let mut fut = pin!(fut);
+    let ctx = &mut Context::from_waker(Waker::noop());
+
+    loop {
+        match fut.as_mut().poll(ctx) {
+            Poll::Pending => {}
+            Poll::Ready(t) => break t,
+        }
+    }
+}
+
+fn main() {
+    block_on(async_main());
+}
+
+async fn call<T>(f: &impl async Fn() -> T) -> T {
+    f().await
+}
+
+async fn call_once<T>(f: impl async FnOnce() -> T) -> T {
+    f().await
+}
+
+#[derive(Debug)]
+#[allow(unused)]
+struct Hello(i32);
+
+async fn async_main() {
+    // Capture something by-ref
+    {
+        let x = Hello(0);
+        let c = async || {
+            println!("{x:?}");
+        };
+        call(&c).await;
+        call_once(c).await;
+
+        let x = &Hello(1);
+        let c = async || {
+            println!("{x:?}");
+        };
+        call(&c).await;
+        call_once(c).await;
+    }
+
+    // Capture something and consume it (force to `AsyncFnOnce`)
+    {
+        let x = Hello(2);
+        let c = async || {
+            println!("{x:?}");
+            drop(x);
+        };
+        call_once(c).await;
+    }
+
+    // Capture something with `move`, don't consume it
+    {
+        let x = Hello(3);
+        let c = async move || {
+            println!("{x:?}");
+        };
+        call(&c).await;
+        call_once(c).await;
+
+        let x = &Hello(4);
+        let c = async move || {
+            println!("{x:?}");
+        };
+        call(&c).await;
+        call_once(c).await;
+    }
+
+    // Capture something with `move`, also consume it (so `AsyncFnOnce`)
+    {
+        let x = Hello(5);
+        let c = async move || {
+            println!("{x:?}");
+            drop(x);
+        };
+        call_once(c).await;
+    }
+}

tests/pass/async-closure-captures.stdout

@@ -0,0 +1,10 @@
+Hello(0)
+Hello(0)
+Hello(1)
+Hello(1)
+Hello(2)
+Hello(3)
+Hello(3)
+Hello(4)
+Hello(4)
+Hello(5)