Rollup merge of #80614 - 1000teslas:issue-78938-fix, r=tmandry

Explain why borrows can't be held across yield point in async blocks

For https://github.com/rust-lang/rust/issues/78938.

compiler/rustc_error_codes/src/error_codes/E0373.md

@@ -50,3 +50,24 @@ fn foo() -> Box<Fn(u32) -> u32> {
 
 Now that the closure has its own copy of the data, there's no need to worry
 about safety.
+
+This error may also be encountered while using `async` blocks:
+
+```compile_fail,E0373,edition2018
+use std::future::Future;
+
+async fn f() {
+    let v = vec![1, 2, 3i32];
+    spawn(async { //~ ERROR E0373
+        println!("{:?}", v)
+    });
+}
+
+fn spawn<F: Future + Send + 'static>(future: F) {
+    unimplemented!()
+}
+```
+
+Similarly to closures, `async` blocks are not executed immediately and may
+capture closed-over data by reference. For more information, see
+https://rust-lang.github.io/async-book/03_async_await/01_chapter.html.