task: add AbortOnDropHandle::detach (#7400)

tokio-util/src/task/abort_on_drop.rs

@@ -5,6 +5,7 @@ use tokio::task::{AbortHandle, JoinError, JoinHandle};
 
 use std::{
     future::Future,
+    mem::ManuallyDrop,
     pin::Pin,
     task::{Context, Poll},
 };
@@ -46,6 +47,15 @@ impl<T> AbortOnDropHandle<T> {
     pub fn abort_handle(&self) -> AbortHandle {
         self.0.abort_handle()
     }
+
+    /// Cancels aborting on drop and returns the original [`JoinHandle`].
+    pub fn detach(self) -> JoinHandle<T> {
+        // Avoid invoking `AbortOnDropHandle`'s `Drop` impl
+        let this = ManuallyDrop::new(self);
+        // SAFETY: `&this.0` is a reference, so it is certainly initialized, and
+        // it won't be double-dropped because it's in a `ManuallyDrop`
+        unsafe { std::ptr::read(&this.0) }
+    }
 }
 
 impl<T> Future for AbortOnDropHandle<T> {