From 79036bac9eec9a5a03404293b1c378d20af333d9 Mon Sep 17 00:00:00 2001
From: Taiki Endo <te316e89@gmail.com>
Date: Thu, 13 Jan 2022 05:23:35 +0900
Subject: [PATCH] Use ManuallyDrop instead of mem::forget-in-disguise

This fixes stacked borrows violation violations.

See https://github.com/tokio-rs/bytes/pull/458 for more.
---
 futures-task/src/future_obj.rs | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/futures-task/src/future_obj.rs b/futures-task/src/future_obj.rs
index d0cd9b64c8..f67494adb6 100644
--- a/futures-task/src/future_obj.rs
+++ b/futures-task/src/future_obj.rs
@@ -252,10 +252,9 @@ mod if_alloc {
     where
         F: Future<Output = T> + 'a,
     {
-        fn into_raw(mut self) -> *mut (dyn Future<Output = T> + 'a) {
-            let ptr = unsafe { self.as_mut().get_unchecked_mut() as *mut _ };
-            mem::forget(self);
-            ptr
+        fn into_raw(self) -> *mut (dyn Future<Output = T> + 'a) {
+            let mut this = mem::ManuallyDrop::new(self);
+            unsafe { this.as_mut().get_unchecked_mut() as *mut _ }
         }
 
         unsafe fn drop(ptr: *mut (dyn Future<Output = T> + 'a)) {
@@ -264,10 +263,9 @@ mod if_alloc {
     }
 
     unsafe impl<'a, T: 'a> UnsafeFutureObj<'a, T> for Pin<Box<dyn Future<Output = T> + 'a>> {
-        fn into_raw(mut self) -> *mut (dyn Future<Output = T> + 'a) {
-            let ptr = unsafe { self.as_mut().get_unchecked_mut() as *mut _ };
-            mem::forget(self);
-            ptr
+        fn into_raw(self) -> *mut (dyn Future<Output = T> + 'a) {
+            let mut this = mem::ManuallyDrop::new(self);
+            unsafe { this.as_mut().get_unchecked_mut() as *mut _ }
         }
 
         unsafe fn drop(ptr: *mut (dyn Future<Output = T> + 'a)) {
@@ -276,10 +274,9 @@ mod if_alloc {
     }
 
     unsafe impl<'a, T: 'a> UnsafeFutureObj<'a, T> for Pin<Box<dyn Future<Output = T> + Send + 'a>> {
-        fn into_raw(mut self) -> *mut (dyn Future<Output = T> + 'a) {
-            let ptr = unsafe { self.as_mut().get_unchecked_mut() as *mut _ };
-            mem::forget(self);
-            ptr
+        fn into_raw(self) -> *mut (dyn Future<Output = T> + 'a) {
+            let mut this = mem::ManuallyDrop::new(self);
+            unsafe { this.as_mut().get_unchecked_mut() as *mut _ }
         }
 
         unsafe fn drop(ptr: *mut (dyn Future<Output = T> + 'a)) {