Rollup merge of #127733 - GrigorenkoPV:don't-forget, r=Amanieu

Replace some `mem::forget`'s with `ManuallyDrop`

              > but I would like to see a larger effort to replace all uses of `mem::forget`.

_Originally posted by `@saethlin` in https://github.com/rust-lang/rust/issues/127584#issuecomment-2226087767_

So,
r? `@saethlin`

Sorry, I have finished writing all of this before I got your response.

7 files changed, 24 insertions, 43 deletions

diff --git a/library/std/src/sys/pal/hermit/thread.rs b/library/std/src/sys/pal/hermit/thread.rs
index a244b953d2a..3723f03081c 100644
--- a/library/std/src/sys/pal/hermit/thread.rs
+++ b/library/std/src/sys/pal/hermit/thread.rs
@@ -3,7 +3,7 @@
 use super::hermit_abi;
 use crate::ffi::CStr;
 use crate::io;
-use crate::mem;
+use crate::mem::ManuallyDrop;
 use crate::num::NonZero;
 use crate::ptr;
 use crate::time::Duration;
@@ -90,9 +90,7 @@ impl Thread {
 
     #[inline]
     pub fn into_id(self) -> Tid {
-        let id = self.tid;
-        mem::forget(self);
-        id
+        ManuallyDrop::new(self).tid
     }
 }
 
diff --git a/library/std/src/sys/pal/sgx/abi/tls/mod.rs b/library/std/src/sys/pal/sgx/abi/tls/mod.rs
index 8a9ea4ac00d..bab59a3422d 100644
--- a/library/std/src/sys/pal/sgx/abi/tls/mod.rs
+++ b/library/std/src/sys/pal/sgx/abi/tls/mod.rs
@@ -95,8 +95,8 @@ impl Tls {
     #[allow(unused)]
     pub unsafe fn activate_persistent(self: Box<Self>) {
         // FIXME: Needs safety information. See entry.S for `set_tls_ptr` definition.
-        unsafe { set_tls_ptr(core::ptr::addr_of!(*self) as _) };
-        mem::forget(self);
+        let ptr = Box::into_raw(self).cast_const().cast::<u8>();
+        unsafe { set_tls_ptr(ptr) };
     }
 
     unsafe fn current<'a>() -> &'a Tls {
diff --git a/library/std/src/sys/pal/sgx/abi/usercalls/alloc.rs b/library/std/src/sys/pal/sgx/abi/usercalls/alloc.rs
index f99cea360f1..b625636752c 100644
--- a/library/std/src/sys/pal/sgx/abi/usercalls/alloc.rs
+++ b/library/std/src/sys/pal/sgx/abi/usercalls/alloc.rs
@@ -5,7 +5,7 @@ use crate::cell::UnsafeCell;
 use crate::cmp;
 use crate::convert::TryInto;
 use crate::intrinsics;
-use crate::mem;
+use crate::mem::{self, ManuallyDrop};
 use crate::ops::{CoerceUnsized, Deref, DerefMut, Index, IndexMut};
 use crate::ptr::{self, NonNull};
 use crate::slice;
@@ -176,6 +176,7 @@ unsafe impl<T: UserSafeSized> UserSafe for [T] {
 /// are used solely to indicate intent: a mutable reference is for writing to
 /// user memory, an immutable reference for reading from user memory.
 #[unstable(feature = "sgx_platform", issue = "56975")]
+#[repr(transparent)]
 pub struct UserRef<T: ?Sized>(UnsafeCell<T>);
 /// An owned type in userspace memory. `User<T>` is equivalent to `Box<T>` in
 /// enclave memory. Access to the memory is only allowed by copying to avoid
@@ -266,9 +267,7 @@ where
     /// Converts this value into a raw pointer. The value will no longer be
     /// automatically freed.
     pub fn into_raw(self) -> *mut T {
-        let ret = self.0;
-        mem::forget(self);
-        ret.as_ptr() as _
+        ManuallyDrop::new(self).0.as_ptr() as _
     }
 }
 
diff --git a/library/std/src/sys/pal/sgx/fd.rs b/library/std/src/sys/pal/sgx/fd.rs
index b3686d0e283..c41b527cff7 100644
--- a/library/std/src/sys/pal/sgx/fd.rs
+++ b/library/std/src/sys/pal/sgx/fd.rs
@@ -2,7 +2,7 @@ use fortanix_sgx_abi::Fd;
 
 use super::abi::usercalls;
 use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut};
-use crate::mem;
+use crate::mem::ManuallyDrop;
 use crate::sys::{AsInner, FromInner, IntoInner};
 
 #[derive(Debug)]
@@ -21,9 +21,7 @@ impl FileDesc {
 
     /// Extracts the actual file descriptor without closing it.
     pub fn into_raw(self) -> Fd {
-        let fd = self.fd;
-        mem::forget(self);
-        fd
+        ManuallyDrop::new(self).fd
     }
 
     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
@@ -70,9 +68,7 @@ impl AsInner<Fd> for FileDesc {
 
 impl IntoInner<Fd> for FileDesc {
     fn into_inner(self) -> Fd {
-        let fd = self.fd;
-        mem::forget(self);
-        fd
+        ManuallyDrop::new(self).fd
     }
 }
 
diff --git a/library/std/src/sys/pal/teeos/thread.rs b/library/std/src/sys/pal/teeos/thread.rs
index 7a27d749f1c..b821e98f9cb 100644
--- a/library/std/src/sys/pal/teeos/thread.rs
+++ b/library/std/src/sys/pal/teeos/thread.rs
@@ -1,9 +1,7 @@
-use core::convert::TryInto;
-
 use crate::cmp;
 use crate::ffi::CStr;
 use crate::io;
-use crate::mem;
+use crate::mem::{self, ManuallyDrop};
 use crate::num::NonZero;
 use crate::ptr;
 use crate::sys::os;
@@ -115,11 +113,9 @@ impl Thread {
 
     /// must join, because no pthread_detach supported
     pub fn join(self) {
-        unsafe {
-            let ret = libc::pthread_join(self.id, ptr::null_mut());
-            mem::forget(self);
-            assert!(ret == 0, "failed to join thread: {}", io::Error::from_raw_os_error(ret));
-        }
+        let id = self.into_id();
+        let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };
+        assert!(ret == 0, "failed to join thread: {}", io::Error::from_raw_os_error(ret));
     }
 
     pub fn id(&self) -> libc::pthread_t {
@@ -127,9 +123,7 @@ impl Thread {
     }
 
     pub fn into_id(self) -> libc::pthread_t {
-        let id = self.id;
-        mem::forget(self);
-        id
+        ManuallyDrop::new(self).id
     }
 }
 
diff --git a/library/std/src/sys/pal/unix/thread.rs b/library/std/src/sys/pal/unix/thread.rs
index 619f4e4121e..483697b8597 100644
--- a/library/std/src/sys/pal/unix/thread.rs
+++ b/library/std/src/sys/pal/unix/thread.rs
@@ -1,7 +1,7 @@
 use crate::cmp;
 use crate::ffi::CStr;
 use crate::io;
-use crate::mem;
+use crate::mem::{self, ManuallyDrop};
 use crate::num::NonZero;
 use crate::ptr;
 use crate::sys::{os, stack_overflow};
@@ -268,11 +268,9 @@ impl Thread {
     }
 
     pub fn join(self) {
-        unsafe {
-            let ret = libc::pthread_join(self.id, ptr::null_mut());
-            mem::forget(self);
-            assert!(ret == 0, "failed to join thread: {}", io::Error::from_raw_os_error(ret));
-        }
+        let id = self.into_id();
+        let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };
+        assert!(ret == 0, "failed to join thread: {}", io::Error::from_raw_os_error(ret));
     }
 
     pub fn id(&self) -> libc::pthread_t {
@@ -280,9 +278,7 @@ impl Thread {
     }
 
     pub fn into_id(self) -> libc::pthread_t {
-        let id = self.id;
-        mem::forget(self);
-        id
+        ManuallyDrop::new(self).id
     }
 }
 
diff --git a/library/std/src/sys/pal/wasi/thread.rs b/library/std/src/sys/pal/wasi/thread.rs
index 975eef2451f..2a3a39aafa7 100644
--- a/library/std/src/sys/pal/wasi/thread.rs
+++ b/library/std/src/sys/pal/wasi/thread.rs
@@ -172,12 +172,10 @@ impl Thread {
     pub fn join(self) {
         cfg_if::cfg_if! {
             if #[cfg(target_feature = "atomics")] {
-                unsafe {
-                    let ret = libc::pthread_join(self.id, ptr::null_mut());
-                    mem::forget(self);
-                    if ret != 0 {
-                        rtabort!("failed to join thread: {}", io::Error::from_raw_os_error(ret));
-                    }
+                let id = mem::ManuallyDrop::new(self).id;
+                let ret = unsafe { libc::pthread_join(id, ptr::null_mut()) };
+                if ret != 0 {
+                    rtabort!("failed to join thread: {}", io::Error::from_raw_os_error(ret));
                 }
             } else {
                 self.0