Rollup merge of rust-lang#127586 - zachs18:more-must-use, r=cuviper

Add `#[must_use]` to some `into_raw*` functions.

cc rust-lang#121287

r? ``@cuviper``

Adds `#[must_use = "losing the pointer will leak memory"]`[^1] to `Box::into_raw(_with_allocator)`, `Vec::into_raw_parts(_with_alloc)`, `String::into_raw_parts`[^2], and `rc::{Rc, Weak}::into_raw_with_allocator` (Rc's normal `into_raw` and all of `Arc`'s `into_raw*`s are already `must_use`).

Adds `#[must_use = "losing the raw <resource name may leak resources"]` to `IntoRawFd::into_raw_fd`, `IntoRawSocket::into_raw_socket`, and `IntoRawHandle::into_raw_handle`.

[^1]: "*will* leak memory" may be too-strong wording (since `Box`/`Vec`/`String`/`rc::Weak` might not have a backing allocation), but I left it as-is for simplicity and consistency.

[^2]: `String::into_raw_parts`'s `must_use` message is changed from the previous (possibly misleading) "`self` will be dropped if the result is not used".

alloc/src/boxed.rs

@@ -1173,6 +1173,7 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
     /// ```
     ///
     /// [memory layout]: self#memory-layout
+    #[must_use = "losing the pointer will leak memory"]
     #[stable(feature = "box_raw", since = "1.4.0")]
     #[inline]
     pub fn into_raw(b: Self) -> *mut T {
@@ -1226,6 +1227,7 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
     /// ```
     ///
     /// [memory layout]: self#memory-layout
+    #[must_use = "losing the pointer will leak memory"]
     #[unstable(feature = "allocator_api", issue = "32838")]
     #[inline]
     pub fn into_raw_with_allocator(b: Self) -> (*mut T, A) {

alloc/src/rc.rs

@@ -1372,6 +1372,7 @@ impl<T: ?Sized, A: Allocator> Rc<T, A> {
     /// let x = unsafe { Rc::from_raw_in(ptr, alloc) };
     /// assert_eq!(&*x, "hello");
     /// ```
+    #[must_use = "losing the pointer will leak memory"]
     #[unstable(feature = "allocator_api", issue = "32838")]
     pub fn into_raw_with_allocator(this: Self) -> (*const T, A) {
         let this = mem::ManuallyDrop::new(this);
@@ -3107,6 +3108,7 @@ impl<T: ?Sized, A: Allocator> Weak<T, A> {
     ///
     /// [`from_raw_in`]: Weak::from_raw_in
     /// [`as_ptr`]: Weak::as_ptr
+    #[must_use = "losing the pointer will leak memory"]
     #[inline]
     #[unstable(feature = "allocator_api", issue = "32838")]
     pub fn into_raw_with_allocator(self) -> (*const T, A) {

alloc/src/string.rs

@@ -900,7 +900,7 @@ impl String {
     /// let rebuilt = unsafe { String::from_raw_parts(ptr, len, cap) };
     /// assert_eq!(rebuilt, "hello");
     /// ```
-    #[must_use = "`self` will be dropped if the result is not used"]
+    #[must_use = "losing the pointer will leak memory"]
     #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
     pub fn into_raw_parts(self) -> (*mut u8, usize, usize) {
         self.vec.into_raw_parts()

alloc/src/vec/mod.rs

@@ -878,6 +878,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// };
     /// assert_eq!(rebuilt, [4294967295, 0, 1]);
     /// ```
+    #[must_use = "losing the pointer will leak memory"]
     #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
     pub fn into_raw_parts(self) -> (*mut T, usize, usize) {
         let mut me = ManuallyDrop::new(self);
@@ -921,6 +922,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// };
     /// assert_eq!(rebuilt, [4294967295, 0, 1]);
     /// ```
+    #[must_use = "losing the pointer will leak memory"]
     #[unstable(feature = "allocator_api", issue = "32838")]
     // #[unstable(feature = "vec_into_raw_parts", reason = "new API", issue = "65816")]
     pub fn into_raw_parts_with_alloc(self) -> (*mut T, usize, usize, A) {

std/src/os/fd/raw.rs

@@ -138,6 +138,7 @@ pub trait IntoRawFd {
     /// let raw_fd: RawFd = f.into_raw_fd();
     /// # Ok::<(), io::Error>(())
     /// ```
+    #[must_use = "losing the raw file descriptor may leak resources"]
     #[stable(feature = "into_raw_os", since = "1.4.0")]
     fn into_raw_fd(self) -> RawFd;
 }

std/src/os/solid/io.rs

@@ -342,6 +342,7 @@ pub trait IntoRawFd {
     /// This function **transfers ownership** of the underlying file descriptor
     /// to the caller. Callers are then the unique owners of the file descriptor
     /// and must close the descriptor once it's no longer needed.
+    #[must_use = "losing the raw file descriptor may leak resources"]
     fn into_raw_fd(self) -> RawFd;
 }
 

std/src/os/windows/io/raw.rs

@@ -85,6 +85,7 @@ pub trait IntoRawHandle {
     /// However, transferring ownership is not strictly required. Use a
     /// `Into<OwnedHandle>::into` implementation for an API which strictly
     /// transfers ownership.
+    #[must_use = "losing the raw handle may leak resources"]
     #[stable(feature = "into_raw_os", since = "1.4.0")]
     fn into_raw_handle(self) -> RawHandle;
 }
@@ -228,6 +229,7 @@ pub trait IntoRawSocket {
     /// However, transferring ownership is not strictly required. Use a
     /// `Into<OwnedSocket>::into` implementation for an API which strictly
     /// transfers ownership.
+    #[must_use = "losing the raw socket may leak resources"]
     #[stable(feature = "into_raw_os", since = "1.4.0")]
     fn into_raw_socket(self) -> RawSocket;
 }

std/src/sys/pal/windows/process.rs

@@ -564,7 +564,7 @@ impl Stdio {
             Ok(io) => unsafe {
                 let io = Handle::from_raw_handle(io);
                 let ret = io.duplicate(0, true, c::DUPLICATE_SAME_ACCESS);
-                io.into_raw_handle();
+                let _ = io.into_raw_handle(); // Don't close the handle
                 ret
             },
             // If no stdio handle is available, then propagate the null value.

std/src/sys/pal/windows/stdio.rs

@@ -94,7 +94,7 @@ fn write(handle_id: u32, data: &[u8], incomplete_utf8: &mut IncompleteUtf8) -> i
         unsafe {
             let handle = Handle::from_raw_handle(handle);
             let ret = handle.write(data);
-            handle.into_raw_handle(); // Don't close the handle
+            let _ = handle.into_raw_handle(); // Don't close the handle
             return ret;
         }
     }
@@ -243,7 +243,7 @@ impl io::Read for Stdin {
             unsafe {
                 let handle = Handle::from_raw_handle(handle);
                 let ret = handle.read(buf);
-                handle.into_raw_handle(); // Don't close the handle
+                let _ = handle.into_raw_handle(); // Don't close the handle
                 return ret;
             }
         }