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

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

cc #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".

4 files changed, 7 insertions, 1 deletions

diff --git a/library/alloc/src/boxed.rs b/library/alloc/src/boxed.rs
index ef40d3b203f..38f50955b12 100644
--- a/library/alloc/src/boxed.rs
+++ b/library/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) {
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index bc0874fc13f..13d218e43a7 100644
--- a/library/alloc/src/rc.rs
+++ b/library/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) {
diff --git a/library/alloc/src/string.rs b/library/alloc/src/string.rs
index 01fe950cf3f..124230812df 100644
--- a/library/alloc/src/string.rs
+++ b/library/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()
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index dfd22204c81..b4e0bc5fcbe 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/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) {