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Partially stabilize box_vec_non_null #157226

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Merged
rust-bors merged 3 commits into from
Jul 29, 2026
+30 −33
Merged

Partially stabilize box_vec_non_null #157226

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2a8215d
Add `rustc_as_ptr` to `Vec::as_non_null`
theemathas Jun 3, 2026
1a2857c
Split `Vec::as_non_null()` into a separate `vec_as_non_null` feature
theemathas Jun 13, 2026
a18a972
Stabilize `box_vec_non_null`
theemathas Jun 1, 2026
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16 changes: 2 additions & 14 deletions library/alloc/src/boxed.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1347,16 +1347,12 @@ impl<T: ?Sized> Box<T> {
/// Recreate a `Box` which was previously converted to a `NonNull`
/// pointer using [`Box::into_non_null`]:
/// ```
/// #![feature(box_vec_non_null)]
///
/// let x = Box::new(5);
/// let non_null = Box::into_non_null(x);
/// let x = unsafe { Box::from_non_null(non_null) };
/// ```
/// Manually create a `Box` from scratch by using the global allocator:
/// ```
/// #![feature(box_vec_non_null)]
///
/// use std::alloc::{alloc, Layout};
/// use std::ptr::NonNull;
///
Expand All @@ -1372,7 +1368,7 @@ impl<T: ?Sized> Box<T> {
///
/// [memory layout]: self#memory-layout
/// [considerations for unsafe code]: self#considerations-for-unsafe-code
#[unstable(feature = "box_vec_non_null", issue = "130364")]
#[stable(feature = "box_vec_non_null", since = "CURRENT_RUSTC_VERSION")]
#[inline]
#[must_use = "call `drop(Box::from_non_null(ptr))` if you intend to drop the `Box`"]
pub unsafe fn from_non_null(ptr: NonNull<T>) -> Self {
Expand Down Expand Up @@ -1461,17 +1457,13 @@ impl<T: ?Sized> Box<T> {
/// Converting the `NonNull` pointer back into a `Box` with [`Box::from_non_null`]
/// for automatic cleanup:
/// ```
/// #![feature(box_vec_non_null)]
///
/// let x = Box::new(String::from("Hello"));
/// let non_null = Box::into_non_null(x);
/// let x = unsafe { Box::from_non_null(non_null) };
/// ```
/// Manual cleanup by explicitly running the destructor and deallocating
/// the memory:
/// ```
/// #![feature(box_vec_non_null)]
///
/// use std::alloc::{dealloc, Layout};
///
/// let x = Box::new(String::from("Hello"));
Expand All @@ -1483,8 +1475,6 @@ impl<T: ?Sized> Box<T> {
/// ```
/// Note: This is equivalent to the following:
/// ```
/// #![feature(box_vec_non_null)]
///
/// let x = Box::new(String::from("Hello"));
/// let non_null = Box::into_non_null(x);
/// unsafe {
Expand All @@ -1494,7 +1484,7 @@ impl<T: ?Sized> Box<T> {
///
/// [memory layout]: self#memory-layout
#[must_use = "losing the pointer will leak memory"]
#[unstable(feature = "box_vec_non_null", issue = "130364")]
#[stable(feature = "box_vec_non_null", since = "CURRENT_RUSTC_VERSION")]
#[inline]
pub fn into_non_null(b: Self) -> NonNull<T> {
// SAFETY: `Box` is guaranteed to be non-null.
Expand Down Expand Up @@ -1611,7 +1601,6 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
/// [memory layout]: self#memory-layout
/// [considerations for unsafe code]: self#considerations-for-unsafe-code
#[unstable(feature = "allocator_api", issue = "32838")]
// #[unstable(feature = "box_vec_non_null", issue = "130364")]
#[inline]
pub unsafe fn from_non_null_in(raw: NonNull<T>, alloc: A) -> Self {
// SAFETY: guaranteed by the caller.
Expand Down Expand Up @@ -1726,7 +1715,6 @@ 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")]
// #[unstable(feature = "box_vec_non_null", issue = "130364")]
#[inline]
pub fn into_non_null_with_allocator(b: Self) -> (NonNull<T>, A) {
let (ptr, alloc) = Box::into_raw_with_allocator(b);
Expand Down
25 changes: 9 additions & 16 deletions library/alloc/src/vec/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -697,8 +697,6 @@ impl<T> Vec<T> {
/// # Examples
///
/// ```
/// #![feature(box_vec_non_null)]
///
/// let v = vec![1, 2, 3];
///
/// // Deconstruct the vector into parts.
Expand All @@ -719,8 +717,6 @@ impl<T> Vec<T> {
/// Using memory that was allocated elsewhere:
///
/// ```rust
/// #![feature(box_vec_non_null)]
///
/// use std::alloc::{alloc, Layout};
/// use std::ptr::NonNull;
///
Expand All @@ -742,8 +738,8 @@ impl<T> Vec<T> {
/// }
/// ```
#[inline]
#[unstable(feature = "box_vec_non_null", issue = "130364")]
#[rustc_const_unstable(feature = "box_vec_non_null", issue = "130364")]
#[stable(feature = "box_vec_non_null", since = "CURRENT_RUSTC_VERSION")]
#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
pub const unsafe fn from_parts(ptr: NonNull<T>, length: usize, capacity: usize) -> Self {
unsafe { Self::from_parts_in(ptr, length, capacity, Global) }
}
Expand Down Expand Up @@ -863,8 +859,6 @@ impl<T> Vec<T> {
/// # Examples
///
/// ```
/// #![feature(box_vec_non_null)]
///
/// let v: Vec<i32> = vec![-1, 0, 1];
///
/// let (ptr, len, cap) = v.into_parts();
Expand All @@ -879,8 +873,8 @@ impl<T> Vec<T> {
/// assert_eq!(rebuilt, [4294967295, 0, 1]);
/// ```
#[must_use = "losing the pointer will leak memory"]
#[unstable(feature = "box_vec_non_null", issue = "130364")]
#[rustc_const_unstable(feature = "box_vec_non_null", issue = "130364")]
#[stable(feature = "box_vec_non_null", since = "CURRENT_RUSTC_VERSION")]
#[rustc_const_unstable(feature = "const_heap", issue = "79597")]
pub const fn into_parts(self) -> (NonNull<T>, usize, usize) {
let (ptr, len, capacity) = self.into_raw_parts();
// SAFETY: A `Vec` always has a non-null pointer.
Expand Down Expand Up @@ -1305,7 +1299,6 @@ impl<T, A: Allocator> Vec<T, A> {
#[inline]
#[unstable(feature = "allocator_api", issue = "32838")]
#[rustc_const_unstable(feature = "allocator_api", issue = "32838")]
// #[unstable(feature = "box_vec_non_null", issue = "130364")]
pub const unsafe fn from_parts_in(
ptr: NonNull<T>,
length: usize,
Expand Down Expand Up @@ -1410,7 +1403,6 @@ impl<T, A: Allocator> Vec<T, A> {
#[must_use = "losing the pointer will leak memory"]
#[unstable(feature = "allocator_api", issue = "32838")]
#[rustc_const_unstable(feature = "allocator_api", issue = "32838")]
// #[unstable(feature = "box_vec_non_null", issue = "130364")]
pub const fn into_parts_with_alloc(self) -> (NonNull<T>, usize, usize, A) {
let (ptr, len, capacity, alloc) = self.into_raw_parts_with_alloc();
// SAFETY: A `Vec` always has a non-null pointer.
Expand Down Expand Up @@ -2079,7 +2071,7 @@ impl<T, A: Allocator> Vec<T, A> {
/// # Examples
///
/// ```
/// #![feature(box_vec_non_null)]
/// #![feature(vec_as_non_null)]
///
/// // Allocate vector big enough for 4 elements.
/// let size = 4;
Expand All @@ -2099,7 +2091,7 @@ impl<T, A: Allocator> Vec<T, A> {
/// Due to the aliasing guarantee, the following code is legal:
///
/// ```rust
/// #![feature(box_vec_non_null)]
/// #![feature(vec_as_non_null)]
///
/// unsafe {
/// let mut v = vec![0];
Expand All @@ -2115,8 +2107,9 @@ impl<T, A: Allocator> Vec<T, A> {
/// [`as_mut_ptr`]: Vec::as_mut_ptr
/// [`as_ptr`]: Vec::as_ptr
/// [`as_non_null`]: Vec::as_non_null
#[unstable(feature = "box_vec_non_null", issue = "130364")]
#[rustc_const_unstable(feature = "box_vec_non_null", issue = "130364")]
#[unstable(feature = "vec_as_non_null", issue = "157843")]
#[rustc_const_unstable(feature = "vec_as_non_null", issue = "157843")]
#[rustc_as_ptr]
#[inline]
pub const fn as_non_null(&mut self) -> NonNull<T> {
self.buf.non_null()
Expand Down
3 changes: 3 additions & 0 deletions tests/ui/lint/dangling-pointers-from-temporaries/methods.rs
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Original file line number Diff line number Diff line change
@@ -1,8 +1,11 @@
#![deny(dangling_pointers_from_temporaries)]
#![feature(vec_as_non_null)]

fn main() {
vec![0u8].as_ptr();
//~^ ERROR dangling pointer
vec![0u8].as_mut_ptr();
//~^ ERROR dangling pointer
vec![0u8].as_non_null();
//~^ ERROR dangling pointer
}
19 changes: 16 additions & 3 deletions tests/ui/lint/dangling-pointers-from-temporaries/methods.stderr
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@@ -1,5 +1,5 @@
error: this creates a dangling pointer because temporary `Vec<u8>` is dropped at end of statement
--> $DIR/methods.rs:4:15
--> $DIR/methods.rs:5:15
|
LL | vec![0u8].as_ptr();
| --------- ^^^^^^ pointer created here
Expand All @@ -17,7 +17,7 @@ LL | #![deny(dangling_pointers_from_temporaries)]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: this creates a dangling pointer because temporary `Vec<u8>` is dropped at end of statement
--> $DIR/methods.rs:6:15
--> $DIR/methods.rs:7:15
|
LL | vec![0u8].as_mut_ptr();
| --------- ^^^^^^^^^^ pointer created here
Expand All @@ -29,5 +29,18 @@ LL | vec![0u8].as_mut_ptr();
= note: returning a pointer to a local variable will always result in a dangling pointer
= note: for more information, see <https://doc.rust-lang.org/reference/destructors.html>

error: aborting due to 2 previous errors
error: this creates a dangling pointer because temporary `Vec<u8>` is dropped at end of statement
--> $DIR/methods.rs:9:15
|
LL | vec![0u8].as_non_null();
| --------- ^^^^^^^^^^^ pointer created here
| |
| this `Vec<u8>` is dropped at end of statement
|
= help: bind the `Vec<u8>` to a variable such that it outlives the pointer returned by `as_non_null`
= note: a dangling pointer is safe, but dereferencing one is undefined behavior
= note: returning a pointer to a local variable will always result in a dangling pointer
= note: for more information, see <https://doc.rust-lang.org/reference/destructors.html>

error: aborting due to 3 previous errors

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