From d6945f6d8c15bd692000cd7f8d76d171ae27b8c9 Mon Sep 17 00:00:00 2001 From: ltdk Date: Thu, 17 Jul 2025 23:28:24 -0400 Subject: [PATCH] Add cast_init and cast_uninit methods for pointers --- library/alloc/src/lib.rs | 1 + library/alloc/src/vec/mod.rs | 2 +- library/core/src/iter/adapters/map_windows.rs | 2 +- library/core/src/ptr/const_ptr.rs | 22 ++++++++++++++++ library/core/src/ptr/mut_ptr.rs | 25 +++++++++++++++++++ library/core/src/ptr/non_null.rs | 22 ++++++++++++++++ library/std/src/lib.rs | 1 + library/std/src/sys/fs/windows.rs | 2 +- 8 files changed, 74 insertions(+), 3 deletions(-) diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs index c091e496c5090..639c5d4c9309f 100644 --- a/library/alloc/src/lib.rs +++ b/library/alloc/src/lib.rs @@ -102,6 +102,7 @@ #![feature(async_iterator)] #![feature(bstr)] #![feature(bstr_internals)] +#![feature(cast_maybe_uninit)] #![feature(char_internals)] #![feature(char_max_len)] #![feature(clone_to_uninit)] diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs index 8001faf9d20a5..2e40227a058af 100644 --- a/library/alloc/src/vec/mod.rs +++ b/library/alloc/src/vec/mod.rs @@ -3176,7 +3176,7 @@ impl Vec { // - but the allocation extends out to `self.buf.capacity()` elements, possibly // uninitialized let spare_ptr = unsafe { ptr.add(self.len) }; - let spare_ptr = spare_ptr.cast::>(); + let spare_ptr = spare_ptr.cast_uninit(); let spare_len = self.buf.capacity() - self.len; // SAFETY: diff --git a/library/core/src/iter/adapters/map_windows.rs b/library/core/src/iter/adapters/map_windows.rs index a9c07fee2a91e..0dada9eb6aacf 100644 --- a/library/core/src/iter/adapters/map_windows.rs +++ b/library/core/src/iter/adapters/map_windows.rs @@ -195,7 +195,7 @@ impl Buffer { // SAFETY: the index is valid and this is element `a` in the // diagram above and has not been dropped yet. - unsafe { ptr::drop_in_place(to_drop.cast::()) }; + unsafe { ptr::drop_in_place(to_drop.cast_init()) }; } } diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs index 8b3703bd4b321..6546dde39ac27 100644 --- a/library/core/src/ptr/const_ptr.rs +++ b/library/core/src/ptr/const_ptr.rs @@ -1430,6 +1430,28 @@ impl *const T { } } +impl *const T { + /// Casts from a type to its maybe-uninitialized version. + #[must_use] + #[inline(always)] + #[unstable(feature = "cast_maybe_uninit", issue = "145036")] + pub const fn cast_uninit(self) -> *const MaybeUninit { + self as _ + } +} +impl *const MaybeUninit { + /// Casts from a maybe-uninitialized type to its initialized version. + /// + /// This is always safe, since UB can only occur if the pointer is read + /// before being initialized. + #[must_use] + #[inline(always)] + #[unstable(feature = "cast_maybe_uninit", issue = "145036")] + pub const fn cast_init(self) -> *const T { + self as _ + } +} + impl *const [T] { /// Returns the length of a raw slice. /// diff --git a/library/core/src/ptr/mut_ptr.rs b/library/core/src/ptr/mut_ptr.rs index af39ec86d7ac8..4add964141ae5 100644 --- a/library/core/src/ptr/mut_ptr.rs +++ b/library/core/src/ptr/mut_ptr.rs @@ -1687,6 +1687,31 @@ impl *mut T { } } +impl *mut T { + /// Casts from a type to its maybe-uninitialized version. + /// + /// This is always safe, since UB can only occur if the pointer is read + /// before being initialized. + #[must_use] + #[inline(always)] + #[unstable(feature = "cast_maybe_uninit", issue = "145036")] + pub const fn cast_uninit(self) -> *mut MaybeUninit { + self as _ + } +} +impl *mut MaybeUninit { + /// Casts from a maybe-uninitialized type to its initialized version. + /// + /// This is always safe, since UB can only occur if the pointer is read + /// before being initialized. + #[must_use] + #[inline(always)] + #[unstable(feature = "cast_maybe_uninit", issue = "145036")] + pub const fn cast_init(self) -> *mut T { + self as _ + } +} + impl *mut [T] { /// Returns the length of a raw slice. /// diff --git a/library/core/src/ptr/non_null.rs b/library/core/src/ptr/non_null.rs index 8667361fecc74..294184ae8e07f 100644 --- a/library/core/src/ptr/non_null.rs +++ b/library/core/src/ptr/non_null.rs @@ -1357,6 +1357,28 @@ impl NonNull { } } +impl NonNull { + /// Casts from a type to its maybe-uninitialized version. + #[must_use] + #[inline(always)] + #[unstable(feature = "cast_maybe_uninit", issue = "145036")] + pub const fn cast_uninit(self) -> NonNull> { + self.cast() + } +} +impl NonNull> { + /// Casts from a maybe-uninitialized type to its initialized version. + /// + /// This is always safe, since UB can only occur if the pointer is read + /// before being initialized. + #[must_use] + #[inline(always)] + #[unstable(feature = "cast_maybe_uninit", issue = "145036")] + pub const fn cast_init(self) -> NonNull { + self.cast() + } +} + impl NonNull<[T]> { /// Creates a non-null raw slice from a thin pointer and a length. /// diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs index 0c53753064724..66d3f71e0ba2b 100644 --- a/library/std/src/lib.rs +++ b/library/std/src/lib.rs @@ -327,6 +327,7 @@ // tidy-alphabetical-start #![feature(bstr)] #![feature(bstr_internals)] +#![feature(cast_maybe_uninit)] #![feature(char_internals)] #![feature(clone_to_uninit)] #![feature(core_intrinsics)] diff --git a/library/std/src/sys/fs/windows.rs b/library/std/src/sys/fs/windows.rs index 09feddd0be9a1..bb3e4bc30ca95 100644 --- a/library/std/src/sys/fs/windows.rs +++ b/library/std/src/sys/fs/windows.rs @@ -1606,7 +1606,7 @@ pub fn junction_point(original: &Path, link: &Path) -> io::Result<()> { }; unsafe { let ptr = header.PathBuffer.as_mut_ptr(); - ptr.copy_from(abs_path.as_ptr().cast::>(), abs_path.len()); + ptr.copy_from(abs_path.as_ptr().cast_uninit(), abs_path.len()); let mut ret = 0; cvt(c::DeviceIoControl(