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Deprecate uninit_array #101179

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2 changes: 1 addition & 1 deletion compiler/rustc_data_structures/src/lib.rs
Original file line number Diff line number Diff line change
@@ -15,7 +15,7 @@
#![feature(extend_one)]
#![feature(hash_raw_entry)]
#![feature(hasher_prefixfree_extras)]
#![feature(maybe_uninit_uninit_array)]
#![feature(maybe_uninit_uninit_array_transpose)]
#![feature(min_specialization)]
#![feature(never_type)]
#![feature(type_alias_impl_trait)]
2 changes: 1 addition & 1 deletion compiler/rustc_data_structures/src/sip128.rs
Original file line number Diff line number Diff line change
@@ -183,7 +183,7 @@ impl SipHasher128 {
pub fn new_with_keys(key0: u64, key1: u64) -> SipHasher128 {
let mut hasher = SipHasher128 {
nbuf: 0,
buf: MaybeUninit::uninit_array(),
buf: MaybeUninit::uninit().transpose(),
state: State {
v0: key0 ^ 0x736f6d6570736575,
// The XOR with 0xee is only done on 128-bit algorithm version.
7 changes: 3 additions & 4 deletions compiler/rustc_serialize/tests/leb128.rs
Original file line number Diff line number Diff line change
@@ -1,5 +1,4 @@
#![feature(maybe_uninit_slice)]
#![feature(maybe_uninit_uninit_array)]
#![feature(maybe_uninit_uninit_array_transpose)]

use rustc_serialize::leb128::*;
use std::mem::MaybeUninit;
@@ -24,7 +23,7 @@ macro_rules! impl_test_unsigned_leb128 {
let mut stream = Vec::new();

for &x in &values {
let mut buf = MaybeUninit::uninit_array();
let mut buf = MaybeUninit::uninit().transpose();
stream.extend($write_fn_name(&mut buf, x));
}

@@ -70,7 +69,7 @@ macro_rules! impl_test_signed_leb128 {
let mut stream = Vec::new();

for &x in &values {
let mut buf = MaybeUninit::uninit_array();
let mut buf = MaybeUninit::uninit().transpose();
stream.extend($write_fn_name(&mut buf, x));
}

2 changes: 1 addition & 1 deletion library/alloc/src/lib.rs
Original file line number Diff line number Diff line change
@@ -127,7 +127,7 @@
#![feature(layout_for_ptr)]
#![feature(maybe_uninit_array_assume_init)]
#![feature(maybe_uninit_slice)]
#![feature(maybe_uninit_uninit_array)]
#![feature(maybe_uninit_uninit_array_transpose)]
#![cfg_attr(test, feature(new_uninit))]
#![feature(nonnull_slice_from_raw_parts)]
#![feature(pattern)]
2 changes: 1 addition & 1 deletion library/alloc/src/vec/into_iter.rs
Original file line number Diff line number Diff line change
@@ -210,7 +210,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {

#[inline]
fn next_chunk<const N: usize>(&mut self) -> Result<[T; N], core::array::IntoIter<T, N>> {
let mut raw_ary = MaybeUninit::uninit_array();
let mut raw_ary = MaybeUninit::uninit().transpose();

let len = self.len();

8 changes: 4 additions & 4 deletions library/core/src/array/iter.rs
Original file line number Diff line number Diff line change
@@ -106,7 +106,6 @@ impl<T, const N: usize> IntoIter<T, N> {
/// #![feature(array_into_iter_constructors)]
///
/// #![feature(maybe_uninit_array_assume_init)]
/// #![feature(maybe_uninit_uninit_array)]
/// use std::array::IntoIter;
/// use std::mem::MaybeUninit;
///
@@ -116,7 +115,7 @@ impl<T, const N: usize> IntoIter<T, N> {
/// fn next_chunk<T: Copy, const N: usize>(
/// it: &mut impl Iterator<Item = T>,
/// ) -> Result<[T; N], IntoIter<T, N>> {
/// let mut buffer = MaybeUninit::uninit_array();
/// let mut buffer = [MaybeUninit::uninit(); N];
/// let mut i = 0;
/// while i < N {
/// match it.next() {
@@ -208,7 +207,7 @@ impl<T, const N: usize> IntoIter<T, N> {
#[unstable(feature = "array_into_iter_constructors", issue = "91583")]
#[rustc_const_unstable(feature = "const_array_into_iter_constructors", issue = "91583")]
pub const fn empty() -> Self {
let buffer = MaybeUninit::uninit_array();
let buffer = MaybeUninit::uninit().transpose();
let initialized = 0..0;

// SAFETY: We're telling it that none of the elements are initialized,
@@ -387,7 +386,8 @@ impl<T: Clone, const N: usize> Clone for IntoIter<T, N> {
fn clone(&self) -> Self {
// Note, we don't really need to match the exact same alive range, so
// we can just clone into offset 0 regardless of where `self` is.
let mut new = Self { data: MaybeUninit::uninit_array(), alive: IndexRange::zero_to(0) };
let mut new =
Self { data: MaybeUninit::uninit().transpose(), alive: IndexRange::zero_to(0) };

// Clone all alive elements.
for (src, dst) in iter::zip(self.as_slice(), &mut new.data) {
2 changes: 1 addition & 1 deletion library/core/src/array/mod.rs
Original file line number Diff line number Diff line change
@@ -879,7 +879,7 @@ where
}
}

let mut array = MaybeUninit::uninit_array::<N>();
let mut array = MaybeUninit::uninit().transpose();
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Is it worth adding a type annotation?

Suggested change
let mut array = MaybeUninit::uninit().transpose();
let mut array = MaybeUninit::<[???; N]>::uninit().transpose();

There's a lot of inference going on here making the code quite hard to follow.

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Hmmm, yeah I was wondering about this too. My reasoning for this being ok was that if the compiler manages to infer the types then I don't need to think about them. I'm guessing this is flawed because if you have no constraints at all, then the compiler will happily give you an i32. An interesting question arises: are integers and floats the only two places where the compiler will ever pull a type out of its 🍑 if there are no constraints? If so, my gut feeling is that we should get rid of that behavior (separate discussion, I know) since not having 🍑 types would let you do what I'm doing now where I say, "well, the compiler did some inferences so whatever the types are they must be correct". Or maybe I'm thinking too hard about this and type annotations would make human consumption easier (though I'm still curious about the above questions).

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In safe code I tend to follow the same approach -- if the compiler found a type that makes it all work, then that seems right (but I will still sometimes add type annotations to make the code more readable).

In unsafe code though, I don't like trusting the compiler like that. Types are much less meaningful in unsafe code (that's why the code is unsafe to begin with), so IMO type inference should only be relied upon for absolutely obvious cases -- which this one is not.

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Good point, will do.

let mut guard = Guard { array_mut: &mut array, initialized: 0 };

for _ in 0..N {
16 changes: 8 additions & 8 deletions library/core/src/fmt/float.rs
Original file line number Diff line number Diff line change
@@ -35,8 +35,8 @@ fn float_to_decimal_common_exact<T>(
where
T: flt2dec::DecodableFloat,
{
let mut buf: [MaybeUninit<u8>; 1024] = MaybeUninit::uninit_array(); // enough for f32 and f64
let mut parts: [MaybeUninit<numfmt::Part<'_>>; 4] = MaybeUninit::uninit_array();
let mut buf = [MaybeUninit::<u8>::uninit(); 1024]; // enough for f32 and f64
let mut parts = [MaybeUninit::<numfmt::Part<'_>>::uninit(); 4];
let formatted = flt2dec::to_exact_fixed_str(
flt2dec::strategy::grisu::format_exact,
*num,
@@ -61,8 +61,8 @@ where
T: flt2dec::DecodableFloat,
{
// enough for f32 and f64
let mut buf: [MaybeUninit<u8>; flt2dec::MAX_SIG_DIGITS] = MaybeUninit::uninit_array();
let mut parts: [MaybeUninit<numfmt::Part<'_>>; 4] = MaybeUninit::uninit_array();
let mut buf = [MaybeUninit::<u8>::uninit(); flt2dec::MAX_SIG_DIGITS];
let mut parts = [MaybeUninit::<numfmt::Part<'_>>::uninit(); 4];
let formatted = flt2dec::to_shortest_str(
flt2dec::strategy::grisu::format_shortest,
*num,
@@ -105,8 +105,8 @@ fn float_to_exponential_common_exact<T>(
where
T: flt2dec::DecodableFloat,
{
let mut buf: [MaybeUninit<u8>; 1024] = MaybeUninit::uninit_array(); // enough for f32 and f64
let mut parts: [MaybeUninit<numfmt::Part<'_>>; 6] = MaybeUninit::uninit_array();
let mut buf = [MaybeUninit::<u8>::uninit(); 1024]; // enough for f32 and f64
let mut parts = [MaybeUninit::<numfmt::Part<'_>>::uninit(); 6];
let formatted = flt2dec::to_exact_exp_str(
flt2dec::strategy::grisu::format_exact,
*num,
@@ -132,8 +132,8 @@ where
T: flt2dec::DecodableFloat,
{
// enough for f32 and f64
let mut buf: [MaybeUninit<u8>; flt2dec::MAX_SIG_DIGITS] = MaybeUninit::uninit_array();
let mut parts: [MaybeUninit<numfmt::Part<'_>>; 6] = MaybeUninit::uninit_array();
let mut buf = [MaybeUninit::<u8>::uninit(); flt2dec::MAX_SIG_DIGITS];
let mut parts = [MaybeUninit::<numfmt::Part<'_>>::uninit(); 6];
let formatted = flt2dec::to_shortest_exp_str(
flt2dec::strategy::grisu::format_shortest,
*num,
3 changes: 1 addition & 2 deletions library/core/src/lib.rs
Original file line number Diff line number Diff line change
@@ -119,7 +119,6 @@
#![feature(const_int_unchecked_arith)]
#![feature(const_intrinsic_forget)]
#![feature(const_likely)]
#![feature(const_maybe_uninit_uninit_array)]
#![feature(const_maybe_uninit_as_mut_ptr)]
#![feature(const_maybe_uninit_assume_init)]
#![feature(const_nonnull_new)]
@@ -151,7 +150,6 @@
#![feature(const_waker)]
#![feature(core_panic)]
#![feature(duration_consts_float)]
#![feature(maybe_uninit_uninit_array)]
#![feature(ptr_alignment_type)]
#![feature(ptr_metadata)]
#![feature(slice_ptr_get)]
@@ -217,6 +215,7 @@
#![feature(unboxed_closures)]
#![feature(unsized_fn_params)]
#![feature(asm_const)]
#![feature(const_transmute_copy)]
//
// Target features:
#![feature(arm_target_feature)]
19 changes: 12 additions & 7 deletions library/core/src/mem/maybe_uninit.rs
Original file line number Diff line number Diff line change
@@ -138,7 +138,7 @@ use crate::slice;
/// unsafe { mem::transmute::<_, [Vec<u32>; 1000]>(data) }
/// };
///
/// assert_eq!(&data[0], &[42]);
/// assert_eq!(&data[42], &[42]);
/// ```
///
/// You can also work with partially initialized arrays, which could
@@ -148,10 +148,9 @@ use crate::slice;
/// use std::mem::MaybeUninit;
/// use std::ptr;
///
/// // Create an uninitialized array of `MaybeUninit`. The `assume_init` is
/// // safe because the type we are claiming to have initialized here is a
/// // bunch of `MaybeUninit`s, which do not require initialization.
/// let mut data: [MaybeUninit<String>; 1000] = unsafe { MaybeUninit::uninit().assume_init() };
/// // Create an uninitialized array of `MaybeUninit`.
/// const UNINIT_STRING: MaybeUninit<String> = MaybeUninit::uninit();
/// let mut data = [UNINIT_STRING; 1000];
/// // Count the number of elements we have assigned.
/// let mut data_len: usize = 0;
///
@@ -348,6 +347,10 @@ impl<T> MaybeUninit<T> {
#[rustc_const_unstable(feature = "const_maybe_uninit_uninit_array", issue = "96097")]
#[must_use]
#[inline(always)]
#[deprecated(
since = "nightly",
note = "Use const array initialization instead or the transpose methods."
)]
pub const fn uninit_array<const N: usize>() -> [Self; N] {
// SAFETY: An uninitialized `[MaybeUninit<_>; LEN]` is valid.
unsafe { MaybeUninit::<[MaybeUninit<T>; N]>::uninit().assume_init() }
@@ -1297,7 +1300,8 @@ impl<T, const N: usize> MaybeUninit<[T; N]> {
/// let data: [MaybeUninit<u8>; 1000] = MaybeUninit::uninit().transpose();
/// ```
#[unstable(feature = "maybe_uninit_uninit_array_transpose", issue = "96097")]
pub fn transpose(self) -> [MaybeUninit<T>; N] {
#[inline(always)]
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Please just use #[inline] for these. always should be avoided without particular justification, so for this PR please just use #[inline].

Then we can discuss changing it to inline(always) in a subsequent PR if you'd like.

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I don't like the scope creep anyway, so lemme just pull this out into a seperate PR.

pub const fn transpose(self) -> [MaybeUninit<T>; N] {
// SAFETY: T and MaybeUninit<T> have the same layout
unsafe { super::transmute_copy(&ManuallyDrop::new(self)) }
}
@@ -1316,7 +1320,8 @@ impl<T, const N: usize> [MaybeUninit<T>; N] {
/// let data: MaybeUninit<[u8; 1000]> = data.transpose();
/// ```
#[unstable(feature = "maybe_uninit_uninit_array_transpose", issue = "96097")]
pub fn transpose(self) -> MaybeUninit<[T; N]> {
#[inline(always)]
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(here too)

pub const fn transpose(self) -> MaybeUninit<[T; N]> {
// SAFETY: T and MaybeUninit<T> have the same layout
unsafe { super::transmute_copy(&ManuallyDrop::new(self)) }
}
1 change: 0 additions & 1 deletion library/core/tests/lib.rs
Original file line number Diff line number Diff line change
@@ -48,7 +48,6 @@
#![feature(slice_take)]
#![feature(slice_from_ptr_range)]
#![feature(split_as_slice)]
#![feature(maybe_uninit_uninit_array)]
#![feature(maybe_uninit_array_assume_init)]
#![feature(maybe_uninit_write_slice)]
#![feature(min_specialization)]
2 changes: 1 addition & 1 deletion library/core/tests/mem.rs
Original file line number Diff line number Diff line change
@@ -163,7 +163,7 @@ fn assume_init_good() {

#[test]
fn uninit_array_assume_init() {
let mut array: [MaybeUninit<i16>; 5] = MaybeUninit::uninit_array();
let mut array = [MaybeUninit::<i16>::uninit(); 5];
array[0].write(3);
array[1].write(1);
array[2].write(4);
3 changes: 1 addition & 2 deletions library/std/src/lib.rs
Original file line number Diff line number Diff line change
@@ -312,8 +312,7 @@
#![feature(std_internals)]
#![feature(str_internals)]
#![feature(strict_provenance)]
#![feature(maybe_uninit_uninit_array)]
#![feature(const_maybe_uninit_uninit_array)]
#![feature(maybe_uninit_uninit_array_transpose)]
#![feature(const_waker)]
//
// Library features (alloc):
2 changes: 1 addition & 1 deletion library/std/src/net/display_buffer.rs
Original file line number Diff line number Diff line change
@@ -11,7 +11,7 @@ pub struct DisplayBuffer<const SIZE: usize> {
impl<const SIZE: usize> DisplayBuffer<SIZE> {
#[inline]
pub const fn new() -> Self {
Self { buf: MaybeUninit::uninit_array(), len: 0 }
Self { buf: MaybeUninit::uninit().transpose(), len: 0 }
}

#[inline]
2 changes: 1 addition & 1 deletion library/std/src/sys/windows/mod.rs
Original file line number Diff line number Diff line change
@@ -205,7 +205,7 @@ where
// This initial size also works around `GetFullPathNameW` returning
// incorrect size hints for some short paths:
// https://github.com/dylni/normpath/issues/5
let mut stack_buf: [MaybeUninit<u16>; 512] = MaybeUninit::uninit_array();
let mut stack_buf = [MaybeUninit::<u16>::uninit(); 512];
let mut heap_buf: Vec<MaybeUninit<u16>> = Vec::new();
unsafe {
let mut n = stack_buf.len();