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Constify conversion traits (part 1) #145279

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f70c98f
Constify Eq, Ord, PartialOrd
Randl Aug 16, 2025
4ebb4b7
Constify conversion traits
clarfonthey Aug 11, 2025
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15 changes: 11 additions & 4 deletions library/alloc/src/borrow.rs
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Expand Up @@ -17,9 +17,11 @@ use crate::fmt;
use crate::string::String;

#[stable(feature = "rust1", since = "1.0.0")]
impl<'a, B: ?Sized> Borrow<B> for Cow<'a, B>
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<'a, B: ?Sized> const Borrow<B> for Cow<'a, B>
where
B: ToOwned,
B::Owned: [const] Borrow<B>,
{
fn borrow(&self) -> &B {
&**self
Expand Down Expand Up @@ -326,9 +328,10 @@ impl<B: ?Sized + ToOwned> Cow<'_, B> {
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<B: ?Sized + ToOwned> Deref for Cow<'_, B>
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<B: ?Sized + ToOwned> const Deref for Cow<'_, B>
where
B::Owned: Borrow<B>,
B::Owned: [const] Borrow<B>,
{
type Target = B;

Expand Down Expand Up @@ -439,7 +442,11 @@ where
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized + ToOwned> AsRef<T> for Cow<'_, T> {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T: ?Sized + ToOwned> const AsRef<T> for Cow<'_, T>
where
T::Owned: [const] Borrow<T>,
{
fn as_ref(&self) -> &T {
self
}
Expand Down
6 changes: 4 additions & 2 deletions library/alloc/src/collections/mod.rs
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Expand Up @@ -128,17 +128,19 @@ pub use realalloc::collections::TryReserveErrorKind;
reason = "Uncertain how much info should be exposed",
issue = "48043"
)]
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
#[cfg(not(test))]
impl From<TryReserveErrorKind> for TryReserveError {
impl const From<TryReserveErrorKind> for TryReserveError {
#[inline]
fn from(kind: TryReserveErrorKind) -> Self {
Self { kind }
}
}

#[unstable(feature = "try_reserve_kind", reason = "new API", issue = "48043")]
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
#[cfg(not(test))]
impl From<LayoutError> for TryReserveErrorKind {
impl const From<LayoutError> for TryReserveErrorKind {
/// Always evaluates to [`TryReserveErrorKind::CapacityOverflow`].
#[inline]
fn from(_: LayoutError) -> Self {
Expand Down
3 changes: 2 additions & 1 deletion library/alloc/src/lib.rs
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Expand Up @@ -107,10 +107,10 @@
#![feature(char_max_len)]
#![feature(clone_to_uninit)]
#![feature(coerce_unsized)]
#![feature(const_convert)]
#![feature(const_default)]
#![feature(const_eval_select)]
#![feature(const_heap)]
#![feature(const_trait_impl)]
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Was listed under library features, and is actually a language feature. Since the diff doesn't make that clear.

#![feature(core_intrinsics)]
#![feature(deprecated_suggestion)]
#![feature(deref_pure_trait)]
Expand Down Expand Up @@ -167,6 +167,7 @@
#![feature(allow_internal_unstable)]
#![feature(cfg_sanitize)]
#![feature(const_precise_live_drops)]
#![feature(const_trait_impl)]
#![feature(coroutine_trait)]
#![feature(decl_macro)]
#![feature(dropck_eyepatch)]
Expand Down
1 change: 1 addition & 0 deletions library/alloctests/lib.rs
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Expand Up @@ -46,6 +46,7 @@
// Language features:
// tidy-alphabetical-start
#![feature(cfg_sanitize)]
#![feature(const_trait_impl)]
#![feature(dropck_eyepatch)]
#![feature(lang_items)]
#![feature(min_specialization)]
Expand Down
3 changes: 2 additions & 1 deletion library/core/src/any.rs
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Expand Up @@ -705,7 +705,8 @@ impl dyn Any + Send + Sync {
/// std::mem::forget(fake_one_ring);
/// }
/// ```
#[derive(Clone, Copy, Eq, PartialOrd, Ord)]
#[derive(Copy, PartialOrd, Ord)]
#[derive_const(Clone, Eq)]
#[stable(feature = "rust1", since = "1.0.0")]
#[lang = "type_id"]
pub struct TypeId {
Expand Down
46 changes: 29 additions & 17 deletions library/core/src/array/equality.rs
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@@ -1,9 +1,10 @@
use crate::cmp::BytewiseEq;

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, U, const N: usize> PartialEq<[U; N]> for [T; N]
#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
impl<T, U, const N: usize> const PartialEq<[U; N]> for [T; N]
where
T: PartialEq<U>,
T: [const] PartialEq<U>,
{
#[inline]
fn eq(&self, other: &[U; N]) -> bool {
Expand All @@ -16,9 +17,10 @@ where
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, U, const N: usize> PartialEq<[U]> for [T; N]
#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
impl<T, U, const N: usize> const PartialEq<[U]> for [T; N]
where
T: PartialEq<U>,
T: [const] PartialEq<U>,
{
#[inline]
fn eq(&self, other: &[U]) -> bool {
Expand All @@ -37,9 +39,10 @@ where
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, U, const N: usize> PartialEq<[U; N]> for [T]
#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
impl<T, U, const N: usize> const PartialEq<[U; N]> for [T]
where
T: PartialEq<U>,
T: [const] PartialEq<U>,
{
#[inline]
fn eq(&self, other: &[U; N]) -> bool {
Expand All @@ -58,9 +61,10 @@ where
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, U, const N: usize> PartialEq<&[U]> for [T; N]
#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
impl<T, U, const N: usize> const PartialEq<&[U]> for [T; N]
where
T: PartialEq<U>,
T: [const] PartialEq<U>,
{
#[inline]
fn eq(&self, other: &&[U]) -> bool {
Expand All @@ -73,9 +77,10 @@ where
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, U, const N: usize> PartialEq<[U; N]> for &[T]
#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
impl<T, U, const N: usize> const PartialEq<[U; N]> for &[T]
where
T: PartialEq<U>,
T: [const] PartialEq<U>,
{
#[inline]
fn eq(&self, other: &[U; N]) -> bool {
Expand All @@ -88,9 +93,10 @@ where
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, U, const N: usize> PartialEq<&mut [U]> for [T; N]
#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
impl<T, U, const N: usize> const PartialEq<&mut [U]> for [T; N]
where
T: PartialEq<U>,
T: [const] PartialEq<U>,
{
#[inline]
fn eq(&self, other: &&mut [U]) -> bool {
Expand All @@ -103,9 +109,10 @@ where
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, U, const N: usize> PartialEq<[U; N]> for &mut [T]
#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
impl<T, U, const N: usize> const PartialEq<[U; N]> for &mut [T]
where
T: PartialEq<U>,
T: [const] PartialEq<U>,
{
#[inline]
fn eq(&self, other: &[U; N]) -> bool {
Expand All @@ -122,14 +129,18 @@ where
// __impl_slice_eq2! { [A; $N], &'b mut [B; $N] }

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Eq, const N: usize> Eq for [T; N] {}
#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
impl<T: [const] Eq, const N: usize> const Eq for [T; N] {}

#[const_trait]
#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
trait SpecArrayEq<Other, const N: usize>: Sized {
fn spec_eq(a: &[Self; N], b: &[Other; N]) -> bool;
fn spec_ne(a: &[Self; N], b: &[Other; N]) -> bool;
}

impl<T: PartialEq<Other>, Other, const N: usize> SpecArrayEq<Other, N> for T {
#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
impl<T: [const] PartialEq<Other>, Other, const N: usize> const SpecArrayEq<Other, N> for T {
default fn spec_eq(a: &[Self; N], b: &[Other; N]) -> bool {
a[..] == b[..]
}
Expand All @@ -138,7 +149,8 @@ impl<T: PartialEq<Other>, Other, const N: usize> SpecArrayEq<Other, N> for T {
}
}

impl<T: BytewiseEq<U>, U, const N: usize> SpecArrayEq<U, N> for T {
#[rustc_const_unstable(feature = "const_cmp", issue = "143800")]
impl<T: [const] BytewiseEq<U>, U, const N: usize> const SpecArrayEq<U, N> for T {
fn spec_eq(a: &[T; N], b: &[U; N]) -> bool {
// SAFETY: Arrays are compared element-wise, and don't add any padding
// between elements, so when the elements are `BytewiseEq`, we can
Expand Down
26 changes: 17 additions & 9 deletions library/core/src/array/mod.rs
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Expand Up @@ -198,38 +198,42 @@ impl Error for TryFromSliceError {
}

#[stable(feature = "try_from_slice_error", since = "1.36.0")]
#[rustc_const_unstable(feature = "const_try", issue = "74935")]
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl const From<Infallible> for TryFromSliceError {
fn from(x: Infallible) -> TryFromSliceError {
match x {}
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, const N: usize> AsRef<[T]> for [T; N] {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T, const N: usize> const AsRef<[T]> for [T; N] {
#[inline]
fn as_ref(&self) -> &[T] {
&self[..]
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T, const N: usize> AsMut<[T]> for [T; N] {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T, const N: usize> const AsMut<[T]> for [T; N] {
#[inline]
fn as_mut(&mut self) -> &mut [T] {
&mut self[..]
}
}

#[stable(feature = "array_borrow", since = "1.4.0")]
impl<T, const N: usize> Borrow<[T]> for [T; N] {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T, const N: usize> const Borrow<[T]> for [T; N] {
fn borrow(&self) -> &[T] {
self
}
}

#[stable(feature = "array_borrow", since = "1.4.0")]
impl<T, const N: usize> BorrowMut<[T]> for [T; N] {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T, const N: usize> const BorrowMut<[T]> for [T; N] {
fn borrow_mut(&mut self) -> &mut [T] {
self
}
Expand All @@ -248,7 +252,8 @@ impl<T, const N: usize> BorrowMut<[T]> for [T; N] {
/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
/// ```
#[stable(feature = "try_from", since = "1.34.0")]
impl<T, const N: usize> TryFrom<&[T]> for [T; N]
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T, const N: usize> const TryFrom<&[T]> for [T; N]
where
T: Copy,
{
Expand All @@ -273,7 +278,8 @@ where
/// assert_eq!(512, u16::from_le_bytes(bytes_tail));
/// ```
#[stable(feature = "try_from_mut_slice_to_array", since = "1.59.0")]
impl<T, const N: usize> TryFrom<&mut [T]> for [T; N]
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T, const N: usize> const TryFrom<&mut [T]> for [T; N]
where
T: Copy,
{
Expand All @@ -298,7 +304,8 @@ where
/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
/// ```
#[stable(feature = "try_from", since = "1.34.0")]
impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N] {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<'a, T, const N: usize> const TryFrom<&'a [T]> for &'a [T; N] {
type Error = TryFromSliceError;

#[inline]
Expand All @@ -320,7 +327,8 @@ impl<'a, T, const N: usize> TryFrom<&'a [T]> for &'a [T; N] {
/// assert_eq!(512, u16::from_le_bytes(*bytes_tail));
/// ```
#[stable(feature = "try_from", since = "1.34.0")]
impl<'a, T, const N: usize> TryFrom<&'a mut [T]> for &'a mut [T; N] {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<'a, T, const N: usize> const TryFrom<&'a mut [T]> for &'a mut [T; N] {
type Error = TryFromSliceError;

#[inline]
Expand Down
5 changes: 3 additions & 2 deletions library/core/src/ascii/ascii_char.rs
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Expand Up @@ -54,7 +54,8 @@ use crate::{assert_unsafe_precondition, fmt};
/// [chart]: https://www.unicode.org/charts/PDF/U0000.pdf
/// [NIST FIPS 1-2]: https://nvlpubs.nist.gov/nistpubs/Legacy/FIPS/fipspub1-2-1977.pdf
/// [NamesList]: https://www.unicode.org/Public/15.0.0/ucd/NamesList.txt
#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
#[derive(Copy, Hash)]
#[derive_const(Clone, Eq, PartialEq, Ord, PartialOrd)]
#[unstable(feature = "ascii_char", issue = "110998")]
#[repr(u8)]
pub enum AsciiChar {
Expand Down Expand Up @@ -1156,7 +1157,7 @@ macro_rules! into_int_impl {
($($ty:ty)*) => {
$(
#[unstable(feature = "ascii_char", issue = "110998")]
#[rustc_const_unstable(feature = "const_try", issue = "74935")]
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl const From<AsciiChar> for $ty {
#[inline]
fn from(chr: AsciiChar) -> $ty {
Expand Down
19 changes: 14 additions & 5 deletions library/core/src/borrow.rs
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Expand Up @@ -154,6 +154,8 @@
/// [`String`]: ../../std/string/struct.String.html
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_diagnostic_item = "Borrow"]
#[const_trait]
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
pub trait Borrow<Borrowed: ?Sized> {
/// Immutably borrows from an owned value.
///
Expand Down Expand Up @@ -185,6 +187,8 @@ pub trait Borrow<Borrowed: ?Sized> {
/// for more information on borrowing as another type.
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_diagnostic_item = "BorrowMut"]
#[const_trait]
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
pub trait BorrowMut<Borrowed: ?Sized>: Borrow<Borrowed> {
/// Mutably borrows from an owned value.
///
Expand All @@ -206,36 +210,41 @@ pub trait BorrowMut<Borrowed: ?Sized>: Borrow<Borrowed> {
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Borrow<T> for T {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T: ?Sized> const Borrow<T> for T {
#[rustc_diagnostic_item = "noop_method_borrow"]
fn borrow(&self) -> &T {
self
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> BorrowMut<T> for T {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T: ?Sized> const BorrowMut<T> for T {
fn borrow_mut(&mut self) -> &mut T {
self
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Borrow<T> for &T {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T: ?Sized> const Borrow<T> for &T {
fn borrow(&self) -> &T {
self
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> Borrow<T> for &mut T {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T: ?Sized> const Borrow<T> for &mut T {
fn borrow(&self) -> &T {
self
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: ?Sized> BorrowMut<T> for &mut T {
#[rustc_const_unstable(feature = "const_convert", issue = "143773")]
impl<T: ?Sized> const BorrowMut<T> for &mut T {
fn borrow_mut(&mut self) -> &mut T {
self
}
Expand Down
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