Constify Try, From, TryFrom and relevant traits

library/core/src/array/mod.rs

@@ -198,7 +198,8 @@ impl Error for TryFromSliceError {
 }
 
 #[stable(feature = "try_from_slice_error", since = "1.36.0")]
-impl From<Infallible> for TryFromSliceError {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl const From<Infallible> for TryFromSliceError {
     fn from(x: Infallible) -> TryFromSliceError {
         match x {}
     }

library/core/src/ascii/ascii_char.rs

@@ -546,7 +546,8 @@ macro_rules! into_int_impl {
     ($($ty:ty)*) => {
         $(
             #[unstable(feature = "ascii_char", issue = "110998")]
-            impl From<AsciiChar> for $ty {
+            #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+            impl const From<AsciiChar> for $ty {
                 #[inline]
                 fn from(chr: AsciiChar) -> $ty {
                     chr as u8 as $ty

library/core/src/char/convert.rs

@@ -36,7 +36,8 @@ pub(super) const unsafe fn from_u32_unchecked(i: u32) -> char {
 }
 
 #[stable(feature = "char_convert", since = "1.13.0")]
-impl From<char> for u32 {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl const From<char> for u32 {
     /// Converts a [`char`] into a [`u32`].
     ///
     /// # Examples
@@ -53,7 +54,8 @@ impl From<char> for u32 {
 }
 
 #[stable(feature = "more_char_conversions", since = "1.51.0")]
-impl From<char> for u64 {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl const From<char> for u64 {
     /// Converts a [`char`] into a [`u64`].
     ///
     /// # Examples
@@ -72,7 +74,8 @@ impl From<char> for u64 {
 }
 
 #[stable(feature = "more_char_conversions", since = "1.51.0")]
-impl From<char> for u128 {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl const From<char> for u128 {
     /// Converts a [`char`] into a [`u128`].
     ///
     /// # Examples
@@ -157,7 +160,8 @@ impl TryFrom<char> for u16 {
 /// for a superset of Windows-1252 that fills the remaining blanks with corresponding
 /// C0 and C1 control codes.
 #[stable(feature = "char_convert", since = "1.13.0")]
-impl From<u8> for char {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl const From<u8> for char {
     /// Converts a [`u8`] into a [`char`].
     ///
     /// # Examples
@@ -247,7 +251,8 @@ const fn char_try_from_u32(i: u32) -> Result<char, CharTryFromError> {
 }
 
 #[stable(feature = "try_from", since = "1.34.0")]
-impl TryFrom<u32> for char {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl const TryFrom<u32> for char {
     type Error = CharTryFromError;
 
     #[inline]

library/core/src/convert/mod.rs

@@ -216,6 +216,8 @@ pub const fn identity<T>(x: T) -> T {
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_diagnostic_item = "AsRef"]
+#[const_trait]
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
 pub trait AsRef<T: PointeeSized>: PointeeSized {
     /// Converts this type into a shared reference of the (usually inferred) input type.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -367,6 +369,8 @@ pub trait AsRef<T: PointeeSized>: PointeeSized {
 /// `&mut Vec<u8>`, for example, is the better choice (callers need to pass the correct type then).
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_diagnostic_item = "AsMut"]
+#[const_trait]
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
 pub trait AsMut<T: PointeeSized>: PointeeSized {
     /// Converts this type into a mutable reference of the (usually inferred) input type.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -445,6 +449,8 @@ pub trait AsMut<T: PointeeSized>: PointeeSized {
 #[rustc_diagnostic_item = "Into"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[doc(search_unbox)]
+#[const_trait]
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
 pub trait Into<T>: Sized {
     /// Converts this type into the (usually inferred) input type.
     #[must_use]
@@ -580,6 +586,8 @@ pub trait Into<T>: Sized {
     note = "to coerce a `{T}` into a `{Self}`, use `&*` as a prefix",
 ))]
 #[doc(search_unbox)]
+#[const_trait]
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
 pub trait From<T>: Sized {
     /// Converts to this type from the input type.
     #[rustc_diagnostic_item = "from_fn"]
@@ -607,6 +615,8 @@ pub trait From<T>: Sized {
 /// [`Into`], see there for details.
 #[rustc_diagnostic_item = "TryInto"]
 #[stable(feature = "try_from", since = "1.34.0")]
+#[const_trait]
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
 pub trait TryInto<T>: Sized {
     /// The type returned in the event of a conversion error.
     #[stable(feature = "try_from", since = "1.34.0")]
@@ -685,6 +695,8 @@ pub trait TryInto<T>: Sized {
 /// [`try_from`]: TryFrom::try_from
 #[rustc_diagnostic_item = "TryFrom"]
 #[stable(feature = "try_from", since = "1.34.0")]
+#[const_trait]
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
 pub trait TryFrom<T>: Sized {
     /// The type returned in the event of a conversion error.
     #[stable(feature = "try_from", since = "1.34.0")]
@@ -702,9 +714,10 @@ pub trait TryFrom<T>: Sized {
 
 // As lifts over &
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: PointeeSized, U: PointeeSized> AsRef<U> for &T
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl<T: PointeeSized, U: PointeeSized> const AsRef<U> for &T
 where
-    T: AsRef<U>,
+    T: ~const AsRef<U>,
 {
     #[inline]
     fn as_ref(&self) -> &U {
@@ -714,9 +727,10 @@ where
 
 // As lifts over &mut
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: PointeeSized, U: PointeeSized> AsRef<U> for &mut T
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl<T: PointeeSized, U: PointeeSized> const AsRef<U> for &mut T
 where
-    T: AsRef<U>,
+    T: ~const AsRef<U>,
 {
     #[inline]
     fn as_ref(&self) -> &U {
@@ -734,9 +748,10 @@ where
 
 // AsMut lifts over &mut
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: PointeeSized, U: PointeeSized> AsMut<U> for &mut T
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl<T: PointeeSized, U: PointeeSized> const AsMut<U> for &mut T
 where
-    T: AsMut<U>,
+    T: ~const AsMut<U>,
 {
     #[inline]
     fn as_mut(&mut self) -> &mut U {
@@ -754,9 +769,10 @@ where
 
 // From implies Into
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T, U> Into<U> for T
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl<T, U> const Into<U> for T
 where
-    U: From<T>,
+    U: ~const From<T>,
 {
     /// Calls `U::from(self)`.
     ///
@@ -771,7 +787,8 @@ where
 
 // From (and thus Into) is reflexive
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> From<T> for T {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl<T> const From<T> for T {
     /// Returns the argument unchanged.
     #[inline(always)]
     fn from(t: T) -> T {
@@ -795,9 +812,10 @@ impl<T> From<!> for T {
 
 // TryFrom implies TryInto
 #[stable(feature = "try_from", since = "1.34.0")]
-impl<T, U> TryInto<U> for T
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl<T, U> const TryInto<U> for T
 where
-    U: TryFrom<T>,
+    U: ~const TryFrom<T>,
 {
     type Error = U::Error;
 
@@ -810,9 +828,10 @@ where
 // Infallible conversions are semantically equivalent to fallible conversions
 // with an uninhabited error type.
 #[stable(feature = "try_from", since = "1.34.0")]
-impl<T, U> TryFrom<U> for T
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl<T, U> const TryFrom<U> for T
 where
-    U: Into<T>,
+    U: ~const Into<T>,
 {
     type Error = Infallible;
 
@@ -827,31 +846,35 @@ where
 ////////////////////////////////////////////////////////////////////////////////
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> AsRef<[T]> for [T] {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl<T> const AsRef<[T]> for [T] {
     #[inline(always)]
     fn as_ref(&self) -> &[T] {
         self
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> AsMut<[T]> for [T] {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl<T> const AsMut<[T]> for [T] {
     #[inline(always)]
     fn as_mut(&mut self) -> &mut [T] {
         self
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl AsRef<str> for str {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl const AsRef<str> for str {
     #[inline(always)]
     fn as_ref(&self) -> &str {
         self
     }
 }
 
 #[stable(feature = "as_mut_str_for_str", since = "1.51.0")]
-impl AsMut<str> for str {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl const AsMut<str> for str {
     #[inline(always)]
     fn as_mut(&mut self) -> &mut str {
         self
@@ -912,7 +935,8 @@ impl AsMut<str> for str {
 pub enum Infallible {}
 
 #[stable(feature = "convert_infallible", since = "1.34.0")]
-impl Clone for Infallible {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl const Clone for Infallible {
     fn clone(&self) -> Infallible {
         match *self {}
     }
@@ -940,7 +964,8 @@ impl Error for Infallible {
 }
 
 #[stable(feature = "convert_infallible", since = "1.34.0")]
-impl PartialEq for Infallible {
+#[rustc_const_unstable(feature = "const_cmp", issue = "92391")]
+impl const PartialEq for Infallible {
     fn eq(&self, _: &Infallible) -> bool {
         match *self {}
     }
@@ -964,7 +989,8 @@ impl Ord for Infallible {
 }
 
 #[stable(feature = "convert_infallible", since = "1.34.0")]
-impl From<!> for Infallible {
+#[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+impl const From<!> for Infallible {
     #[inline]
     fn from(x: !) -> Self {
         x

library/core/src/convert/num.rs

@@ -69,7 +69,8 @@ macro_rules! impl_from {
     };
     ($Small:ty => $Large:ty, #[$attr:meta], $doc:expr $(,)?) => {
         #[$attr]
-        impl From<$Small> for $Large {
+        #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+        impl const From<$Small> for $Large {
             // Rustdocs on the impl block show a "[+] show undocumented items" toggle.
             // Rustdocs on functions do not.
             #[doc = $doc]
@@ -200,7 +201,8 @@ macro_rules! impl_float_from_bool {
         )?
     ) => {
         #[stable(feature = "float_from_bool", since = "1.68.0")]
-        impl From<bool> for $float {
+        #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+            impl const From<bool> for $float {
             #[doc = concat!("Converts a [`bool`] to [`", stringify!($float),"`] losslessly.")]
             /// The resulting value is positive `0.0` for `false` and `1.0` for `true` values.
             ///
@@ -250,7 +252,8 @@ impl_float_from_bool!(
 macro_rules! impl_try_from_unbounded {
     ($source:ty => $($target:ty),+) => {$(
         #[stable(feature = "try_from", since = "1.34.0")]
-        impl TryFrom<$source> for $target {
+        #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+        impl const TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
             /// Tries to create the target number type from a source
@@ -268,7 +271,8 @@ macro_rules! impl_try_from_unbounded {
 macro_rules! impl_try_from_lower_bounded {
     ($source:ty => $($target:ty),+) => {$(
         #[stable(feature = "try_from", since = "1.34.0")]
-        impl TryFrom<$source> for $target {
+        #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+        impl const TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
             /// Tries to create the target number type from a source
@@ -290,7 +294,8 @@ macro_rules! impl_try_from_lower_bounded {
 macro_rules! impl_try_from_upper_bounded {
     ($source:ty => $($target:ty),+) => {$(
         #[stable(feature = "try_from", since = "1.34.0")]
-        impl TryFrom<$source> for $target {
+        #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+        impl const TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
             /// Tries to create the target number type from a source
@@ -312,7 +317,8 @@ macro_rules! impl_try_from_upper_bounded {
 macro_rules! impl_try_from_both_bounded {
     ($source:ty => $($target:ty),+) => {$(
         #[stable(feature = "try_from", since = "1.34.0")]
-        impl TryFrom<$source> for $target {
+        #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+        impl const TryFrom<$source> for $target {
             type Error = TryFromIntError;
 
             /// Tries to create the target number type from a source
@@ -450,7 +456,8 @@ use crate::num::NonZero;
 macro_rules! impl_nonzero_int_from_nonzero_int {
     ($Small:ty => $Large:ty) => {
         #[stable(feature = "nz_int_conv", since = "1.41.0")]
-        impl From<NonZero<$Small>> for NonZero<$Large> {
+        #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+        impl const From<NonZero<$Small>> for NonZero<$Large> {
             // Rustdocs on the impl block show a "[+] show undocumented items" toggle.
             // Rustdocs on functions do not.
             #[doc = concat!("Converts <code>[NonZero]\\<[", stringify!($Small), "]></code> ")]
@@ -540,7 +547,8 @@ impl_nonzero_int_try_from_int!(isize);
 macro_rules! impl_nonzero_int_try_from_nonzero_int {
     ($source:ty => $($target:ty),+) => {$(
         #[stable(feature = "nzint_try_from_nzint_conv", since = "1.49.0")]
-        impl TryFrom<NonZero<$source>> for NonZero<$target> {
+        #[rustc_const_unstable(feature = "const_trait_impl", issue = "67792")]
+        impl const TryFrom<NonZero<$source>> for NonZero<$target> {
             type Error = TryFromIntError;
 
             // Rustdocs on the impl block show a "[+] show undocumented items" toggle.