Revert "HACK: Remove all const trait impls and ~const from libcore/libstd"

This reverts commit 7dc2fab2895041f82fabc6525c895cc574b3d044.

Author: fee1-dead

compiler/rustc_ast/src/ptr.rs

@@ -127,7 +127,7 @@ impl<S: Encoder, T: Encodable<S>> Encodable<S> for P<T> {
 }
 
 impl<T> P<[T]> {
-    pub fn new() -> P<[T]> {
+    pub const fn new() -> P<[T]> {
         P { ptr: Box::default() }
     }
 

library/alloc/src/alloc.rs

@@ -14,6 +14,8 @@ use core::ptr::{self, NonNull};
 #[doc(inline)]
 pub use core::alloc::*;
 
+use core::marker::Destruct;
+
 #[cfg(test)]
 mod tests;
 
@@ -323,12 +325,16 @@ unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
 
 #[cfg_attr(not(test), lang = "box_free")]
 #[inline]
+#[rustc_const_unstable(feature = "const_box", issue = "92521")]
 // This signature has to be the same as `Box`, otherwise an ICE will happen.
 // When an additional parameter to `Box` is added (like `A: Allocator`), this has to be added here as
 // well.
 // For example if `Box` is changed to  `struct Box<T: ?Sized, A: Allocator>(Unique<T>, A)`,
 // this function has to be changed to `fn box_free<T: ?Sized, A: Allocator>(Unique<T>, A)` as well.
-pub(crate) unsafe fn box_free<T: ?Sized, A: Allocator>(ptr: Unique<T>, alloc: A) {
+pub(crate) const unsafe fn box_free<T: ?Sized, A: ~const Allocator + ~const Destruct>(
+    ptr: Unique<T>,
+    alloc: A,
+) {
     unsafe {
         let size = size_of_val(ptr.as_ref());
         let align = min_align_of_val(ptr.as_ref());
@@ -360,12 +366,21 @@ extern "Rust" {
 /// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
 /// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
 #[stable(feature = "global_alloc", since = "1.28.0")]
+#[rustc_const_unstable(feature = "const_alloc_error", issue = "92523")]
 #[cfg(all(not(no_global_oom_handling), not(test)))]
 #[cold]
-pub fn handle_alloc_error(layout: Layout) -> ! {
-    unsafe {
-        __rust_alloc_error_handler(layout.size(), layout.align());
+pub const fn handle_alloc_error(layout: Layout) -> ! {
+    const fn ct_error(_: Layout) -> ! {
+        panic!("allocation failed");
+    }
+
+    fn rt_error(layout: Layout) -> ! {
+        unsafe {
+            __rust_alloc_error_handler(layout.size(), layout.align());
+        }
     }
+
+    unsafe { core::intrinsics::const_eval_select((layout,), ct_error, rt_error) }
 }
 
 // For alloc test `std::alloc::handle_alloc_error` can be used directly.

library/alloc/src/borrow.rs

@@ -329,9 +329,10 @@ 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_deref", issue = "88955")]
+impl<B: ?Sized + ToOwned> const Deref for Cow<'_, B>
 where
-    B::Owned: Borrow<B>,
+    B::Owned: ~const Borrow<B>,
 {
     type Target = B;
 

library/alloc/src/boxed.rs

@@ -157,7 +157,7 @@ use core::hash::{Hash, Hasher};
 #[cfg(not(no_global_oom_handling))]
 use core::iter::FromIterator;
 use core::iter::{FusedIterator, Iterator};
-use core::marker::{Unpin, Unsize};
+use core::marker::{Destruct, Unpin, Unsize};
 use core::mem;
 use core::ops::{
     CoerceUnsized, Deref, DerefMut, DispatchFromDyn, Generator, GeneratorState, Receiver,
@@ -373,11 +373,12 @@ impl<T, A: Allocator> Box<T, A> {
     /// ```
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "allocator_api", issue = "32838")]
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
     #[must_use]
     #[inline]
-    pub fn new_in(x: T, alloc: A) -> Self
+    pub const fn new_in(x: T, alloc: A) -> Self
     where
-        A: Allocator,
+        A: ~const Allocator + ~const Destruct,
     {
         let mut boxed = Self::new_uninit_in(alloc);
         unsafe {
@@ -402,10 +403,12 @@ impl<T, A: Allocator> Box<T, A> {
     /// # Ok::<(), std::alloc::AllocError>(())
     /// ```
     #[unstable(feature = "allocator_api", issue = "32838")]
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
     #[inline]
-    pub fn try_new_in(x: T, alloc: A) -> Result<Self, AllocError>
+    pub const fn try_new_in(x: T, alloc: A) -> Result<Self, AllocError>
     where
-        A: Allocator,
+        T: ~const Destruct,
+        A: ~const Allocator + ~const Destruct,
     {
         let mut boxed = Self::try_new_uninit_in(alloc)?;
         unsafe {
@@ -435,12 +438,13 @@ impl<T, A: Allocator> Box<T, A> {
     /// assert_eq!(*five, 5)
     /// ```
     #[unstable(feature = "allocator_api", issue = "32838")]
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
     #[cfg(not(no_global_oom_handling))]
     #[must_use]
     // #[unstable(feature = "new_uninit", issue = "63291")]
-    pub fn new_uninit_in(alloc: A) -> Box<mem::MaybeUninit<T>, A>
+    pub const fn new_uninit_in(alloc: A) -> Box<mem::MaybeUninit<T>, A>
     where
-        A: Allocator,
+        A: ~const Allocator + ~const Destruct,
     {
         let layout = Layout::new::<mem::MaybeUninit<T>>();
         // NOTE: Prefer match over unwrap_or_else since closure sometimes not inlineable.
@@ -475,9 +479,10 @@ impl<T, A: Allocator> Box<T, A> {
     /// ```
     #[unstable(feature = "allocator_api", issue = "32838")]
     // #[unstable(feature = "new_uninit", issue = "63291")]
-    pub fn try_new_uninit_in(alloc: A) -> Result<Box<mem::MaybeUninit<T>, A>, AllocError>
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
+    pub const fn try_new_uninit_in(alloc: A) -> Result<Box<mem::MaybeUninit<T>, A>, AllocError>
     where
-        A: Allocator,
+        A: ~const Allocator + ~const Destruct,
     {
         let layout = Layout::new::<mem::MaybeUninit<T>>();
         let ptr = alloc.allocate(layout)?.cast();
@@ -505,12 +510,13 @@ impl<T, A: Allocator> Box<T, A> {
     ///
     /// [zeroed]: mem::MaybeUninit::zeroed
     #[unstable(feature = "allocator_api", issue = "32838")]
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
     #[cfg(not(no_global_oom_handling))]
     // #[unstable(feature = "new_uninit", issue = "63291")]
     #[must_use]
-    pub fn new_zeroed_in(alloc: A) -> Box<mem::MaybeUninit<T>, A>
+    pub const fn new_zeroed_in(alloc: A) -> Box<mem::MaybeUninit<T>, A>
     where
-        A: Allocator,
+        A: ~const Allocator + ~const Destruct,
     {
         let layout = Layout::new::<mem::MaybeUninit<T>>();
         // NOTE: Prefer match over unwrap_or_else since closure sometimes not inlineable.
@@ -545,9 +551,10 @@ impl<T, A: Allocator> Box<T, A> {
     /// [zeroed]: mem::MaybeUninit::zeroed
     #[unstable(feature = "allocator_api", issue = "32838")]
     // #[unstable(feature = "new_uninit", issue = "63291")]
-    pub fn try_new_zeroed_in(alloc: A) -> Result<Box<mem::MaybeUninit<T>, A>, AllocError>
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
+    pub const fn try_new_zeroed_in(alloc: A) -> Result<Box<mem::MaybeUninit<T>, A>, AllocError>
     where
-        A: Allocator,
+        A: ~const Allocator + ~const Destruct,
     {
         let layout = Layout::new::<mem::MaybeUninit<T>>();
         let ptr = alloc.allocate_zeroed(layout)?.cast();
@@ -563,11 +570,12 @@ impl<T, A: Allocator> Box<T, A> {
     /// construct a (pinned) `Box` in a different way than with [`Box::new_in`].
     #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "allocator_api", issue = "32838")]
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
     #[must_use]
     #[inline(always)]
-    pub fn pin_in(x: T, alloc: A) -> Pin<Self>
+    pub const fn pin_in(x: T, alloc: A) -> Pin<Self>
     where
-        A: 'static + Allocator,
+        A: 'static + ~const Allocator + ~const Destruct,
     {
         Self::into_pin(Self::new_in(x, alloc))
     }
@@ -576,7 +584,8 @@ impl<T, A: Allocator> Box<T, A> {
     ///
     /// This conversion does not allocate on the heap and happens in place.
     #[unstable(feature = "box_into_boxed_slice", issue = "71582")]
-    pub fn into_boxed_slice(boxed: Self) -> Box<[T], A> {
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
+    pub const fn into_boxed_slice(boxed: Self) -> Box<[T], A> {
         let (raw, alloc) = Box::into_raw_with_allocator(boxed);
         unsafe { Box::from_raw_in(raw as *mut [T; 1], alloc) }
     }
@@ -593,8 +602,12 @@ impl<T, A: Allocator> Box<T, A> {
     /// assert_eq!(Box::into_inner(c), 5);
     /// ```
     #[unstable(feature = "box_into_inner", issue = "80437")]
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
     #[inline]
-    pub fn into_inner(boxed: Self) -> T {
+    pub const fn into_inner(boxed: Self) -> T
+    where
+        Self: ~const Destruct,
+    {
         *boxed
     }
 }
@@ -808,8 +821,9 @@ impl<T, A: Allocator> Box<mem::MaybeUninit<T>, A> {
     /// assert_eq!(*five, 5)
     /// ```
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
     #[inline]
-    pub unsafe fn assume_init(self) -> Box<T, A> {
+    pub const unsafe fn assume_init(self) -> Box<T, A> {
         let (raw, alloc) = Box::into_raw_with_allocator(self);
         unsafe { Box::from_raw_in(raw as *mut T, alloc) }
     }
@@ -842,8 +856,9 @@ impl<T, A: Allocator> Box<mem::MaybeUninit<T>, A> {
     /// }
     /// ```
     #[unstable(feature = "new_uninit", issue = "63291")]
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
     #[inline]
-    pub fn write(mut boxed: Self, value: T) -> Box<T, A> {
+    pub const fn write(mut boxed: Self, value: T) -> Box<T, A> {
         unsafe {
             (*boxed).write(value);
             boxed.assume_init()
@@ -1086,8 +1101,9 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
     ///
     /// [memory layout]: self#memory-layout
     #[unstable(feature = "allocator_api", issue = "32838")]
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
     #[inline]
-    pub fn into_raw_with_allocator(b: Self) -> (*mut T, A) {
+    pub const fn into_raw_with_allocator(b: Self) -> (*mut T, A) {
         let (leaked, alloc) = Box::into_unique(b);
         (leaked.as_ptr(), alloc)
     }
@@ -1097,9 +1113,10 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
         issue = "none",
         reason = "use `Box::leak(b).into()` or `Unique::from(Box::leak(b))` instead"
     )]
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
     #[inline]
     #[doc(hidden)]
-    pub fn into_unique(b: Self) -> (Unique<T>, A) {
+    pub const fn into_unique(b: Self) -> (Unique<T>, A) {
         // Box is recognized as a "unique pointer" by Stacked Borrows, but internally it is a
         // raw pointer for the type system. Turning it directly into a raw pointer would not be
         // recognized as "releasing" the unique pointer to permit aliased raw accesses,
@@ -1157,8 +1174,9 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {
     /// assert_eq!(*static_ref, [4, 2, 3]);
     /// ```
     #[stable(feature = "box_leak", since = "1.26.0")]
+    #[rustc_const_unstable(feature = "const_box", issue = "92521")]
     #[inline]
-    pub fn leak<'a>(b: Self) -> &'a mut T
+    pub const fn leak<'a>(b: Self) -> &'a mut T
     where
         A: 'a,
     {
@@ -1228,7 +1246,7 @@ impl<T: Default> Default for Box<T> {
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
-impl<T> Default for Box<[T]> {
+impl<T> const Default for Box<[T]> {
     fn default() -> Self {
         let ptr: Unique<[T]> = Unique::<[T; 0]>::dangling();
         Box(ptr, Global)
@@ -1238,7 +1256,7 @@ impl<T> Default for Box<[T]> {
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "default_box_extra", since = "1.17.0")]
 #[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
-impl Default for Box<str> {
+impl const Default for Box<str> {
     fn default() -> Self {
         // SAFETY: This is the same as `Unique::cast<U>` but with an unsized `U = str`.
         let ptr: Unique<str> = unsafe {
@@ -1434,7 +1452,8 @@ impl<T> From<T> for Box<T> {
 }
 
 #[stable(feature = "pin", since = "1.33.0")]
-impl<T: ?Sized, A: Allocator> From<Box<T, A>> for Pin<Box<T, A>>
+#[rustc_const_unstable(feature = "const_box", issue = "92521")]
+impl<T: ?Sized, A: Allocator> const From<Box<T, A>> for Pin<Box<T, A>>
 where
     A: 'static,
 {
@@ -1822,7 +1841,8 @@ impl<T: ?Sized, A: Allocator> fmt::Pointer for Box<T, A> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized, A: Allocator> Deref for Box<T, A> {
+#[rustc_const_unstable(feature = "const_box", issue = "92521")]
+impl<T: ?Sized, A: Allocator> const Deref for Box<T, A> {
     type Target = T;
 
     fn deref(&self) -> &T {
@@ -1831,7 +1851,8 @@ impl<T: ?Sized, A: Allocator> Deref for Box<T, A> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized, A: Allocator> DerefMut for Box<T, A> {
+#[rustc_const_unstable(feature = "const_box", issue = "92521")]
+impl<T: ?Sized, A: Allocator> const DerefMut for Box<T, A> {
     fn deref_mut(&mut self) -> &mut T {
         &mut **self
     }
@@ -2010,7 +2031,8 @@ impl<T: ?Sized, A: Allocator> AsMut<T> for Box<T, A> {
  *  could have a method to project a Pin<T> from it.
  */
 #[stable(feature = "pin", since = "1.33.0")]
-impl<T: ?Sized, A: Allocator> Unpin for Box<T, A> where A: 'static {}
+#[rustc_const_unstable(feature = "const_box", issue = "92521")]
+impl<T: ?Sized, A: Allocator> const Unpin for Box<T, A> where A: 'static {}
 
 #[unstable(feature = "generator_trait", issue = "43122")]
 impl<G: ?Sized + Generator<R> + Unpin, R, A: Allocator> Generator<R> for Box<G, A>

library/alloc/src/lib.rs

@@ -95,9 +95,11 @@
 #![feature(assert_matches)]
 #![feature(async_iterator)]
 #![feature(coerce_unsized)]
+#![cfg_attr(not(no_global_oom_handling), feature(const_alloc_error))]
 #![feature(const_box)]
 #![cfg_attr(not(no_global_oom_handling), feature(const_btree_new))]
 #![feature(const_cow_is_borrowed)]
+#![feature(const_convert)]
 #![feature(const_size_of_val)]
 #![feature(const_align_of_val)]
 #![feature(const_ptr_read)]
@@ -107,6 +109,7 @@
 #![feature(core_c_str)]
 #![feature(core_intrinsics)]
 #![feature(core_ffi_c)]
+#![feature(const_eval_select)]
 #![feature(const_pin)]
 #![feature(cstr_from_bytes_until_nul)]
 #![feature(dispatch_from_dyn)]
@@ -147,6 +150,7 @@
 #![feature(allow_internal_unstable)]
 #![feature(associated_type_bounds)]
 #![feature(cfg_sanitize)]
+#![feature(const_deref)]
 #![feature(const_mut_refs)]
 #![feature(const_ptr_write)]
 #![feature(const_precise_live_drops)]

library/alloc/src/string.rs

@@ -2212,7 +2212,8 @@ impl_eq! { Cow<'a, str>, &'b str }
 impl_eq! { Cow<'a, str>, String }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl Default for String {
+#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
+impl const Default for String {
     /// Creates an empty `String`.
     #[inline]
     fn default() -> String {

library/alloc/src/vec/mod.rs

@@ -2924,7 +2924,8 @@ unsafe impl<#[may_dangle] T, A: Allocator> Drop for Vec<T, A> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Default for Vec<T> {
+#[rustc_const_unstable(feature = "const_default_impls", issue = "87864")]
+impl<T> const Default for Vec<T> {
     /// Creates an empty `Vec<T>`.
     fn default() -> Vec<T> {
         Vec::new()