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Auto merge of #117905 - RalfJung:no-const-mut, r=<try>
revert stabilization of const_intrinsic_copy `@rust-lang/wg-const-eval` I don't know what we were thinking when we approved #97276... const-eval isn't supposed to be able to mutate anything yet! It's also near impossible to actually call `copy` in const on stable since `&mut` expressions are generally unstable. However, there's one exception... ```rust static mut INT: i32 = unsafe { let val = &mut [1]; // `&mut` on arrays is allowed in `static mut` (val as *mut [i32; 1]).copy_from(&[42], 1); val[0] }; fn main() { unsafe { dbg!(INT); } } ``` Inside `static mut`, we accept some `&mut` since ~forever, to make `static mut FOO: &mut [T] = &mut [...];` work. We reject any attempt to actually write to that mutable reference though... except for the `copy` functions. I think we should revert stabilizing these functions that take `*mut`, and then re-stabilize them together with `ptr.write` once mutable references are stable. (This will likely fail on PowerPC until rust-lang/stdarch#1497 lands. But we'll need a crater run first anyway.)
2 parents d97bb19 + 215e10e commit 1930f26

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‎library/core/src/intrinsics.rs

+4-4
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@@ -2665,13 +2665,13 @@ pub(crate) fn is_nonoverlapping<T>(src: *const T, dst: *const T, count: usize) -
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#[doc(alias = "memcpy")]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[rustc_allowed_through_unstable_modules]
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#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
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#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
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#[inline(always)]
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#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
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#[rustc_diagnostic_item = "ptr_copy_nonoverlapping"]
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pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize) {
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extern "rust-intrinsic" {
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#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
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#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
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#[rustc_nounwind]
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pub fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
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}
@@ -2761,13 +2761,13 @@ pub const unsafe fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: us
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#[doc(alias = "memmove")]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[rustc_allowed_through_unstable_modules]
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#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
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#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
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#[inline(always)]
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#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
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#[rustc_diagnostic_item = "ptr_copy"]
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pub const unsafe fn copy<T>(src: *const T, dst: *mut T, count: usize) {
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extern "rust-intrinsic" {
2770-
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
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#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
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#[rustc_nounwind]
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fn copy<T>(src: *const T, dst: *mut T, count: usize);
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}

‎library/core/src/lib.rs

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@@ -135,6 +135,7 @@
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#![feature(const_heap)]
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#![feature(const_index_range_slice_index)]
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#![feature(const_int_unchecked_arith)]
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#![feature(const_intrinsic_copy)]
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#![feature(const_intrinsic_forget)]
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#![feature(const_ipv4)]
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#![feature(const_ipv6)]

‎library/core/src/ptr/const_ptr.rs

+2-2
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@@ -1283,7 +1283,7 @@ impl<T: ?Sized> *const T {
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/// See [`ptr::copy`] for safety concerns and examples.
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///
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/// [`ptr::copy`]: crate::ptr::copy()
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#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
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#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
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#[stable(feature = "pointer_methods", since = "1.26.0")]
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#[inline]
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#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
@@ -1303,7 +1303,7 @@ impl<T: ?Sized> *const T {
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/// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
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///
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/// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
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#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
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#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
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#[stable(feature = "pointer_methods", since = "1.26.0")]
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#[inline]
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#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces

‎library/core/src/ptr/mod.rs

+5-2
Original file line numberDiff line numberDiff line change
@@ -1161,7 +1161,6 @@ pub const unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
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#[inline]
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#[stable(feature = "rust1", since = "1.0.0")]
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#[rustc_const_stable(feature = "const_ptr_read", since = "1.71.0")]
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#[rustc_allow_const_fn_unstable(const_mut_refs, const_maybe_uninit_as_mut_ptr)]
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#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
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#[rustc_diagnostic_item = "ptr_read"]
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pub const unsafe fn read<T>(src: *const T) -> T {
@@ -1279,7 +1278,11 @@ pub const unsafe fn read<T>(src: *const T) -> T {
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#[inline]
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#[stable(feature = "ptr_unaligned", since = "1.17.0")]
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#[rustc_const_stable(feature = "const_ptr_read", since = "1.71.0")]
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#[rustc_allow_const_fn_unstable(const_mut_refs, const_maybe_uninit_as_mut_ptr)]
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#[rustc_allow_const_fn_unstable(
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const_mut_refs,
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const_maybe_uninit_as_mut_ptr,
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const_intrinsic_copy
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)]
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#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
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#[rustc_diagnostic_item = "ptr_read_unaligned"]
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pub const unsafe fn read_unaligned<T>(src: *const T) -> T {

‎library/core/src/ptr/mut_ptr.rs

+4-4
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@@ -1384,7 +1384,7 @@ impl<T: ?Sized> *mut T {
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/// See [`ptr::copy`] for safety concerns and examples.
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///
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/// [`ptr::copy`]: crate::ptr::copy()
1387-
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
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#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
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#[stable(feature = "pointer_methods", since = "1.26.0")]
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#[inline(always)]
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#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
@@ -1404,7 +1404,7 @@ impl<T: ?Sized> *mut T {
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/// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
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///
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/// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
1407-
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
1407+
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
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#[stable(feature = "pointer_methods", since = "1.26.0")]
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#[inline(always)]
14101410
#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
@@ -1424,7 +1424,7 @@ impl<T: ?Sized> *mut T {
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/// See [`ptr::copy`] for safety concerns and examples.
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///
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/// [`ptr::copy`]: crate::ptr::copy()
1427-
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
1427+
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
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#[stable(feature = "pointer_methods", since = "1.26.0")]
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#[inline(always)]
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#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
@@ -1444,7 +1444,7 @@ impl<T: ?Sized> *mut T {
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/// See [`ptr::copy_nonoverlapping`] for safety concerns and examples.
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///
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/// [`ptr::copy_nonoverlapping`]: crate::ptr::copy_nonoverlapping()
1447-
#[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
1447+
#[rustc_const_unstable(feature = "const_intrinsic_copy", issue = "80697")]
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#[stable(feature = "pointer_methods", since = "1.26.0")]
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#[inline(always)]
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#[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces

‎library/core/tests/lib.rs

+1
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@@ -14,6 +14,7 @@
1414
#![feature(const_cell_into_inner)]
1515
#![feature(const_hash)]
1616
#![feature(const_heap)]
17+
#![feature(const_intrinsic_copy)]
1718
#![feature(const_maybe_uninit_as_mut_ptr)]
1819
#![feature(const_nonnull_new)]
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#![feature(const_pointer_is_aligned)]

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