Stabilize &mut (and *mut) as well as &Cell (and *const Cell) in const

compiler/rustc_const_eval/messages.ftl

@@ -134,9 +134,6 @@ const_eval_incompatible_return_types =
 const_eval_incompatible_types =
     calling a function with argument of type {$callee_ty} passing data of type {$caller_ty}
 
-const_eval_interior_mutability_borrow =
-    cannot borrow here, since the borrowed element may contain interior mutability
-
 const_eval_interior_mutable_data_refer =
     {const_eval_const_context}s cannot refer to interior mutable data
     .label = this borrow of an interior mutable value may end up in the final value
@@ -230,9 +227,6 @@ const_eval_memory_exhausted =
 const_eval_modified_global =
     modifying a static's initial value from another static's initializer
 
-const_eval_mut_deref =
-    mutation through a reference is not allowed in {const_eval_const_context}s
-
 const_eval_mutable_ptr_in_final = encountered mutable pointer in final value of {const_eval_intern_kind}
 
 const_eval_nested_static_in_thread_local = #[thread_local] does not support implicit nested statics, please create explicit static items and refer to them instead
@@ -363,10 +357,6 @@ const_eval_too_generic =
 const_eval_too_many_caller_args =
     calling a function with more arguments than it expected
 
-const_eval_transient_mut_borrow = mutable references are not allowed in {const_eval_const_context}s
-
-const_eval_transient_mut_raw = raw mutable pointers are not allowed in {const_eval_const_context}s
-
 const_eval_try_block_from_output_non_const =
     `try` block cannot convert `{$ty}` to the result in {const_eval_const_context}s
 const_eval_unallowed_fn_pointer_call = function pointer calls are not allowed in {const_eval_const_context}s

compiler/rustc_const_eval/src/check_consts/ops.rs

@@ -8,7 +8,7 @@ use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::{ImplSource, Obligation, ObligationCause};
-use rustc_middle::mir::{self, CallSource};
+use rustc_middle::mir::CallSource;
 use rustc_middle::span_bug;
 use rustc_middle::ty::print::{with_no_trimmed_paths, PrintTraitRefExt as _};
 use rustc_middle::ty::{
@@ -391,27 +391,12 @@ impl<'tcx> NonConstOp<'tcx> for LiveDrop<'tcx> {
     }
 }
 
-#[derive(Debug)]
-/// A borrow of a type that contains an `UnsafeCell` somewhere. The borrow never escapes to
-/// the final value of the constant.
-pub(crate) struct TransientCellBorrow;
-impl<'tcx> NonConstOp<'tcx> for TransientCellBorrow {
-    fn status_in_item(&self, _: &ConstCx<'_, 'tcx>) -> Status {
-        Status::Unstable(sym::const_refs_to_cell)
-    }
-    fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> Diag<'tcx> {
-        ccx.tcx
-            .sess
-            .create_feature_err(errors::InteriorMutabilityBorrow { span }, sym::const_refs_to_cell)
-    }
-}
-
 #[derive(Debug)]
 /// A borrow of a type that contains an `UnsafeCell` somewhere. The borrow might escape to
 /// the final value of the constant, and thus we cannot allow this (for now). We may allow
 /// it in the future for static items.
-pub(crate) struct CellBorrow;
-impl<'tcx> NonConstOp<'tcx> for CellBorrow {
+pub(crate) struct EscapingCellBorrow;
+impl<'tcx> NonConstOp<'tcx> for EscapingCellBorrow {
     fn importance(&self) -> DiagImportance {
         // Most likely the code will try to do mutation with these borrows, which
         // triggers its own errors. Only show this one if that does not happen.
@@ -431,9 +416,9 @@ impl<'tcx> NonConstOp<'tcx> for CellBorrow {
 /// This op is for `&mut` borrows in the trailing expression of a constant
 /// which uses the "enclosing scopes rule" to leak its locals into anonymous
 /// static or const items.
-pub(crate) struct MutBorrow(pub hir::BorrowKind);
+pub(crate) struct EscapingMutBorrow(pub hir::BorrowKind);
 
-impl<'tcx> NonConstOp<'tcx> for MutBorrow {
+impl<'tcx> NonConstOp<'tcx> for EscapingMutBorrow {
     fn status_in_item(&self, _ccx: &ConstCx<'_, 'tcx>) -> Status {
         Status::Forbidden
     }
@@ -460,49 +445,6 @@ impl<'tcx> NonConstOp<'tcx> for MutBorrow {
     }
 }
 
-#[derive(Debug)]
-pub(crate) struct TransientMutBorrow(pub hir::BorrowKind);
-
-impl<'tcx> NonConstOp<'tcx> for TransientMutBorrow {
-    fn status_in_item(&self, _: &ConstCx<'_, 'tcx>) -> Status {
-        Status::Unstable(sym::const_mut_refs)
-    }
-
-    fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> Diag<'tcx> {
-        let kind = ccx.const_kind();
-        match self.0 {
-            hir::BorrowKind::Raw => ccx
-                .tcx
-                .sess
-                .create_feature_err(errors::TransientMutRawErr { span, kind }, sym::const_mut_refs),
-            hir::BorrowKind::Ref => ccx.tcx.sess.create_feature_err(
-                errors::TransientMutBorrowErr { span, kind },
-                sym::const_mut_refs,
-            ),
-        }
-    }
-}
-
-#[derive(Debug)]
-pub(crate) struct MutDeref;
-impl<'tcx> NonConstOp<'tcx> for MutDeref {
-    fn status_in_item(&self, _: &ConstCx<'_, 'tcx>) -> Status {
-        Status::Unstable(sym::const_mut_refs)
-    }
-
-    fn importance(&self) -> DiagImportance {
-        // Usually a side-effect of a `TransientMutBorrow` somewhere.
-        DiagImportance::Secondary
-    }
-
-    fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> Diag<'tcx> {
-        ccx.tcx.sess.create_feature_err(
-            errors::MutDerefErr { span, kind: ccx.const_kind() },
-            sym::const_mut_refs,
-        )
-    }
-}
-
 /// A call to a `panic()` lang item where the first argument is _not_ a `&str`.
 #[derive(Debug)]
 pub(crate) struct PanicNonStr;
@@ -524,24 +466,6 @@ impl<'tcx> NonConstOp<'tcx> for RawPtrComparison {
     }
 }
 
-#[derive(Debug)]
-pub(crate) struct RawMutPtrDeref;
-impl<'tcx> NonConstOp<'tcx> for RawMutPtrDeref {
-    fn status_in_item(&self, _: &ConstCx<'_, '_>) -> Status {
-        Status::Unstable(sym::const_mut_refs)
-    }
-
-    #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
-    fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> Diag<'tcx> {
-        feature_err(
-            &ccx.tcx.sess,
-            sym::const_mut_refs,
-            span,
-            format!("dereferencing raw mutable pointers in {}s is unstable", ccx.const_kind(),),
-        )
-    }
-}
-
 /// Casting raw pointer or function pointer to an integer.
 /// Not currently intended to ever be allowed, even behind a feature gate: operation depends on
 /// allocation base addresses that are not known at compile-time.
@@ -588,33 +512,3 @@ impl<'tcx> NonConstOp<'tcx> for ThreadLocalAccess {
         ccx.dcx().create_err(errors::ThreadLocalAccessErr { span })
     }
 }
-
-/// Types that cannot appear in the signature or locals of a `const fn`.
-pub(crate) mod mut_ref {
-    use super::*;
-
-    #[derive(Debug)]
-    pub(crate) struct MutRef(pub mir::LocalKind);
-    impl<'tcx> NonConstOp<'tcx> for MutRef {
-        fn status_in_item(&self, _ccx: &ConstCx<'_, 'tcx>) -> Status {
-            Status::Unstable(sym::const_mut_refs)
-        }
-
-        fn importance(&self) -> DiagImportance {
-            match self.0 {
-                mir::LocalKind::Temp => DiagImportance::Secondary,
-                mir::LocalKind::ReturnPointer | mir::LocalKind::Arg => DiagImportance::Primary,
-            }
-        }
-
-        #[allow(rustc::untranslatable_diagnostic)] // FIXME: make this translatable
-        fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> Diag<'tcx> {
-            feature_err(
-                &ccx.tcx.sess,
-                sym::const_mut_refs,
-                span,
-                format!("mutable references are not allowed in {}s", ccx.const_kind()),
-            )
-        }
-    }
-}

compiler/rustc_const_eval/src/errors.rs

@@ -93,30 +93,6 @@ pub(crate) struct PanicNonStrErr {
     pub span: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag(const_eval_mut_deref, code = E0658)]
-pub(crate) struct MutDerefErr {
-    #[primary_span]
-    pub span: Span,
-    pub kind: ConstContext,
-}
-
-#[derive(Diagnostic)]
-#[diag(const_eval_transient_mut_borrow, code = E0658)]
-pub(crate) struct TransientMutBorrowErr {
-    #[primary_span]
-    pub span: Span,
-    pub kind: ConstContext,
-}
-
-#[derive(Diagnostic)]
-#[diag(const_eval_transient_mut_raw, code = E0658)]
-pub(crate) struct TransientMutRawErr {
-    #[primary_span]
-    pub span: Span,
-    pub kind: ConstContext,
-}
-
 #[derive(Diagnostic)]
 #[diag(const_eval_max_num_nodes_in_const)]
 pub(crate) struct MaxNumNodesInConstErr {
@@ -217,13 +193,6 @@ pub(crate) struct InteriorMutableDataRefer {
     pub teach: bool,
 }
 
-#[derive(Diagnostic)]
-#[diag(const_eval_interior_mutability_borrow)]
-pub(crate) struct InteriorMutabilityBorrow {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(LintDiagnostic)]
 #[diag(const_eval_long_running)]
 #[note]

compiler/rustc_error_codes/src/error_codes/E0764.md

@@ -3,8 +3,6 @@ A mutable reference was used in a constant.
 Erroneous code example:
 
 ```compile_fail,E0764
-#![feature(const_mut_refs)]
-
 fn main() {
     const OH_NO: &'static mut usize = &mut 1; // error!
 }
@@ -26,8 +24,6 @@ Remember: you cannot use a function call inside a constant or static. However,
 you can totally use it in constant functions:
 
 ```
-#![feature(const_mut_refs)]
-
 const fn foo(x: usize) -> usize {
     let mut y = 1;
     let z = &mut y;

compiler/rustc_feature/src/accepted.rs

@@ -143,10 +143,14 @@ declare_features! (
     (accepted, const_let, "1.33.0", Some(48821)),
     /// Allows the use of `loop` and `while` in constants.
     (accepted, const_loop, "1.46.0", Some(52000)),
+    /// Allows using `&mut` in constant functions.
+    (accepted, const_mut_refs, "CURRENT_RUSTC_VERSION", Some(57349)),
     /// Allows panicking during const eval (producing compile-time errors).
     (accepted, const_panic, "1.57.0", Some(51999)),
     /// Allows dereferencing raw pointers during const eval.
     (accepted, const_raw_ptr_deref, "1.58.0", Some(51911)),
+    /// Allows references to types with interior mutability within constants
+    (accepted, const_refs_to_cell, "CURRENT_RUSTC_VERSION", Some(80384)),
     /// Allows implementing `Copy` for closures where possible (RFC 2132).
     (accepted, copy_closures, "1.26.0", Some(44490)),
     /// Allows `crate` in paths.

compiler/rustc_feature/src/unstable.rs

@@ -403,12 +403,8 @@ declare_features! (
     (incomplete, const_closures, "1.68.0", Some(106003)),
     /// Allows `for _ in _` loops in const contexts.
     (unstable, const_for, "1.56.0", Some(87575)),
-    /// Allows using `&mut` in constant functions.
-    (unstable, const_mut_refs, "1.41.0", Some(57349)),
     /// Be more precise when looking for live drops in a const context.
     (unstable, const_precise_live_drops, "1.46.0", Some(73255)),
-    /// Allows references to types with interior mutability within constants
-    (unstable, const_refs_to_cell, "1.51.0", Some(80384)),
     /// Allows creating pointers and references to `static` items in constants.
     (unstable, const_refs_to_static, "1.78.0", Some(119618)),
     /// Allows `impl const Trait for T` syntax.

library/alloc/src/lib.rs

@@ -114,7 +114,6 @@
 #![feature(const_maybe_uninit_write)]
 #![feature(const_option)]
 #![feature(const_pin)]
-#![feature(const_refs_to_cell)]
 #![feature(const_size_of_val)]
 #![feature(core_intrinsics)]
 #![feature(deprecated_suggestion)]
@@ -164,13 +163,14 @@
 //
 // Language features:
 // tidy-alphabetical-start
+#![cfg_attr(bootstrap, feature(const_mut_refs))]
+#![cfg_attr(bootstrap, feature(const_refs_to_cell))]
 #![cfg_attr(not(test), feature(coroutine_trait))]
 #![cfg_attr(test, feature(panic_update_hook))]
 #![cfg_attr(test, feature(test))]
 #![feature(allocator_internals)]
 #![feature(allow_internal_unstable)]
 #![feature(cfg_sanitize)]
-#![feature(const_mut_refs)]
 #![feature(const_precise_live_drops)]
 #![feature(const_ptr_write)]
 #![feature(const_try)]

library/alloc/tests/lib.rs

@@ -6,7 +6,7 @@
 #![feature(cow_is_borrowed)]
 #![feature(const_cow_is_borrowed)]
 #![feature(const_heap)]
-#![feature(const_mut_refs)]
+#![cfg_attr(bootstrap, feature(const_mut_refs))]
 #![feature(const_slice_from_raw_parts_mut)]
 #![feature(const_ptr_write)]
 #![feature(const_try)]

library/core/src/lib.rs

@@ -191,6 +191,8 @@
 //
 // Language features:
 // tidy-alphabetical-start
+#![cfg_attr(bootstrap, feature(const_mut_refs))]
+#![cfg_attr(bootstrap, feature(const_refs_to_cell))]
 #![feature(abi_unadjusted)]
 #![feature(adt_const_params)]
 #![feature(allow_internal_unsafe)]
@@ -201,9 +203,7 @@
 #![feature(cfg_target_has_atomic_equal_alignment)]
 #![feature(cfg_ub_checks)]
 #![feature(const_for)]
-#![feature(const_mut_refs)]
 #![feature(const_precise_live_drops)]
-#![feature(const_refs_to_cell)]
 #![feature(decl_macro)]
 #![feature(deprecated_suggestion)]
 #![feature(doc_cfg)]

library/core/src/ptr/mut_ptr.rs

@@ -1569,7 +1569,7 @@ impl<T: ?Sized> *mut T {
     ///
     /// ```
     /// #![feature(const_pointer_is_aligned)]
-    /// #![feature(const_mut_refs)]
+    /// # #![cfg_attr(bootstrap, feature(const_mut_refs))]
     ///
     /// // On some platforms, the alignment of primitives is less than their size.
     /// #[repr(align(4))]
@@ -1695,7 +1695,7 @@ impl<T: ?Sized> *mut T {
     /// ```
     /// #![feature(pointer_is_aligned_to)]
     /// #![feature(const_pointer_is_aligned)]
-    /// #![feature(const_mut_refs)]
+    /// # #![cfg_attr(bootstrap, feature(const_mut_refs))]
     ///
     /// // On some platforms, the alignment of i32 is less than 4.
     /// #[repr(align(4))]

library/core/src/slice/mod.rs

@@ -846,7 +846,7 @@ impl<T> [T] {
     /// [`as_mut_ptr`]: slice::as_mut_ptr
     #[stable(feature = "slice_ptr_range", since = "1.48.0")]
     #[rustc_const_stable(feature = "const_ptr_offset", since = "1.61.0")]
-    #[rustc_allow_const_fn_unstable(const_mut_refs)]
+    #[cfg_attr(bootstrap, rustc_allow_const_fn_unstable(const_mut_refs, const_refs_to_cell))]
     #[inline]
     #[must_use]
     pub const fn as_mut_ptr_range(&mut self) -> Range<*mut T> {

library/core/tests/lib.rs

@@ -1,4 +1,5 @@
 // tidy-alphabetical-start
+#![cfg_attr(bootstrap, feature(const_mut_refs))]
 #![cfg_attr(target_has_atomic = "128", feature(integer_atomics))]
 #![cfg_attr(test, feature(cfg_match))]
 #![feature(alloc_layout_extra)]
@@ -26,7 +27,6 @@
 #![feature(const_ipv6)]
 #![feature(const_likely)]
 #![feature(const_maybe_uninit_as_mut_ptr)]
-#![feature(const_mut_refs)]
 #![feature(const_nonnull_new)]
 #![feature(const_option)]
 #![feature(const_option_ext)]

library/std/src/lib.rs

@@ -272,6 +272,7 @@
 //
 // Language features:
 // tidy-alphabetical-start
+#![cfg_attr(bootstrap, feature(const_mut_refs))]
 #![feature(alloc_error_handler)]
 #![feature(allocator_internals)]
 #![feature(allow_internal_unsafe)]
@@ -281,7 +282,6 @@
 #![feature(cfg_target_thread_local)]
 #![feature(cfi_encoding)]
 #![feature(concat_idents)]
-#![feature(const_mut_refs)]
 #![feature(decl_macro)]
 #![feature(deprecated_suggestion)]
 #![feature(doc_cfg)]