const-eval interning: accpt interior mutable pointers in final value (but keep rejecting mutable references)

Author: RalfJung

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -10,21 +10,19 @@ use rustc_middle::traits::Reveal;
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, Ty, TyCtxt};
-use rustc_session::lint;
 use rustc_span::def_id::LocalDefId;
 use rustc_span::{Span, DUMMY_SP};
 use rustc_target::abi::{self, Abi};
 use tracing::{debug, instrument, trace};
 
 use super::{CanAccessMutGlobal, CompileTimeInterpCx, CompileTimeMachine};
 use crate::const_eval::CheckAlignment;
-use crate::errors::{self, ConstEvalError, DanglingPtrInFinal};
 use crate::interpret::{
     create_static_alloc, eval_nullary_intrinsic, intern_const_alloc_recursive, throw_exhaust,
     CtfeValidationMode, GlobalId, Immediate, InternKind, InternResult, InterpCx, InterpError,
     InterpResult, MPlaceTy, MemoryKind, OpTy, RefTracking, StackPopCleanup,
 };
-use crate::CTRL_C_RECEIVED;
+use crate::{errors, CTRL_C_RECEIVED};
 
 // Returns a pointer to where the result lives
 #[instrument(level = "trace", skip(ecx, body))]
@@ -105,18 +103,15 @@ fn eval_body_using_ecx<'tcx, R: InterpretationResult<'tcx>>(
             return Err(ecx
                 .tcx
                 .dcx()
-                .emit_err(DanglingPtrInFinal { span: ecx.tcx.span, kind: intern_kind })
+                .emit_err(errors::DanglingPtrInFinal { span: ecx.tcx.span, kind: intern_kind })
                 .into());
         }
         Err(InternResult::FoundBadMutablePointer) => {
-            // only report mutable pointers if there were no dangling pointers
-            let err_diag = errors::MutablePtrInFinal { span: ecx.tcx.span, kind: intern_kind };
-            ecx.tcx.emit_node_span_lint(
-                lint::builtin::CONST_EVAL_MUTABLE_PTR_IN_FINAL_VALUE,
-                ecx.machine.best_lint_scope(*ecx.tcx),
-                err_diag.span,
-                err_diag,
-            )
+            return Err(ecx
+                .tcx
+                .dcx()
+                .emit_err(errors::MutablePtrInFinal { span: ecx.tcx.span, kind: intern_kind })
+                .into());
         }
     }
 
@@ -448,7 +443,12 @@ fn report_eval_error<'tcx>(
         error,
         DUMMY_SP,
         || super::get_span_and_frames(ecx.tcx, ecx.stack()),
-        |span, frames| ConstEvalError { span, error_kind: kind, instance, frame_notes: frames },
+        |span, frames| errors::ConstEvalError {
+            span,
+            error_kind: kind,
+            instance,
+            frame_notes: frames,
+        },
     )
 }
 

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -712,16 +712,29 @@ impl<'tcx> interpret::Machine<'tcx> for CompileTimeMachine<'tcx> {
         _kind: mir::RetagKind,
         val: &ImmTy<'tcx, CtfeProvenance>,
     ) -> InterpResult<'tcx, ImmTy<'tcx, CtfeProvenance>> {
-        // If it's a frozen shared reference that's not already immutable, make it immutable.
+        // If it's a frozen shared reference that's not already immutable, potentially make it immutable.
         // (Do nothing on `None` provenance, that cannot store immutability anyway.)
         if let ty::Ref(_, ty, mutbl) = val.layout.ty.kind()
             && *mutbl == Mutability::Not
-            && val.to_scalar_and_meta().0.to_pointer(ecx)?.provenance.is_some_and(|p| !p.immutable())
-            // That next check is expensive, that's why we have all the guards above.
-            && ty.is_freeze(*ecx.tcx, ecx.param_env)
+            && val
+                .to_scalar_and_meta()
+                .0
+                .to_pointer(ecx)?
+                .provenance
+                .is_some_and(|p| !p.immutable())
         {
+            // That next check is expensive, that's why we have all the guards above.
+            let is_immutable = ty.is_freeze(*ecx.tcx, ecx.param_env);
             let place = ecx.ref_to_mplace(val)?;
-            let new_place = place.map_provenance(CtfeProvenance::as_immutable);
+            let new_place = if is_immutable {
+                place.map_provenance(CtfeProvenance::as_immutable)
+            } else {
+                // Even if it is not immutable, remember that it is a shared reference.
+                // This allows it to become part of the final value of the constant.
+                // (See <https://github.com/rust-lang/rust/pull/128543> for why we allow this
+                // even when there is interior mutability.)
+                place.map_provenance(CtfeProvenance::as_shared_ref)
+            };
             Ok(ImmTy::from_immediate(new_place.to_ref(ecx), val.layout))
         } else {
             Ok(val.clone())

compiler/rustc_const_eval/src/errors.rs

@@ -35,13 +35,10 @@ pub(crate) struct NestedStaticInThreadLocal {
     pub span: Span,
 }
 
-#[derive(LintDiagnostic)]
+#[derive(Diagnostic)]
 #[diag(const_eval_mutable_ptr_in_final)]
 pub(crate) struct MutablePtrInFinal {
-    // rust-lang/rust#122153: This was marked as `#[primary_span]` under
-    // `derive(Diagnostic)`. Since we expect we may hard-error in future, we are
-    // keeping the field (and skipping it under `derive(LintDiagnostic)`).
-    #[skip_arg]
+    #[primary_span]
     pub span: Span,
     pub kind: InternKind,
 }

compiler/rustc_const_eval/src/interpret/intern.rs

@@ -223,16 +223,20 @@ pub fn intern_const_alloc_recursive<'tcx, M: CompileTimeMachine<'tcx, const_eval
             continue;
         }
 
-        // Crucially, we check this *before* checking whether the `alloc_id`
-        // has already been interned. The point of this check is to ensure that when
-        // there are multiple pointers to the same allocation, they are *all* immutable.
-        // Therefore it would be bad if we only checked the first pointer to any given
-        // allocation.
+        // Ensure that this is is derived from a shared reference. Crucially, we check this *before*
+        // checking whether the `alloc_id` has already been interned. The point of this check is to
+        // ensure that when there are multiple pointers to the same allocation, they are *all*
+        // derived from a shared reference. Therefore it would be bad if we only checked the first
+        // pointer to any given allocation.
         // (It is likely not possible to actually have multiple pointers to the same allocation,
         // so alternatively we could also check that and ICE if there are multiple such pointers.)
+        // See <https://github.com/rust-lang/rust/pull/128543> for why we are checking for
+        // "shared reference" and not "immutable", i.e., for why we are allowed interior-mutable
+        // shared references: they can actually be created in safe code while pointing to apparently
+        // "immutable" values, via promotion of `&None::<Cell<T>>`.
         if intern_kind != InternKind::Promoted
             && inner_mutability == Mutability::Not
-            && !prov.immutable()
+            && !prov.shared_ref()
         {
             if ecx.tcx.try_get_global_alloc(alloc_id).is_some()
                 && !just_interned.contains(&alloc_id)
@@ -245,7 +249,7 @@ pub fn intern_const_alloc_recursive<'tcx, M: CompileTimeMachine<'tcx, const_eval
                 // this to the todo list, since after all it is already interned.
                 continue;
             }
-            // Found a mutable pointer inside a const where inner allocations should be
+            // Found a mutable reference inside a const where inner allocations should be
             // immutable. We exclude promoteds from this, since things like `&mut []` and
             // `&None::<Cell<i32>>` lead to promotion that can produce mutable pointers. We rely
             // on the promotion analysis not screwing up to ensure that it is sound to intern

compiler/rustc_lint/src/lib.rs

@@ -569,7 +569,11 @@ fn register_builtins(store: &mut LintStore) {
         "byte_slice_in_packed_struct_with_derive",
         "converted into hard error, see issue #107457 \
          <https://github.com/rust-lang/rust/issues/107457> for more information",
-    )
+    );
+    store.register_removed(
+        "const_eval_mutable_ptr_in_final_value",
+        "partially allowed now, otherwise turned into a hard error",
+    );
 }
 
 fn register_internals(store: &mut LintStore) {

compiler/rustc_lint_defs/src/builtin.rs

@@ -29,7 +29,6 @@ declare_lint_pass! {
         CENUM_IMPL_DROP_CAST,
         COHERENCE_LEAK_CHECK,
         CONFLICTING_REPR_HINTS,
-        CONST_EVAL_MUTABLE_PTR_IN_FINAL_VALUE,
         CONST_EVALUATABLE_UNCHECKED,
         CONST_ITEM_MUTATION,
         DEAD_CODE,
@@ -2772,51 +2771,6 @@ declare_lint! {
     @feature_gate = strict_provenance;
 }
 
-declare_lint! {
-    /// The `const_eval_mutable_ptr_in_final_value` lint detects if a mutable pointer
-    /// has leaked into the final value of a const expression.
-    ///
-    /// ### Example
-    ///
-    /// ```rust
-    /// pub enum JsValue {
-    ///     Undefined,
-    ///     Object(std::cell::Cell<bool>),
-    /// }
-    ///
-    /// impl ::std::ops::Drop for JsValue {
-    ///     fn drop(&mut self) {}
-    /// }
-    ///
-    /// const UNDEFINED: &JsValue = &JsValue::Undefined;
-    ///
-    /// fn main() {
-    /// }
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// In the 1.77 release, the const evaluation machinery adopted some
-    /// stricter rules to reject expressions with values that could
-    /// end up holding mutable references to state stored in static memory
-    /// (which is inherently immutable).
-    ///
-    /// This is a [future-incompatible] lint to ease the transition to an error.
-    /// See [issue #122153] for more details.
-    ///
-    /// [issue #122153]: https://github.com/rust-lang/rust/issues/122153
-    /// [future-incompatible]: ../index.md#future-incompatible-lints
-    pub CONST_EVAL_MUTABLE_PTR_IN_FINAL_VALUE,
-    Warn,
-    "detects a mutable pointer that has leaked into final value of a const expression",
-    @future_incompatible = FutureIncompatibleInfo {
-        reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
-        reference: "issue #122153 <https://github.com/rust-lang/rust/issues/122153>",
-    };
-}
-
 declare_lint! {
     /// The `const_evaluatable_unchecked` lint detects a generic constant used
     /// in a type.

compiler/rustc_middle/src/mir/interpret/pointer.rs

@@ -80,14 +80,23 @@ pub trait Provenance: Copy + fmt::Debug + 'static {
 }
 
 /// The type of provenance in the compile-time interpreter.
-/// This is a packed representation of an `AllocId` and an `immutable: bool`.
+/// This is a packed representation of:
+/// - an `AllocId` (non-zero)
+/// - an `immutable: bool`
+/// - a `shared_ref: bool`
+///
+/// with the extra invariant that if `immutable` is `true`, then so
+/// is `shared_ref`.
 #[derive(Copy, Clone, Eq, Hash, Ord, PartialEq, PartialOrd)]
 pub struct CtfeProvenance(NonZero<u64>);
 
 impl From<AllocId> for CtfeProvenance {
     fn from(value: AllocId) -> Self {
         let prov = CtfeProvenance(value.0);
-        assert!(!prov.immutable(), "`AllocId` with the highest bit set cannot be used in CTFE");
+        assert!(
+            prov.alloc_id() == value,
+            "`AllocId` with the highest bits set cannot be used in CTFE"
+        );
         prov
     }
 }
@@ -103,12 +112,14 @@ impl fmt::Debug for CtfeProvenance {
 }
 
 const IMMUTABLE_MASK: u64 = 1 << 63; // the highest bit
+const SHARED_REF_MASK: u64 = 1 << 62;
+const ALLOC_ID_MASK: u64 = u64::MAX & !IMMUTABLE_MASK & !SHARED_REF_MASK;
 
 impl CtfeProvenance {
     /// Returns the `AllocId` of this provenance.
     #[inline(always)]
     pub fn alloc_id(self) -> AllocId {
-        AllocId(NonZero::new(self.0.get() & !IMMUTABLE_MASK).unwrap())
+        AllocId(NonZero::new(self.0.get() & ALLOC_ID_MASK).unwrap())
     }
 
     /// Returns whether this provenance is immutable.
@@ -117,10 +128,38 @@ impl CtfeProvenance {
         self.0.get() & IMMUTABLE_MASK != 0
     }
 
+    /// Returns whether this provenance is derived from a shared reference.
+    #[inline]
+    pub fn shared_ref(self) -> bool {
+        self.0.get() & SHARED_REF_MASK != 0
+    }
+
+    pub fn into_parts(self) -> (AllocId, bool, bool) {
+        (self.alloc_id(), self.immutable(), self.shared_ref())
+    }
+
+    pub fn from_parts((alloc_id, immutable, shared_ref): (AllocId, bool, bool)) -> Self {
+        let prov = CtfeProvenance::from(alloc_id);
+        if immutable {
+            // This sets both flas, so we don't even have to check `shared_ref`.
+            prov.as_immutable()
+        } else if shared_ref {
+            prov.as_shared_ref()
+        } else {
+            prov
+        }
+    }
+
     /// Returns an immutable version of this provenance.
     #[inline]
     pub fn as_immutable(self) -> Self {
-        CtfeProvenance(self.0 | IMMUTABLE_MASK)
+        CtfeProvenance(self.0 | IMMUTABLE_MASK | SHARED_REF_MASK)
+    }
+
+    /// Returns a "shared reference" (but not necessarily immutable!) version of this provenance.
+    #[inline]
+    pub fn as_shared_ref(self) -> Self {
+        CtfeProvenance(self.0 | SHARED_REF_MASK)
     }
 }
 

compiler/rustc_middle/src/ty/codec.rs

@@ -165,8 +165,7 @@ impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for AllocId {
 
 impl<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>> Encodable<E> for CtfeProvenance {
     fn encode(&self, e: &mut E) {
-        self.alloc_id().encode(e);
-        self.immutable().encode(e);
+        self.into_parts().encode(e);
     }
 }
 
@@ -295,10 +294,8 @@ impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for AllocId {
 
 impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for CtfeProvenance {
     fn decode(decoder: &mut D) -> Self {
-        let alloc_id: AllocId = Decodable::decode(decoder);
-        let prov = CtfeProvenance::from(alloc_id);
-        let immutable: bool = Decodable::decode(decoder);
-        if immutable { prov.as_immutable() } else { prov }
+        let parts = Decodable::decode(decoder);
+        CtfeProvenance::from_parts(parts)
     }
 }
 

compiler/rustc_middle/src/ty/impls_ty.rs

@@ -75,11 +75,9 @@ impl<'a> HashStable<StableHashingContext<'a>> for mir::interpret::AllocId {
     }
 }
 
-// CtfeProvenance is an AllocId and a bool.
 impl<'a> HashStable<StableHashingContext<'a>> for mir::interpret::CtfeProvenance {
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
-        self.alloc_id().hash_stable(hcx, hasher);
-        self.immutable().hash_stable(hcx, hasher);
+        self.into_parts().hash_stable(hcx, hasher);
     }
 }
 

tests/ui/consts/const-eval/heap/alloc_intrinsic_untyped.rs

@@ -1,11 +1,9 @@
 #![feature(core_intrinsics)]
 #![feature(const_heap)]
 #![feature(const_mut_refs)]
-#![deny(const_eval_mutable_ptr_in_final_value)]
 use std::intrinsics;
 
 const BAR: *mut i32 = unsafe { intrinsics::const_allocate(4, 4) as *mut i32 };
 //~^ error: mutable pointer in final value of constant
-//~| WARNING this was previously accepted by the compiler
 
 fn main() {}

tests/ui/consts/const-eval/heap/alloc_intrinsic_untyped.stderr

@@ -1,31 +1,8 @@
 error: encountered mutable pointer in final value of constant
-  --> $DIR/alloc_intrinsic_untyped.rs:7:1
+  --> $DIR/alloc_intrinsic_untyped.rs:6:1
    |
 LL | const BAR: *mut i32 = unsafe { intrinsics::const_allocate(4, 4) as *mut i32 };
    | ^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
-note: the lint level is defined here
-  --> $DIR/alloc_intrinsic_untyped.rs:4:9
-   |
-LL | #![deny(const_eval_mutable_ptr_in_final_value)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error
 
-Future incompatibility report: Future breakage diagnostic:
-error: encountered mutable pointer in final value of constant
-  --> $DIR/alloc_intrinsic_untyped.rs:7:1
-   |
-LL | const BAR: *mut i32 = unsafe { intrinsics::const_allocate(4, 4) as *mut i32 };
-   | ^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
-note: the lint level is defined here
-  --> $DIR/alloc_intrinsic_untyped.rs:4:9
-   |
-LL | #![deny(const_eval_mutable_ptr_in_final_value)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-

tests/ui/consts/future-incompat-mutable-in-final-value-issue-121610.rs

@@ -3,7 +3,6 @@
 //@ normalize-stderr-test: "([0-9a-f][0-9a-f] |╾─*ALLOC[0-9]+(\+[a-z0-9]+)?(<imm>)?─*╼ )+ *│.*" -> "HEX_DUMP"
 
 #![allow(static_mut_refs)]
-#![deny(const_eval_mutable_ptr_in_final_value)]
 use std::cell::UnsafeCell;
 use std::sync::atomic::*;
 
@@ -18,13 +17,11 @@ static OH_YES: &mut i32 = &mut 42;
 //~| pointing to read-only memory
 static BAR: &mut () = &mut ();
 //~^ ERROR encountered mutable pointer in final value of static
-//~| WARNING this was previously accepted by the compiler
 
 struct Foo<T>(T);
 
 static BOO: &mut Foo<()> = &mut Foo(());
 //~^ ERROR encountered mutable pointer in final value of static
-//~| WARNING this was previously accepted by the compiler
 
 const BLUNT: &mut i32 = &mut 42;
 //~^ ERROR: it is undefined behavior to use this value
@@ -81,36 +78,32 @@ const POINTS_TO_MUTABLE2: &i32 = unsafe { &*MUTABLE_REF };
 
 const POINTS_TO_MUTABLE_INNER: *const i32 = &mut 42 as *mut _ as *const _;
 //~^ ERROR: mutable pointer in final value
-//~| WARNING this was previously accepted by the compiler
 
 const POINTS_TO_MUTABLE_INNER2: *const i32 = &mut 42 as *const _;
 //~^ ERROR: mutable pointer in final value
-//~| WARNING this was previously accepted by the compiler
 
+// This does *not* error since it uses a shared reference, and we have to ignore
+// those. See <https://github.com/rust-lang/rust/pull/128543>.
 const INTERIOR_MUTABLE_BEHIND_RAW: *mut i32 = &UnsafeCell::new(42) as *const _ as *mut _;
-//~^ ERROR: mutable pointer in final value
-//~| WARNING this was previously accepted by the compiler
 
 struct SyncPtr<T> {
     x: *const T,
 }
 unsafe impl<T> Sync for SyncPtr<T> {}
 
-// These pass the lifetime checks because of the "tail expression" / "outer scope" rule.
-// (This relies on `SyncPtr` being a curly brace struct.)
-// However, we intern the inner memory as read-only, so this must be rejected.
+// These pass the lifetime checks because of the "tail expression" / "outer scope" rule. (This
+// relies on `SyncPtr` being a curly brace struct.) However, we intern the inner memory as
+// read-only, so ideally this should be rejected. Unfortunately, as explained in
+// <https://github.com/rust-lang/rust/pull/128543>, we have to accept it.
 // (Also see `static-no-inner-mut` for similar tests on `static`.)
 const RAW_SYNC: SyncPtr<AtomicI32> = SyncPtr { x: &AtomicI32::new(42) };
-//~^ ERROR mutable pointer in final value
-//~| WARNING this was previously accepted by the compiler
 
+// With mutable references at least, we can detect this and error.
 const RAW_MUT_CAST: SyncPtr<i32> = SyncPtr { x: &mut 42 as *mut _ as *const _ };
 //~^ ERROR mutable pointer in final value
-//~| WARNING this was previously accepted by the compiler
 
 const RAW_MUT_COERCE: SyncPtr<i32> = SyncPtr { x: &mut 0 };
 //~^ ERROR mutable pointer in final value
-//~| WARNING this was previously accepted by the compiler
 
 
 fn main() {

tests/ui/consts/future-incompat-mutable-in-final-value-issue-121610.stderr

@@ -1,5 +1,5 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/static-no-inner-mut.rs:9:1
+  --> $DIR/static-no-inner-mut.rs:8:1
    |
 LL | static REF: &AtomicI32 = &AtomicI32::new(42);
    | ^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>.v: encountered `UnsafeCell` in read-only memory
@@ -10,7 +10,7 @@ LL | static REF: &AtomicI32 = &AtomicI32::new(42);
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/static-no-inner-mut.rs:12:1
+  --> $DIR/static-no-inner-mut.rs:11:1
    |
 LL | static REFMUT: &mut i32 = &mut 0;
    | ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered mutable reference or box pointing to read-only memory
@@ -21,7 +21,7 @@ LL | static REFMUT: &mut i32 = &mut 0;
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/static-no-inner-mut.rs:16:1
+  --> $DIR/static-no-inner-mut.rs:15:1
    |
 LL | static REF2: &AtomicI32 = {let x = AtomicI32::new(42); &{x}};
    | ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>.v: encountered `UnsafeCell` in read-only memory
@@ -32,7 +32,7 @@ LL | static REF2: &AtomicI32 = {let x = AtomicI32::new(42); &{x}};
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/static-no-inner-mut.rs:18:1
+  --> $DIR/static-no-inner-mut.rs:17:1
    |
 LL | static REFMUT2: &mut i32 = {let mut x = 0; &mut {x}};
    | ^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered mutable reference or box pointing to read-only memory
@@ -45,118 +45,53 @@ LL | static REFMUT2: &mut i32 = {let mut x = 0; &mut {x}};
 error: encountered mutable pointer in final value of static
   --> $DIR/static-no-inner-mut.rs:34:1
    |
-LL | static RAW_SYNC: SyncPtr<AtomicI32> = SyncPtr { x: &AtomicI32::new(42) };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
-note: the lint level is defined here
-  --> $DIR/static-no-inner-mut.rs:6:9
-   |
-LL | #![deny(const_eval_mutable_ptr_in_final_value)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: encountered mutable pointer in final value of static
-  --> $DIR/static-no-inner-mut.rs:38:1
-   |
 LL | static RAW_MUT_CAST: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
 
 error: encountered mutable pointer in final value of static
-  --> $DIR/static-no-inner-mut.rs:42:1
+  --> $DIR/static-no-inner-mut.rs:37:1
    |
 LL | static RAW_MUT_COERCE: SyncPtr<i32> = SyncPtr { x: &mut 0 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
 
 warning: skipping const checks
    |
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:9:26
+  --> $DIR/static-no-inner-mut.rs:8:26
    |
 LL | static REF: &AtomicI32 = &AtomicI32::new(42);
    |                          ^^^^^^^^^^^^^^^^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:12:27
+  --> $DIR/static-no-inner-mut.rs:11:27
    |
 LL | static REFMUT: &mut i32 = &mut 0;
    |                           ^^^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:16:56
+  --> $DIR/static-no-inner-mut.rs:15:56
    |
 LL | static REF2: &AtomicI32 = {let x = AtomicI32::new(42); &{x}};
    |                                                        ^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:18:44
+  --> $DIR/static-no-inner-mut.rs:17:44
    |
 LL | static REFMUT2: &mut i32 = {let mut x = 0; &mut {x}};
    |                                            ^^^^^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:34:52
+  --> $DIR/static-no-inner-mut.rs:31:52
    |
 LL | static RAW_SYNC: SyncPtr<AtomicI32> = SyncPtr { x: &AtomicI32::new(42) };
    |                                                    ^^^^^^^^^^^^^^^^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:38:51
+  --> $DIR/static-no-inner-mut.rs:34:51
    |
 LL | static RAW_MUT_CAST: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
    |                                                   ^^^^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:42:52
+  --> $DIR/static-no-inner-mut.rs:37:52
    |
 LL | static RAW_MUT_COERCE: SyncPtr<i32> = SyncPtr { x: &mut 0 };
    |                                                    ^^^^^^
 
-error: aborting due to 7 previous errors; 1 warning emitted
+error: aborting due to 6 previous errors; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0080`.
-Future incompatibility report: Future breakage diagnostic:
-error: encountered mutable pointer in final value of static
-  --> $DIR/static-no-inner-mut.rs:34:1
-   |
-LL | static RAW_SYNC: SyncPtr<AtomicI32> = SyncPtr { x: &AtomicI32::new(42) };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
-note: the lint level is defined here
-  --> $DIR/static-no-inner-mut.rs:6:9
-   |
-LL | #![deny(const_eval_mutable_ptr_in_final_value)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-Future breakage diagnostic:
-error: encountered mutable pointer in final value of static
-  --> $DIR/static-no-inner-mut.rs:38:1
-   |
-LL | static RAW_MUT_CAST: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
-note: the lint level is defined here
-  --> $DIR/static-no-inner-mut.rs:6:9
-   |
-LL | #![deny(const_eval_mutable_ptr_in_final_value)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-Future breakage diagnostic:
-error: encountered mutable pointer in final value of static
-  --> $DIR/static-no-inner-mut.rs:42:1
-   |
-LL | static RAW_MUT_COERCE: SyncPtr<i32> = SyncPtr { x: &mut 0 };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
-note: the lint level is defined here
-  --> $DIR/static-no-inner-mut.rs:6:9
-   |
-LL | #![deny(const_eval_mutable_ptr_in_final_value)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-

tests/ui/consts/miri_unleashed/mutable_references.rs

@@ -1,5 +1,5 @@
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/static-no-inner-mut.rs:9:1
+  --> $DIR/static-no-inner-mut.rs:8:1
    |
 LL | static REF: &AtomicI32 = &AtomicI32::new(42);
    | ^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>.v: encountered `UnsafeCell` in read-only memory
@@ -10,7 +10,7 @@ LL | static REF: &AtomicI32 = &AtomicI32::new(42);
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/static-no-inner-mut.rs:12:1
+  --> $DIR/static-no-inner-mut.rs:11:1
    |
 LL | static REFMUT: &mut i32 = &mut 0;
    | ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered mutable reference or box pointing to read-only memory
@@ -21,7 +21,7 @@ LL | static REFMUT: &mut i32 = &mut 0;
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/static-no-inner-mut.rs:16:1
+  --> $DIR/static-no-inner-mut.rs:15:1
    |
 LL | static REF2: &AtomicI32 = {let x = AtomicI32::new(42); &{x}};
    | ^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>.v: encountered `UnsafeCell` in read-only memory
@@ -32,7 +32,7 @@ LL | static REF2: &AtomicI32 = {let x = AtomicI32::new(42); &{x}};
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/static-no-inner-mut.rs:18:1
+  --> $DIR/static-no-inner-mut.rs:17:1
    |
 LL | static REFMUT2: &mut i32 = {let mut x = 0; &mut {x}};
    | ^^^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered mutable reference or box pointing to read-only memory
@@ -45,118 +45,53 @@ LL | static REFMUT2: &mut i32 = {let mut x = 0; &mut {x}};
 error: encountered mutable pointer in final value of static
   --> $DIR/static-no-inner-mut.rs:34:1
    |
-LL | static RAW_SYNC: SyncPtr<AtomicI32> = SyncPtr { x: &AtomicI32::new(42) };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
-note: the lint level is defined here
-  --> $DIR/static-no-inner-mut.rs:6:9
-   |
-LL | #![deny(const_eval_mutable_ptr_in_final_value)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: encountered mutable pointer in final value of static
-  --> $DIR/static-no-inner-mut.rs:38:1
-   |
 LL | static RAW_MUT_CAST: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
 
 error: encountered mutable pointer in final value of static
-  --> $DIR/static-no-inner-mut.rs:42:1
+  --> $DIR/static-no-inner-mut.rs:37:1
    |
 LL | static RAW_MUT_COERCE: SyncPtr<i32> = SyncPtr { x: &mut 0 };
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
 
 warning: skipping const checks
    |
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:9:26
+  --> $DIR/static-no-inner-mut.rs:8:26
    |
 LL | static REF: &AtomicI32 = &AtomicI32::new(42);
    |                          ^^^^^^^^^^^^^^^^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:12:27
+  --> $DIR/static-no-inner-mut.rs:11:27
    |
 LL | static REFMUT: &mut i32 = &mut 0;
    |                           ^^^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:16:56
+  --> $DIR/static-no-inner-mut.rs:15:56
    |
 LL | static REF2: &AtomicI32 = {let x = AtomicI32::new(42); &{x}};
    |                                                        ^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:18:44
+  --> $DIR/static-no-inner-mut.rs:17:44
    |
 LL | static REFMUT2: &mut i32 = {let mut x = 0; &mut {x}};
    |                                            ^^^^^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:34:52
+  --> $DIR/static-no-inner-mut.rs:31:52
    |
 LL | static RAW_SYNC: SyncPtr<AtomicI32> = SyncPtr { x: &AtomicI32::new(42) };
    |                                                    ^^^^^^^^^^^^^^^^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:38:51
+  --> $DIR/static-no-inner-mut.rs:34:51
    |
 LL | static RAW_MUT_CAST: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
    |                                                   ^^^^^^^
 help: skipping check that does not even have a feature gate
-  --> $DIR/static-no-inner-mut.rs:42:52
+  --> $DIR/static-no-inner-mut.rs:37:52
    |
 LL | static RAW_MUT_COERCE: SyncPtr<i32> = SyncPtr { x: &mut 0 };
    |                                                    ^^^^^^
 
-error: aborting due to 7 previous errors; 1 warning emitted
+error: aborting due to 6 previous errors; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0080`.
-Future incompatibility report: Future breakage diagnostic:
-error: encountered mutable pointer in final value of static
-  --> $DIR/static-no-inner-mut.rs:34:1
-   |
-LL | static RAW_SYNC: SyncPtr<AtomicI32> = SyncPtr { x: &AtomicI32::new(42) };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
-note: the lint level is defined here
-  --> $DIR/static-no-inner-mut.rs:6:9
-   |
-LL | #![deny(const_eval_mutable_ptr_in_final_value)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-Future breakage diagnostic:
-error: encountered mutable pointer in final value of static
-  --> $DIR/static-no-inner-mut.rs:38:1
-   |
-LL | static RAW_MUT_CAST: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
-note: the lint level is defined here
-  --> $DIR/static-no-inner-mut.rs:6:9
-   |
-LL | #![deny(const_eval_mutable_ptr_in_final_value)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-Future breakage diagnostic:
-error: encountered mutable pointer in final value of static
-  --> $DIR/static-no-inner-mut.rs:42:1
-   |
-LL | static RAW_MUT_COERCE: SyncPtr<i32> = SyncPtr { x: &mut 0 };
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
-note: the lint level is defined here
-  --> $DIR/static-no-inner-mut.rs:6:9
-   |
-LL | #![deny(const_eval_mutable_ptr_in_final_value)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-

tests/ui/consts/miri_unleashed/mutable_references.stderr

@@ -3,7 +3,6 @@
 #![feature(const_refs_to_cell, const_mut_refs)]
 // All "inner" allocations that come with a `static` are interned immutably. This means it is
 // crucial that we do not accept any form of (interior) mutability there.
-#![deny(const_eval_mutable_ptr_in_final_value)]
 use std::sync::atomic::*;
 
 static REF: &AtomicI32 = &AtomicI32::new(42);
@@ -27,20 +26,15 @@ unsafe impl<T> Sync for SyncPtr<T> {}
 
 // All of these pass the lifetime checks because of the "tail expression" / "outer scope" rule.
 // (This relies on `SyncPtr` being a curly brace struct.)
-// Then they get interned immutably, which is not great.
-// `mut_ref_in_final.rs` and `std/cell.rs` ensure that we don't accept this even with the feature
-// fate, but for unleashed Miri there's not really any way we can reject them: it's just
-// non-dangling raw pointers.
+// Then they get interned immutably, which is not great. See
+// <https://github.com/rust-lang/rust/pull/128543> for why we accept such code.
 static RAW_SYNC: SyncPtr<AtomicI32> = SyncPtr { x: &AtomicI32::new(42) };
-//~^ ERROR mutable pointer in final value
-//~| WARNING this was previously accepted by the compiler
 
+// With mutable references at least, we can detect this and error.
 static RAW_MUT_CAST: SyncPtr<i32> = SyncPtr { x : &mut 42 as *mut _ as *const _ };
 //~^ ERROR mutable pointer in final value
-//~| WARNING this was previously accepted by the compiler
 
 static RAW_MUT_COERCE: SyncPtr<i32> = SyncPtr { x: &mut 0 };
 //~^ ERROR mutable pointer in final value
-//~| WARNING this was previously accepted by the compiler
 
 fn main() {}

tests/ui/consts/miri_unleashed/static-no-inner-mut.32bit.stderr

@@ -18,8 +18,8 @@ const RAW_SYNC_C: SyncPtr<Cell<i32>> = SyncPtr { x: &Cell::new(42) };
 // This one does not get promoted because of `Drop`, and then enters interesting codepaths because
 // as a value it has no interior mutability, but as a type it does. See
 // <https://github.com/rust-lang/rust/issues/121610>. Value-based reasoning for interior mutability
-// is questionable (https://github.com/rust-lang/unsafe-code-guidelines/issues/493) so for now we
-// reject this, though not with a great error message.
+// is questionable (https://github.com/rust-lang/unsafe-code-guidelines/issues/493) but we've
+// done it since Rust 1.0 so we can't stop now.
 pub enum JsValue {
     Undefined,
     Object(Cell<bool>),
@@ -28,10 +28,8 @@ impl Drop for JsValue {
     fn drop(&mut self) {}
 }
 const UNDEFINED: &JsValue = &JsValue::Undefined;
-//~^ WARNING: mutable pointer in final value of constant
-//~| WARNING: this was previously accepted by the compiler but is being phased out
 
-// In contrast, this one works since it is being promoted.
+// Here's a variant of the above that uses promotion instead of the "outer scope rule" rule.
 const NONE: &'static Option<Cell<i32>> = &None;
 // Making it clear that this is promotion, not "outer scope".
 const NONE_EXPLICIT_PROMOTED: &'static Option<Cell<i32>> = {

tests/ui/consts/miri_unleashed/static-no-inner-mut.64bit.stderr

@@ -12,27 +12,6 @@ error[E0492]: constants cannot refer to interior mutable data
 LL | const RAW_SYNC_C: SyncPtr<Cell<i32>> = SyncPtr { x: &Cell::new(42) };
    |                                                     ^^^^^^^^^^^^^^ this borrow of an interior mutable value may end up in the final value
 
-warning: encountered mutable pointer in final value of constant
-  --> $DIR/refs-to-cell-in-final.rs:30:1
-   |
-LL | const UNDEFINED: &JsValue = &JsValue::Undefined;
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
-   = note: `#[warn(const_eval_mutable_ptr_in_final_value)]` on by default
-
-error: aborting due to 2 previous errors; 1 warning emitted
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0492`.
-Future incompatibility report: Future breakage diagnostic:
-warning: encountered mutable pointer in final value of constant
-  --> $DIR/refs-to-cell-in-final.rs:30:1
-   |
-LL | const UNDEFINED: &JsValue = &JsValue::Undefined;
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #122153 <https://github.com/rust-lang/rust/issues/122153>
-   = note: `#[warn(const_eval_mutable_ptr_in_final_value)]` on by default
-