From 544a6a7df382fbe6ae13c05f4b2cfa251e448050 Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Wed, 21 Aug 2024 22:30:16 +0200
Subject: [PATCH] const_refs_to_cell: dont let mutable references sneak past
the interior mutability check
---
.../src/check_consts/check.rs | 13 +++++++-
library/core/src/slice/mod.rs | 2 +-
.../feature-gate-const_refs_to_cell.rs | 20 ++++++-----
.../feature-gate-const_refs_to_cell.stderr | 33 +++++++++++++++++++
tests/ui/statics/mutable_memory_validation.rs | 2 +-
5 files changed, 59 insertions(+), 11 deletions(-)
create mode 100644 tests/ui/feature-gates/feature-gate-const_refs_to_cell.stderr
diff --git a/compiler/rustc_const_eval/src/check_consts/check.rs b/compiler/rustc_const_eval/src/check_consts/check.rs
index 88c8c6475e8..da51ecb359f 100644
--- a/compiler/rustc_const_eval/src/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/check_consts/check.rs
@@ -433,7 +433,18 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
// `TransientCellBorrow` (we consider the equivalent mutable case a
// `TransientMutBorrow`), but such reborrows got accidentally stabilized already and
// it is too much of a breaking change to take back.
- if borrowed_place_has_mut_interior && !place.is_indirect() {
+ // However, we only want to consider places that are obtained by dereferencing
+ // a *shared* reference. Mutable references to interior mutable data are stable,
+ // and we don't want `&*&mut interior_mut` to be accepted.
+ let is_indirect = place.iter_projections().any(|(base, proj)| {
+ matches!(proj, ProjectionElem::Deref)
+ && matches!(
+ base.ty(self.body, self.tcx).ty.kind(),
+ ty::Ref(_, _, Mutability::Not) | ty::RawPtr(_, Mutability::Not)
+ )
+ });
+
+ if borrowed_place_has_mut_interior && !is_indirect {
match self.const_kind() {
// In a const fn all borrows are transient or point to the places given via
// references in the arguments (so we already checked them with
diff --git a/library/core/src/slice/mod.rs b/library/core/src/slice/mod.rs
index 8b661d1202c..c74a7666919 100644
--- a/library/core/src/slice/mod.rs
+++ b/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)]
+ #[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> {
diff --git a/tests/ui/feature-gates/feature-gate-const_refs_to_cell.rs b/tests/ui/feature-gates/feature-gate-const_refs_to_cell.rs
index bd908676c8b..d8628cb41e5 100644
--- a/tests/ui/feature-gates/feature-gate-const_refs_to_cell.rs
+++ b/tests/ui/feature-gates/feature-gate-const_refs_to_cell.rs
@@ -1,12 +1,16 @@
-//@ check-pass
-
-#![feature(const_refs_to_cell)]
-
const FOO: () = {
let x = std::cell::Cell::new(42);
- let y = &x;
+ let y = &x; //~ERROR: cannot borrow here
};
-fn main() {
- FOO;
-}
+const FOO2: () = {
+ let mut x = std::cell::Cell::new(42);
+ let y = &*&mut x; //~ERROR: cannot borrow here
+};
+
+const FOO3: () = unsafe {
+ let mut x = std::cell::Cell::new(42);
+ let y = &*(&mut x as *mut _); //~ERROR: cannot borrow here
+};
+
+fn main() {}
diff --git a/tests/ui/feature-gates/feature-gate-const_refs_to_cell.stderr b/tests/ui/feature-gates/feature-gate-const_refs_to_cell.stderr
new file mode 100644
index 00000000000..553140750b7
--- /dev/null
+++ b/tests/ui/feature-gates/feature-gate-const_refs_to_cell.stderr
@@ -0,0 +1,33 @@
+error[E0658]: cannot borrow here, since the borrowed element may contain interior mutability
+ --> $DIR/feature-gate-const_refs_to_cell.rs:3:13
+ |
+LL | let y = &x;
+ | ^^
+ |
+ = note: see issue #80384 <https://github.com/rust-lang/rust/issues/80384> for more information
+ = help: add `#![feature(const_refs_to_cell)]` to the crate attributes to enable
+ = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: cannot borrow here, since the borrowed element may contain interior mutability
+ --> $DIR/feature-gate-const_refs_to_cell.rs:8:13
+ |
+LL | let y = &*&mut x;
+ | ^^^^^^^^
+ |
+ = note: see issue #80384 <https://github.com/rust-lang/rust/issues/80384> for more information
+ = help: add `#![feature(const_refs_to_cell)]` to the crate attributes to enable
+ = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error[E0658]: cannot borrow here, since the borrowed element may contain interior mutability
+ --> $DIR/feature-gate-const_refs_to_cell.rs:13:13
+ |
+LL | let y = &*(&mut x as *mut _);
+ | ^^^^^^^^^^^^^^^^^^^^
+ |
+ = note: see issue #80384 <https://github.com/rust-lang/rust/issues/80384> for more information
+ = help: add `#![feature(const_refs_to_cell)]` to the crate attributes to enable
+ = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/statics/mutable_memory_validation.rs b/tests/ui/statics/mutable_memory_validation.rs
index d16b787fef8..0dc42c37bed 100644
--- a/tests/ui/statics/mutable_memory_validation.rs
+++ b/tests/ui/statics/mutable_memory_validation.rs
@@ -4,7 +4,7 @@
//@ normalize-stderr-test: "(the raw bytes of the constant) \(size: [0-9]*, align: [0-9]*\)" -> "$1 (size: $$SIZE, align: $$ALIGN)"
//@ normalize-stderr-test: "([0-9a-f][0-9a-f] |╾─*A(LLOC)?[0-9]+(\+[a-z0-9]+)?(<imm>)?─*╼ )+ *│.*" -> "HEX_DUMP"
-#![feature(const_refs_to_static)]
+#![feature(const_refs_to_static, const_refs_to_cell)]
use std::cell::UnsafeCell;