Rollup merge of #129199 - RalfJung:writes_through_immutable_pointer, r=compiler-errors

make writes_through_immutable_pointer a hard error

This turns the lint added in https://github.com/rust-lang/rust/pull/118324 into a hard error. This has been reported in cargo's future-compat reports since Rust 1.76 (released in February). Given that const_mut_refs is still unstable, it should be impossible to even hit this error on stable: we did accidentally stabilize some functions that can cause this error, but that got reverted in https://github.com/rust-lang/rust/pull/117905. Still, let's do a crater run just to be sure.

Given that this should only affect unstable code, I don't think it needs an FCP, but let's Cc ``@rust-lang/lang`` anyway -- any objection to making this unambiguous UB into a hard error during const-eval? This can be viewed as part of https://github.com/rust-lang/rust/pull/129195 which is already nominated for discussion.

1 files changed, 0 insertions, 35 deletions

diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index a65d30eb817..44c72e0c4fe 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -142,7 +142,6 @@ declare_lint_pass! {
         USELESS_DEPRECATED,
         WARNINGS,
         WASM_C_ABI,
-        WRITES_THROUGH_IMMUTABLE_POINTER,
         // tidy-alphabetical-end
     ]
 }
@@ -4697,40 +4696,6 @@ declare_lint! {
 }
 
 declare_lint! {
-    /// The `writes_through_immutable_pointer` lint detects writes through pointers derived from
-    /// shared references.
-    ///
-    /// ### Example
-    ///
-    /// ```rust,compile_fail
-    /// #![feature(const_mut_refs)]
-    /// const WRITE_AFTER_CAST: () = unsafe {
-    ///     let mut x = 0;
-    ///     let ptr = &x as *const i32 as *mut i32;
-    ///     *ptr = 0;
-    /// };
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// Shared references are immutable (when there is no `UnsafeCell` involved),
-    /// and writing through them or through pointers derived from them is Undefined Behavior.
-    /// The compiler recently learned to detect such Undefined Behavior during compile-time
-    /// evaluation, and in the future this will raise a hard error.
-    ///
-    /// [future-incompatible]: ../index.md#future-incompatible-lints
-    pub WRITES_THROUGH_IMMUTABLE_POINTER,
-    Warn,
-    "shared references are immutable, and pointers derived from them must not be written to",
-    @future_incompatible = FutureIncompatibleInfo {
-        reason: FutureIncompatibilityReason::FutureReleaseErrorReportInDeps,
-        reference: "issue #X <https://github.com/rust-lang/rust/issues/X>",
-    };
-}
-
-declare_lint! {
     /// The `private_macro_use` lint detects private macros that are imported
     /// with `#[macro_use]`.
     ///