Rename and allow cast_ref_to_mut lint

compiler/rustc_lint/messages.ftl

@@ -155,8 +155,6 @@ lint_builtin_unused_doc_comment = unused doc comment
 lint_builtin_while_true = denote infinite loops with `loop {"{"} ... {"}"}`
     .suggestion = use `loop`
 
-lint_cast_ref_to_mut = casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-
 lint_check_name_deprecated = lint name `{$lint_name}` is deprecated and does not have an effect anymore. Use: {$new_name}
 
 lint_check_name_unknown = unknown lint: `{$lint_name}`
@@ -322,6 +320,8 @@ lint_invalid_nan_comparisons_eq_ne = incorrect NaN comparison, NaN cannot be dir
 
 lint_invalid_nan_comparisons_lt_le_gt_ge = incorrect NaN comparison, NaN is not orderable
 
+lint_invalid_reference_casting = casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
+
 lint_lintpass_by_hand = implementing `LintPass` by hand
     .help = try using `declare_lint_pass!` or `impl_lint_pass!` instead
 

compiler/rustc_lint/src/lib.rs

@@ -50,7 +50,6 @@ extern crate tracing;
 
 mod array_into_iter;
 pub mod builtin;
-mod cast_ref_to_mut;
 mod context;
 mod deref_into_dyn_supertrait;
 mod drop_forget_useless;
@@ -78,6 +77,7 @@ mod opaque_hidden_inferred_bound;
 mod pass_by_value;
 mod passes;
 mod redundant_semicolon;
+mod reference_casting;
 mod traits;
 mod types;
 mod unused;
@@ -99,7 +99,6 @@ use rustc_span::Span;
 
 use array_into_iter::ArrayIntoIter;
 use builtin::*;
-use cast_ref_to_mut::*;
 use deref_into_dyn_supertrait::*;
 use drop_forget_useless::*;
 use enum_intrinsics_non_enums::EnumIntrinsicsNonEnums;
@@ -119,6 +118,7 @@ use noop_method_call::*;
 use opaque_hidden_inferred_bound::*;
 use pass_by_value::*;
 use redundant_semicolon::*;
+use reference_casting::*;
 use traits::*;
 use types::*;
 use unused::*;
@@ -218,7 +218,7 @@ late_lint_methods!(
             BoxPointers: BoxPointers,
             PathStatements: PathStatements,
             LetUnderscore: LetUnderscore,
-            CastRefToMut: CastRefToMut,
+            InvalidReferenceCasting: InvalidReferenceCasting,
             // Depends on referenced function signatures in expressions
             UnusedResults: UnusedResults,
             NonUpperCaseGlobals: NonUpperCaseGlobals,

compiler/rustc_lint/src/lints.rs

@@ -743,10 +743,10 @@ pub enum InvalidFromUtf8Diag {
     },
 }
 
-// cast_ref_to_mut.rs
+// reference_casting.rs
 #[derive(LintDiagnostic)]
-#[diag(lint_cast_ref_to_mut)]
-pub struct CastRefToMutDiag;
+#[diag(lint_invalid_reference_casting)]
+pub struct InvalidReferenceCastingDiag;
 
 // hidden_unicode_codepoints.rs
 #[derive(LintDiagnostic)]

compiler/rustc_lint/src/cast_ref_to_mut.rs → compiler/rustc_lint/src/reference_casting.rs

@@ -3,15 +3,16 @@ use rustc_hir::{Expr, ExprKind, MutTy, TyKind, UnOp};
 use rustc_middle::ty;
 use rustc_span::sym;
 
-use crate::{lints::CastRefToMutDiag, LateContext, LateLintPass, LintContext};
+use crate::{lints::InvalidReferenceCastingDiag, LateContext, LateLintPass, LintContext};
 
 declare_lint! {
-    /// The `cast_ref_to_mut` lint checks for casts of `&T` to `&mut T`
+    /// The `invalid_reference_casting` lint checks for casts of `&T` to `&mut T`
     /// without using interior mutability.
     ///
     /// ### Example
     ///
     /// ```rust,compile_fail
+    /// # #![deny(invalid_reference_casting)]
     /// fn x(r: &i32) {
     ///     unsafe {
     ///         *(r as *const i32 as *mut i32) += 1;
@@ -28,14 +29,14 @@ declare_lint! {
     ///
     /// `UnsafeCell` is the only way to obtain aliasable data that is considered
     /// mutable.
-    CAST_REF_TO_MUT,
-    Deny,
+    INVALID_REFERENCE_CASTING,
+    Allow,
     "casts of `&T` to `&mut T` without interior mutability"
 }
 
-declare_lint_pass!(CastRefToMut => [CAST_REF_TO_MUT]);
+declare_lint_pass!(InvalidReferenceCasting => [INVALID_REFERENCE_CASTING]);
 
-impl<'tcx> LateLintPass<'tcx> for CastRefToMut {
+impl<'tcx> LateLintPass<'tcx> for InvalidReferenceCasting {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
         let ExprKind::Unary(UnOp::Deref, e) = &expr.kind else {
             return;
@@ -68,7 +69,7 @@ impl<'tcx> LateLintPass<'tcx> for CastRefToMut {
 
         let e = e.peel_blocks();
         if let ty::Ref(..) = cx.typeck_results().node_type(e.hir_id).kind() {
-            cx.emit_spanned_lint(CAST_REF_TO_MUT, expr.span, CastRefToMutDiag);
+            cx.emit_spanned_lint(INVALID_REFERENCE_CASTING, expr.span, InvalidReferenceCastingDiag);
         }
     }
 }

src/tools/clippy/clippy_lints/src/renamed_lints.rs

@@ -31,7 +31,7 @@ pub static RENAMED_LINTS: &[(&str, &str)] = &[
     ("clippy::stutter", "clippy::module_name_repetitions"),
     ("clippy::to_string_in_display", "clippy::recursive_format_impl"),
     ("clippy::zero_width_space", "clippy::invisible_characters"),
-    ("clippy::cast_ref_to_mut", "cast_ref_to_mut"),
+    ("clippy::cast_ref_to_mut", "invalid_reference_casting"),
     ("clippy::clone_double_ref", "suspicious_double_ref_op"),
     ("clippy::cmp_nan", "invalid_nan_comparisons"),
     ("clippy::drop_bounds", "drop_bounds"),

src/tools/clippy/tests/ui/rename.fixed

@@ -28,9 +28,9 @@
 #![allow(clippy::module_name_repetitions)]
 #![allow(clippy::recursive_format_impl)]
 #![allow(clippy::invisible_characters)]
-#![allow(cast_ref_to_mut)]
 #![allow(suspicious_double_ref_op)]
 #![allow(invalid_nan_comparisons)]
+#![allow(invalid_reference_casting)]
 #![allow(drop_bounds)]
 #![allow(dropping_copy_types)]
 #![allow(dropping_references)]
@@ -79,7 +79,7 @@
 #![warn(clippy::module_name_repetitions)]
 #![warn(clippy::recursive_format_impl)]
 #![warn(clippy::invisible_characters)]
-#![warn(cast_ref_to_mut)]
+#![warn(invalid_reference_casting)]
 #![warn(suspicious_double_ref_op)]
 #![warn(invalid_nan_comparisons)]
 #![warn(drop_bounds)]

src/tools/clippy/tests/ui/rename.rs

@@ -28,9 +28,9 @@
 #![allow(clippy::module_name_repetitions)]
 #![allow(clippy::recursive_format_impl)]
 #![allow(clippy::invisible_characters)]
-#![allow(cast_ref_to_mut)]
 #![allow(suspicious_double_ref_op)]
 #![allow(invalid_nan_comparisons)]
+#![allow(invalid_reference_casting)]
 #![allow(drop_bounds)]
 #![allow(dropping_copy_types)]
 #![allow(dropping_references)]

src/tools/clippy/tests/ui/rename.stderr

@@ -174,11 +174,11 @@ error: lint `clippy::zero_width_space` has been renamed to `clippy::invisible_ch
 LL | #![warn(clippy::zero_width_space)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^ help: use the new name: `clippy::invisible_characters`
 
-error: lint `clippy::cast_ref_to_mut` has been renamed to `cast_ref_to_mut`
+error: lint `clippy::cast_ref_to_mut` has been renamed to `invalid_reference_casting`
   --> $DIR/rename.rs:82:9
    |
 LL | #![warn(clippy::cast_ref_to_mut)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^ help: use the new name: `cast_ref_to_mut`
+   |         ^^^^^^^^^^^^^^^^^^^^^^^ help: use the new name: `invalid_reference_casting`
 
 error: lint `clippy::clone_double_ref` has been renamed to `suspicious_double_ref_op`
   --> $DIR/rename.rs:83:9

src/tools/miri/tests/fail/both_borrows/shr_frozen_violation1.rs

@@ -1,7 +1,7 @@
 //@revisions: stack tree
 //@[tree]compile-flags: -Zmiri-tree-borrows
 
-#![allow(cast_ref_to_mut)]
+#![allow(invalid_reference_casting)]
 
 fn foo(x: &mut i32) -> i32 {
     *x = 5;

src/tools/miri/tests/fail/modifying_constants.rs

@@ -1,7 +1,7 @@
 // This should fail even without validation/SB
 //@compile-flags: -Zmiri-disable-validation -Zmiri-disable-stacked-borrows
 
-#![allow(cast_ref_to_mut)]
+#![allow(invalid_reference_casting)]
 
 fn main() {
     let x = &1; // the `&1` is promoted to a constant, but it used to be that only the pointer is marked static, not the pointee

tests/ui/const-generics/issues/issue-100313.rs

@@ -9,7 +9,6 @@ impl <const B: &'static bool> T<B> {
         unsafe {
             *(B as *const bool as *mut bool) = false;
             //~^ ERROR evaluation of constant value failed [E0080]
-            //~| ERROR casting `&T` to `&mut T` is undefined behavior
         }
     }
 }

tests/ui/const-generics/issues/issue-100313.stderr

@@ -1,11 +1,3 @@
-error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-  --> $DIR/issue-100313.rs:10:13
-   |
-LL |             *(B as *const bool as *mut bool) = false;
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: `#[deny(cast_ref_to_mut)]` on by default
-
 error[E0080]: evaluation of constant value failed
   --> $DIR/issue-100313.rs:10:13
    |
@@ -18,11 +10,11 @@ note: inside `T::<&true>::set_false`
 LL |             *(B as *const bool as *mut bool) = false;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: inside `_`
-  --> $DIR/issue-100313.rs:19:5
+  --> $DIR/issue-100313.rs:18:5
    |
 LL |     x.set_false();
    |     ^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0080`.

tests/ui/lint/cast_ref_to_mut.rs → tests/ui/lint/reference_casting.rs

@@ -1,6 +1,7 @@
 // check-fail
 
 #![feature(ptr_from_ref)]
+#![deny(invalid_reference_casting)]
 
 extern "C" {
     // N.B., mutability can be easily incorrect in FFI calls -- as

tests/ui/lint/cast_ref_to_mut.stderr → tests/ui/lint/reference_casting.stderr

@@ -1,61 +1,65 @@
 error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-  --> $DIR/cast_ref_to_mut.rs:19:9
+  --> $DIR/reference_casting.rs:20:9
    |
 LL |         (*(a as *const _ as *mut String)).push_str(" world");
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: `#[deny(cast_ref_to_mut)]` on by default
+note: the lint level is defined here
+  --> $DIR/reference_casting.rs:4:9
+   |
+LL | #![deny(invalid_reference_casting)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-  --> $DIR/cast_ref_to_mut.rs:21:9
+  --> $DIR/reference_casting.rs:22:9
    |
 LL |         *(a as *const _ as *mut _) = String::from("Replaced");
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-  --> $DIR/cast_ref_to_mut.rs:23:9
+  --> $DIR/reference_casting.rs:24:9
    |
 LL |         *(a as *const _ as *mut String) += " world";
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-  --> $DIR/cast_ref_to_mut.rs:25:25
+  --> $DIR/reference_casting.rs:26:25
    |
 LL |         let _num = &mut *(num as *const i32 as *mut i32);
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-  --> $DIR/cast_ref_to_mut.rs:27:25
+  --> $DIR/reference_casting.rs:28:25
    |
 LL |         let _num = &mut *(num as *const i32).cast_mut();
    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-  --> $DIR/cast_ref_to_mut.rs:29:20
+  --> $DIR/reference_casting.rs:30:20
    |
 LL |         let _num = *{ num as *const i32 }.cast_mut();
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-  --> $DIR/cast_ref_to_mut.rs:31:9
+  --> $DIR/reference_casting.rs:32:9
    |
 LL |         *std::ptr::from_ref(num).cast_mut() += 1;
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-  --> $DIR/cast_ref_to_mut.rs:33:9
+  --> $DIR/reference_casting.rs:34:9
    |
 LL |         *std::ptr::from_ref({ num }).cast_mut() += 1;
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-  --> $DIR/cast_ref_to_mut.rs:35:9
+  --> $DIR/reference_casting.rs:36:9
    |
 LL |         *{ std::ptr::from_ref(num) }.cast_mut() += 1;
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
-  --> $DIR/cast_ref_to_mut.rs:37:9
+  --> $DIR/reference_casting.rs:38:9
    |
 LL |         *(std::ptr::from_ref({ num }) as *mut i32) += 1;
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^