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Uplift clippy::cast_ref_to_mut to rustc
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‎compiler/rustc_lint/messages.ftl

+2
Original file line numberDiff line numberDiff line change
@@ -155,6 +155,8 @@ lint_builtin_unused_doc_comment = unused doc comment
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lint_builtin_while_true = denote infinite loops with `loop {"{"} ... {"}"}`
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.suggestion = use `loop`
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lint_cast_ref_to_mut = casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
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lint_check_name_deprecated = lint name `{$lint_name}` is deprecated and does not have an effect anymore. Use: {$new_name}
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lint_check_name_unknown = unknown lint: `{$lint_name}`

‎compiler/rustc_lint/src/cast_ref_to_mut.rs

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@@ -0,0 +1,72 @@
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use rustc_ast::Mutability;
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use rustc_hir::{Expr, ExprKind, MutTy, TyKind, UnOp};
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use rustc_middle::ty;
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use rustc_span::sym;
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use crate::{lints::CastRefToMutDiag, LateContext, LateLintPass, LintContext};
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declare_lint! {
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/// The `cast_ref_to_mut` lint checks for casts of `&T` to `&mut T`
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/// without using interior mutability.
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///
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/// ### Example
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///
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/// ```rust,compile_fail
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/// fn x(r: &i32) {
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/// unsafe {
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/// *(r as *const i32 as *mut i32) += 1;
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/// }
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/// }
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/// ```
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///
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/// {{produces}}
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///
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/// ### Explanation
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///
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/// Casting `&T` to `&mut T` without using interior mutability is undefined behavior,
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/// as it's a violation of Rust reference aliasing requirements.
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///
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/// `UnsafeCell` is the only way to obtain aliasable data that is considered
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/// mutable.
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CAST_REF_TO_MUT,
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Deny,
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"casts of `&T` to `&mut T` without interior mutability"
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}
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declare_lint_pass!(CastRefToMut => [CAST_REF_TO_MUT]);
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impl<'tcx> LateLintPass<'tcx> for CastRefToMut {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
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let ExprKind::Unary(UnOp::Deref, e) = &expr.kind else { return; };
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let e = e.peel_blocks();
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let e = if let ExprKind::Cast(e, t) = e.kind
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&& let TyKind::Ptr(MutTy { mutbl: Mutability::Mut, .. }) = t.kind {
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e
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} else if let ExprKind::MethodCall(_, expr, [], _) = e.kind
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&& let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
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&& cx.tcx.is_diagnostic_item(sym::ptr_cast_mut, def_id) {
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expr
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} else {
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return;
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};
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let e = e.peel_blocks();
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let e = if let ExprKind::Cast(e, t) = e.kind
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&& let TyKind::Ptr(MutTy { mutbl: Mutability::Not, .. }) = t.kind {
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e
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} else if let ExprKind::Call(path, [arg]) = e.kind
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&& let ExprKind::Path(ref qpath) = path.kind
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&& let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
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&& cx.tcx.is_diagnostic_item(sym::ptr_from_ref, def_id) {
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arg
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} else {
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return;
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};
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let e = e.peel_blocks();
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if let ty::Ref(..) = cx.typeck_results().node_type(e.hir_id).kind() {
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cx.emit_spanned_lint(CAST_REF_TO_MUT, expr.span, CastRefToMutDiag);
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}
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}
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}

‎compiler/rustc_lint/src/lib.rs

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@@ -50,6 +50,7 @@ extern crate tracing;
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mod array_into_iter;
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pub mod builtin;
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mod cast_ref_to_mut;
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mod context;
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mod deref_into_dyn_supertrait;
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mod drop_forget_useless;
@@ -97,6 +98,7 @@ use rustc_span::Span;
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use array_into_iter::ArrayIntoIter;
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use builtin::*;
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use cast_ref_to_mut::*;
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use deref_into_dyn_supertrait::*;
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use drop_forget_useless::*;
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use enum_intrinsics_non_enums::EnumIntrinsicsNonEnums;
@@ -214,6 +216,7 @@ late_lint_methods!(
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BoxPointers: BoxPointers,
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PathStatements: PathStatements,
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LetUnderscore: LetUnderscore,
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CastRefToMut: CastRefToMut,
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// Depends on referenced function signatures in expressions
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UnusedResults: UnusedResults,
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NonUpperCaseGlobals: NonUpperCaseGlobals,

‎compiler/rustc_lint/src/lints.rs

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@@ -718,6 +718,11 @@ pub enum InvalidFromUtf8Diag {
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},
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}
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// cast_ref_to_mut.rs
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#[derive(LintDiagnostic)]
723+
#[diag(lint_cast_ref_to_mut)]
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pub struct CastRefToMutDiag;
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// hidden_unicode_codepoints.rs
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#[derive(LintDiagnostic)]
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#[diag(lint_hidden_unicode_codepoints)]

‎tests/ui/lint/cast_ref_to_mut.rs

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// check-fail
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#![feature(ptr_from_ref)]
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extern "C" {
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// N.B., mutability can be easily incorrect in FFI calls -- as
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// in C, the default is mutable pointers.
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fn ffi(c: *mut u8);
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fn int_ffi(c: *mut i32);
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}
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fn main() {
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let s = String::from("Hello");
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let a = &s;
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unsafe {
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let num = &3i32;
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let mut_num = &mut 3i32;
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(*(a as *const _ as *mut String)).push_str(" world");
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//~^ ERROR casting `&T` to `&mut T` is undefined behavior
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*(a as *const _ as *mut _) = String::from("Replaced");
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//~^ ERROR casting `&T` to `&mut T` is undefined behavior
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*(a as *const _ as *mut String) += " world";
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//~^ ERROR casting `&T` to `&mut T` is undefined behavior
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let _num = &mut *(num as *const i32 as *mut i32);
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//~^ ERROR casting `&T` to `&mut T` is undefined behavior
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let _num = &mut *(num as *const i32).cast_mut();
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//~^ ERROR casting `&T` to `&mut T` is undefined behavior
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let _num = *{ num as *const i32 }.cast_mut();
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//~^ ERROR casting `&T` to `&mut T` is undefined behavior
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*std::ptr::from_ref(num).cast_mut() += 1;
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//~^ ERROR casting `&T` to `&mut T` is undefined behavior
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*std::ptr::from_ref({ num }).cast_mut() += 1;
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//~^ ERROR casting `&T` to `&mut T` is undefined behavior
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*{ std::ptr::from_ref(num) }.cast_mut() += 1;
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//~^ ERROR casting `&T` to `&mut T` is undefined behavior
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*(std::ptr::from_ref({ num }) as *mut i32) += 1;
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//~^ ERROR casting `&T` to `&mut T` is undefined behavior
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40+
// Shouldn't be warned against
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println!("{}", *(num as *const _ as *const i16));
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println!("{}", *(mut_num as *mut _ as *mut i16));
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ffi(a.as_ptr() as *mut _);
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int_ffi(num as *const _ as *mut _);
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int_ffi(&3 as *const _ as *mut _);
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let mut value = 3;
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let value: *const i32 = &mut value;
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*(value as *const i16 as *mut i16) = 42;
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}
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}

‎tests/ui/lint/cast_ref_to_mut.stderr

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@@ -0,0 +1,64 @@
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error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
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--> $DIR/cast_ref_to_mut.rs:19:9
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|
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LL | (*(a as *const _ as *mut String)).push_str(" world");
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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|
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= note: `#[deny(cast_ref_to_mut)]` on by default
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error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
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--> $DIR/cast_ref_to_mut.rs:21:9
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|
12+
LL | *(a as *const _ as *mut _) = String::from("Replaced");
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
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--> $DIR/cast_ref_to_mut.rs:23:9
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|
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LL | *(a as *const _ as *mut String) += " world";
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
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--> $DIR/cast_ref_to_mut.rs:25:25
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|
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LL | let _num = &mut *(num as *const i32 as *mut i32);
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
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--> $DIR/cast_ref_to_mut.rs:27:25
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|
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LL | let _num = &mut *(num as *const i32).cast_mut();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
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--> $DIR/cast_ref_to_mut.rs:29:20
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|
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LL | let _num = *{ num as *const i32 }.cast_mut();
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
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--> $DIR/cast_ref_to_mut.rs:31:9
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|
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LL | *std::ptr::from_ref(num).cast_mut() += 1;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
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--> $DIR/cast_ref_to_mut.rs:33:9
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|
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LL | *std::ptr::from_ref({ num }).cast_mut() += 1;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
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--> $DIR/cast_ref_to_mut.rs:35:9
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|
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LL | *{ std::ptr::from_ref(num) }.cast_mut() += 1;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: casting `&T` to `&mut T` is undefined behavior, even if the reference is unused, consider instead using an `UnsafeCell`
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--> $DIR/cast_ref_to_mut.rs:37:9
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|
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LL | *(std::ptr::from_ref({ num }) as *mut i32) += 1;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error: aborting due to 10 previous errors
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