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use rustc_ast::Mutability;
use rustc_hir::{Expr, ExprKind, MutTy, TyKind, UnOp};
use rustc_middle::ty;
use rustc_span::sym;
use crate::{lints::InvalidReferenceCastingDiag, LateContext, LateLintPass, LintContext};
declare_lint! {
/// 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;
/// }
/// }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// Casting `&T` to `&mut T` without using interior mutability is undefined behavior,
/// as it's a violation of Rust reference aliasing requirements.
///
/// `UnsafeCell` is the only way to obtain aliasable data that is considered
/// mutable.
INVALID_REFERENCE_CASTING,
Allow,
"casts of `&T` to `&mut T` without interior mutability"
}
declare_lint_pass!(InvalidReferenceCasting => [INVALID_REFERENCE_CASTING]);
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; };
let e = e.peel_blocks();
let e = if let ExprKind::Cast(e, t) = e.kind
&& let TyKind::Ptr(MutTy { mutbl: Mutability::Mut, .. }) = t.kind {
e
} else if let ExprKind::MethodCall(_, expr, [], _) = e.kind
&& let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
&& cx.tcx.is_diagnostic_item(sym::ptr_cast_mut, def_id) {
expr
} else {
return;
};
let e = e.peel_blocks();
let e = if let ExprKind::Cast(e, t) = e.kind
&& let TyKind::Ptr(MutTy { mutbl: Mutability::Not, .. }) = t.kind {
e
} else if let ExprKind::Call(path, [arg]) = e.kind
&& let ExprKind::Path(ref qpath) = path.kind
&& let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
&& cx.tcx.is_diagnostic_item(sym::ptr_from_ref, def_id) {
arg
} else {
return;
};
let e = e.peel_blocks();
if let ty::Ref(..) = cx.typeck_results().node_type(e.hir_id).kind() {
cx.emit_spanned_lint(INVALID_REFERENCE_CASTING, expr.span, InvalidReferenceCastingDiag);
}
}
}
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