1 use clippy_utils::diagnostics::span_lint;
2 use clippy_utils::higher;
4 use rustc_hir::intravisit;
5 use rustc_lint::{LateContext, LateLintPass, LintContext};
6 use rustc_middle::lint::in_external_macro;
8 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 declare_clippy_lint! {
12 /// Checks for instances of `mut mut` references.
14 /// ### Why is this bad?
15 /// Multiple `mut`s don't add anything meaningful to the
16 /// source. This is either a copy'n'paste error, or it shows a fundamental
17 /// misunderstanding of references.
22 /// let x = &mut &mut y;
24 #[clippy::version = "pre 1.29.0"]
27 "usage of double-mut refs, e.g., `&mut &mut ...`"
30 declare_lint_pass!(MutMut => [MUT_MUT]);
32 impl<'tcx> LateLintPass<'tcx> for MutMut {
33 fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) {
34 intravisit::walk_block(&mut MutVisitor { cx }, block);
37 fn check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx hir::Ty<'_>) {
38 use rustc_hir::intravisit::Visitor;
40 MutVisitor { cx }.visit_ty(ty);
44 pub struct MutVisitor<'a, 'tcx> {
45 cx: &'a LateContext<'tcx>,
48 impl<'a, 'tcx> intravisit::Visitor<'tcx> for MutVisitor<'a, 'tcx> {
49 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
50 if in_external_macro(self.cx.sess(), expr.span) {
54 if let Some(higher::ForLoop { arg, body, .. }) = higher::ForLoop::hir(expr) {
55 // A `for` loop lowers to:
57 // match ::std::iter::Iterator::next(&mut iter) {
60 // Let's ignore the generated code.
61 intravisit::walk_expr(self, arg);
62 intravisit::walk_expr(self, body);
63 } else if let hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, e) = expr.kind {
64 if let hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, _) = e.kind {
69 "generally you want to avoid `&mut &mut _` if possible",
71 } else if let ty::Ref(_, _, hir::Mutability::Mut) = self.cx.typeck_results().expr_ty(e).kind() {
76 "this expression mutably borrows a mutable reference. Consider reborrowing",
82 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'_>) {
83 if in_external_macro(self.cx.sess(), ty.span) {
87 if let hir::TyKind::Rptr(
91 mutbl: hir::Mutability::Mut,
95 if let hir::TyKind::Rptr(
98 mutbl: hir::Mutability::Mut,
107 "generally you want to avoid `&mut &mut _` if possible",
112 intravisit::walk_ty(self, ty);