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::hir::map::Map;
7 use rustc_middle::lint::in_external_macro;
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
11 declare_clippy_lint! {
12 /// **What it does:** Checks for instances of `mut mut` references.
14 /// **Why is this bad?** Multiple `mut`s don't add anything meaningful to the
15 /// source. This is either a copy'n'paste error, or it shows a fundamental
16 /// misunderstanding of references.
18 /// **Known problems:** None.
23 /// let x = &mut &mut y;
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> {
51 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
52 if in_external_macro(self.cx.sess(), expr.span) {
56 if let Some((_, arg, body, _)) = higher::for_loop(expr) {
57 // A `for` loop lowers to:
59 // match ::std::iter::Iterator::next(&mut iter) {
62 // Let's ignore the generated code.
63 intravisit::walk_expr(self, arg);
64 intravisit::walk_expr(self, body);
65 } else if let hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, ref e) = expr.kind {
66 if let hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mut, _) = e.kind {
71 "generally you want to avoid `&mut &mut _` if possible",
73 } else if let ty::Ref(_, _, hir::Mutability::Mut) = self.cx.typeck_results().expr_ty(e).kind() {
78 "this expression mutably borrows a mutable reference. Consider reborrowing",
84 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'_>) {
85 if let hir::TyKind::Rptr(
89 mutbl: hir::Mutability::Mut,
93 if let hir::TyKind::Rptr(
96 mutbl: hir::Mutability::Mut,
105 "generally you want to avoid `&mut &mut _` if possible",
110 intravisit::walk_ty(self, ty);
112 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
113 intravisit::NestedVisitorMap::None