1 use crate::utils::{higher, span_lint};
2 use rustc::hir::map::Map;
3 use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintContext};
6 use rustc_hir::intravisit;
7 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 /// **What it does:** Checks for instances of `mut mut` references.
12 /// **Why is this bad?** Multiple `mut`s don't add anything meaningful to the
13 /// source. This is either a copy'n'paste error, or it shows a fundamental
14 /// misunderstanding of references.
16 /// **Known problems:** None.
21 /// let x = &mut &mut y;
25 "usage of double-mut refs, e.g., `&mut &mut ...`"
28 declare_lint_pass!(MutMut => [MUT_MUT]);
30 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MutMut {
31 fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx hir::Block<'_>) {
32 intravisit::walk_block(&mut MutVisitor { cx }, block);
35 fn check_ty(&mut self, cx: &LateContext<'a, 'tcx>, ty: &'tcx hir::Ty<'_>) {
36 use rustc_hir::intravisit::Visitor;
38 MutVisitor { cx }.visit_ty(ty);
42 pub struct MutVisitor<'a, 'tcx> {
43 cx: &'a LateContext<'a, 'tcx>,
46 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((_, arg, body)) = higher::for_loop(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, ref 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.tables.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 let hir::TyKind::Rptr(
87 mutbl: hir::Mutability::Mut,
91 if let hir::TyKind::Rptr(
94 mutbl: hir::Mutability::Mut,
103 "generally you want to avoid `&mut &mut _` if possible",
108 intravisit::walk_ty(self, ty);
110 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<'_, Self::Map> {
111 intravisit::NestedVisitorMap::None