1 use clippy_utils::diagnostics::span_lint; 2 use clippy_utils::higher; 3 use rustc_hir as hir; 4 use rustc_hir::intravisit; 5 use rustc_lint::{LateContext, LateLintPass, LintContext}; 6 use rustc_middle::lint::in_external_macro; 7 use rustc_middle::ty; 8 use rustc_session::{declare_lint_pass, declare_tool_lint}; 9 10 declare_clippy_lint! { 11 /// ### What it does 12 /// Checks for instances of `mut mut` references. 13 /// 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. 18 /// 19 /// ### Example 20 /// ```rust 21 /// # let mut y = 1; 22 /// let x = &mut &mut y; 23 /// ``` 24 #[clippy::version = "pre 1.29.0"] 25 pub MUT_MUT, 26 pedantic, 27 "usage of double-mut refs, e.g., `&mut &mut ...`" 28 } 29 30 declare_lint_pass!(MutMut => [MUT_MUT]); 31 32 impl<'tcx> LateLintPass<'tcx> for MutMut { check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>)33 fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx hir::Block<'_>) { 34 intravisit::walk_block(&mut MutVisitor { cx }, block); 35 } 36 check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx hir::Ty<'_>)37 fn check_ty(&mut self, cx: &LateContext<'tcx>, ty: &'tcx hir::Ty<'_>) { 38 use rustc_hir::intravisit::Visitor; 39 40 MutVisitor { cx }.visit_ty(ty); 41 } 42 } 43 44 pub struct MutVisitor<'a, 'tcx> { 45 cx: &'a LateContext<'tcx>, 46 } 47 48 impl<'a, 'tcx> intravisit::Visitor<'tcx> for MutVisitor<'a, 'tcx> { visit_expr(&mut self, expr: &'tcx hir::Expr<'_>)49 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) { 50 if in_external_macro(self.cx.sess(), expr.span) { 51 return; 52 } 53 54 if let Some(higher::ForLoop { arg, body, .. }) = higher::ForLoop::hir(expr) { 55 // A `for` loop lowers to: 56 // ```rust 57 // match ::std::iter::Iterator::next(&mut iter) { 58 // // ^^^^ 59 // ``` 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 { 65 span_lint( 66 self.cx, 67 MUT_MUT, 68 expr.span, 69 "generally you want to avoid `&mut &mut _` if possible", 70 ); 71 } else if let ty::Ref(_, ty, hir::Mutability::Mut) = self.cx.typeck_results().expr_ty(e).kind() { 72 if ty.peel_refs().is_sized(self.cx.tcx, self.cx.param_env) { 73 span_lint( 74 self.cx, 75 MUT_MUT, 76 expr.span, 77 "this expression mutably borrows a mutable reference. Consider reborrowing", 78 ); 79 } 80 } 81 } 82 } 83 visit_ty(&mut self, ty: &'tcx hir::Ty<'_>)84 fn visit_ty(&mut self, ty: &'tcx hir::Ty<'_>) { 85 if in_external_macro(self.cx.sess(), ty.span) { 86 return; 87 } 88 89 if let hir::TyKind::Ref( 90 _, 91 hir::MutTy { 92 ty: pty, 93 mutbl: hir::Mutability::Mut, 94 }, 95 ) = ty.kind 96 { 97 if let hir::TyKind::Ref( 98 _, 99 hir::MutTy { 100 mutbl: hir::Mutability::Mut, 101 .. 102 }, 103 ) = pty.kind 104 { 105 span_lint( 106 self.cx, 107 MUT_MUT, 108 ty.span, 109 "generally you want to avoid `&mut &mut _` if possible", 110 ); 111 } 112 } 113 114 intravisit::walk_ty(self, ty); 115 } 116 } 117