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| 1 | +use crate::reference::DEREF_ADDROF; |
| 2 | +use clippy_utils::diagnostics::span_lint_and_then; |
| 3 | +use clippy_utils::source::snippet_opt; |
| 4 | +use clippy_utils::ty::implements_trait; |
| 5 | +use clippy_utils::{get_parent_expr, is_lint_allowed}; |
| 6 | +use rustc_errors::Applicability; |
| 7 | +use rustc_hir::{ExprKind, UnOp}; |
| 8 | +use rustc_lint::{LateContext, LateLintPass}; |
| 9 | +use rustc_middle::mir::Mutability; |
| 10 | +use rustc_middle::ty; |
| 11 | +use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| 12 | + |
| 13 | +declare_clippy_lint! { |
| 14 | + /// ### What it does |
| 15 | + /// Checks for `&*(&T)`. |
| 16 | + /// |
| 17 | + /// ### Why is this bad? |
| 18 | + /// Dereferencing and then borrowing a reference value has no effect in most cases. |
| 19 | + /// |
| 20 | + /// ### Known problems |
| 21 | + /// false negative on such code: |
| 22 | + /// ``` |
| 23 | + /// let x = &12; |
| 24 | + /// let addr_x = &x as *const _ as usize; |
| 25 | + /// let addr_y = &&*x as *const _ as usize; // assert ok now, and lint triggerd. |
| 26 | + /// // But if we fix it, assert will fail. |
| 27 | + /// assert_ne!(addr_x, addr_y); |
| 28 | + /// ``` |
| 29 | + /// |
| 30 | + /// ### Example |
| 31 | + /// ```rust |
| 32 | + /// let s = &String::new(); |
| 33 | + /// |
| 34 | + /// // Bad |
| 35 | + /// let a: &String = &* s; |
| 36 | + /// foo(&*s); |
| 37 | + /// |
| 38 | + /// // Good |
| 39 | + /// let a: &String = s; |
| 40 | + /// foo(&**s); |
| 41 | + /// |
| 42 | + /// fn foo(_: &str){ } |
| 43 | + /// ``` |
| 44 | + #[clippy::version = "1.59.0"] |
| 45 | + pub BORROW_DEREF_REF, |
| 46 | + complexity, |
| 47 | + "deref on an immutable reference returns the same type as itself" |
| 48 | +} |
| 49 | + |
| 50 | +declare_lint_pass!(BorrowDerefRef => [BORROW_DEREF_REF]); |
| 51 | + |
| 52 | +impl LateLintPass<'_> for BorrowDerefRef { |
| 53 | + fn check_expr(&mut self, cx: &LateContext<'_>, e: &rustc_hir::Expr<'_>) { |
| 54 | + if_chain! { |
| 55 | + if !e.span.from_expansion(); |
| 56 | + if let ExprKind::AddrOf(_, Mutability::Not, addrof_target) = e.kind; |
| 57 | + if !addrof_target.span.from_expansion(); |
| 58 | + if let ExprKind::Unary(UnOp::Deref, deref_target) = addrof_target.kind; |
| 59 | + if !deref_target.span.from_expansion(); |
| 60 | + if !matches!(deref_target.kind, ExprKind::Unary(UnOp::Deref, ..) ); |
| 61 | + let ref_ty = cx.typeck_results().expr_ty(deref_target); |
| 62 | + if let ty::Ref(_, inner_ty, Mutability::Not) = ref_ty.kind(); |
| 63 | + then{ |
| 64 | + |
| 65 | + if let Some(parent_expr) = get_parent_expr(cx, e){ |
| 66 | + if matches!(parent_expr.kind, ExprKind::Unary(UnOp::Deref, ..)) && |
| 67 | + !is_lint_allowed(cx, DEREF_ADDROF, parent_expr.hir_id) { |
| 68 | + return; |
| 69 | + } |
| 70 | + |
| 71 | + // modification to `&mut &*x` is different from `&mut x` |
| 72 | + if matches!(deref_target.kind, ExprKind::Path(..) |
| 73 | + | ExprKind::Field(..) |
| 74 | + | ExprKind::Index(..) |
| 75 | + | ExprKind::Unary(UnOp::Deref, ..)) |
| 76 | + && matches!(parent_expr.kind, ExprKind::AddrOf(_, Mutability::Mut, _)) { |
| 77 | + return; |
| 78 | + } |
| 79 | + } |
| 80 | + |
| 81 | + span_lint_and_then( |
| 82 | + cx, |
| 83 | + BORROW_DEREF_REF, |
| 84 | + e.span, |
| 85 | + "deref on an immutable reference", |
| 86 | + |diag| { |
| 87 | + diag.span_suggestion( |
| 88 | + e.span, |
| 89 | + "if you would like to reborrow, try removing `&*`", |
| 90 | + snippet_opt(cx, deref_target.span).unwrap(), |
| 91 | + Applicability::MachineApplicable |
| 92 | + ); |
| 93 | + |
| 94 | + // has deref trait -> give 2 help |
| 95 | + // doesn't have deref trait -> give 1 help |
| 96 | + if let Some(deref_trait_id) = cx.tcx.lang_items().deref_trait(){ |
| 97 | + if !implements_trait(cx, *inner_ty, deref_trait_id, &[]) { |
| 98 | + return; |
| 99 | + } |
| 100 | + } |
| 101 | + |
| 102 | + diag.span_suggestion( |
| 103 | + e.span, |
| 104 | + "if you would like to deref, try using `&**`", |
| 105 | + format!( |
| 106 | + "&**{}", |
| 107 | + &snippet_opt(cx, deref_target.span).unwrap(), |
| 108 | + ), |
| 109 | + Applicability::MaybeIncorrect |
| 110 | + ); |
| 111 | + |
| 112 | + } |
| 113 | + ); |
| 114 | + |
| 115 | + } |
| 116 | + } |
| 117 | + } |
| 118 | +} |
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