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| 1 | +use crate::{lints::PtrNullChecksDiag, LateContext, LateLintPass, LintContext}; |
| 2 | +use rustc_ast::LitKind; |
| 3 | +use rustc_hir::{BinOpKind, Expr, ExprKind, TyKind}; |
| 4 | +use rustc_session::{declare_lint, declare_lint_pass}; |
| 5 | +use rustc_span::sym; |
| 6 | + |
| 7 | +declare_lint! { |
| 8 | + /// The `useless_ptr_null_checks` lint checks for useless null checks against pointers |
| 9 | + /// obtained from non-null types. |
| 10 | + /// |
| 11 | + /// ### Example |
| 12 | + /// |
| 13 | + /// ```rust |
| 14 | + /// # fn test() {} |
| 15 | + /// let fn_ptr: fn() = /* somehow obtained nullable function pointer */ |
| 16 | + /// # test; |
| 17 | + /// |
| 18 | + /// if (fn_ptr as *const ()).is_null() { /* ... */ } |
| 19 | + /// ``` |
| 20 | + /// |
| 21 | + /// {{produces}} |
| 22 | + /// |
| 23 | + /// ### Explanation |
| 24 | + /// |
| 25 | + /// Function pointers and references are assumed to be non-null, checking them for null |
| 26 | + /// will always return false. |
| 27 | + USELESS_PTR_NULL_CHECKS, |
| 28 | + Warn, |
| 29 | + "useless checking of non-null-typed pointer" |
| 30 | +} |
| 31 | + |
| 32 | +declare_lint_pass!(PtrNullChecks => [USELESS_PTR_NULL_CHECKS]); |
| 33 | + |
| 34 | +/// This function detects and returns the original expression from a series of consecutive casts, |
| 35 | +/// ie. `(my_fn as *const _ as *mut _).cast_mut()` would return the expression for `my_fn`. |
| 36 | +fn ptr_cast_chain<'a>(cx: &'a LateContext<'_>, mut e: &'a Expr<'a>) -> Option<&'a Expr<'a>> { |
| 37 | + let mut had_at_least_one_cast = false; |
| 38 | + loop { |
| 39 | + e = e.peel_blocks(); |
| 40 | + e = if let ExprKind::Cast(expr, t) = e.kind |
| 41 | + && let TyKind::Ptr(_) = t.kind { |
| 42 | + had_at_least_one_cast = true; |
| 43 | + expr |
| 44 | + } else if let ExprKind::MethodCall(_, expr, [], _) = e.kind |
| 45 | + && let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id) |
| 46 | + && matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::ptr_cast | sym::ptr_cast_mut)) { |
| 47 | + had_at_least_one_cast = true; |
| 48 | + expr |
| 49 | + } else if let ExprKind::Call(path, [arg]) = e.kind |
| 50 | + && let ExprKind::Path(ref qpath) = path.kind |
| 51 | + && let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() |
| 52 | + && matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::ptr_from_ref | sym::ptr_from_mut)) { |
| 53 | + had_at_least_one_cast = true; |
| 54 | + arg |
| 55 | + } else if had_at_least_one_cast { |
| 56 | + return Some(e); |
| 57 | + } else { |
| 58 | + return None; |
| 59 | + }; |
| 60 | + } |
| 61 | +} |
| 62 | + |
| 63 | +fn incorrect_check<'a>(cx: &LateContext<'a>, expr: &Expr<'_>) -> Option<PtrNullChecksDiag<'a>> { |
| 64 | + let expr = ptr_cast_chain(cx, expr)?; |
| 65 | + |
| 66 | + let orig_ty = cx.typeck_results().expr_ty(expr); |
| 67 | + if orig_ty.is_fn() { |
| 68 | + Some(PtrNullChecksDiag::FnPtr { orig_ty, label: expr.span }) |
| 69 | + } else if orig_ty.is_ref() { |
| 70 | + Some(PtrNullChecksDiag::Ref { orig_ty, label: expr.span }) |
| 71 | + } else { |
| 72 | + None |
| 73 | + } |
| 74 | +} |
| 75 | + |
| 76 | +impl<'tcx> LateLintPass<'tcx> for PtrNullChecks { |
| 77 | + fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { |
| 78 | + match expr.kind { |
| 79 | + // Catching: |
| 80 | + // <*<const/mut> <ty>>::is_null(fn_ptr as *<const/mut> <ty>) |
| 81 | + ExprKind::Call(path, [arg]) |
| 82 | + if let ExprKind::Path(ref qpath) = path.kind |
| 83 | + && let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() |
| 84 | + && matches!( |
| 85 | + cx.tcx.get_diagnostic_name(def_id), |
| 86 | + Some(sym::ptr_const_is_null | sym::ptr_is_null) |
| 87 | + ) |
| 88 | + && let Some(diag) = incorrect_check(cx, arg) => |
| 89 | + { |
| 90 | + cx.emit_spanned_lint(USELESS_PTR_NULL_CHECKS, expr.span, diag) |
| 91 | + } |
| 92 | + |
| 93 | + // Catching: |
| 94 | + // (fn_ptr as *<const/mut> <ty>).is_null() |
| 95 | + ExprKind::MethodCall(_, receiver, _, _) |
| 96 | + if let Some(def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) |
| 97 | + && matches!( |
| 98 | + cx.tcx.get_diagnostic_name(def_id), |
| 99 | + Some(sym::ptr_const_is_null | sym::ptr_is_null) |
| 100 | + ) |
| 101 | + && let Some(diag) = incorrect_check(cx, receiver) => |
| 102 | + { |
| 103 | + cx.emit_spanned_lint(USELESS_PTR_NULL_CHECKS, expr.span, diag) |
| 104 | + } |
| 105 | + |
| 106 | + ExprKind::Binary(op, left, right) if matches!(op.node, BinOpKind::Eq) => { |
| 107 | + let to_check: &Expr<'_>; |
| 108 | + let diag: PtrNullChecksDiag<'_>; |
| 109 | + if let Some(ddiag) = incorrect_check(cx, left) { |
| 110 | + to_check = right; |
| 111 | + diag = ddiag; |
| 112 | + } else if let Some(ddiag) = incorrect_check(cx, right) { |
| 113 | + to_check = left; |
| 114 | + diag = ddiag; |
| 115 | + } else { |
| 116 | + return; |
| 117 | + } |
| 118 | + |
| 119 | + match to_check.kind { |
| 120 | + // Catching: |
| 121 | + // (fn_ptr as *<const/mut> <ty>) == (0 as <ty>) |
| 122 | + ExprKind::Cast(cast_expr, _) |
| 123 | + if let ExprKind::Lit(spanned) = cast_expr.kind |
| 124 | + && let LitKind::Int(v, _) = spanned.node && v == 0 => |
| 125 | + { |
| 126 | + cx.emit_spanned_lint(USELESS_PTR_NULL_CHECKS, expr.span, diag) |
| 127 | + }, |
| 128 | + |
| 129 | + // Catching: |
| 130 | + // (fn_ptr as *<const/mut> <ty>) == std::ptr::null() |
| 131 | + ExprKind::Call(path, []) |
| 132 | + if let ExprKind::Path(ref qpath) = path.kind |
| 133 | + && let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id() |
| 134 | + && let Some(diag_item) = cx.tcx.get_diagnostic_name(def_id) |
| 135 | + && (diag_item == sym::ptr_null || diag_item == sym::ptr_null_mut) => |
| 136 | + { |
| 137 | + cx.emit_spanned_lint(USELESS_PTR_NULL_CHECKS, expr.span, diag) |
| 138 | + }, |
| 139 | + |
| 140 | + _ => {}, |
| 141 | + } |
| 142 | + } |
| 143 | + _ => {} |
| 144 | + } |
| 145 | + } |
| 146 | +} |
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