1 use clippy_utils::source::snippet;
2 use rustc_hir::{BinOp, BinOpKind, Expr, ExprKind};
3 use rustc_lint::{LateContext, LateLintPass};
5 use rustc_session::{declare_lint_pass, declare_tool_lint};
6 use rustc_span::source_map::Span;
8 use clippy_utils::consts::{constant_full_int, constant_simple, Constant, FullInt};
9 use clippy_utils::diagnostics::span_lint;
10 use clippy_utils::{clip, unsext};
12 declare_clippy_lint! {
14 /// Checks for identity operations, e.g., `x + 0`.
16 /// ### Why is this bad?
17 /// This code can be removed without changing the
18 /// meaning. So it just obscures what's going on. Delete it mercilessly.
23 /// x / 1 + 0 * 1 - 0 | 0;
25 #[clippy::version = "pre 1.29.0"]
28 "using identity operations, e.g., `x + 0` or `y / 1`"
31 declare_lint_pass!(IdentityOp => [IDENTITY_OP]);
33 impl<'tcx> LateLintPass<'tcx> for IdentityOp {
34 fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
35 if e.span.from_expansion() {
38 if let ExprKind::Binary(cmp, left, right) = e.kind {
39 if is_allowed(cx, cmp, left, right) {
43 BinOpKind::Add | BinOpKind::BitOr | BinOpKind::BitXor => {
44 check(cx, left, 0, e.span, right.span);
45 check(cx, right, 0, e.span, left.span);
47 BinOpKind::Shl | BinOpKind::Shr | BinOpKind::Sub => check(cx, right, 0, e.span, left.span),
49 check(cx, left, 1, e.span, right.span);
50 check(cx, right, 1, e.span, left.span);
52 BinOpKind::Div => check(cx, right, 1, e.span, left.span),
53 BinOpKind::BitAnd => {
54 check(cx, left, -1, e.span, right.span);
55 check(cx, right, -1, e.span, left.span);
57 BinOpKind::Rem => check_remainder(cx, left, right, e.span, left.span),
64 fn is_allowed(cx: &LateContext<'_>, cmp: BinOp, left: &Expr<'_>, right: &Expr<'_>) -> bool {
65 // This lint applies to integers
66 !cx.typeck_results().expr_ty(left).peel_refs().is_integral()
67 || !cx.typeck_results().expr_ty(right).peel_refs().is_integral()
68 // `1 << 0` is a common pattern in bit manipulation code
69 || (cmp.node == BinOpKind::Shl
70 && constant_simple(cx, cx.typeck_results(), right) == Some(Constant::Int(0))
71 && constant_simple(cx, cx.typeck_results(), left) == Some(Constant::Int(1)))
74 fn check_remainder(cx: &LateContext<'_>, left: &Expr<'_>, right: &Expr<'_>, span: Span, arg: Span) {
75 let lhs_const = constant_full_int(cx, cx.typeck_results(), left);
76 let rhs_const = constant_full_int(cx, cx.typeck_results(), right);
77 if match (lhs_const, rhs_const) {
78 (Some(FullInt::S(lv)), Some(FullInt::S(rv))) => lv.abs() < rv.abs(),
79 (Some(FullInt::U(lv)), Some(FullInt::U(rv))) => lv < rv,
82 span_ineffective_operation(cx, span, arg);
86 fn check(cx: &LateContext<'_>, e: &Expr<'_>, m: i8, span: Span, arg: Span) {
87 if let Some(Constant::Int(v)) = constant_simple(cx, cx.typeck_results(), e).map(Constant::peel_refs) {
88 let check = match *cx.typeck_results().expr_ty(e).peel_refs().kind() {
89 ty::Int(ity) => unsext(cx.tcx, -1_i128, ity),
90 ty::Uint(uty) => clip(cx.tcx, !0, uty),
99 span_ineffective_operation(cx, span, arg);
104 fn span_ineffective_operation(cx: &LateContext<'_>, span: Span, arg: Span) {
110 "the operation is ineffective. Consider reducing it to `{}`",
111 snippet(cx, arg, "..")