2022-05-05 14:12:52 +00:00
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use clippy_utils::get_parent_expr;
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2021-03-25 18:29:11 +00:00
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use clippy_utils::source::snippet;
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2020-05-17 15:36:26 +00:00
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use rustc_hir::{BinOp, BinOpKind, Expr, ExprKind};
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2020-01-12 06:08:41 +00:00
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use rustc_lint::{LateContext, LateLintPass};
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2020-03-30 09:02:14 +00:00
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use rustc_middle::ty;
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2020-01-11 11:37:08 +00:00
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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2020-01-04 10:00:00 +00:00
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use rustc_span::source_map::Span;
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2015-07-09 15:02:21 +00:00
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2022-04-07 17:39:59 +00:00
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use clippy_utils::consts::{constant_full_int, constant_simple, Constant, FullInt};
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2021-03-25 18:29:11 +00:00
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use clippy_utils::diagnostics::span_lint;
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use clippy_utils::{clip, unsext};
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2019-01-31 01:15:29 +00:00
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2018-03-28 13:24:26 +00:00
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declare_clippy_lint! {
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2021-07-29 10:16:06 +00:00
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/// ### What it does
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/// Checks for identity operations, e.g., `x + 0`.
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2019-03-05 16:50:33 +00:00
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///
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2021-07-29 10:16:06 +00:00
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/// ### Why is this bad?
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/// This code can be removed without changing the
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2019-03-05 16:50:33 +00:00
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/// meaning. So it just obscures what's going on. Delete it mercilessly.
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///
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2021-07-29 10:16:06 +00:00
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/// ### Example
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2019-03-05 16:50:33 +00:00
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/// ```rust
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2019-08-02 06:13:54 +00:00
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/// # let x = 1;
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/// x / 1 + 0 * 1 - 0 | 0;
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2019-03-05 16:50:33 +00:00
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/// ```
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2022-05-05 14:12:52 +00:00
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///
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/// ### Known problems
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/// False negatives: `f(0 + if b { 1 } else { 2 } + 3);` is reducible to
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/// `f(if b { 1 } else { 2 } + 3);`. But the lint doesn't trigger for the code.
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/// See [#8724](https://github.com/rust-lang/rust-clippy/issues/8724)
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2021-12-06 11:33:31 +00:00
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#[clippy::version = "pre 1.29.0"]
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2016-08-06 08:18:36 +00:00
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pub IDENTITY_OP,
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2018-03-28 13:24:26 +00:00
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complexity,
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2019-01-31 01:15:29 +00:00
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"using identity operations, e.g., `x + 0` or `y / 1`"
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2016-02-05 23:13:29 +00:00
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}
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2015-08-11 18:22:20 +00:00
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2019-04-08 20:43:55 +00:00
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declare_lint_pass!(IdentityOp => [IDENTITY_OP]);
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2015-05-22 22:49:13 +00:00
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2020-06-25 20:41:36 +00:00
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impl<'tcx> LateLintPass<'tcx> for IdentityOp {
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2022-05-05 14:12:52 +00:00
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if expr.span.from_expansion() {
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2016-01-04 04:26:12 +00:00
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return;
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}
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2022-05-05 14:12:52 +00:00
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if let ExprKind::Binary(cmp, left, right) = &expr.kind {
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if !is_allowed(cx, *cmp, left, right) {
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match cmp.node {
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BinOpKind::Add | BinOpKind::BitOr | BinOpKind::BitXor => {
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if reducible_to_right(cx, expr, right) {
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check(cx, left, 0, expr.span, right.span);
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}
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check(cx, right, 0, expr.span, left.span);
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},
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BinOpKind::Shl | BinOpKind::Shr | BinOpKind::Sub => {
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check(cx, right, 0, expr.span, left.span);
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},
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BinOpKind::Mul => {
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if reducible_to_right(cx, expr, right) {
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check(cx, left, 1, expr.span, right.span);
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}
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check(cx, right, 1, expr.span, left.span);
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},
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BinOpKind::Div => check(cx, right, 1, expr.span, left.span),
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BinOpKind::BitAnd => {
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if reducible_to_right(cx, expr, right) {
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check(cx, left, -1, expr.span, right.span);
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}
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check(cx, right, -1, expr.span, left.span);
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},
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BinOpKind::Rem => {
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// Don't call reducible_to_right because N % N is always reducible to 1
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check_remainder(cx, left, right, expr.span, left.span);
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},
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_ => (),
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}
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2015-05-22 22:49:13 +00:00
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}
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}
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2015-05-15 16:46:43 +00:00
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}
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}
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2022-05-05 14:12:52 +00:00
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/// Checks if `left op ..right` can be actually reduced to `right`
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/// e.g. `0 + if b { 1 } else { 2 } + if b { 3 } else { 4 }`
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/// cannot be reduced to `if b { 1 } else { 2 } + if b { 3 } else { 4 }`
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/// See #8724
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fn reducible_to_right(cx: &LateContext<'_>, binary: &Expr<'_>, right: &Expr<'_>) -> bool {
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if let ExprKind::If(..) | ExprKind::Match(..) | ExprKind::Block(..) | ExprKind::Loop(..) = right.kind {
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is_toplevel_binary(cx, binary)
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} else {
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true
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}
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}
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fn is_toplevel_binary(cx: &LateContext<'_>, must_be_binary: &Expr<'_>) -> bool {
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if let Some(parent) = get_parent_expr(cx, must_be_binary) && let ExprKind::Binary(..) = &parent.kind {
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false
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} else {
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true
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}
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}
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2020-06-25 20:41:36 +00:00
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fn is_allowed(cx: &LateContext<'_>, cmp: BinOp, left: &Expr<'_>, right: &Expr<'_>) -> bool {
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2021-12-30 14:10:43 +00:00
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// This lint applies to integers
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!cx.typeck_results().expr_ty(left).peel_refs().is_integral()
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|| !cx.typeck_results().expr_ty(right).peel_refs().is_integral()
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// `1 << 0` is a common pattern in bit manipulation code
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|| (cmp.node == BinOpKind::Shl
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&& constant_simple(cx, cx.typeck_results(), right) == Some(Constant::Int(0))
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&& constant_simple(cx, cx.typeck_results(), left) == Some(Constant::Int(1)))
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2020-05-17 15:36:26 +00:00
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}
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2022-04-07 17:39:59 +00:00
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fn check_remainder(cx: &LateContext<'_>, left: &Expr<'_>, right: &Expr<'_>, span: Span, arg: Span) {
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let lhs_const = constant_full_int(cx, cx.typeck_results(), left);
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let rhs_const = constant_full_int(cx, cx.typeck_results(), right);
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if match (lhs_const, rhs_const) {
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(Some(FullInt::S(lv)), Some(FullInt::S(rv))) => lv.abs() < rv.abs(),
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(Some(FullInt::U(lv)), Some(FullInt::U(rv))) => lv < rv,
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_ => return,
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} {
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span_ineffective_operation(cx, span, arg);
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}
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}
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2020-06-25 20:41:36 +00:00
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fn check(cx: &LateContext<'_>, e: &Expr<'_>, m: i8, span: Span, arg: Span) {
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2021-12-30 14:10:43 +00:00
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if let Some(Constant::Int(v)) = constant_simple(cx, cx.typeck_results(), e).map(Constant::peel_refs) {
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let check = match *cx.typeck_results().expr_ty(e).peel_refs().kind() {
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2018-08-22 21:34:52 +00:00
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ty::Int(ity) => unsext(cx.tcx, -1_i128, ity),
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ty::Uint(uty) => clip(cx.tcx, !0, uty),
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2018-03-13 10:38:11 +00:00
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_ => return,
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};
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2015-09-06 08:53:55 +00:00
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if match m {
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2018-03-13 10:38:11 +00:00
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0 => v == 0,
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-1 => v == check,
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1 => v == 1,
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2015-09-06 08:53:55 +00:00
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_ => unreachable!(),
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2017-09-05 09:33:04 +00:00
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} {
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2022-04-07 17:39:59 +00:00
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span_ineffective_operation(cx, span, arg);
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2015-08-16 21:09:56 +00:00
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}
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2015-05-22 22:49:13 +00:00
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}
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2015-05-15 16:46:43 +00:00
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}
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2022-04-07 17:39:59 +00:00
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fn span_ineffective_operation(cx: &LateContext<'_>, span: Span, arg: Span) {
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span_lint(
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cx,
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IDENTITY_OP,
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span,
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&format!(
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"the operation is ineffective. Consider reducing it to `{}`",
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snippet(cx, arg, "..")
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),
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);
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}
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