98 lines
3.4 KiB
Rust
98 lines
3.4 KiB
Rust
use clippy_utils::source::snippet;
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use rustc_hir::{BinOp, BinOpKind, Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::Span;
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use clippy_utils::consts::{constant_simple, Constant};
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use clippy_utils::diagnostics::span_lint;
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use clippy_utils::{clip, unsext};
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for identity operations, e.g., `x + 0`.
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///
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/// ### Why is this bad?
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/// This code can be removed without changing the
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/// meaning. So it just obscures what's going on. Delete it mercilessly.
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///
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/// ### Example
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/// ```rust
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/// # let x = 1;
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/// x / 1 + 0 * 1 - 0 | 0;
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub IDENTITY_OP,
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complexity,
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"using identity operations, e.g., `x + 0` or `y / 1`"
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}
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declare_lint_pass!(IdentityOp => [IDENTITY_OP]);
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impl<'tcx> LateLintPass<'tcx> for IdentityOp {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
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if e.span.from_expansion() {
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return;
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}
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if let ExprKind::Binary(cmp, left, right) = e.kind {
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if is_allowed(cx, cmp, left, right) {
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return;
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}
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match cmp.node {
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BinOpKind::Add | BinOpKind::BitOr | BinOpKind::BitXor => {
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check(cx, left, 0, e.span, right.span);
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check(cx, right, 0, e.span, left.span);
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},
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BinOpKind::Shl | BinOpKind::Shr | BinOpKind::Sub => check(cx, right, 0, e.span, left.span),
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BinOpKind::Mul => {
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check(cx, left, 1, e.span, right.span);
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check(cx, right, 1, e.span, left.span);
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},
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BinOpKind::Div => check(cx, right, 1, e.span, left.span),
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BinOpKind::BitAnd => {
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check(cx, left, -1, e.span, right.span);
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check(cx, right, -1, e.span, left.span);
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},
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_ => (),
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}
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}
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}
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}
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fn is_allowed(cx: &LateContext<'_>, cmp: BinOp, left: &Expr<'_>, right: &Expr<'_>) -> bool {
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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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}
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fn check(cx: &LateContext<'_>, e: &Expr<'_>, m: i8, span: Span, arg: Span) {
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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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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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_ => return,
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};
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if match m {
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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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_ => unreachable!(),
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} {
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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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}
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}
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