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use clippy_utils::source::snippet;
use rustc_hir::{BinOp, BinOpKind, Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
use clippy_utils::consts::{constant_simple, Constant};
use clippy_utils::diagnostics::span_lint;
use clippy_utils::{clip, unsext};
declare_clippy_lint! {
/// ### What it does
/// Checks for identity operations, e.g., `x + 0`.
///
/// ### Why is this bad?
/// This code can be removed without changing the
/// meaning. So it just obscures what's going on. Delete it mercilessly.
///
/// ### Example
/// ```rust
/// # let x = 1;
/// x / 1 + 0 * 1 - 0 | 0;
/// ```
#[clippy::version = "pre 1.29.0"]
pub IDENTITY_OP,
complexity,
"using identity operations, e.g., `x + 0` or `y / 1`"
}
declare_lint_pass!(IdentityOp => [IDENTITY_OP]);
impl<'tcx> LateLintPass<'tcx> for IdentityOp {
fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
if e.span.from_expansion() {
return;
}
if let ExprKind::Binary(cmp, left, right) = e.kind {
if is_allowed(cx, cmp, left, right) {
return;
}
match cmp.node {
BinOpKind::Add | BinOpKind::BitOr | BinOpKind::BitXor => {
check(cx, left, 0, e.span, right.span);
check(cx, right, 0, e.span, left.span);
},
BinOpKind::Shl | BinOpKind::Shr | BinOpKind::Sub => check(cx, right, 0, e.span, left.span),
BinOpKind::Mul => {
check(cx, left, 1, e.span, right.span);
check(cx, right, 1, e.span, left.span);
},
BinOpKind::Div => check(cx, right, 1, e.span, left.span),
BinOpKind::BitAnd => {
check(cx, left, -1, e.span, right.span);
check(cx, right, -1, e.span, left.span);
},
_ => (),
}
}
}
}
fn is_allowed(cx: &LateContext<'_>, cmp: BinOp, left: &Expr<'_>, right: &Expr<'_>) -> bool {
// This lint applies to integers
!cx.typeck_results().expr_ty(left).peel_refs().is_integral()
|| !cx.typeck_results().expr_ty(right).peel_refs().is_integral()
// `1 << 0` is a common pattern in bit manipulation code
|| (cmp.node == BinOpKind::Shl
&& constant_simple(cx, cx.typeck_results(), right) == Some(Constant::Int(0))
&& constant_simple(cx, cx.typeck_results(), left) == Some(Constant::Int(1)))
}
fn check(cx: &LateContext<'_>, e: &Expr<'_>, m: i8, span: Span, arg: Span) {
if let Some(Constant::Int(v)) = constant_simple(cx, cx.typeck_results(), e) {
let check = match *cx.typeck_results().expr_ty(e).kind() {
ty::Int(ity) => unsext(cx.tcx, -1_i128, ity),
ty::Uint(uty) => clip(cx.tcx, !0, uty),
_ => return,
};
if match m {
0 => v == 0,
-1 => v == check,
1 => v == 1,
_ => unreachable!(),
} {
span_lint(
cx,
IDENTITY_OP,
span,
&format!(
"the operation is ineffective. Consider reducing it to `{}`",
snippet(cx, arg, "..")
),
);
}
}
}
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