rust/clippy_lints/src/erasing_op.rs

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use clippy_utils::consts::{constant_simple, Constant};
use clippy_utils::diagnostics::span_lint;
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use rustc_hir::{BinOpKind, Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
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declare_clippy_lint! {
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/// **What it does:** Checks for erasing operations, e.g., `x * 0`.
///
/// **Why is this bad?** The whole expression can be replaced by zero.
/// This is most likely not the intended outcome and should probably be
/// corrected
///
/// **Known problems:** None.
///
/// **Example:**
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/// ```rust
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/// let x = 1;
/// 0 / x;
/// 0 * x;
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/// x & 0;
/// ```
pub ERASING_OP,
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correctness,
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"using erasing operations, e.g., `x * 0` or `y & 0`"
}
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declare_lint_pass!(ErasingOp => [ERASING_OP]);
impl<'tcx> LateLintPass<'tcx> for ErasingOp {
fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
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if e.span.from_expansion() {
return;
}
if let ExprKind::Binary(ref cmp, left, right) = e.kind {
match cmp.node {
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BinOpKind::Mul | BinOpKind::BitAnd => {
check(cx, left, e.span);
check(cx, right, e.span);
},
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BinOpKind::Div => check(cx, left, e.span),
_ => (),
}
}
}
}
fn check(cx: &LateContext<'_>, e: &Expr<'_>, span: Span) {
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if let Some(Constant::Int(0)) = constant_simple(cx, cx.typeck_results(), e) {
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span_lint(
cx,
ERASING_OP,
span,
"this operation will always return zero. This is likely not the intended outcome",
);
}
}