rust/clippy_lints/src/erasing_op.rs

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use crate::consts::{constant_simple, Constant};
use rustc::hir::*;
use rustc::lint::*;
use syntax::codemap::Span;
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use crate::utils::{in_macro, span_lint};
/// **What it does:** Checks for erasing operations, e.g. `x * 0`.
///
/// **Why is this bad?** The whole expression can be replaced by zero.
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/// This is most likely not the intended outcome and should probably be
/// corrected
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// 0 / x; 0 * x; x & 0
/// ```
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declare_clippy_lint! {
pub ERASING_OP,
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correctness,
"using erasing operations, e.g. `x * 0` or `y & 0`"
}
#[derive(Copy, Clone)]
pub struct ErasingOp;
impl LintPass for ErasingOp {
fn get_lints(&self) -> LintArray {
lint_array!(ERASING_OP)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ErasingOp {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
if in_macro(e.span) {
return;
}
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if let ExprKind::Binary(ref cmp, ref left, ref right) = e.node {
match cmp.node {
BiMul | BiBitAnd => {
check(cx, left, e.span);
check(cx, right, e.span);
},
BiDiv => check(cx, left, e.span),
_ => (),
}
}
}
}
fn check(cx: &LateContext, e: &Expr, span: Span) {
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if let Some(Constant::Int(v)) = constant_simple(cx, cx.tables, e) {
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if v == 0 {
span_lint(
cx,
ERASING_OP,
span,
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"this operation will always return zero. This is likely not the intended outcome",
);
}
}
}