2018-05-30 08:15:50 +00:00
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use crate::consts::{constant_simple, Constant};
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2017-09-30 17:14:00 +00:00
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use rustc::hir::*;
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use rustc::lint::*;
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use syntax::codemap::Span;
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2018-05-30 08:15:50 +00:00
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use crate::utils::{in_macro, span_lint};
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2017-09-30 17:14:00 +00:00
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/// **What it does:** Checks for erasing operations, e.g. `x * 0`.
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///
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/// **Why is this bad?** The whole expression can be replaced by zero.
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2017-10-15 07:32:47 +00:00
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/// This is most likely not the intended outcome and should probably be
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/// corrected
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2017-09-30 17:14:00 +00:00
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// 0 / x; 0 * x; x & 0
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/// ```
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2018-03-28 13:24:26 +00:00
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declare_clippy_lint! {
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2017-09-30 17:14:00 +00:00
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pub ERASING_OP,
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2018-03-28 13:24:26 +00:00
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correctness,
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2017-09-30 17:14:00 +00:00
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"using erasing operations, e.g. `x * 0` or `y & 0`"
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}
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#[derive(Copy, Clone)]
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pub struct ErasingOp;
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impl LintPass for ErasingOp {
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fn get_lints(&self) -> LintArray {
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lint_array!(ERASING_OP)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ErasingOp {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
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if in_macro(e.span) {
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return;
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}
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2018-07-12 07:30:57 +00:00
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if let ExprKind::Binary(ref cmp, ref left, ref right) = e.node {
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2017-09-30 17:14:00 +00:00
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match cmp.node {
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2018-07-12 07:50:09 +00:00
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BinOpKind::Mul | BinOpKind::BitAnd => {
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2017-09-30 17:14:00 +00:00
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check(cx, left, e.span);
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check(cx, right, e.span);
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},
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2018-07-12 07:50:09 +00:00
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BinOpKind::Div => check(cx, left, e.span),
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2017-09-30 17:14:00 +00:00
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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 check(cx: &LateContext, e: &Expr, span: Span) {
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2018-05-13 11:16:31 +00:00
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if let Some(Constant::Int(v)) = constant_simple(cx, cx.tables, e) {
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2018-03-13 10:38:11 +00:00
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if v == 0 {
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2017-09-30 17:14:00 +00:00
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span_lint(
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cx,
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ERASING_OP,
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span,
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2017-10-15 07:32:47 +00:00
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"this operation will always return zero. This is likely not the intended outcome",
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2017-09-30 17:14:00 +00:00
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);
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}
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}
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}
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