--- /dev/null
+use consts::{constant_simple, Constant};
+use rustc::hir::*;
+use rustc::lint::*;
+use syntax::codemap::Span;
+use 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.
+/// Most likely mistake was made and code should be reviewed or simplified.
+///
+/// **Known problems:** None.
+///
+/// **Example:**
+/// ```rust
+/// 0 / x; 0 * x; x & 0
+/// ```
+declare_lint! {
+ pub ERASING_OP,
+ Warn,
+ "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;
+ }
+ if let ExprBinary(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) {
+ if let Some(Constant::Int(v)) = constant_simple(cx, e) {
+ if v.to_u128_unchecked() == 0 {
+ span_lint(
+ cx,
+ ERASING_OP,
+ span,
+ "the operation is ineffective. Consider reducing it to `0`",
+ );
+ }
+ }
+}
pub mod enum_clike;
pub mod enum_glob_use;
pub mod enum_variants;
+pub mod erasing_op;
pub mod eq_op;
pub mod escape;
pub mod eta_reduction;
reg.register_early_lint_pass(box needless_continue::NeedlessContinue);
reg.register_late_lint_pass(box eta_reduction::EtaPass);
reg.register_late_lint_pass(box identity_op::IdentityOp);
+ reg.register_late_lint_pass(box erasing_op::ErasingOp);
reg.register_early_lint_pass(box items_after_statements::ItemsAfterStatements);
reg.register_late_lint_pass(box mut_mut::MutMut);
reg.register_late_lint_pass(box mut_reference::UnnecessaryMutPassed);
|
= note: `-D bad-bit-mask` implied by `-D warnings`
+error: the operation is ineffective. Consider reducing it to `0`
+ --> $DIR/bit_masks.rs:12:5
+ |
+12 | x & 0 == 0;
+ | ^^^^^
+ |
+ = note: `-D erasing-op` implied by `-D warnings`
+
error: incompatible bit mask: `_ & 2` can never be equal to `1`
--> $DIR/bit_masks.rs:15:5
|
35 | 0 & x == 0;
| ^^^^^^^^^^
+error: the operation is ineffective. Consider reducing it to `0`
+ --> $DIR/bit_masks.rs:35:5
+ |
+35 | 0 & x == 0;
+ | ^^^^^
+
error: incompatible bit mask: `_ | 2` will always be higher than `1`
--> $DIR/bit_masks.rs:39:5
|
--- /dev/null
+error: the operation is ineffective. Consider reducing it to `0`
+ --> $DIR/erasing_op.rs:9:5
+ |
+9 | x * 0;
+ | ^^^^^
+ |
+ = note: `-D erasing-op` implied by `-D warnings`
+
+error: the operation is ineffective. Consider reducing it to `0`
+ --> $DIR/erasing_op.rs:10:5
+ |
+10 | 0 & x;
+ | ^^^^^
+
+error: the operation is ineffective. Consider reducing it to `0`
+ --> $DIR/erasing_op.rs:11:5
+ |
+11 | 0 / x;
+ | ^^^^^
+