--- /dev/null
+//! Lint on unnecessary double comparisons. Some examples:
+
+use rustc::hir::*;
+use rustc::lint::*;
+use syntax::codemap::Span;
+
+use utils::{snippet, span_lint_and_sugg, SpanlessEq};
+
+/// **What it does:** Checks for double comparions that could be simpified to a single expression.
+///
+///
+/// **Why is this bad?** Readability.
+///
+/// **Known problems:** None.
+///
+/// **Example:**
+/// ```rust
+/// x == y || x < y
+/// ```
+///
+/// Could be written as:
+///
+/// ```rust
+/// x <= y
+/// ```
+declare_lint! {
+ pub DOUBLE_COMPARISONS,
+ Deny,
+ "unnecessary double comparisons that can be simplified"
+}
+
+pub struct DoubleComparisonPass;
+
+impl LintPass for DoubleComparisonPass {
+ fn get_lints(&self) -> LintArray {
+ lint_array!(DOUBLE_COMPARISONS)
+ }
+}
+
+impl<'a, 'tcx> DoubleComparisonPass {
+ fn check_binop(
+ &self,
+ cx: &LateContext<'a, 'tcx>,
+ op: BinOp_,
+ lhs: &'tcx Expr,
+ rhs: &'tcx Expr,
+ span: Span,
+ ) {
+ let (lkind, llhs, lrhs, rkind, rlhs, rrhs) = match (lhs.node.clone(), rhs.node.clone()) {
+ (ExprBinary(lb, llhs, lrhs), ExprBinary(rb, rlhs, rrhs)) => {
+ (lb.node, llhs, lrhs, rb.node, rlhs, rrhs)
+ }
+ _ => return,
+ };
+ let spanless_eq = SpanlessEq::new(cx).ignore_fn();
+ if !(spanless_eq.eq_expr(&llhs, &rlhs) && spanless_eq.eq_expr(&lrhs, &rrhs)) {
+ return;
+ }
+ macro_rules! lint_double_comparison {
+ ($op:tt) => {{
+ let lhs_str = snippet(cx, llhs.span, "");
+ let rhs_str = snippet(cx, lrhs.span, "");
+ let sugg = format!("{} {} {}", lhs_str, stringify!($op), rhs_str);
+ span_lint_and_sugg(cx, DOUBLE_COMPARISONS, span,
+ "This binary expression can be simplified",
+ "try", sugg);
+ }}
+ }
+ match (op, lkind, rkind) {
+ (BiOr, BiEq, BiLt) | (BiOr, BiLt, BiEq) => lint_double_comparison!(<=),
+ (BiOr, BiEq, BiGt) | (BiOr, BiGt, BiEq) => lint_double_comparison!(>=),
+ (BiOr, BiLt, BiGt) | (BiOr, BiGt, BiLt) => lint_double_comparison!(!=),
+ (BiAnd, BiLe, BiGe) | (BiAnd, BiGe, BiLe) => lint_double_comparison!(==),
+ _ => (),
+ };
+ }
+}
+
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DoubleComparisonPass {
+ fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
+ if let ExprBinary(ref kind, ref lhs, ref rhs) = expr.node {
+ self.check_binop(cx, kind.node, lhs, rhs, expr.span);
+ }
+ }
+}
// *arg impls PartialEq<other>
if !arg_ty
- .builtin_deref(true, ty::LvaluePreference::NoPreference)
+ .builtin_deref(true)
.map_or(false, |tam| implements_trait(cx, tam.ty, partial_eq_trait_id, &[other_ty]))
// arg impls PartialEq<*other>
&& !other_ty
- .builtin_deref(true, ty::LvaluePreference::NoPreference)
+ .builtin_deref(true)
.map_or(false, |tam| implements_trait(cx, arg_ty, partial_eq_trait_id, &[tam.ty]))
// arg impls PartialEq<other>
&& !implements_trait(cx, arg_ty, partial_eq_trait_id, &[other_ty])
--- /dev/null
+error: This binary expression can be simplified
+ --> $DIR/double_comparison.rs:4:8
+ |
+4 | if x == y || x < y {
+ | ^^^^^^^^^^^^^^^ help: try: `x <= y`
+ |
+ = note: #[deny(double_comparisons)] on by default
+
+error: This binary expression can be simplified
+ --> $DIR/double_comparison.rs:7:8
+ |
+7 | if x < y || x == y {
+ | ^^^^^^^^^^^^^^^ help: try: `x <= y`
+
+error: This binary expression can be simplified
+ --> $DIR/double_comparison.rs:10:8
+ |
+10 | if x == y || x > y {
+ | ^^^^^^^^^^^^^^^ help: try: `x >= y`
+
+error: This binary expression can be simplified
+ --> $DIR/double_comparison.rs:13:8
+ |
+13 | if x > y || x == y {
+ | ^^^^^^^^^^^^^^^ help: try: `x >= y`
+
+error: This binary expression can be simplified
+ --> $DIR/double_comparison.rs:16:8
+ |
+16 | if x < y || x > y {
+ | ^^^^^^^^^^^^^^ help: try: `x != y`
+
+error: This binary expression can be simplified
+ --> $DIR/double_comparison.rs:19:8
+ |
+19 | if x > y || x < y {
+ | ^^^^^^^^^^^^^^ help: try: `x != y`
+
+error: This binary expression can be simplified
+ --> $DIR/double_comparison.rs:22:8
+ |
+22 | if x <= y && x >= y {
+ | ^^^^^^^^^^^^^^^^ help: try: `x == y`
+
+error: This binary expression can be simplified
+ --> $DIR/double_comparison.rs:25:8
+ |
+25 | if x >= y && x <= y {
+ | ^^^^^^^^^^^^^^^^ help: try: `x == y`
+
+error: aborting due to 8 previous errors
+