refactor(double_comparison): clean-up, simplify lint logic (#15955)

- use let-chains
- rm macro
- add comments explaining linted cases

changelog: none

Author: samueltardieu

clippy_lints/src/operators/double_comparison.rs

@@ -8,46 +8,52 @@ use rustc_span::Span;
 
 use super::DOUBLE_COMPARISONS;
 
-pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, op: BinOpKind, lhs: &'tcx Expr<'_>, rhs: &'tcx Expr<'_>, span: Span) {
-    let (lkind, llhs, lrhs, rkind, rlhs, rrhs) = match (&lhs.kind, &rhs.kind) {
-        (ExprKind::Binary(lb, llhs, lrhs), ExprKind::Binary(rb, rlhs, rrhs)) => {
-            (lb.node, llhs, lrhs, rb.node, rlhs, rrhs)
-        },
-        _ => return,
-    };
-    if !(eq_expr_value(cx, llhs, rlhs) && eq_expr_value(cx, lrhs, rrhs)) {
-        return;
-    }
-    macro_rules! lint_double_comparison {
-        ($op:tt) => {{
-            let mut applicability = Applicability::MachineApplicable;
-            let lhs_str = snippet_with_applicability(cx, llhs.span, "", &mut applicability);
-            let rhs_str = snippet_with_applicability(cx, lrhs.span, "", &mut applicability);
-            let sugg = format!("{} {} {}", lhs_str, stringify!($op), rhs_str);
-            span_lint_and_sugg(
-                cx,
-                DOUBLE_COMPARISONS,
-                span,
-                "this binary expression can be simplified",
-                "try",
-                sugg,
-                applicability,
-            );
-        }};
-    }
-    match (op, lkind, rkind) {
-        (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Lt) | (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Eq) => {
-            lint_double_comparison!(<=);
-        },
-        (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Gt) | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Eq) => {
-            lint_double_comparison!(>=);
-        },
-        (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Gt) | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Lt) => {
-            lint_double_comparison!(!=);
-        },
-        (BinOpKind::And, BinOpKind::Le, BinOpKind::Ge) | (BinOpKind::And, BinOpKind::Ge, BinOpKind::Le) => {
-            lint_double_comparison!(==);
-        },
-        _ => (),
+pub(super) fn check(cx: &LateContext<'_>, op: BinOpKind, lhs: &Expr<'_>, rhs: &Expr<'_>, span: Span) {
+    if let ExprKind::Binary(lop, llhs, lrhs) = lhs.kind
+        && let ExprKind::Binary(rop, rlhs, rrhs) = rhs.kind
+        && eq_expr_value(cx, llhs, rlhs)
+        && eq_expr_value(cx, lrhs, rrhs)
+    {
+        let op = match (op, lop.node, rop.node) {
+            // x == y || x < y => x <= y
+            (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Lt)
+            // x < y || x == y => x <= y
+            | (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Eq) => {
+                "<="
+            },
+            // x == y || x > y => x >= y
+            (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Gt)
+            // x > y || x == y => x >= y
+            | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Eq) => {
+                ">="
+            },
+            // x < y || x > y => x != y
+            (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Gt)
+            // x > y || x < y => x != y
+            | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Lt) => {
+                "!="
+            },
+            // x <= y && x >= y => x == y
+            (BinOpKind::And, BinOpKind::Le, BinOpKind::Ge)
+            // x >= y && x <= y => x == y
+            | (BinOpKind::And, BinOpKind::Ge, BinOpKind::Le) => {
+                "=="
+            },
+            _ => return,
+        };
+
+        let mut applicability = Applicability::MachineApplicable;
+        let lhs_str = snippet_with_applicability(cx, llhs.span, "", &mut applicability);
+        let rhs_str = snippet_with_applicability(cx, lrhs.span, "", &mut applicability);
+        let sugg = format!("{lhs_str} {op} {rhs_str}");
+        span_lint_and_sugg(
+            cx,
+            DOUBLE_COMPARISONS,
+            span,
+            "this binary expression can be simplified",
+            "try",
+            sugg,
+            applicability,
+        );
     }
 }