2 get_trait_def_id, if_sequence, implements_trait, parent_node_is_if_expr, paths, span_lint_and_help, SpanlessEq,
4 use rustc_hir::{BinOpKind, Expr, ExprKind};
5 use rustc_lint::{LateContext, LateLintPass};
6 use rustc_session::{declare_lint_pass, declare_tool_lint};
9 /// **What it does:** Checks comparison chains written with `if` that can be
10 /// rewritten with `match` and `cmp`.
12 /// **Why is this bad?** `if` is not guaranteed to be exhaustive and conditionals can get
15 /// **Known problems:** The match statement may be slower due to the compiler
16 /// not inlining the call to cmp. See issue [#5354](https://github.com/rust-lang/rust-clippy/issues/5354)
23 /// fn f(x: u8, y: u8) {
37 /// use std::cmp::Ordering;
41 /// fn f(x: u8, y: u8) {
43 /// Ordering::Greater => a(),
44 /// Ordering::Less => b(),
45 /// Ordering::Equal => c()
51 "`if`s that can be rewritten with `match` and `cmp`"
54 declare_lint_pass!(ComparisonChain => [COMPARISON_CHAIN]);
56 impl<'tcx> LateLintPass<'tcx> for ComparisonChain {
57 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
58 if expr.span.from_expansion() {
62 // We only care about the top-most `if` in the chain
63 if parent_node_is_if_expr(expr, cx) {
67 // Check that there exists at least one explicit else condition
68 let (conds, _) = if_sequence(expr);
73 for cond in conds.windows(2) {
75 &ExprKind::Binary(ref kind1, ref lhs1, ref rhs1),
76 &ExprKind::Binary(ref kind2, ref lhs2, ref rhs2),
77 ) = (&cond[0].kind, &cond[1].kind)
79 if !kind_is_cmp(kind1.node) || !kind_is_cmp(kind2.node) {
83 // Check that both sets of operands are equal
84 let mut spanless_eq = SpanlessEq::new(cx);
85 let same_fixed_operands = spanless_eq.eq_expr(lhs1, lhs2) && spanless_eq.eq_expr(rhs1, rhs2);
86 let same_transposed_operands = spanless_eq.eq_expr(lhs1, rhs2) && spanless_eq.eq_expr(rhs1, lhs2);
88 if !same_fixed_operands && !same_transposed_operands {
92 // Check that if the operation is the same, either it's not `==` or the operands are transposed
93 if kind1.node == kind2.node {
94 if kind1.node == BinOpKind::Eq {
97 if !same_transposed_operands {
102 // Check that the type being compared implements `core::cmp::Ord`
103 let ty = cx.typeck_results().expr_ty(lhs1);
104 let is_ord = get_trait_def_id(cx, &paths::ORD).map_or(false, |id| implements_trait(cx, ty, id, &[]));
110 // We only care about comparison chains
118 "`if` chain can be rewritten with `match`",
120 "Consider rewriting the `if` chain to use `cmp` and `match`.",
125 fn kind_is_cmp(kind: BinOpKind) -> bool {
126 matches!(kind, BinOpKind::Lt | BinOpKind::Gt | BinOpKind::Eq)