1 use clippy_utils::diagnostics::span_lint_and_help;
2 use clippy_utils::ty::implements_trait;
3 use clippy_utils::{get_trait_def_id, if_sequence, in_constant, is_else_clause, paths, SpanlessEq};
4 use rustc_hir::{BinOpKind, Expr, ExprKind};
5 use rustc_lint::{LateContext, LateLintPass};
6 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 /// Checks comparison chains written with `if` that can be
11 /// rewritten with `match` and `cmp`.
13 /// ### Why is this bad?
14 /// `if` is not guaranteed to be exhaustive and conditionals can get
17 /// ### Known problems
18 /// The match statement may be slower due to the compiler
19 /// not inlining the call to cmp. See issue [#5354](https://github.com/rust-lang/rust-clippy/issues/5354)
26 /// fn f(x: u8, y: u8) {
40 /// use std::cmp::Ordering;
44 /// fn f(x: u8, y: u8) {
46 /// Ordering::Greater => a(),
47 /// Ordering::Less => b(),
48 /// Ordering::Equal => c()
52 #[clippy::version = "1.40.0"]
55 "`if`s that can be rewritten with `match` and `cmp`"
58 declare_lint_pass!(ComparisonChain => [COMPARISON_CHAIN]);
60 impl<'tcx> LateLintPass<'tcx> for ComparisonChain {
61 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
62 if expr.span.from_expansion() {
66 // We only care about the top-most `if` in the chain
67 if is_else_clause(cx.tcx, expr) {
71 if in_constant(cx, expr.hir_id) {
75 // Check that there exists at least one explicit else condition
76 let (conds, _) = if_sequence(expr);
81 for cond in conds.windows(2) {
82 if let (&ExprKind::Binary(ref kind1, lhs1, rhs1), &ExprKind::Binary(ref kind2, lhs2, rhs2)) =
83 (&cond[0].kind, &cond[1].kind)
85 if !kind_is_cmp(kind1.node) || !kind_is_cmp(kind2.node) {
89 // Check that both sets of operands are equal
90 let mut spanless_eq = SpanlessEq::new(cx);
91 let same_fixed_operands = spanless_eq.eq_expr(lhs1, lhs2) && spanless_eq.eq_expr(rhs1, rhs2);
92 let same_transposed_operands = spanless_eq.eq_expr(lhs1, rhs2) && spanless_eq.eq_expr(rhs1, lhs2);
94 if !same_fixed_operands && !same_transposed_operands {
98 // Check that if the operation is the same, either it's not `==` or the operands are transposed
99 if kind1.node == kind2.node {
100 if kind1.node == BinOpKind::Eq {
103 if !same_transposed_operands {
108 // Check that the type being compared implements `core::cmp::Ord`
109 let ty = cx.typeck_results().expr_ty(lhs1);
110 let is_ord = get_trait_def_id(cx, &paths::ORD).map_or(false, |id| implements_trait(cx, ty, id, &[]));
116 // We only care about comparison chains
124 "`if` chain can be rewritten with `match`",
126 "consider rewriting the `if` chain to use `cmp` and `match`",
131 fn kind_is_cmp(kind: BinOpKind) -> bool {
132 matches!(kind, BinOpKind::Lt | BinOpKind::Gt | BinOpKind::Eq)