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()
54 "`if`s that can be rewritten with `match` and `cmp`"
57 declare_lint_pass!(ComparisonChain => [COMPARISON_CHAIN]);
59 impl<'tcx> LateLintPass<'tcx> for ComparisonChain {
60 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
61 if expr.span.from_expansion() {
65 // We only care about the top-most `if` in the chain
66 if is_else_clause(cx.tcx, expr) {
70 if in_constant(cx, expr.hir_id) {
74 // Check that there exists at least one explicit else condition
75 let (conds, _) = if_sequence(expr);
80 for cond in conds.windows(2) {
81 if let (&ExprKind::Binary(ref kind1, lhs1, rhs1), &ExprKind::Binary(ref kind2, lhs2, rhs2)) =
82 (&cond[0].kind, &cond[1].kind)
84 if !kind_is_cmp(kind1.node) || !kind_is_cmp(kind2.node) {
88 // Check that both sets of operands are equal
89 let mut spanless_eq = SpanlessEq::new(cx);
90 let same_fixed_operands = spanless_eq.eq_expr(lhs1, lhs2) && spanless_eq.eq_expr(rhs1, rhs2);
91 let same_transposed_operands = spanless_eq.eq_expr(lhs1, rhs2) && spanless_eq.eq_expr(rhs1, lhs2);
93 if !same_fixed_operands && !same_transposed_operands {
97 // Check that if the operation is the same, either it's not `==` or the operands are transposed
98 if kind1.node == kind2.node {
99 if kind1.node == BinOpKind::Eq {
102 if !same_transposed_operands {
107 // Check that the type being compared implements `core::cmp::Ord`
108 let ty = cx.typeck_results().expr_ty(lhs1);
109 let is_ord = get_trait_def_id(cx, &paths::ORD).map_or(false, |id| implements_trait(cx, ty, id, &[]));
115 // We only care about comparison chains
123 "`if` chain can be rewritten with `match`",
125 "consider rewriting the `if` chain to use `cmp` and `match`",
130 fn kind_is_cmp(kind: BinOpKind) -> bool {
131 matches!(kind, BinOpKind::Lt | BinOpKind::Gt | BinOpKind::Eq)