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:** None.
22 /// fn f(x: u8, y: u8) {
36 /// use std::cmp::Ordering;
40 /// fn f(x: u8, y: u8) {
42 /// Ordering::Greater => a(),
43 /// Ordering::Less => b(),
44 /// Ordering::Equal => c()
50 "`if`s that can be rewritten with `match` and `cmp`"
53 declare_lint_pass!(ComparisonChain => [COMPARISON_CHAIN]);
55 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for ComparisonChain {
56 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
57 if expr.span.from_expansion() {
61 // We only care about the top-most `if` in the chain
62 if parent_node_is_if_expr(expr, cx) {
66 // Check that there exists at least one explicit else condition
67 let (conds, _) = if_sequence(expr);
72 for cond in conds.windows(2) {
74 &ExprKind::Binary(ref kind1, ref lhs1, ref rhs1),
75 &ExprKind::Binary(ref kind2, ref lhs2, ref rhs2),
76 ) = (&cond[0].kind, &cond[1].kind)
78 if !kind_is_cmp(kind1.node) || !kind_is_cmp(kind2.node) {
82 // Check that both sets of operands are equal
83 let mut spanless_eq = SpanlessEq::new(cx);
84 if (!spanless_eq.eq_expr(lhs1, lhs2) || !spanless_eq.eq_expr(rhs1, rhs2))
85 && (!spanless_eq.eq_expr(lhs1, rhs2) || !spanless_eq.eq_expr(rhs1, lhs2))
90 // Check that the type being compared implements `core::cmp::Ord`
91 let ty = cx.tables.expr_ty(lhs1);
92 let is_ord = get_trait_def_id(cx, &paths::ORD).map_or(false, |id| implements_trait(cx, ty, id, &[]));
98 // We only care about comparison chains
106 "`if` chain can be rewritten with `match`",
108 "Consider rewriting the `if` chain to use `cmp` and `match`.",
113 fn kind_is_cmp(kind: BinOpKind) -> bool {
115 BinOpKind::Lt | BinOpKind::Gt | BinOpKind::Eq => true,