1 use clippy_utils::consts::{constant_simple, Constant};
2 use clippy_utils::diagnostics::span_lint;
3 use clippy_utils::is_trait_method;
4 use rustc_hir::{Expr, ExprKind};
5 use rustc_lint::{LateContext, LateLintPass};
6 use rustc_session::{declare_lint_pass, declare_tool_lint};
8 use std::cmp::Ordering;
10 declare_clippy_lint! {
12 /// Checks for expressions where `std::cmp::min` and `max` are
13 /// used to clamp values, but switched so that the result is constant.
15 /// ### Why is this bad?
16 /// This is in all probability not the intended outcome. At
17 /// the least it hurts readability of the code.
21 /// min(0, max(100, x))
27 /// It will always be equal to `0`. Probably the author meant to clamp the value
28 /// between 0 and 100, but has erroneously swapped `min` and `max`.
29 #[clippy::version = "pre 1.29.0"]
32 "`min(_, max(_, _))` (or vice versa) with bounds clamping the result to a constant"
35 declare_lint_pass!(MinMaxPass => [MIN_MAX]);
37 impl<'tcx> LateLintPass<'tcx> for MinMaxPass {
38 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
39 if let Some((outer_max, outer_c, oe)) = min_max(cx, expr) {
40 if let Some((inner_max, inner_c, ie)) = min_max(cx, oe) {
41 if outer_max == inner_max {
46 Constant::partial_cmp(cx.tcx, cx.typeck_results().expr_ty(ie), &outer_c, &inner_c),
48 (_, None) | (MinMax::Max, Some(Ordering::Less)) | (MinMax::Min, Some(Ordering::Greater)) => (),
54 "this `min`/`max` combination leads to constant result",
63 #[derive(PartialEq, Eq, Debug, Clone, Copy)]
69 fn min_max<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
71 ExprKind::Call(path, args) => {
72 if let ExprKind::Path(ref qpath) = path.kind {
74 .qpath_res(qpath, path.hir_id)
76 .and_then(|def_id| match cx.tcx.get_diagnostic_name(def_id) {
77 Some(sym::cmp_min) => fetch_const(cx, None, args, MinMax::Min),
78 Some(sym::cmp_max) => fetch_const(cx, None, args, MinMax::Max),
85 ExprKind::MethodCall(path, receiver, args @ [_], _) => {
86 if cx.typeck_results().expr_ty(receiver).is_floating_point() || is_trait_method(cx, expr, sym::Ord) {
87 if path.ident.name == sym!(max) {
88 fetch_const(cx, Some(receiver), args, MinMax::Max)
89 } else if path.ident.name == sym!(min) {
90 fetch_const(cx, Some(receiver), args, MinMax::Min)
103 cx: &LateContext<'_>,
104 receiver: Option<&'a Expr<'a>>,
105 args: &'a [Expr<'a>],
107 ) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
108 let mut args = receiver.into_iter().chain(args);
109 let first_arg = args.next()?;
110 let second_arg = args.next()?;
111 if args.next().is_some() {
114 constant_simple(cx, cx.typeck_results(), first_arg).map_or_else(
115 || constant_simple(cx, cx.typeck_results(), second_arg).map(|c| (m, c, first_arg)),
117 if constant_simple(cx, cx.typeck_results(), second_arg).is_none() {
119 Some((m, c, second_arg))