1 use clippy_utils::consts::{constant_simple, Constant};
2 use clippy_utils::diagnostics::span_lint;
3 use clippy_utils::{match_trait_method, paths};
4 use if_chain::if_chain;
5 use rustc_hir::{Expr, ExprKind};
6 use rustc_lint::{LateContext, LateLintPass};
7 use rustc_session::{declare_lint_pass, declare_tool_lint};
9 use std::cmp::Ordering;
11 declare_clippy_lint! {
13 /// Checks for expressions where `std::cmp::min` and `max` are
14 /// used to clamp values, but switched so that the result is constant.
16 /// ### Why is this bad?
17 /// This is in all probability not the intended outcome. At
18 /// the least it hurts readability of the code.
22 /// min(0, max(100, x))
28 /// It will always be equal to `0`. Probably the author meant to clamp the value
29 /// between 0 and 100, but has erroneously swapped `min` and `max`.
30 #[clippy::version = "pre 1.29.0"]
33 "`min(_, max(_, _))` (or vice versa) with bounds clamping the result to a constant"
36 declare_lint_pass!(MinMaxPass => [MIN_MAX]);
38 impl<'tcx> LateLintPass<'tcx> for MinMaxPass {
39 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
40 if let Some((outer_max, outer_c, oe)) = min_max(cx, expr) {
41 if let Some((inner_max, inner_c, ie)) = min_max(cx, oe) {
42 if outer_max == inner_max {
47 Constant::partial_cmp(cx.tcx, cx.typeck_results().expr_ty(ie), &outer_c, &inner_c),
49 (_, None) | (MinMax::Max, Some(Ordering::Less)) | (MinMax::Min, Some(Ordering::Greater)) => (),
55 "this `min`/`max` combination leads to constant result",
64 #[derive(PartialEq, Eq, Debug, Clone, Copy)]
70 fn min_max<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
72 ExprKind::Call(path, args) => {
73 if let ExprKind::Path(ref qpath) = path.kind {
75 .qpath_res(qpath, path.hir_id)
77 .and_then(|def_id| match cx.tcx.get_diagnostic_name(def_id) {
78 Some(sym::cmp_min) => fetch_const(cx, None, args, MinMax::Min),
79 Some(sym::cmp_max) => fetch_const(cx, None, args, MinMax::Max),
86 ExprKind::MethodCall(path, receiver, args @ [_], _) => {
88 if cx.typeck_results().expr_ty(receiver).is_floating_point() || match_trait_method(cx, expr, &paths::ORD);
90 if path.ident.name == sym!(max) {
91 fetch_const(cx, Some(receiver), args, MinMax::Max)
92 } else if path.ident.name == sym!(min) {
93 fetch_const(cx, Some(receiver), args, MinMax::Min)
107 cx: &LateContext<'_>,
108 receiver: Option<&'a Expr<'a>>,
109 args: &'a [Expr<'a>],
111 ) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
112 let mut args = receiver.into_iter().chain(args.into_iter());
113 let arg0 = args.next()?;
114 let arg1 = args.next()?;
115 if args.next().is_some() {
118 constant_simple(cx, cx.typeck_results(), arg0).map_or_else(
119 || constant_simple(cx, cx.typeck_results(), arg1).map(|c| (m, c, arg0)),
121 if constant_simple(cx, cx.typeck_results(), arg1).is_none() {