1 use clippy_utils::consts::{constant_simple, Constant};
2 use clippy_utils::diagnostics::span_lint;
3 use clippy_utils::{match_def_path, 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};
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`.
31 "`min(_, max(_, _))` (or vice versa) with bounds clamping the result to a constant"
34 declare_lint_pass!(MinMaxPass => [MIN_MAX]);
36 impl<'tcx> LateLintPass<'tcx> for MinMaxPass {
37 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
38 if let Some((outer_max, outer_c, oe)) = min_max(cx, expr) {
39 if let Some((inner_max, inner_c, ie)) = min_max(cx, oe) {
40 if outer_max == inner_max {
45 Constant::partial_cmp(cx.tcx, cx.typeck_results().expr_ty(ie), &outer_c, &inner_c),
47 (_, None) | (MinMax::Max, Some(Ordering::Less)) | (MinMax::Min, Some(Ordering::Greater)) => (),
53 "this `min`/`max` combination leads to constant result",
62 #[derive(PartialEq, Eq, Debug, Clone, Copy)]
68 fn min_max<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
70 ExprKind::Call(path, args) => {
71 if let ExprKind::Path(ref qpath) = path.kind {
73 .qpath_res(qpath, path.hir_id)
76 if match_def_path(cx, def_id, &paths::CMP_MIN) {
77 fetch_const(cx, args, MinMax::Min)
78 } else if match_def_path(cx, def_id, &paths::CMP_MAX) {
79 fetch_const(cx, args, MinMax::Max)
88 ExprKind::MethodCall(path, _, args, _) => {
90 if let [obj, _] = args;
91 if cx.typeck_results().expr_ty(obj).is_floating_point() || match_trait_method(cx, expr, &paths::ORD);
93 if path.ident.name == sym!(max) {
94 fetch_const(cx, args, MinMax::Max)
95 } else if path.ident.name == sym!(min) {
96 fetch_const(cx, args, MinMax::Min)
109 fn fetch_const<'a>(cx: &LateContext<'_>, args: &'a [Expr<'a>], m: MinMax) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
113 constant_simple(cx, cx.typeck_results(), &args[0]).map_or_else(
114 || constant_simple(cx, cx.typeck_results(), &args[1]).map(|c| (m, c, &args[0])),
116 if constant_simple(cx, cx.typeck_results(), &args[1]).is_none() {
118 Some((m, c, &args[1]))