1 use crate::consts::{constant_simple, Constant};
2 use crate::utils::{match_def_path, opt_def_id, paths, sext, span_lint};
5 use rustc::ty::{self, TyCtxt};
6 use std::cmp::{Ordering, PartialOrd};
8 /// **What it does:** Checks for expressions where `std::cmp::min` and `max` are
9 /// used to clamp values, but switched so that the result is constant.
11 /// **Why is this bad?** This is in all probability not the intended outcome. At
12 /// the least it hurts readability of the code.
14 /// **Known problems:** None
18 /// min(0, max(100, x))
20 /// It will always be equal to `0`. Probably the author meant to clamp the value
21 /// between 0 and 100, but has erroneously swapped `min` and `max`.
22 declare_clippy_lint! {
25 "`min(_, max(_, _))` (or vice versa) with bounds clamping the result to a constant"
28 #[allow(missing_copy_implementations)]
29 pub struct MinMaxPass;
31 impl LintPass for MinMaxPass {
32 fn get_lints(&self) -> LintArray {
37 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MinMaxPass {
38 fn check_expr(&mut self, cx: &LateContext<'a, '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 const_partial_cmp(cx.tcx, &outer_c, &inner_c, &cx.tables.expr_ty(ie).sty),
48 (_, None) | (MinMax::Max, Some(Ordering::Less)) | (MinMax::Min, Some(Ordering::Greater)) => (),
54 "this min/max combination leads to constant result",
63 // Constant::partial_cmp incorrectly orders signed integers
64 fn const_partial_cmp(tcx: TyCtxt, a: &Constant, b: &Constant, expr_ty: &ty::TypeVariants) -> Option<Ordering> {
66 ty::TyInt(int_ty) => {
67 if let (&Constant::Int(a), &Constant::Int(b)) = (a, b) {
68 Some(sext(tcx, a, int_ty).cmp(&sext(tcx, b, int_ty)))
73 _ => a.partial_cmp(&b),
77 #[derive(PartialEq, Eq, Debug)]
83 fn min_max<'a>(cx: &LateContext, expr: &'a Expr) -> Option<(MinMax, Constant, &'a Expr)> {
84 if let ExprCall(ref path, ref args) = expr.node {
85 if let ExprPath(ref qpath) = path.node {
86 opt_def_id(cx.tables.qpath_def(qpath, path.hir_id)).and_then(|def_id| {
87 if match_def_path(cx.tcx, def_id, &paths::CMP_MIN) {
88 fetch_const(cx, args, MinMax::Min)
89 } else if match_def_path(cx.tcx, def_id, &paths::CMP_MAX) {
90 fetch_const(cx, args, MinMax::Max)
103 fn fetch_const<'a>(cx: &LateContext, args: &'a [Expr], m: MinMax) -> Option<(MinMax, Constant, &'a Expr)> {
107 if let Some(c) = constant_simple(cx, cx.tables, &args[0]) {
108 if constant_simple(cx, cx.tables, &args[1]).is_none() {
110 Some((m, c, &args[1]))
114 } else if let Some(c) = constant_simple(cx, cx.tables, &args[1]) {
115 Some((m, c, &args[0]))