2018-05-30 03:15:50 -05:00
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use crate::consts::{constant_simple, Constant};
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2019-05-14 03:06:21 -05:00
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use crate::utils::{match_def_path, paths, span_lint};
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2020-01-06 10:39:50 -06:00
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use rustc_hir::*;
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2020-01-12 00:08:41 -06:00
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use rustc_lint::{LateContext, LateLintPass};
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2020-01-11 05:37:08 -06:00
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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2018-06-19 00:37:09 -05:00
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use std::cmp::Ordering;
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2015-09-05 05:46:34 -05:00
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2018-03-28 08:24:26 -05:00
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declare_clippy_lint! {
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2019-03-05 10:50:33 -06:00
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/// **What it does:** Checks for expressions where `std::cmp::min` and `max` are
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/// used to clamp values, but switched so that the result is constant.
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///
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/// **Why is this bad?** This is in all probability not the intended outcome. At
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/// the least it hurts readability of the code.
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///
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/// **Known problems:** None
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///
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/// **Example:**
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2019-03-05 16:23:50 -06:00
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/// ```ignore
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2019-03-05 10:50:33 -06:00
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/// min(0, max(100, x))
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/// ```
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/// It will always be equal to `0`. Probably the author meant to clamp the value
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/// between 0 and 100, but has erroneously swapped `min` and `max`.
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2016-08-06 03:18:36 -05:00
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pub MIN_MAX,
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2018-03-28 08:24:26 -05:00
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correctness,
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2016-02-05 17:13:29 -06:00
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"`min(_, max(_, _))` (or vice versa) with bounds clamping the result to a constant"
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}
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2015-09-05 05:46:34 -05:00
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2019-04-08 15:43:55 -05:00
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declare_lint_pass!(MinMaxPass => [MIN_MAX]);
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2015-09-05 05:46:34 -05:00
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2016-12-07 06:13:40 -06:00
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MinMaxPass {
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2019-12-27 01:12:26 -06:00
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
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2015-11-11 10:08:33 -06:00
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if let Some((outer_max, outer_c, oe)) = min_max(cx, expr) {
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2018-06-16 11:33:11 -05:00
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if let Some((inner_max, inner_c, ie)) = min_max(cx, oe) {
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2016-01-03 22:26:12 -06:00
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if outer_max == inner_max {
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return;
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}
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2018-06-16 11:33:11 -05:00
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match (
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outer_max,
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2018-12-04 17:14:44 -06:00
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Constant::partial_cmp(cx.tcx, cx.tables.expr_ty(ie), &outer_c, &inner_c),
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2018-06-16 11:33:11 -05:00
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) {
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2017-09-05 04:33:04 -05:00
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(_, None) | (MinMax::Max, Some(Ordering::Less)) | (MinMax::Min, Some(Ordering::Greater)) => (),
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2015-09-05 05:46:34 -05:00
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_ => {
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2018-06-16 11:33:11 -05:00
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span_lint(
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cx,
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MIN_MAX,
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expr.span,
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2020-01-06 00:30:43 -06:00
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"this `min`/`max` combination leads to constant result",
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2018-06-16 11:33:11 -05:00
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);
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2016-12-20 11:21:30 -06:00
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},
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2015-09-05 05:46:34 -05:00
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}
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}
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}
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}
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}
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#[derive(PartialEq, Eq, Debug)]
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enum MinMax {
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Min,
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Max,
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}
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2019-12-27 01:12:26 -06:00
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fn min_max<'a>(cx: &LateContext<'_, '_>, expr: &'a Expr<'a>) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
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2019-09-27 10:16:06 -05:00
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if let ExprKind::Call(ref path, ref args) = expr.kind {
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if let ExprKind::Path(ref qpath) = path.kind {
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2019-05-03 19:03:12 -05:00
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cx.tables.qpath_res(qpath, path.hir_id).opt_def_id().and_then(|def_id| {
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2019-05-17 16:53:54 -05:00
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if match_def_path(cx, def_id, &paths::CMP_MIN) {
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2017-09-12 07:26:40 -05:00
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fetch_const(cx, args, MinMax::Min)
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2019-05-17 16:53:54 -05:00
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} else if match_def_path(cx, def_id, &paths::CMP_MAX) {
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2017-09-12 07:26:40 -05:00
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fetch_const(cx, args, MinMax::Max)
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} else {
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None
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}
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})
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2016-01-03 22:26:12 -06:00
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} else {
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None
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}
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} else {
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None
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}
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}
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2015-09-05 05:46:34 -05:00
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2019-12-27 01:12:26 -06:00
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fn fetch_const<'a>(
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cx: &LateContext<'_, '_>,
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args: &'a [Expr<'a>],
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m: MinMax,
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) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
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2016-01-03 22:26:12 -06:00
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if args.len() != 2 {
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return None;
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}
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2018-05-13 06:16:31 -05:00
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if let Some(c) = constant_simple(cx, cx.tables, &args[0]) {
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if constant_simple(cx, cx.tables, &args[1]).is_none() {
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2016-01-03 22:26:12 -06:00
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// otherwise ignore
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2015-09-05 05:46:34 -05:00
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Some((m, c, &args[1]))
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2016-01-03 22:26:12 -06:00
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} else {
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None
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}
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2018-05-13 06:16:31 -05:00
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} else if let Some(c) = constant_simple(cx, cx.tables, &args[1]) {
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2016-06-21 16:53:24 -05:00
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Some((m, c, &args[0]))
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2015-09-05 05:46:34 -05:00
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} else {
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2016-06-21 16:53:24 -05:00
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None
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2015-09-05 05:46:34 -05:00
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}
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}
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