126 lines
4.2 KiB
Rust
126 lines
4.2 KiB
Rust
use clippy_utils::consts::{constant_simple, Constant};
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use clippy_utils::diagnostics::span_lint;
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use clippy_utils::is_trait_method;
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use rustc_hir::{Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::declare_lint_pass;
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use rustc_span::sym;
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use std::cmp::Ordering;
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declare_clippy_lint! {
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/// ### What it does
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/// 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?
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/// 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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/// ### Example
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/// ```rust,ignore
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/// min(0, max(100, x))
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///
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/// // or
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///
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/// x.max(100).min(0)
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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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#[clippy::version = "pre 1.29.0"]
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pub MIN_MAX,
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correctness,
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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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declare_lint_pass!(MinMaxPass => [MIN_MAX]);
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impl<'tcx> LateLintPass<'tcx> for MinMaxPass {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if let Some((outer_max, outer_c, oe)) = min_max(cx, expr) {
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if let Some((inner_max, inner_c, ie)) = min_max(cx, oe) {
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if outer_max == inner_max {
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return;
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}
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match (
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outer_max,
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Constant::partial_cmp(cx.tcx, cx.typeck_results().expr_ty(ie), &outer_c, &inner_c),
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) {
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(_, None) | (MinMax::Max, Some(Ordering::Less)) | (MinMax::Min, Some(Ordering::Greater)) => (),
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_ => {
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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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"this `min`/`max` combination leads to constant result",
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);
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},
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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, Clone, Copy)]
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enum MinMax {
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Min,
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Max,
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}
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fn min_max<'a, 'tcx>(cx: &LateContext<'tcx>, expr: &'a Expr<'a>) -> Option<(MinMax, Constant<'tcx>, &'a Expr<'a>)> {
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match expr.kind {
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ExprKind::Call(path, args) => {
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if let ExprKind::Path(ref qpath) = path.kind {
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cx.typeck_results()
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.qpath_res(qpath, path.hir_id)
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.opt_def_id()
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.and_then(|def_id| match cx.tcx.get_diagnostic_name(def_id) {
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Some(sym::cmp_min) => fetch_const(cx, None, args, MinMax::Min),
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Some(sym::cmp_max) => fetch_const(cx, None, args, MinMax::Max),
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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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ExprKind::MethodCall(path, receiver, args @ [_], _) => {
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if cx.typeck_results().expr_ty(receiver).is_floating_point() || is_trait_method(cx, expr, sym::Ord) {
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if path.ident.name == sym!(max) {
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fetch_const(cx, Some(receiver), args, MinMax::Max)
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} else if path.ident.name == sym!(min) {
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fetch_const(cx, Some(receiver), args, MinMax::Min)
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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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_ => None,
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}
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}
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fn fetch_const<'a, 'tcx>(
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cx: &LateContext<'tcx>,
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receiver: Option<&'a Expr<'a>>,
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args: &'a [Expr<'a>],
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m: MinMax,
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) -> Option<(MinMax, Constant<'tcx>, &'a Expr<'a>)> {
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let mut args = receiver.into_iter().chain(args);
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let first_arg = args.next()?;
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let second_arg = args.next()?;
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if args.next().is_some() {
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return None;
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}
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constant_simple(cx, cx.typeck_results(), first_arg).map_or_else(
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|| constant_simple(cx, cx.typeck_results(), second_arg).map(|c| (m, c, first_arg)),
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|c| {
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if constant_simple(cx, cx.typeck_results(), second_arg).is_none() {
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// otherwise ignore
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Some((m, c, second_arg))
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} else {
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None
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}
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},
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)
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}
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