124 lines
4.3 KiB
Rust
124 lines
4.3 KiB
Rust
use crate::consts::{constant_simple, Constant};
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use crate::utils::{match_def_path, match_trait_method, paths, span_lint};
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use if_chain::if_chain;
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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, declare_tool_lint};
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use std::cmp::Ordering;
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declare_clippy_lint! {
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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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/// ```ignore
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/// min(0, max(100, x))
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/// ```
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/// or
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/// ```ignore
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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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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>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
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match expr.kind {
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ExprKind::Call(ref path, ref 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| {
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if match_def_path(cx, def_id, &paths::CMP_MIN) {
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fetch_const(cx, args, MinMax::Min)
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} else if match_def_path(cx, def_id, &paths::CMP_MAX) {
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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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} else {
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None
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}
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},
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ExprKind::MethodCall(ref path, _, ref args, _) => {
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if_chain! {
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if let [obj, _] = args;
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if cx.typeck_results().expr_ty(obj).is_floating_point() || match_trait_method(cx, expr, &paths::ORD);
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then {
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if path.ident.as_str() == sym!(max).as_str() {
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fetch_const(cx, args, MinMax::Max)
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} else if path.ident.as_str() == sym!(min).as_str() {
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fetch_const(cx, 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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},
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_ => None,
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}
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}
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fn fetch_const<'a>(cx: &LateContext<'_>, args: &'a [Expr<'a>], m: MinMax) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
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if args.len() != 2 {
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return None;
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}
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constant_simple(cx, cx.typeck_results(), &args[0]).map_or_else(
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|| constant_simple(cx, cx.typeck_results(), &args[1]).map(|c| (m, c, &args[0])),
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|c| {
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if constant_simple(cx, cx.typeck_results(), &args[1]).is_none() {
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// otherwise ignore
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Some((m, c, &args[1]))
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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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