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|
use clippy_utils::consts::{constant_simple, Constant};
use clippy_utils::diagnostics::span_lint;
use clippy_utils::is_trait_method;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
use std::cmp::Ordering;
declare_clippy_lint! {
/// ### What it does
/// Checks for expressions where `std::cmp::min` and `max` are
/// used to clamp values, but switched so that the result is constant.
///
/// ### Why is this bad?
/// This is in all probability not the intended outcome. At
/// the least it hurts readability of the code.
///
/// ### Example
/// ```rust,ignore
/// min(0, max(100, x))
///
/// // or
///
/// x.max(100).min(0)
/// ```
/// It will always be equal to `0`. Probably the author meant to clamp the value
/// between 0 and 100, but has erroneously swapped `min` and `max`.
#[clippy::version = "pre 1.29.0"]
pub MIN_MAX,
correctness,
"`min(_, max(_, _))` (or vice versa) with bounds clamping the result to a constant"
}
declare_lint_pass!(MinMaxPass => [MIN_MAX]);
impl<'tcx> LateLintPass<'tcx> for MinMaxPass {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if let Some((outer_max, outer_c, oe)) = min_max(cx, expr) {
if let Some((inner_max, inner_c, ie)) = min_max(cx, oe) {
if outer_max == inner_max {
return;
}
match (
outer_max,
Constant::partial_cmp(cx.tcx, cx.typeck_results().expr_ty(ie), &outer_c, &inner_c),
) {
(_, None) | (MinMax::Max, Some(Ordering::Less)) | (MinMax::Min, Some(Ordering::Greater)) => (),
_ => {
span_lint(
cx,
MIN_MAX,
expr.span,
"this `min`/`max` combination leads to constant result",
);
},
}
}
}
}
}
#[derive(PartialEq, Eq, Debug, Clone, Copy)]
enum MinMax {
Min,
Max,
}
fn min_max<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
match expr.kind {
ExprKind::Call(path, args) => {
if let ExprKind::Path(ref qpath) = path.kind {
cx.typeck_results()
.qpath_res(qpath, path.hir_id)
.opt_def_id()
.and_then(|def_id| match cx.tcx.get_diagnostic_name(def_id) {
Some(sym::cmp_min) => fetch_const(cx, None, args, MinMax::Min),
Some(sym::cmp_max) => fetch_const(cx, None, args, MinMax::Max),
_ => None,
})
} else {
None
}
},
ExprKind::MethodCall(path, receiver, args @ [_], _) => {
if cx.typeck_results().expr_ty(receiver).is_floating_point() || is_trait_method(cx, expr, sym::Ord) {
if path.ident.name == sym!(max) {
fetch_const(cx, Some(receiver), args, MinMax::Max)
} else if path.ident.name == sym!(min) {
fetch_const(cx, Some(receiver), args, MinMax::Min)
} else {
None
}
} else {
None
}
},
_ => None,
}
}
fn fetch_const<'a>(
cx: &LateContext<'_>,
receiver: Option<&'a Expr<'a>>,
args: &'a [Expr<'a>],
m: MinMax,
) -> Option<(MinMax, Constant, &'a Expr<'a>)> {
let mut args = receiver.into_iter().chain(args);
let first_arg = args.next()?;
let second_arg = args.next()?;
if args.next().is_some() {
return None;
}
constant_simple(cx, cx.typeck_results(), first_arg).map_or_else(
|| constant_simple(cx, cx.typeck_results(), second_arg).map(|c| (m, c, first_arg)),
|c| {
if constant_simple(cx, cx.typeck_results(), second_arg).is_none() {
// otherwise ignore
Some((m, c, second_arg))
} else {
None
}
},
)
}
|
