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use consts::{Constant, constant_simple};
use rustc::lint::*;
use rustc::hir::*;
use std::cmp::{PartialOrd, Ordering};
use utils::{match_def_path, paths, span_lint};
declare_lint! {
pub MIN_MAX,
Warn,
"`min(_, max(_, _))` (or vice versa) with bounds clamping the result to a constant"
}
#[allow(missing_copy_implementations)]
pub struct MinMaxPass;
impl LintPass for MinMaxPass {
fn get_lints(&self) -> LintArray {
lint_array!(MIN_MAX)
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MinMaxPass {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
if let Some((outer_max, outer_c, oe)) = min_max(cx, expr) {
if let Some((inner_max, inner_c, _)) = min_max(cx, oe) {
if outer_max == inner_max {
return;
}
match (outer_max, outer_c.partial_cmp(&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)]
enum MinMax {
Min,
Max,
}
fn min_max<'a>(cx: &LateContext, expr: &'a Expr) -> Option<(MinMax, Constant, &'a Expr)> {
if let ExprCall(ref path, ref args) = expr.node {
if let ExprPath(ref qpath) = path.node {
let def_id = cx.tables.qpath_def(qpath, path.id).def_id();
if match_def_path(cx.tcx, def_id, &paths::CMP_MIN) {
fetch_const(cx, args, MinMax::Min)
} else if match_def_path(cx.tcx, def_id, &paths::CMP_MAX) {
fetch_const(cx, args, MinMax::Max)
} else {
None
}
} else {
None
}
} else {
None
}
}
fn fetch_const<'a>(cx: &LateContext, args: &'a [Expr], m: MinMax) -> Option<(MinMax, Constant, &'a Expr)> {
if args.len() != 2 {
return None;
}
if let Some(c) = constant_simple(cx, &args[0]) {
if constant_simple(cx, &args[1]).is_none() {
Some((m, c, &args[1]))
} else {
None
}
} else if let Some(c) = constant_simple(cx, &args[1]) {
Some((m, c, &args[0]))
} else {
None
}
}