use consts::{Constant, constant_simple};
use rustc::lint::*;
use rustc::hir::*;
use std::cmp::{PartialOrd, Ordering};
use syntax::ptr::P;
use utils::{match_def_path, 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 LateLintPass for MinMaxPass {
fn check_expr(&mut self, cx: &LateContext, expr: &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(None, _) = path.node {
let def_id = cx.tcx.def_map.borrow()[&path.id].def_id();
if match_def_path(cx, def_id, &["core", "cmp", "min"]) {
fetch_const(args, MinMax::Min)
} else if match_def_path(cx, def_id, &["core", "cmp", "max"]) {
fetch_const(args, MinMax::Max)
} else {
None
}
} else {
None
}
} else {
None
}
}
fn fetch_const(args: &[P<Expr>], m: MinMax) -> Option<(MinMax, Constant, &Expr)> {
if args.len() != 2 {
return None;
}
if let Some(c) = constant_simple(&args[0]) {
if let None = constant_simple(&args[1]) {
Some((m, c, &args[1]))
} else {
None
}
} else {
if let Some(c) = constant_simple(&args[1]) {
Some((m, c, &args[0]))
} else {
None
}
}
}