94 lines
2.8 KiB
Rust
94 lines
2.8 KiB
Rust
use rustc::lint::*;
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use rustc_front::hir::*;
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use syntax::ptr::P;
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use std::cmp::{PartialOrd, Ordering};
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use consts::{Constant, constant_simple};
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use utils::{match_def_path, span_lint};
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use self::MinMax::{Min, Max};
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/// **What it does:** This lint checks for expressions where `std::cmp::min` and `max` are 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 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:** `min(0, max(100, x))` 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`.
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declare_lint! {
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pub MIN_MAX, Warn,
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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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#[allow(missing_copy_implementations)]
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pub struct MinMaxPass;
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impl LintPass for MinMaxPass {
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fn get_lints(&self) -> LintArray {
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lint_array!(MIN_MAX)
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}
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}
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impl LateLintPass for MinMaxPass {
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fn check_expr(&mut self, cx: &LateContext, expr: &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, _)) = 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 (outer_max, outer_c.partial_cmp(&inner_c)) {
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(_, None) | (Max, Some(Ordering::Less)) | (Min, Some(Ordering::Greater)) => (),
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_ => {
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span_lint(cx, MIN_MAX, expr.span, "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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#[derive(PartialEq, Eq, Debug)]
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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) -> Option<(MinMax, Constant, &'a Expr)> {
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if let ExprCall(ref path, ref args) = expr.node {
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if let ExprPath(None, _) = path.node {
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let def_id = cx.tcx.def_map.borrow()[&path.id].def_id();
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if match_def_path(cx, def_id, &["core", "cmp", "min"]) {
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fetch_const(args, Min)
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} else if match_def_path(cx, def_id, &["core", "cmp", "max"]) {
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fetch_const(args, Max)
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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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} else {
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None
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}
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}
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fn fetch_const(args: &[P<Expr>], m: MinMax) -> Option<(MinMax, Constant, &Expr)> {
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if args.len() != 2 {
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return None;
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}
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if let Some(c) = constant_simple(&args[0]) {
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if let None = constant_simple(&args[1]) {
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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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} else {
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if let Some(c) = constant_simple(&args[1]) {
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Some((m, c, &args[0]))
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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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