97 lines
3.0 KiB
Rust
97 lines
3.0 KiB
Rust
use consts::{constant_simple, Constant};
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use rustc::lint::*;
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use rustc::hir::*;
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use std::cmp::{Ordering, PartialOrd};
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use utils::{match_def_path, opt_def_id, paths, span_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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/// ```rust
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/// min(0, max(100, x))
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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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declare_lint! {
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pub MIN_MAX,
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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<'a, 'tcx> LateLintPass<'a, 'tcx> for MinMaxPass {
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fn check_expr(&mut self, cx: &LateContext<'a, '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, _)) = 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) | (MinMax::Max, Some(Ordering::Less)) | (MinMax::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(ref qpath) = path.node {
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opt_def_id(cx.tables.qpath_def(qpath, path.hir_id)).and_then(|def_id| {
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if match_def_path(cx.tcx, 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.tcx, 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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} else {
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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], m: MinMax) -> Option<(MinMax, Constant, &'a 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(cx, &args[0]) {
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if constant_simple(cx, &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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} else if let Some(c) = constant_simple(cx, &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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