91 lines
2.7 KiB
Rust
91 lines
2.7 KiB
Rust
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use rustc::lint::{Context, LintPass, LintArray};
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use rustc_front::hir::*;
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use syntax::codemap::Spanned;
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use syntax::ptr::P;
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use std::cmp::PartialOrd;
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use std::cmp::Ordering::*;
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use consts::{Constant, constant};
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use utils::{match_path, span_lint};
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use self::MinMax::{Min, Max};
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declare_lint!(pub MIN_MAX, Deny,
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"`min(_, max(_, _))` (or vice versa) with bounds clamping the result \
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to a constant");
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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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fn check_expr(&mut self, cx: &Context, 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 { return; }
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match (outer_max, outer_c.partial_cmp(&inner_c)) {
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(_, None) | (Max, Some(Less)) | (Min, Some(Greater)) => (),
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_ => {
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span_lint(cx, MIN_MAX, expr.span,
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"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<'e>(cx: &Context, expr: &'e Expr) ->
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Option<(MinMax, Constant, &'e Expr)> {
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match expr.node {
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ExprMethodCall(Spanned{node: ref ident, ..}, _, ref args) => {
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let name = ident.name;
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if name == "min" {
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fetch_const(cx, args, Min)
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} else {
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if name == "max" {
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fetch_const(cx, args, Max)
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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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ExprCall(ref path, ref args) => {
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if let &ExprPath(None, ref path) = &path.node {
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if match_path(path, &["min"]) {
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fetch_const(cx, args, Min)
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} else {
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if match_path(path, &["max"]) {
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fetch_const(cx, args, Max)
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} else {
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None
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}
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}
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} else { None }
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},
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_ => None,
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}
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}
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fn fetch_const<'e>(cx: &Context, args: &'e Vec<P<Expr>>, m: MinMax) ->
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Option<(MinMax, Constant, &'e Expr)> {
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if args.len() != 2 { return None }
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if let Some((c, _)) = constant(cx, &args[0]) {
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if let None = constant(cx, &args[1]) { // otherwise ignore
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Some((m, c, &args[1]))
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} else { None }
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} else {
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if let Some((c, _)) = constant(cx, &args[1]) {
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Some((m, c, &args[0]))
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} else { None }
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}
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}
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