| use crate::consts::{constant_simple, Constant}; |
| use crate::utils::{match_def_path, paths, span_lint}; |
| use rustc_hir::{Expr, ExprKind}; |
| use rustc_lint::{LateContext, LateLintPass}; |
| use rustc_session::{declare_lint_pass, declare_tool_lint}; |
| use std::cmp::Ordering; |
| |
| declare_clippy_lint! { |
| /// **What it does:** Checks for expressions where `std::cmp::min` and `max` are |
| /// used to clamp values, but switched so that the result is constant. |
| /// |
| /// **Why is this bad?** This is in all probability not the intended outcome. At |
| /// the least it hurts readability of the code. |
| /// |
| /// **Known problems:** None |
| /// |
| /// **Example:** |
| /// ```ignore |
| /// min(0, max(100, x)) |
| /// ``` |
| /// It 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`. |
| pub MIN_MAX, |
| correctness, |
| "`min(_, max(_, _))` (or vice versa) with bounds clamping the result to a constant" |
| } |
| |
| declare_lint_pass!(MinMaxPass => [MIN_MAX]); |
| |
| impl<'tcx> LateLintPass<'tcx> for MinMaxPass { |
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { |
| if let Some((outer_max, outer_c, oe)) = min_max(cx, expr) { |
| if let Some((inner_max, inner_c, ie)) = min_max(cx, oe) { |
| if outer_max == inner_max { |
| return; |
| } |
| match ( |
| outer_max, |
| Constant::partial_cmp(cx.tcx, cx.tables().expr_ty(ie), &outer_c, &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<'a>) -> Option<(MinMax, Constant, &'a Expr<'a>)> { |
| if let ExprKind::Call(ref path, ref args) = expr.kind { |
| if let ExprKind::Path(ref qpath) = path.kind { |
| cx.tables() |
| .qpath_res(qpath, path.hir_id) |
| .opt_def_id() |
| .and_then(|def_id| { |
| if match_def_path(cx, def_id, &paths::CMP_MIN) { |
| fetch_const(cx, args, MinMax::Min) |
| } else if match_def_path(cx, 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<'a>], m: MinMax) -> Option<(MinMax, Constant, &'a Expr<'a>)> { |
| if args.len() != 2 { |
| return None; |
| } |
| if let Some(c) = constant_simple(cx, cx.tables(), &args[0]) { |
| if constant_simple(cx, cx.tables(), &args[1]).is_none() { |
| // otherwise ignore |
| Some((m, c, &args[1])) |
| } else { |
| None |
| } |
| } else if let Some(c) = constant_simple(cx, cx.tables(), &args[1]) { |
| Some((m, c, &args[0])) |
| } else { |
| None |
| } |
| } |