clippy_lints/src/double_comparison.rs

   1 //! Lint on unnecessary double comparisons. Some examples:
   2
   3 use clippy_utils::diagnostics::span_lint_and_sugg;
   4 use clippy_utils::eq_expr_value;
   5 use clippy_utils::source::snippet_with_applicability;
   6 use rustc_errors::Applicability;
   7 use rustc_hir::{BinOpKind, Expr, ExprKind};
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10 use rustc_span::source_map::Span;
  11
  12 declare_clippy_lint! {
  13     /// ### What it does
  14     /// Checks for double comparisons that could be simplified to a single expression.
  15     ///
  16     ///
  17     /// ### Why is this bad?
  18     /// Readability.
  19     ///
  20     /// ### Example
  21     /// ```rust
  22     /// # let x = 1;
  23     /// # let y = 2;
  24     /// if x == y || x < y {}
  25     /// ```
  26     ///
  27     /// Could be written as:
  28     ///
  29     /// ```rust
  30     /// # let x = 1;
  31     /// # let y = 2;
  32     /// if x <= y {}
  33     /// ```
  34     #[clippy::version = "pre 1.29.0"]
  35     pub DOUBLE_COMPARISONS,
  36     complexity,
  37     "unnecessary double comparisons that can be simplified"
  38 }
  39
  40 declare_lint_pass!(DoubleComparisons => [DOUBLE_COMPARISONS]);
  41
  42 impl<'tcx> DoubleComparisons {
  43     #[expect(clippy::similar_names)]
  44     fn check_binop(cx: &LateContext<'tcx>, op: BinOpKind, lhs: &'tcx Expr<'_>, rhs: &'tcx Expr<'_>, span: Span) {
  45         let (lkind, llhs, lrhs, rkind, rlhs, rrhs) = match (&lhs.kind, &rhs.kind) {
  46             (ExprKind::Binary(lb, llhs, lrhs), ExprKind::Binary(rb, rlhs, rrhs)) => {
  47                 (lb.node, llhs, lrhs, rb.node, rlhs, rrhs)
  48             },
  49             _ => return,
  50         };
  51         if !(eq_expr_value(cx, llhs, rlhs) && eq_expr_value(cx, lrhs, rrhs)) {
  52             return;
  53         }
  54         macro_rules! lint_double_comparison {
  55             ($op:tt) => {{
  56                 let mut applicability = Applicability::MachineApplicable;
  57                 let lhs_str = snippet_with_applicability(cx, llhs.span, "", &mut applicability);
  58                 let rhs_str = snippet_with_applicability(cx, lrhs.span, "", &mut applicability);
  59                 let sugg = format!("{} {} {}", lhs_str, stringify!($op), rhs_str);
  60                 span_lint_and_sugg(
  61                     cx,
  62                     DOUBLE_COMPARISONS,
  63                     span,
  64                     "this binary expression can be simplified",
  65                     "try",
  66                     sugg,
  67                     applicability,
  68                 );
  69             }};
  70         }
  71         #[rustfmt::skip]
  72         match (op, lkind, rkind) {
  73             (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Lt) | (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Eq) => {
  74                 lint_double_comparison!(<=);
  75             },
  76             (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Gt) | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Eq) => {
  77                 lint_double_comparison!(>=);
  78             },
  79             (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Gt) | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Lt) => {
  80                 lint_double_comparison!(!=);
  81             },
  82             (BinOpKind::And, BinOpKind::Le, BinOpKind::Ge) | (BinOpKind::And, BinOpKind::Ge, BinOpKind::Le) => {
  83                 lint_double_comparison!(==);
  84             },
  85             _ => (),
  86         };
  87     }
  88 }
  89
  90 impl<'tcx> LateLintPass<'tcx> for DoubleComparisons {
  91     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  92         if let ExprKind::Binary(ref kind, lhs, rhs) = expr.kind {
  93             Self::check_binop(cx, kind.node, lhs, rhs, expr.span);
  94         }
  95     }
  96 }