clippy_lints/src/double_comparison.rs

   1 //! Lint on unnecessary double comparisons. Some examples:
   2
   3 use rustc_errors::Applicability;
   4 use rustc_hir::{BinOpKind, Expr, ExprKind};
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7 use rustc_span::source_map::Span;
   8
   9 use crate::utils::{snippet_with_applicability, span_lint_and_sugg, SpanlessEq};
  10
  11 declare_clippy_lint! {
  12     /// **What it does:** Checks for double comparisons that could be simplified to a single expression.
  13     ///
  14     ///
  15     /// **Why is this bad?** Readability.
  16     ///
  17     /// **Known problems:** None.
  18     ///
  19     /// **Example:**
  20     /// ```rust
  21     /// # let x = 1;
  22     /// # let y = 2;
  23     /// if x == y || x < y {}
  24     /// ```
  25     ///
  26     /// Could be written as:
  27     ///
  28     /// ```rust
  29     /// # let x = 1;
  30     /// # let y = 2;
  31     /// if x <= y {}
  32     /// ```
  33     pub DOUBLE_COMPARISONS,
  34     complexity,
  35     "unnecessary double comparisons that can be simplified"
  36 }
  37
  38 declare_lint_pass!(DoubleComparisons => [DOUBLE_COMPARISONS]);
  39
  40 impl<'tcx> DoubleComparisons {
  41     #[allow(clippy::similar_names)]
  42     fn check_binop(cx: &LateContext<'tcx>, op: BinOpKind, lhs: &'tcx Expr<'_>, rhs: &'tcx Expr<'_>, span: Span) {
  43         let (lkind, llhs, lrhs, rkind, rlhs, rrhs) = match (&lhs.kind, &rhs.kind) {
  44             (ExprKind::Binary(lb, llhs, lrhs), ExprKind::Binary(rb, rlhs, rrhs)) => {
  45                 (lb.node, llhs, lrhs, rb.node, rlhs, rrhs)
  46             },
  47             _ => return,
  48         };
  49         let mut spanless_eq = SpanlessEq::new(cx).ignore_fn();
  50         if !(spanless_eq.eq_expr(&llhs, &rlhs) && spanless_eq.eq_expr(&lrhs, &rrhs)) {
  51             return;
  52         }
  53         macro_rules! lint_double_comparison {
  54             ($op:tt) => {{
  55                 let mut applicability = Applicability::MachineApplicable;
  56                 let lhs_str = snippet_with_applicability(cx, llhs.span, "", &mut applicability);
  57                 let rhs_str = snippet_with_applicability(cx, lrhs.span, "", &mut applicability);
  58                 let sugg = format!("{} {} {}", lhs_str, stringify!($op), rhs_str);
  59                 span_lint_and_sugg(
  60                     cx,
  61                     DOUBLE_COMPARISONS,
  62                     span,
  63                     "this binary expression can be simplified",
  64                     "try",
  65                     sugg,
  66                     applicability,
  67                 );
  68             }};
  69         }
  70         #[rustfmt::skip]
  71         match (op, lkind, rkind) {
  72             (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Lt) | (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Eq) => {
  73                 lint_double_comparison!(<=)
  74             },
  75             (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Gt) | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Eq) => {
  76                 lint_double_comparison!(>=)
  77             },
  78             (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Gt) | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Lt) => {
  79                 lint_double_comparison!(!=)
  80             },
  81             (BinOpKind::And, BinOpKind::Le, BinOpKind::Ge) | (BinOpKind::And, BinOpKind::Ge, BinOpKind::Le) => {
  82                 lint_double_comparison!(==)
  83             },
  84             _ => (),
  85         };
  86     }
  87 }
  88
  89 impl<'tcx> LateLintPass<'tcx> for DoubleComparisons {
  90     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  91         if let ExprKind::Binary(ref kind, ref lhs, ref rhs) = expr.kind {
  92             Self::check_binop(cx, kind.node, lhs, rhs, expr.span);
  93         }
  94     }
  95 }