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::{eq_expr_value, snippet_with_applicability, span_lint_and_sugg};
  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         if !(eq_expr_value(cx, &llhs, &rlhs) && eq_expr_value(cx, &lrhs, &rrhs)) {
  50             return;
  51         }
  52         macro_rules! lint_double_comparison {
  53             ($op:tt) => {{
  54                 let mut applicability = Applicability::MachineApplicable;
  55                 let lhs_str = snippet_with_applicability(cx, llhs.span, "", &mut applicability);
  56                 let rhs_str = snippet_with_applicability(cx, lrhs.span, "", &mut applicability);
  57                 let sugg = format!("{} {} {}", lhs_str, stringify!($op), rhs_str);
  58                 span_lint_and_sugg(
  59                     cx,
  60                     DOUBLE_COMPARISONS,
  61                     span,
  62                     "this binary expression can be simplified",
  63                     "try",
  64                     sugg,
  65                     applicability,
  66                 );
  67             }};
  68         }
  69         #[rustfmt::skip]
  70         match (op, lkind, rkind) {
  71             (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Lt) | (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Eq) => {
  72                 lint_double_comparison!(<=)
  73             },
  74             (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Gt) | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Eq) => {
  75                 lint_double_comparison!(>=)
  76             },
  77             (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Gt) | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Lt) => {
  78                 lint_double_comparison!(!=)
  79             },
  80             (BinOpKind::And, BinOpKind::Le, BinOpKind::Ge) | (BinOpKind::And, BinOpKind::Ge, BinOpKind::Le) => {
  81                 lint_double_comparison!(==)
  82             },
  83             _ => (),
  84         };
  85     }
  86 }
  87
  88 impl<'tcx> LateLintPass<'tcx> for DoubleComparisons {
  89     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  90         if let ExprKind::Binary(ref kind, ref lhs, ref rhs) = expr.kind {
  91             Self::check_binop(cx, kind.node, lhs, rhs, expr.span);
  92         }
  93     }
  94 }