clippy_lints/src/double_comparison.rs

   1 //! Lint on unnecessary double comparisons. Some examples:
   2
   3 use rustc::declare_lint_pass;
   4 use rustc::hir::*;
   5 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   6 use rustc_errors::Applicability;
   7 use rustc_session::declare_tool_lint;
   8 use syntax::source_map::Span;
   9
  10 use crate::utils::{snippet_with_applicability, span_lint_and_sugg, SpanlessEq};
  11
  12 declare_clippy_lint! {
  13     /// **What it does:** Checks for double comparisons that could be simplified to a single expression.
  14     ///
  15     ///
  16     /// **Why is this bad?** Readability.
  17     ///
  18     /// **Known problems:** None.
  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     pub DOUBLE_COMPARISONS,
  35     complexity,
  36     "unnecessary double comparisons that can be simplified"
  37 }
  38
  39 declare_lint_pass!(DoubleComparisons => [DOUBLE_COMPARISONS]);
  40
  41 impl<'a, 'tcx> DoubleComparisons {
  42     #[allow(clippy::similar_names)]
  43     fn check_binop(cx: &LateContext<'a, 'tcx>, op: BinOpKind, lhs: &'tcx Expr, rhs: &'tcx Expr, span: Span) {
  44         let (lkind, llhs, lrhs, rkind, rlhs, rrhs) = match (&lhs.kind, &rhs.kind) {
  45             (ExprKind::Binary(lb, llhs, lrhs), ExprKind::Binary(rb, rlhs, rrhs)) => {
  46                 (lb.node, llhs, lrhs, rb.node, rlhs, rrhs)
  47             },
  48             _ => return,
  49         };
  50         let mut spanless_eq = SpanlessEq::new(cx).ignore_fn();
  51         if !(spanless_eq.eq_expr(&llhs, &rlhs) && spanless_eq.eq_expr(&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<'a, 'tcx> LateLintPass<'a, 'tcx> for DoubleComparisons {
  91     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  92         if let ExprKind::Binary(ref kind, ref lhs, ref rhs) = expr.kind {
  93             Self::check_binop(cx, kind.node, lhs, rhs, expr.span);
  94         }
  95     }
  96 }