src/tools/clippy/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     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<'tcx> DoubleComparisons {
  42     #[allow(clippy::similar_names)]
  43     fn check_binop(cx: &LateContext<'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         if !(eq_expr_value(cx, llhs, rlhs) && eq_expr_value(cx, 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, lhs, rhs) = expr.kind {
  92             Self::check_binop(cx, kind.node, lhs, rhs, expr.span);
  93         }
  94     }
  95 }