clippy_lints/src/double_comparison.rs

   1 //! Lint on unnecessary double comparisons. Some examples:
   2
   3 use rustc::hir::*;
   4 use rustc::lint::*;
   5 use syntax::codemap::Span;
   6
   7 use crate::utils::{snippet, span_lint_and_sugg, SpanlessEq};
   8
   9 /// **What it does:** Checks for double comparions that could be simpified to a single expression.
  10 ///
  11 ///
  12 /// **Why is this bad?** Readability.
  13 ///
  14 /// **Known problems:** None.
  15 ///
  16 /// **Example:**
  17 /// ```rust
  18 /// x == y || x < y
  19 /// ```
  20 ///
  21 /// Could be written as:
  22 ///
  23 /// ```rust
  24 /// x <= y
  25 /// ```
  26 declare_clippy_lint! {
  27     pub DOUBLE_COMPARISONS,
  28     complexity,
  29     "unnecessary double comparisons that can be simplified"
  30 }
  31
  32 pub struct DoubleComparisonPass;
  33
  34 impl LintPass for DoubleComparisonPass {
  35     fn get_lints(&self) -> LintArray {
  36         lint_array!(DOUBLE_COMPARISONS)
  37     }
  38 }
  39
  40 impl<'a, 'tcx> DoubleComparisonPass {
  41     fn check_binop(
  42         &self,
  43         cx: &LateContext<'a, 'tcx>,
  44         op: BinOp_,
  45         lhs: &'tcx Expr,
  46         rhs: &'tcx Expr,
  47         span: Span,
  48     ) {
  49         let (lkind, llhs, lrhs, rkind, rlhs, rrhs) = match (lhs.node.clone(), rhs.node.clone()) {
  50             (ExprBinary(lb, llhs, lrhs), ExprBinary(rb, rlhs, rrhs)) => {
  51                 (lb.node, llhs, lrhs, rb.node, rlhs, rrhs)
  52             }
  53             _ => return,
  54         };
  55         let mut spanless_eq = SpanlessEq::new(cx).ignore_fn();
  56         if !(spanless_eq.eq_expr(&llhs, &rlhs) && spanless_eq.eq_expr(&lrhs, &rrhs)) {
  57             return;
  58         }
  59         macro_rules! lint_double_comparison {
  60             ($op:tt) => {{
  61                 let lhs_str = snippet(cx, llhs.span, "");
  62                 let rhs_str = snippet(cx, lrhs.span, "");
  63                 let sugg = format!("{} {} {}", lhs_str, stringify!($op), rhs_str);
  64                 span_lint_and_sugg(cx, DOUBLE_COMPARISONS, span,
  65                                    "This binary expression can be simplified",
  66                                    "try", sugg);
  67             }}
  68         }
  69         match (op, lkind, rkind) {
  70             (BiOr, BiEq, BiLt) | (BiOr, BiLt, BiEq) => lint_double_comparison!(<=),
  71             (BiOr, BiEq, BiGt) | (BiOr, BiGt, BiEq) => lint_double_comparison!(>=),
  72             (BiOr, BiLt, BiGt) | (BiOr, BiGt, BiLt) => lint_double_comparison!(!=),
  73             (BiAnd, BiLe, BiGe) | (BiAnd, BiGe, BiLe) => lint_double_comparison!(==),
  74             _ => (),
  75         };
  76     }
  77 }
  78
  79 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DoubleComparisonPass {
  80     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  81         if let ExprBinary(ref kind, ref lhs, ref rhs) = expr.node {
  82             self.check_binop(cx, kind.node, lhs, rhs, expr.span);
  83         }
  84     }
  85 }