clippy_lints/src/double_comparison.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10
  11 //! Lint on unnecessary double comparisons. Some examples:
  12
  13 use crate::rustc::hir::*;
  14 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  15 use crate::rustc::{declare_tool_lint, lint_array};
  16 use crate::syntax::source_map::Span;
  17
  18 use crate::utils::{snippet, span_lint_and_sugg, SpanlessEq};
  19
  20 /// **What it does:** Checks for double comparions that could be simpified to a single expression.
  21 ///
  22 ///
  23 /// **Why is this bad?** Readability.
  24 ///
  25 /// **Known problems:** None.
  26 ///
  27 /// **Example:**
  28 /// ```rust
  29 /// x == y || x < y
  30 /// ```
  31 ///
  32 /// Could be written as:
  33 ///
  34 /// ```rust
  35 /// x <= y
  36 /// ```
  37 declare_clippy_lint! {
  38     pub DOUBLE_COMPARISONS,
  39     complexity,
  40     "unnecessary double comparisons that can be simplified"
  41 }
  42
  43 pub struct DoubleComparisonPass;
  44
  45 impl LintPass for DoubleComparisonPass {
  46     fn get_lints(&self) -> LintArray {
  47         lint_array!(DOUBLE_COMPARISONS)
  48     }
  49 }
  50
  51 impl<'a, 'tcx> DoubleComparisonPass {
  52     fn check_binop(
  53         &self,
  54         cx: &LateContext<'a, 'tcx>,
  55         op: BinOpKind,
  56         lhs: &'tcx Expr,
  57         rhs: &'tcx Expr,
  58         span: Span,
  59     ) {
  60         let (lkind, llhs, lrhs, rkind, rlhs, rrhs) = match (lhs.node.clone(), rhs.node.clone()) {
  61             (ExprKind::Binary(lb, llhs, lrhs), ExprKind::Binary(rb, rlhs, rrhs)) => {
  62                 (lb.node, llhs, lrhs, rb.node, rlhs, rrhs)
  63             }
  64             _ => return,
  65         };
  66         let mut spanless_eq = SpanlessEq::new(cx).ignore_fn();
  67         if !(spanless_eq.eq_expr(&llhs, &rlhs) && spanless_eq.eq_expr(&lrhs, &rrhs)) {
  68             return;
  69         }
  70         macro_rules! lint_double_comparison {
  71             ($op:tt) => {{
  72                 let lhs_str = snippet(cx, llhs.span, "");
  73                 let rhs_str = snippet(cx, lrhs.span, "");
  74                 let sugg = format!("{} {} {}", lhs_str, stringify!($op), rhs_str);
  75                 span_lint_and_sugg(cx, DOUBLE_COMPARISONS, span,
  76                                    "This binary expression can be simplified",
  77                                    "try", sugg);
  78             }}
  79         }
  80         match (op, lkind, rkind) {
  81             (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Lt) | (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Eq) => lint_double_comparison!(<=),
  82             (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Gt) | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Eq) => lint_double_comparison!(>=),
  83             (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Gt) | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Lt) => lint_double_comparison!(!=),
  84             (BinOpKind::And, BinOpKind::Le, BinOpKind::Ge) | (BinOpKind::And, BinOpKind::Ge, BinOpKind::Le) => lint_double_comparison!(==),
  85             _ => (),
  86         };
  87     }
  88 }
  89
  90 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DoubleComparisonPass {
  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.node {
  93             self.check_binop(cx, kind.node, lhs, rhs, expr.span);
  94         }
  95     }
  96 }