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::rustc_errors::Applicability;
  17 use crate::syntax::source_map::Span;
  18
  19 use crate::utils::{snippet_with_applicability, span_lint_and_sugg, SpanlessEq};
  20
  21 /// **What it does:** Checks for double comparions that could be simpified to a single expression.
  22 ///
  23 ///
  24 /// **Why is this bad?** Readability.
  25 ///
  26 /// **Known problems:** None.
  27 ///
  28 /// **Example:**
  29 /// ```rust
  30 /// x == y || x < y
  31 /// ```
  32 ///
  33 /// Could be written as:
  34 ///
  35 /// ```rust
  36 /// x <= y
  37 /// ```
  38 declare_clippy_lint! {
  39     pub DOUBLE_COMPARISONS,
  40     complexity,
  41     "unnecessary double comparisons that can be simplified"
  42 }
  43
  44 pub struct Pass;
  45
  46 impl LintPass for Pass {
  47     fn get_lints(&self) -> LintArray {
  48         lint_array!(DOUBLE_COMPARISONS)
  49     }
  50 }
  51
  52 impl<'a, 'tcx> Pass {
  53     #[allow(clippy::similar_names)]
  54     fn check_binop(
  55         &self,
  56         cx: &LateContext<'a, 'tcx>,
  57         op: BinOpKind,
  58         lhs: &'tcx Expr,
  59         rhs: &'tcx Expr,
  60         span: Span,
  61     ) {
  62         let (lkind, llhs, lrhs, rkind, rlhs, rrhs) = match (lhs.node.clone(), rhs.node.clone()) {
  63             (ExprKind::Binary(lb, llhs, lrhs), ExprKind::Binary(rb, rlhs, rrhs)) => {
  64                 (lb.node, llhs, lrhs, rb.node, rlhs, rrhs)
  65             }
  66             _ => return,
  67         };
  68         let mut spanless_eq = SpanlessEq::new(cx).ignore_fn();
  69         if !(spanless_eq.eq_expr(&llhs, &rlhs) && spanless_eq.eq_expr(&lrhs, &rrhs)) {
  70             return;
  71         }
  72         macro_rules! lint_double_comparison {
  73             ($op:tt) => {{
  74                 let mut applicability = Applicability::MachineApplicable;
  75                 let lhs_str = snippet_with_applicability(cx, llhs.span, "", &mut applicability);
  76                 let rhs_str = snippet_with_applicability(cx, lrhs.span, "", &mut applicability);
  77                 let sugg = format!("{} {} {}", lhs_str, stringify!($op), rhs_str);
  78                 span_lint_and_sugg(
  79                     cx,
  80                     DOUBLE_COMPARISONS,
  81                     span,
  82                     "This binary expression can be simplified",
  83                     "try",
  84                     sugg,
  85                     applicability,
  86                 );
  87             }}
  88         }
  89         match (op, lkind, rkind) {
  90             (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Lt) | (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Eq) => lint_double_comparison!(<=),
  91             (BinOpKind::Or, BinOpKind::Eq, BinOpKind::Gt) | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Eq) => lint_double_comparison!(>=),
  92             (BinOpKind::Or, BinOpKind::Lt, BinOpKind::Gt) | (BinOpKind::Or, BinOpKind::Gt, BinOpKind::Lt) => lint_double_comparison!(!=),
  93             (BinOpKind::And, BinOpKind::Le, BinOpKind::Ge) | (BinOpKind::And, BinOpKind::Ge, BinOpKind::Le) => lint_double_comparison!(==),
  94             _ => (),
  95         };
  96     }
  97 }
  98
  99 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
 100     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
 101         if let ExprKind::Binary(ref kind, ref lhs, ref rhs) = expr.node {
 102             self.check_binop(cx, kind.node, lhs, rhs, expr.span);
 103         }
 104     }
 105 }