src/if_not_else.rs

   1 //! lint on if branches that could be swapped so no `!` operation is necessary on the condition
   2
   3 use rustc::lint::*;
   4 use syntax::ast::*;
   5
   6 use utils::span_help_and_lint;
   7
   8 /// **What it does:** Warns on the use of `!` or `!=` in an if condition with an else branch
   9 ///
  10 /// **Why is this bad?** Negations reduce the readability of statements
  11 ///
  12 /// **Known problems:** None
  13 ///
  14 /// **Example:** if !v.is_empty() { a() } else { b() }
  15 declare_lint! {
  16     pub IF_NOT_ELSE, Allow,
  17     "finds if branches that could be swapped so no negation operation is necessary on the condition"
  18 }
  19
  20 pub struct IfNotElse;
  21
  22 impl LintPass for IfNotElse {
  23     fn get_lints(&self) -> LintArray {
  24         lint_array!(IF_NOT_ELSE)
  25     }
  26 }
  27
  28 impl EarlyLintPass for IfNotElse {
  29     fn check_expr(&mut self, cx: &EarlyContext, item: &Expr) {
  30         if let ExprKind::If(ref cond, _, Some(ref els)) = item.node {
  31             if let ExprKind::Block(..) = els.node {
  32                 match cond.node {
  33                     ExprKind::Unary(UnOp::Not, _) => {
  34                         span_help_and_lint(cx,
  35                                            IF_NOT_ELSE,
  36                                            item.span,
  37                                            "Unnecessary boolean `not` operation",
  38                                            "remove the `!` and swap the blocks of the if/else");
  39                     }
  40                     ExprKind::Binary(ref kind, _, _) if kind.node == BinOpKind::Ne => {
  41                         span_help_and_lint(cx,
  42                                            IF_NOT_ELSE,
  43                                            item.span,
  44                                            "Unnecessary `!=` operation",
  45                                            "change to `==` and swap the blocks of the if/else");
  46                     }
  47                     _ => (),
  48                 }
  49             }
  50         }
  51     }
  52 }