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::attr::*;
   5 use syntax::ast::*;
   6
   7 use utils::span_help_and_lint;
   8
   9 /// **What it does:** Warns on the use of `!` or `!=` in an if condition with an else branch
  10 ///
  11 /// **Why is this bad?** Negations reduce the readability of statements
  12 ///
  13 /// **Known problems:** None
  14 ///
  15 /// **Example:** if !v.is_empty() { a() } else { b() }
  16 declare_lint! {
  17     pub IF_NOT_ELSE, Allow,
  18     "finds if branches that could be swapped so no negation operation is necessary on the condition"
  19 }
  20
  21 pub struct IfNotElse;
  22
  23 impl LintPass for IfNotElse {
  24     fn get_lints(&self) -> LintArray {
  25         lint_array!(IF_NOT_ELSE)
  26     }
  27 }
  28
  29 impl EarlyLintPass for IfNotElse {
  30     fn check_expr(&mut self, cx: &EarlyContext, item: &Expr) {
  31         if let ExprKind::If(ref cond, _, Some(ref els)) = item.node {
  32             if let ExprKind::Block(..) = els.node {
  33                 match cond.node {
  34                     ExprKind::Unary(UnOp::Not, _) => {
  35                         span_help_and_lint(cx,
  36                                            IF_NOT_ELSE,
  37                                            item.span,
  38                                            "Unnecessary boolean `not` operation",
  39                                            "remove the `!` and swap the blocks of the if/else");
  40                     }
  41                     ExprKind::Binary(ref kind, _, _) if kind.node == BinOpKind::Ne => {
  42                         span_help_and_lint(cx,
  43                                            IF_NOT_ELSE,
  44                                            item.span,
  45                                            "Unnecessary `!=` operation",
  46                                            "change to `==` and swap the blocks of the if/else");
  47                     }
  48                     _ => (),
  49                 }
  50             }
  51         }
  52     }
  53 }