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//! lint on if branches that could be swapped so no `!` operation is necessary on the condition
use rustc::lint::*;
use syntax::attr::*;
use syntax::ast::*;
use utils::span_help_and_lint;
/// **What it does:** Warns on the use of `!` or `!=` in an if condition with an else branch
///
/// **Why is this bad?** Negations reduce the readability of statements
///
/// **Known problems:** None
///
/// **Example:** if !v.is_empty() { a() } else { b() }
declare_lint! {
pub IF_NOT_ELSE, Warn,
"finds if branches that could be swapped so no negation operation is necessary on the condition"
}
pub struct IfNotElse;
impl LintPass for IfNotElse {
fn get_lints(&self) -> LintArray {
lint_array!(IF_NOT_ELSE)
}
}
impl EarlyLintPass for IfNotElse {
fn check_expr(&mut self, cx: &EarlyContext, item: &Expr) {
if let ExprKind::If(ref cond, _, Some(ref els)) = item.node {
if let ExprKind::Block(..) = els.node {
match cond.node {
ExprKind::Unary(UnOp::Not, _) => {
span_help_and_lint(cx,
IF_NOT_ELSE,
item.span,
"Unnecessary boolean `not` operation",
"remove the `!` and swap the blocks of the if/else");
},
ExprKind::Binary(ref kind, _, _) if kind.node == BinOpKind::Ne => {
span_help_and_lint(cx,
IF_NOT_ELSE,
item.span,
"Unnecessary `!=` operation",
"change to `==` and swap the blocks of the if/else");
},
_ => {},
}
}
}
}
}