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//! lint on if branches that could be swapped so no `!` operation is necessary
//! on the condition
use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::is_else_clause;
use rustc_hir::{BinOpKind, Expr, ExprKind, UnOp};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// Checks for usage of `!` or `!=` in an if condition with an
/// else branch.
///
/// ### Why is this bad?
/// Negations reduce the readability of statements.
///
/// ### Example
/// ```rust
/// # let v: Vec<usize> = vec![];
/// # fn a() {}
/// # fn b() {}
/// if !v.is_empty() {
/// a()
/// } else {
/// b()
/// }
/// ```
///
/// Could be written:
///
/// ```rust
/// # let v: Vec<usize> = vec![];
/// # fn a() {}
/// # fn b() {}
/// if v.is_empty() {
/// b()
/// } else {
/// a()
/// }
/// ```
#[clippy::version = "pre 1.29.0"]
pub IF_NOT_ELSE,
pedantic,
"`if` branches that could be swapped so no negation operation is necessary on the condition"
}
declare_lint_pass!(IfNotElse => [IF_NOT_ELSE]);
impl LateLintPass<'_> for IfNotElse {
fn check_expr(&mut self, cx: &LateContext<'_>, item: &Expr<'_>) {
// While loops will be desugared to ExprKind::If. This will cause the lint to fire.
// To fix this, return early if this span comes from a macro or desugaring.
if item.span.from_expansion() {
return;
}
if let ExprKind::If(cond, _, Some(els)) = item.kind {
if let ExprKind::Block(..) = els.kind {
// Disable firing the lint in "else if" expressions.
if is_else_clause(cx.tcx, item) {
return;
}
match cond.peel_drop_temps().kind {
ExprKind::Unary(UnOp::Not, _) => {
span_lint_and_help(
cx,
IF_NOT_ELSE,
item.span,
"unnecessary boolean `not` operation",
None,
"remove the `!` and swap the blocks of the `if`/`else`",
);
},
ExprKind::Binary(ref kind, _, _) if kind.node == BinOpKind::Ne => {
span_lint_and_help(
cx,
IF_NOT_ELSE,
item.span,
"unnecessary `!=` operation",
None,
"change to `==` and swap the blocks of the `if`/`else`",
);
},
_ => (),
}
}
}
}
}
|
