90 lines
2.8 KiB
Rust
90 lines
2.8 KiB
Rust
//! lint on if branches that could be swapped so no `!` operation is necessary
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//! on the condition
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use clippy_utils::consts::{constant_simple, Constant};
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use clippy_utils::diagnostics::span_lint_and_help;
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use clippy_utils::is_else_clause;
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use rustc_hir::{BinOpKind, Expr, ExprKind, UnOp};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::declare_lint_pass;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for usage of `!` or `!=` in an if condition with an
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/// else branch.
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///
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/// ### Why is this bad?
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/// Negations reduce the readability of statements.
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///
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/// ### Example
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/// ```no_run
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/// # let v: Vec<usize> = vec![];
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/// # fn a() {}
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/// # fn b() {}
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/// if !v.is_empty() {
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/// a()
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/// } else {
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/// b()
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/// }
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/// ```
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///
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/// Could be written:
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///
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/// ```no_run
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/// # let v: Vec<usize> = vec![];
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/// # fn a() {}
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/// # fn b() {}
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/// if v.is_empty() {
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/// b()
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/// } else {
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/// a()
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/// }
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub IF_NOT_ELSE,
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pedantic,
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"`if` branches that could be swapped so no negation operation is necessary on the condition"
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}
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declare_lint_pass!(IfNotElse => [IF_NOT_ELSE]);
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fn is_zero_const(expr: &Expr<'_>, cx: &LateContext<'_>) -> bool {
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if let Some(value) = constant_simple(cx, cx.typeck_results(), expr) {
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return Constant::Int(0) == value;
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}
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false
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}
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impl LateLintPass<'_> for IfNotElse {
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fn check_expr(&mut self, cx: &LateContext<'_>, e: &Expr<'_>) {
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if let ExprKind::If(cond, _, Some(els)) = e.kind
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&& let ExprKind::DropTemps(cond) = cond.kind
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&& let ExprKind::Block(..) = els.kind
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{
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let (msg, help) = match cond.kind {
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ExprKind::Unary(UnOp::Not, _) => (
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"unnecessary boolean `not` operation",
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"remove the `!` and swap the blocks of the `if`/`else`",
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),
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// Don't lint on `… != 0`, as these are likely to be bit tests.
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// For example, `if foo & 0x0F00 != 0 { … } else { … }` is already in the "proper" order.
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ExprKind::Binary(op, _, rhs) if op.node == BinOpKind::Ne && !is_zero_const(rhs, cx) => (
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"unnecessary `!=` operation",
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"change to `==` and swap the blocks of the `if`/`else`",
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),
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_ => return,
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};
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// `from_expansion` will also catch `while` loops which appear in the HIR as:
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// ```rust
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// loop {
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// if cond { ... } else { break; }
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// }
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// ```
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if !e.span.from_expansion() && !is_else_clause(cx.tcx, e) {
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span_lint_and_help(cx, IF_NOT_ELSE, e.span, msg, None, help);
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}
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}
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}
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}
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