62 lines
2.2 KiB
Rust
62 lines
2.2 KiB
Rust
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use clippy_utils::{diagnostics::span_lint_and_help, is_default_equivalent, path_def_id};
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use rustc_hir::{Expr, ExprKind, QPath};
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use rustc_lint::{LateContext, LateLintPass, LintContext};
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use rustc_middle::lint::in_external_macro;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::sym;
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declare_clippy_lint! {
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/// ### What it does
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/// checks for `Box::new(T::default())`, which is better written as
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/// `Box::<T>::default()`.
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///
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/// ### Why is this bad?
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/// First, it's more complex, involving two calls instead of one.
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/// Second, `Box::default()` can be faster
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/// [in certain cases](https://nnethercote.github.io/perf-book/standard-library-types.html#box).
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///
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/// ### Known problems
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/// The lint may miss some cases (e.g. Box::new(String::from(""))).
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/// On the other hand, it will trigger on cases where the `default`
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/// code comes from a macro that does something different based on
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/// e.g. target operating system.
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///
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/// ### Example
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/// ```rust
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/// let x: Box<String> = Box::new(Default::default());
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/// ```
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/// Use instead:
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/// ```rust
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/// let x: Box<String> = Box::default();
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/// ```
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#[clippy::version = "1.65.0"]
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pub BOX_DEFAULT,
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perf,
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"Using Box::new(T::default()) instead of Box::default()"
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}
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declare_lint_pass!(BoxDefault => [BOX_DEFAULT]);
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impl LateLintPass<'_> for BoxDefault {
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fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
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if let ExprKind::Call(box_new, [arg]) = expr.kind
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&& let ExprKind::Path(QPath::TypeRelative(ty, seg)) = box_new.kind
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&& let ExprKind::Call(..) = arg.kind
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&& !in_external_macro(cx.sess(), expr.span)
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&& expr.span.eq_ctxt(arg.span)
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&& seg.ident.name == sym::new
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&& path_def_id(cx, ty) == cx.tcx.lang_items().owned_box()
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&& is_default_equivalent(cx, arg)
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{
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span_lint_and_help(
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cx,
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BOX_DEFAULT,
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expr.span,
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"`Box::new(_)` of default value",
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None,
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"use `Box::default()` instead",
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);
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}
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}
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}
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