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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,61 @@ | ||
| use clippy_utils::{diagnostics::span_lint_and_help, is_default_equivalent, path_def_id}; | ||
| use rustc_hir::{Expr, ExprKind, QPath}; | ||
| use rustc_lint::{LateContext, LateLintPass, LintContext}; | ||
| use rustc_middle::lint::in_external_macro; | ||
| use rustc_session::{declare_lint_pass, declare_tool_lint}; | ||
| use rustc_span::sym; | ||
|
|
||
| declare_clippy_lint! { | ||
| /// ### What it does | ||
| /// checks for `Box::new(T::default())`, which is better written as | ||
| /// `Box::<T>::default()`. | ||
| /// | ||
| /// ### Why is this bad? | ||
| /// First, it's more complex, involving two calls instead of one. | ||
| /// Second, `Box::default()` can be faster | ||
| /// [in certain cases](https://nnethercote.github.io/perf-book/standard-library-types.html#box). | ||
| /// | ||
| /// ### Known problems | ||
| /// The lint may miss some cases (e.g. Box::new(String::from(""))). | ||
| /// On the other hand, it will trigger on cases where the `default` | ||
| /// code comes from a macro that does something different based on | ||
| /// e.g. target operating system. | ||
| /// | ||
| /// ### Example | ||
| /// ```rust | ||
| /// let x: Box<String> = Box::new(Default::default()); | ||
| /// ``` | ||
| /// Use instead: | ||
| /// ```rust | ||
| /// let x: Box<String> = Box::default(); | ||
| /// ``` | ||
| #[clippy::version = "1.65.0"] | ||
| pub BOX_DEFAULT, | ||
| perf, | ||
| "Using Box::new(T::default()) instead of Box::default()" | ||
| } | ||
|
|
||
| declare_lint_pass!(BoxDefault => [BOX_DEFAULT]); | ||
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| impl LateLintPass<'_> for BoxDefault { | ||
| fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) { | ||
| if let ExprKind::Call(box_new, [arg]) = expr.kind | ||
| && let ExprKind::Path(QPath::TypeRelative(ty, seg)) = box_new.kind | ||
| && let ExprKind::Call(..) = arg.kind | ||
| && !in_external_macro(cx.sess(), expr.span) | ||
| && expr.span.eq_ctxt(arg.span) | ||
| && seg.ident.name == sym::new | ||
| && path_def_id(cx, ty) == cx.tcx.lang_items().owned_box() | ||
| && is_default_equivalent(cx, arg) | ||
| { | ||
| span_lint_and_help( | ||
| cx, | ||
| BOX_DEFAULT, | ||
| expr.span, | ||
| "`Box::new(_)` of default value", | ||
| None, | ||
| "use `Box::default()` instead", | ||
| ); | ||
| } | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,23 @@ | ||
| ### What it does | ||
| checks for `Box::new(T::default())`, which is better written as | ||
| `Box::<T>::default()`. | ||
|
|
||
| ### Why is this bad? | ||
| First, it's more complex, involving two calls instead of one. | ||
| Second, `Box::default()` can be faster | ||
| [in certain cases](https://nnethercote.github.io/perf-book/standard-library-types.html#box). | ||
|
|
||
| ### Known problems | ||
| The lint may miss some cases (e.g. Box::new(String::from(""))). | ||
| On the other hand, it will trigger on cases where the `default` | ||
| code comes from a macro that does something different based on | ||
| e.g. target operating system. | ||
|
|
||
| ### Example | ||
| ``` | ||
| let x: Box<String> = Box::new(Default::default()); | ||
| ``` | ||
| Use instead: | ||
| ``` | ||
| let x: Box<String> = Box::default(); | ||
| ``` |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,31 @@ | ||
| #![warn(clippy::box_default)] | ||
|
|
||
| #[derive(Default)] | ||
| struct ImplementsDefault; | ||
|
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| struct OwnDefault; | ||
|
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| impl OwnDefault { | ||
| fn default() -> Self { | ||
| Self | ||
| } | ||
| } | ||
|
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| macro_rules! outer { | ||
| ($e: expr) => { | ||
| $e | ||
| }; | ||
| } | ||
|
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||
| fn main() { | ||
| let _string: Box<String> = Box::new(Default::default()); | ||
| let _byte = Box::new(u8::default()); | ||
| let _vec = Box::new(Vec::<u8>::new()); | ||
| let _impl = Box::new(ImplementsDefault::default()); | ||
| let _impl2 = Box::new(<ImplementsDefault as Default>::default()); | ||
| let _impl3: Box<ImplementsDefault> = Box::new(Default::default()); | ||
| let _own = Box::new(OwnDefault::default()); // should not lint | ||
| let _in_macro = outer!(Box::new(String::new())); | ||
| // false negative: default is from different expansion | ||
| let _vec2: Box<Vec<ImplementsDefault>> = Box::new(vec![]); | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,59 @@ | ||
| error: `Box::new(_)` of default value | ||
| --> $DIR/box_default.rs:21:32 | ||
| | | ||
| LL | let _string: Box<String> = Box::new(Default::default()); | ||
| | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | ||
| | | ||
| = note: `-D clippy::box-default` implied by `-D warnings` | ||
| = help: use `Box::default()` instead | ||
|
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||
| error: `Box::new(_)` of default value | ||
| --> $DIR/box_default.rs:22:17 | ||
| | | ||
| LL | let _byte = Box::new(u8::default()); | ||
| | ^^^^^^^^^^^^^^^^^^^^^^^ | ||
| | | ||
| = help: use `Box::default()` instead | ||
|
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||
| error: `Box::new(_)` of default value | ||
| --> $DIR/box_default.rs:23:16 | ||
| | | ||
| LL | let _vec = Box::new(Vec::<u8>::new()); | ||
| | ^^^^^^^^^^^^^^^^^^^^^^^^^^ | ||
| | | ||
| = help: use `Box::default()` instead | ||
|
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||
| error: `Box::new(_)` of default value | ||
| --> $DIR/box_default.rs:24:17 | ||
| | | ||
| LL | let _impl = Box::new(ImplementsDefault::default()); | ||
| | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | ||
| | | ||
| = help: use `Box::default()` instead | ||
|
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||
| error: `Box::new(_)` of default value | ||
| --> $DIR/box_default.rs:25:18 | ||
| | | ||
| LL | let _impl2 = Box::new(<ImplementsDefault as Default>::default()); | ||
| | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | ||
| | | ||
| = help: use `Box::default()` instead | ||
|
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||
| error: `Box::new(_)` of default value | ||
| --> $DIR/box_default.rs:26:42 | ||
| | | ||
| LL | let _impl3: Box<ImplementsDefault> = Box::new(Default::default()); | ||
| | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | ||
| | | ||
| = help: use `Box::default()` instead | ||
|
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||
| error: `Box::new(_)` of default value | ||
| --> $DIR/box_default.rs:28:28 | ||
| | | ||
| LL | let _in_macro = outer!(Box::new(String::new())); | ||
| | ^^^^^^^^^^^^^^^^^^^^^^^ | ||
| | | ||
| = help: use `Box::default()` instead | ||
|
|
||
| error: aborting due to 7 previous errors | ||
|
|