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Auto merge of #12601 - Alexendoo:box-default-style, r=llogiq
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Move `box_default` to style, do not suggest turbofishes

`Box::default()` [had its `#[rustc_box]` attribute removed](https://github.com/rust-lang/rust/pull/108476/files#r1120930164) in 1.69 so is no longer a perf related lint

The lint is moved to style but no longer produces suggestions containing turbofishes, as they're often longer/more annoying to type

changelog: [`box_default`]: Move to style

r? `@llogiq`
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@bors
bors committed Apr 1, 2024
2 parents 797d50d + 0f63fa8 commit cb87a57
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Showing 4 changed files with 122 additions and 193 deletions.
51 changes: 8 additions & 43 deletions clippy_lints/src/box_default.rs
View file
Original file line number Diff line number Diff line change
@@ -1,6 +1,5 @@
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::macros::macro_backtrace;
use clippy_utils::source::snippet_opt;
use clippy_utils::ty::expr_sig;
use clippy_utils::{is_default_equivalent, path_def_id};
use rustc_errors::Applicability;
Expand All @@ -9,20 +8,16 @@ use rustc_hir::intravisit::{walk_ty, Visitor};
use rustc_hir::{Block, Expr, ExprKind, Local, Node, QPath, Ty, TyKind};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::print::with_forced_trimmed_paths;
use rustc_middle::ty::IsSuggestable;
use rustc_session::declare_lint_pass;
use rustc_span::sym;

declare_clippy_lint! {
/// ### What it does
/// checks for `Box::new(T::default())`, which is better written as
/// `Box::<T>::default()`.
/// checks for `Box::new(Default::default())`, which can be written as
/// `Box::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).
/// `Box::default()` is equivalent and more concise.
///
/// ### Example
/// ```no_run
Expand All @@ -34,7 +29,7 @@ declare_clippy_lint! {
/// ```
#[clippy::version = "1.66.0"]
pub BOX_DEFAULT,
perf,
style,
"Using Box::new(T::default()) instead of Box::default()"
}

Expand All @@ -53,38 +48,22 @@ impl LateLintPass<'_> for BoxDefault {
&& path_def_id(cx, ty).map_or(false, |id| Some(id) == cx.tcx.lang_items().owned_box())
// And the single argument to the call is another function call
// This is the `T::default()` of `Box::new(T::default())`
&& let ExprKind::Call(arg_path, inner_call_args) = arg.kind
&& let ExprKind::Call(arg_path, _) = arg.kind
// And we are not in a foreign crate's macro
&& !in_external_macro(cx.sess(), expr.span)
// And the argument expression has the same context as the outer call expression
// or that we are inside a `vec!` macro expansion
&& (expr.span.eq_ctxt(arg.span) || is_local_vec_expn(cx, arg, expr))
// And the argument is equivalent to `Default::default()`
&& is_default_equivalent(cx, arg)
// And the argument is `Default::default()` or the type is specified
&& (is_plain_default(cx, arg_path) || (given_type(cx, expr) && is_default_equivalent(cx, arg)))
{
span_lint_and_sugg(
cx,
BOX_DEFAULT,
expr.span,
"`Box::new(_)` of default value",
"try",
if is_plain_default(cx, arg_path) || given_type(cx, expr) {
"Box::default()".into()
} else if let Some(arg_ty) = cx.typeck_results().expr_ty(arg).make_suggestable(cx.tcx, true) {
// Check if we can copy from the source expression in the replacement.
// We need the call to have no argument (see `explicit_default_type`).
if inner_call_args.is_empty()
&& let Some(ty) = explicit_default_type(arg_path)
&& let Some(s) = snippet_opt(cx, ty.span)
{
format!("Box::<{s}>::default()")
} else {
// Otherwise, use the inferred type's formatting.
with_forced_trimmed_paths!(format!("Box::<{arg_ty}>::default()"))
}
} else {
return;
},
"Box::default()".into(),
Applicability::MachineApplicable,
);
}
Expand All @@ -103,20 +82,6 @@ fn is_plain_default(cx: &LateContext<'_>, arg_path: &Expr<'_>) -> bool {
}
}

// Checks whether the call is of the form `A::B::f()`. Returns `A::B` if it is.
//
// In the event we have this kind of construct, it's easy to use `A::B` as a replacement in the
// quickfix. `f` must however have no parameter. Should `f` have some, then some of the type of
// `A::B` may be inferred from the arguments. This would be the case for `Vec::from([0; false])`,
// where the argument to `from` allows inferring this is a `Vec<bool>`
fn explicit_default_type<'a>(arg_path: &'a Expr<'_>) -> Option<&'a Ty<'a>> {
if let ExprKind::Path(QPath::TypeRelative(ty, _)) = &arg_path.kind {
Some(ty)
} else {
None
}
}

fn is_local_vec_expn(cx: &LateContext<'_>, expr: &Expr<'_>, ref_expr: &Expr<'_>) -> bool {
macro_backtrace(expr.span).next().map_or(false, |call| {
cx.tcx.is_diagnostic_item(sym::vec_macro, call.def_id) && call.span.eq_ctxt(ref_expr.span)
Expand Down
85 changes: 47 additions & 38 deletions tests/ui/box_default.fixed
View file
Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
#![warn(clippy::box_default)]
#![allow(clippy::default_constructed_unit_structs)]
#![allow(clippy::boxed_local, clippy::default_constructed_unit_structs)]

#[derive(Default)]
struct ImplementsDefault;
Expand All @@ -12,26 +12,50 @@ impl OwnDefault {
}
}

macro_rules! outer {
($e: expr) => {
$e
macro_rules! default {
() => {
Default::default()
};
}

macro_rules! string_new {
() => {
String::new()
};
}

macro_rules! box_new {
($e:expr) => {
Box::new($e)
};
}

fn main() {
let _string: Box<String> = Box::default();
let _byte = Box::<u8>::default();
let _vec = Box::<Vec::<u8>>::default();
let _impl = Box::<ImplementsDefault>::default();
let _impl2 = Box::<ImplementsDefault>::default();
let _impl3: Box<ImplementsDefault> = Box::default();
let _own = Box::new(OwnDefault::default()); // should not lint
let _in_macro = outer!(Box::<String>::default());
let _string_default = outer!(Box::<String>::default());
let _vec2: Box<Vec<ImplementsDefault>> = Box::default();
let _vec3: Box<Vec<bool>> = Box::default();
let _vec4: Box<_> = Box::<Vec<bool>>::default();
let _more = ret_ty_fn();
let string1: Box<String> = Box::default();
let string2: Box<String> = Box::default();
let impl1: Box<ImplementsDefault> = Box::default();
let vec: Box<Vec<u8>> = Box::default();
let byte: Box<u8> = Box::default();
let vec2: Box<Vec<ImplementsDefault>> = Box::default();
let vec3: Box<Vec<bool>> = Box::default();

let plain_default = Box::default();
let _: Box<String> = plain_default;

let _: Box<String> = Box::new(default!());
let _: Box<String> = Box::new(string_new!());
let _: Box<String> = box_new!(Default::default());
let _: Box<String> = box_new!(String::new());
let _: Box<String> = box_new!(default!());
let _: Box<String> = box_new!(string_new!());

let own: Box<OwnDefault> = Box::new(OwnDefault::default()); // should not lint

// Do not suggest where a turbofish would be required
let impl2 = Box::new(ImplementsDefault::default());
let impl3 = Box::new(<ImplementsDefault as Default>::default());
let vec4: Box<_> = Box::new(Vec::from([false; 0]));
let more = ret_ty_fn();
call_ty_fn(Box::default());
issue_10381();

Expand All @@ -44,10 +68,9 @@ fn main() {
}

fn ret_ty_fn() -> Box<bool> {
Box::<bool>::default()
Box::new(bool::default()) // Could lint, currently doesn't
}

#[allow(clippy::boxed_local)]
fn call_ty_fn(_b: Box<u8>) {
issue_9621_dyn_trait();
}
Expand All @@ -61,7 +84,7 @@ impl Read for ImplementsDefault {
}

fn issue_9621_dyn_trait() {
let _: Box<dyn Read> = Box::<ImplementsDefault>::default();
let _: Box<dyn Read> = Box::new(ImplementsDefault::default());
issue_10089();
}

Expand All @@ -70,7 +93,7 @@ fn issue_10089() {
#[derive(Default)]
struct WeirdPathed;

let _ = Box::<WeirdPathed>::default();
let _ = Box::new(WeirdPathed::default());
};
}

Expand All @@ -82,7 +105,7 @@ fn issue_10381() {

fn maybe_get_bar(i: u32) -> Option<Box<dyn Bar>> {
if i % 2 == 0 {
Some(Box::<Foo>::default())
Some(Box::new(Foo::default()))
} else {
None
}
Expand All @@ -91,20 +114,6 @@ fn issue_10381() {
assert!(maybe_get_bar(2).is_some());
}

#[allow(unused)]
fn issue_11868() {
fn foo(_: &mut Vec<usize>) {}

macro_rules! bar {
($baz:expr) => {
Box::leak(Box::new($baz))
};
}

foo(bar!(vec![]));
foo(bar!(vec![1]));
}

// Issue #11927: The quickfix for the `Box::new` suggests replacing with `Box::<Inner>::default()`,
// removing the `outer::` segment.
fn issue_11927() {
Expand All @@ -116,7 +125,7 @@ fn issue_11927() {
}

fn foo() {
let _b = Box::<outer::Inner>::default();
let _b = Box::<std::collections::HashSet::<i32>>::default();
let _b = Box::new(outer::Inner::default());
let _b = Box::new(std::collections::HashSet::<i32>::new());
}
}
75 changes: 42 additions & 33 deletions tests/ui/box_default.rs
View file
Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
#![warn(clippy::box_default)]
#![allow(clippy::default_constructed_unit_structs)]
#![allow(clippy::boxed_local, clippy::default_constructed_unit_structs)]

#[derive(Default)]
struct ImplementsDefault;
Expand All @@ -12,26 +12,50 @@ impl OwnDefault {
}
}

macro_rules! outer {
($e: expr) => {
$e
macro_rules! default {
() => {
Default::default()
};
}

macro_rules! string_new {
() => {
String::new()
};
}

macro_rules! box_new {
($e:expr) => {
Box::new($e)
};
}

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()));
let _string_default = outer!(Box::new(String::from("")));
let _vec2: Box<Vec<ImplementsDefault>> = Box::new(vec![]);
let _vec3: Box<Vec<bool>> = Box::new(Vec::from([]));
let _vec4: Box<_> = Box::new(Vec::from([false; 0]));
let _more = ret_ty_fn();
let string1: Box<String> = Box::new(Default::default());
let string2: Box<String> = Box::new(String::new());
let impl1: Box<ImplementsDefault> = Box::new(Default::default());
let vec: Box<Vec<u8>> = Box::new(Vec::new());
let byte: Box<u8> = Box::new(u8::default());
let vec2: Box<Vec<ImplementsDefault>> = Box::new(vec![]);
let vec3: Box<Vec<bool>> = Box::new(Vec::from([]));

let plain_default = Box::new(Default::default());
let _: Box<String> = plain_default;

let _: Box<String> = Box::new(default!());
let _: Box<String> = Box::new(string_new!());
let _: Box<String> = box_new!(Default::default());
let _: Box<String> = box_new!(String::new());
let _: Box<String> = box_new!(default!());
let _: Box<String> = box_new!(string_new!());

let own: Box<OwnDefault> = Box::new(OwnDefault::default()); // should not lint

// Do not suggest where a turbofish would be required
let impl2 = Box::new(ImplementsDefault::default());
let impl3 = Box::new(<ImplementsDefault as Default>::default());
let vec4: Box<_> = Box::new(Vec::from([false; 0]));
let more = ret_ty_fn();
call_ty_fn(Box::new(u8::default()));
issue_10381();

Expand All @@ -44,10 +68,9 @@ fn main() {
}

fn ret_ty_fn() -> Box<bool> {
Box::new(bool::default())
Box::new(bool::default()) // Could lint, currently doesn't
}

#[allow(clippy::boxed_local)]
fn call_ty_fn(_b: Box<u8>) {
issue_9621_dyn_trait();
}
Expand Down Expand Up @@ -91,20 +114,6 @@ fn issue_10381() {
assert!(maybe_get_bar(2).is_some());
}

#[allow(unused)]
fn issue_11868() {
fn foo(_: &mut Vec<usize>) {}

macro_rules! bar {
($baz:expr) => {
Box::leak(Box::new($baz))
};
}

foo(bar!(vec![]));
foo(bar!(vec![1]));
}

// Issue #11927: The quickfix for the `Box::new` suggests replacing with `Box::<Inner>::default()`,
// removing the `outer::` segment.
fn issue_11927() {
Expand Down
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