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Auto merge of #9585 - rust-lang:extend-box-default, r=Alexendoo

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extend `box-default` lint, add suggestion

This extends the recently added `box-default` lint to also cover `Box::new(vec![])`, `Box::new(String::from(""))` and `Box::new(Vec::from([]))`. Also the lint now suggests a suitable replacement. I did not find a simple way to check whether the type is fully determined by the outside, so I at least checked for some variations to remove the turbofish in those cases.

---

changelog: none
This commit is contained in:
bors 2022-10-07 14:49:54 +00:00
commit 2c8e473ffe
6 changed files with 212 additions and 48 deletions
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94
clippy_lints/src/box_default.rs
View File

@ -1,5 +1,12 @@
use clippy_utils::{diagnostics::span_lint_and_help, is_default_equivalent, path_def_id};
use rustc_hir::{Expr, ExprKind, QPath};
use clippy_utils::{
diagnostics::span_lint_and_sugg, get_parent_node, is_default_equivalent, macros::macro_backtrace, match_path,
path_def_id, paths, ty::expr_sig,
};
use rustc_errors::Applicability;
use rustc_hir::{
intravisit::{walk_ty, Visitor},
Block, Expr, ExprKind, Local, Node, QPath, TyKind,
};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_session::{declare_lint_pass, declare_tool_lint};
@ -15,12 +22,6 @@
/// 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());
@ -41,21 +42,88 @@ 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
&& let ExprKind::Call(arg_path, ..) = arg.kind
&& !in_external_macro(cx.sess(), expr.span)
&& expr.span.eq_ctxt(arg.span)
&& (expr.span.eq_ctxt(arg.span) || is_vec_expn(cx, arg))
&& 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(
let arg_ty = cx.typeck_results().expr_ty(arg);
span_lint_and_sugg(
cx,
BOX_DEFAULT,
expr.span,
"`Box::new(_)` of default value",
None,
"use `Box::default()` instead",
"try",
if is_plain_default(arg_path) || given_type(cx, expr) {
"Box::default()".into()
} else {
format!("Box::<{arg_ty}>::default()")
},
Applicability::MachineApplicable
);
}
}
}
fn is_plain_default(arg_path: &Expr<'_>) -> bool {
// we need to match the actual path so we don't match e.g. "u8::default"
if let ExprKind::Path(QPath::Resolved(None, path)) = &arg_path.kind {
// avoid generic parameters
match_path(path, &paths::DEFAULT_TRAIT_METHOD) && path.segments.iter().all(|seg| seg.args.is_none())
} else {
false
}
}
fn is_vec_expn(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
macro_backtrace(expr.span)
.next()
.map_or(false, |call| cx.tcx.is_diagnostic_item(sym::vec_macro, call.def_id))
}
#[derive(Default)]
struct InferVisitor(bool);
impl<'tcx> Visitor<'tcx> for InferVisitor {
fn visit_ty(&mut self, t: &rustc_hir::Ty<'_>) {
self.0 |= matches!(t.kind, TyKind::Infer);
if !self.0 {
walk_ty(self, t);
}
}
}
fn given_type(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
match get_parent_node(cx.tcx, expr.hir_id) {
Some(Node::Local(Local { ty: Some(ty), .. })) => {
let mut v = InferVisitor::default();
v.visit_ty(ty);
!v.0
},
Some(
Node::Expr(Expr {
kind: ExprKind::Call(path, args),
..
}) | Node::Block(Block {
expr:
Some(Expr {
kind: ExprKind::Call(path, args),
..
}),
..
}),
) => {
if let Some(index) = args.iter().position(|arg| arg.hir_id == expr.hir_id) &&
let Some(sig) = expr_sig(cx, path) &&
let Some(input) = sig.input(index)
{
input.no_bound_vars().is_some()
} else {
false
}
},
_ => false,
}
}

26
clippy_utils/src/lib.rs
View File

@ -815,13 +815,37 @@ pub fn is_default_equivalent(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
false
}
},
ExprKind::Call(repl_func, _) => is_default_equivalent_call(cx, repl_func),
ExprKind::Call(repl_func, []) => is_default_equivalent_call(cx, repl_func),
ExprKind::Call(from_func, [ref arg]) => is_default_equivalent_from(cx, from_func, arg),
ExprKind::Path(qpath) => is_res_lang_ctor(cx, cx.qpath_res(qpath, e.hir_id), OptionNone),
ExprKind::AddrOf(rustc_hir::BorrowKind::Ref, _, expr) => matches!(expr.kind, ExprKind::Array([])),
_ => false,
}
}
fn is_default_equivalent_from(cx: &LateContext<'_>, from_func: &Expr<'_>, arg: &Expr<'_>) -> bool {
if let ExprKind::Path(QPath::TypeRelative(ty, seg)) = from_func.kind &&
seg.ident.name == sym::from
{
match arg.kind {
ExprKind::Lit(hir::Lit {
node: LitKind::Str(ref sym, _),
..
}) => return sym.is_empty() && is_path_diagnostic_item(cx, ty, sym::String),
ExprKind::Array([]) => return is_path_diagnostic_item(cx, ty, sym::Vec),
ExprKind::Repeat(_, ArrayLen::Body(len)) => {
if let ExprKind::Lit(ref const_lit) = cx.tcx.hir().body(len.body).value.kind &&
let LitKind::Int(v, _) = const_lit.node
{
return v == 0 && is_path_diagnostic_item(cx, ty, sym::Vec);
}
}
_ => (),
}
}
false
}
/// Checks if the top level expression can be moved into a closure as is.
/// Currently checks for:
/// * Break/Continue outside the given loop HIR ids.

6
src/docs/box_default.txt
View File

@ -7,12 +7,6 @@ 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());

43
tests/ui/box_default.fixed Normal file
View File

@ -0,0 +1,43 @@
// run-rustfix
#![warn(clippy::box_default)]
#[derive(Default)]
struct ImplementsDefault;
struct OwnDefault;
impl OwnDefault {
fn default() -> Self {
Self
}
}
macro_rules! outer {
($e: expr) => {
$e
};
}
fn main() {
let _string: Box<String> = Box::default();
let _byte = Box::<u8>::default();
let _vec = Box::<std::vec::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::<std::string::String>::default());
let _string_default = outer!(Box::<std::string::String>::default());
let _vec2: Box<Vec<ImplementsDefault>> = Box::default();
let _vec3: Box<Vec<bool>> = Box::default();
let _vec4: Box<_> = Box::<std::vec::Vec<bool>>::default();
let _more = ret_ty_fn();
call_ty_fn(Box::default());
}
fn ret_ty_fn() -> Box<bool> {
Box::<bool>::default()
}
#[allow(clippy::boxed_local)]
fn call_ty_fn(_b: Box<u8>) {}

14
tests/ui/box_default.rs
View File

@ -1,3 +1,4 @@
// run-rustfix
#![warn(clippy::box_default)]
#[derive(Default)]
@ -26,6 +27,17 @@ fn main() {
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 _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();
call_ty_fn(Box::new(u8::default()));
}
fn ret_ty_fn() -> Box<bool> {
Box::new(bool::default())
}
#[allow(clippy::boxed_local)]
fn call_ty_fn(_b: Box<u8>) {}

77
tests/ui/box_default.stderr
View File

@ -1,59 +1,82 @@
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:21:32
--> $DIR/box_default.rs:22:32
|
LL | let _string: Box<String> = Box::new(Default::default());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::default()`
|
= help: use `Box::default()` instead
= note: `-D clippy::box-default` implied by `-D warnings`
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:22:17
--> $DIR/box_default.rs:23:17
|
LL | let _byte = Box::new(u8::default());
| ^^^^^^^^^^^^^^^^^^^^^^^
|
= help: use `Box::default()` instead
| ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::<u8>::default()`
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:23:16
--> $DIR/box_default.rs:24:16
|
LL | let _vec = Box::new(Vec::<u8>::new());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: use `Box::default()` instead
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::<std::vec::Vec<u8>>::default()`
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:24:17
--> $DIR/box_default.rs:25:17
|
LL | let _impl = Box::new(ImplementsDefault::default());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: use `Box::default()` instead
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::<ImplementsDefault>::default()`
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:25:18
--> $DIR/box_default.rs:26:18
|
LL | let _impl2 = Box::new(<ImplementsDefault as Default>::default());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: use `Box::default()` instead
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::<ImplementsDefault>::default()`
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:26:42
--> $DIR/box_default.rs:27:42
|
LL | let _impl3: Box<ImplementsDefault> = Box::new(Default::default());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= help: use `Box::default()` instead
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::default()`
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:28:28
--> $DIR/box_default.rs:29:28
|
LL | let _in_macro = outer!(Box::new(String::new()));
| ^^^^^^^^^^^^^^^^^^^^^^^
| ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::<std::string::String>::default()`
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:30:34
|
= help: use `Box::default()` instead
LL | let _string_default = outer!(Box::new(String::from("")));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::<std::string::String>::default()`
error: aborting due to 7 previous errors
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:31:46
|
LL | let _vec2: Box<Vec<ImplementsDefault>> = Box::new(vec![]);
| ^^^^^^^^^^^^^^^^ help: try: `Box::default()`
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:32:33
|
LL | let _vec3: Box<Vec<bool>> = Box::new(Vec::from([]));
| ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::default()`
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:33:25
|
LL | let _vec4: Box<_> = Box::new(Vec::from([false; 0]));
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::<std::vec::Vec<bool>>::default()`
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:35:16
|
LL | call_ty_fn(Box::new(u8::default()));
| ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::default()`
error: `Box::new(_)` of default value
--> $DIR/box_default.rs:39:5
|
LL | Box::new(bool::default())
| ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `Box::<bool>::default()`
error: aborting due to 13 previous errors