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Correctly handle bracketed type in default_constructed_unit_struct (#14367)

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There were two bugs here. Let's assume `T` is a singleton type
implementing `Default` and that `f()` takes a `T`:

- `f(<T>::default())` cannot be replaced by `f(<T)` as it was (incorrect
spans – this is tricky because the type relative path uses a base span
covering only `T`, not `<T>`) (third commit)
- The argument of `f(<_>::default())` is inferred correctly, but cannot
be replaced by `<_>` or `_`, as this cannot be used to infer an instance
of a singleton type (first commit).

The second commit offers better error messages by pointing at the whole
expression.

Fix #12654

changelog: [`default_constructed_unit_struct`]: do not suggest incorrect
fix when using a type surrounded by brackets
This commit is contained in:
Samuel Tardieu 2025-04-10 05:51:39 +00:00 • committed by GitHub
commit 529bb5f253
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GPG key ID: B5690EEEBB952194
4 changed files with 83 additions and 19 deletions
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24
clippy_lints/src/default_constructed_unit_structs.rs
View file

@ -1,5 +1,6 @@
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::is_ty_alias;
use clippy_utils::source::SpanRangeExt as _;
use hir::ExprKind;
use hir::def::Res;
use rustc_errors::Applicability;
@ -70,15 +71,26 @@ impl LateLintPass<'_> for DefaultConstructedUnitStructs {
&& let var @ ty::VariantDef { ctor: Some((hir::def::CtorKind::Const, _)), .. } = def.non_enum_variant()
&& !var.is_field_list_non_exhaustive()
&& !expr.span.from_expansion() && !qpath.span().from_expansion()
// do not suggest replacing an expression by a type name with placeholders
&& !base.is_suggestable_infer_ty()
{
span_lint_and_sugg(
let mut removals = vec![(expr.span.with_lo(qpath.qself_span().hi()), String::new())];
if expr.span.with_source_text(cx, |s| s.starts_with('<')) == Some(true) {
// Remove `<`, '>` has already been removed by the existing removal expression.
removals.push((expr.span.with_hi(qpath.qself_span().lo()), String::new()));
}
span_lint_and_then(
cx,
DEFAULT_CONSTRUCTED_UNIT_STRUCTS,
expr.span.with_lo(qpath.qself_span().hi()),
expr.span,
"use of `default` to create a unit struct",
"remove this call to `default`",
String::new(),
Applicability::MachineApplicable,
|diag| {
diag.multipart_suggestion(
"remove this call to `default`",
removals,
Applicability::MachineApplicable,
);
},
);
}
}

14
tests/ui/default_constructed_unit_structs.fixed
View file

@ -161,3 +161,17 @@ fn main() {
let _ = <struct_from_macro!()>::default();
}
fn issue12654() {
#[derive(Default)]
struct G;
fn f(_g: G) {}
f(<_>::default());
f(G);
//~^ default_constructed_unit_structs
// No lint because `as Default` hides the singleton
f(<G as Default>::default());
}

14
tests/ui/default_constructed_unit_structs.rs
View file

@ -161,3 +161,17 @@ fn main() {
let _ = <struct_from_macro!()>::default();
}
fn issue12654() {
#[derive(Default)]
struct G;
fn f(_g: G) {}
f(<_>::default());
f(<G>::default());
//~^ default_constructed_unit_structs
// No lint because `as Default` hides the singleton
f(<G as Default>::default());
}

50
tests/ui/default_constructed_unit_structs.stderr
View file

@ -1,41 +1,65 @@
error: use of `default` to create a unit struct
--> tests/ui/default_constructed_unit_structs.rs:11:13
--> tests/ui/default_constructed_unit_structs.rs:11:9
|
LL | Self::default()
| ^^^^^^^^^^^ help: remove this call to `default`
| ^^^^-----------
| |
| help: remove this call to `default`
|
= note: `-D clippy::default-constructed-unit-structs` implied by `-D warnings`
= help: to override `-D warnings` add `#[allow(clippy::default_constructed_unit_structs)]`
error: use of `default` to create a unit struct
--> tests/ui/default_constructed_unit_structs.rs:54:31
--> tests/ui/default_constructed_unit_structs.rs:54:20
|
LL | inner: PhantomData::default(),
| ^^^^^^^^^^^ help: remove this call to `default`
| ^^^^^^^^^^^-----------
| |
| help: remove this call to `default`
error: use of `default` to create a unit struct
--> tests/ui/default_constructed_unit_structs.rs:128:33
--> tests/ui/default_constructed_unit_structs.rs:128:13
|
LL | let _ = PhantomData::<usize>::default();
| ^^^^^^^^^^^ help: remove this call to `default`
| ^^^^^^^^^^^^^^^^^^^^-----------
| |
| help: remove this call to `default`
error: use of `default` to create a unit struct
--> tests/ui/default_constructed_unit_structs.rs:130:42
--> tests/ui/default_constructed_unit_structs.rs:130:31
|
LL | let _: PhantomData<i32> = PhantomData::default();
| ^^^^^^^^^^^ help: remove this call to `default`
| ^^^^^^^^^^^-----------
| |
| help: remove this call to `default`
error: use of `default` to create a unit struct
--> tests/ui/default_constructed_unit_structs.rs:132:55
--> tests/ui/default_constructed_unit_structs.rs:132:31
|
LL | let _: PhantomData<i32> = std::marker::PhantomData::default();
| ^^^^^^^^^^^ help: remove this call to `default`
| ^^^^^^^^^^^^^^^^^^^^^^^^-----------
| |
| help: remove this call to `default`
error: use of `default` to create a unit struct
--> tests/ui/default_constructed_unit_structs.rs:134:23
--> tests/ui/default_constructed_unit_structs.rs:134:13
|
LL | let _ = UnitStruct::default();
| ^^^^^^^^^^^ help: remove this call to `default`
| ^^^^^^^^^^-----------
| |
| help: remove this call to `default`
error: aborting due to 6 previous errors
error: use of `default` to create a unit struct
--> tests/ui/default_constructed_unit_structs.rs:172:7
|
LL | f(<G>::default());
| ^^^^^^^^^^^^^^
|
help: remove this call to `default`
|
LL - f(<G>::default());
LL + f(G);
|
error: aborting due to 7 previous errors