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[ty] dataclasses: Allow using dataclasses.dataclass as a function. #18440

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Merged
merged 1 commit into from
Jun 3, 2025
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[ty] dataclasses: Allow using dataclasses.dataclass as a function. #18440

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15 changes: 14 additions & 1 deletion crates/ty_python_semantic/resources/mdtest/dataclasses.md
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Expand Up @@ -797,7 +797,20 @@ C(1) < C(2) # ok

### Using `dataclass` as a function

To do
```py
from dataclasses import dataclass

class B:
x: int

# error: [missing-argument]
dataclass(B)()

# error: [invalid-argument-type]
dataclass(B)("a")

reveal_type(dataclass(B)(3).x) # revealed: int
```

## Internals

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19 changes: 17 additions & 2 deletions crates/ty_python_semantic/src/types/call/bind.rs
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Expand Up @@ -22,8 +22,8 @@ use crate::types::function::{DataclassTransformerParams, FunctionDecorators, Kno
use crate::types::generics::{Specialization, SpecializationBuilder, SpecializationError};
use crate::types::signatures::{Parameter, ParameterForm};
use crate::types::{
BoundMethodType, DataclassParams, KnownClass, KnownInstanceType, MethodWrapperKind,
PropertyInstanceType, SpecialFormType, TupleType, TypeMapping, UnionType,
BoundMethodType, ClassLiteral, DataclassParams, KnownClass, KnownInstanceType,
MethodWrapperKind, PropertyInstanceType, SpecialFormType, TupleType, TypeMapping, UnionType,
WrapperDescriptorKind, ide_support, todo_type,
};
use ruff_db::diagnostic::{Annotation, Diagnostic, Severity, SubDiagnostic};
Expand Down Expand Up @@ -839,6 +839,21 @@ impl<'db> Bindings<'db> {

overload.set_return_type(Type::DataclassDecorator(params));
}

// `dataclass` being used as a non-decorator
if let [Some(Type::ClassLiteral(class_literal))] =
overload.parameter_types()
{
let params = DataclassParams::default();
overload.set_return_type(Type::from(ClassLiteral::new(
db,
class_literal.name(db),
class_literal.body_scope(db),
class_literal.known(db),
Some(params),
class_literal.dataclass_transformer_params(db),
)));
}
}

Some(KnownFunction::DataclassTransform) => {
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