fix(dataclass): unify and clarify overloads for cls None

stdlib/@tests/test_cases/check_dataclasses.py

@@ -99,3 +99,14 @@ def check_other_isdataclass_overloads(x: type, y: object) -> None:
 # in case a type checker decides to add some special-casing for
 # `make_dataclass` in the future)
 assert_type(D.__mro__, Tuple[type, ...])
+
+
+@dc.dataclass(None, frozen=True)
+class Bar:
+    attr: str
+
+
+b = Bar(attr="attr")
+
+if dc.is_dataclass(b):
+    assert_type(b, Bar)

stdlib/dataclasses.pyi

@@ -55,13 +55,51 @@ def astuple(obj: DataclassInstance) -> tuple[Any, ...]: ...
 @overload
 def astuple(obj: DataclassInstance, *, tuple_factory: Callable[[list[Any]], _T]) -> _T: ...
 @overload
-def dataclass(cls: None, /) -> Callable[[type[_T]], type[_T]]: ...
+def dataclass(
+    cls: type[_T],
+    /,
+    *,
+    init: bool = True,
+    repr: bool = True,
+    eq: bool = True,
+    order: bool = False,
+    unsafe_hash: bool = False,
+    frozen: bool = False,
+) -> type[_T]: ...
 @overload
-def dataclass(cls: type[_T], /) -> type[_T]: ...
+def dataclass(
+    cls: None = ...,
+    /,
+    *,
+    init: bool = True,
+    repr: bool = True,
+    eq: bool = True,
+    order: bool = False,
+    unsafe_hash: bool = False,
+    frozen: bool = False,
+) -> Callable[[type[_T]], type[_T]]: ...
 
 if sys.version_info >= (3, 11):
     @overload
     def dataclass(
+        cls: type[_T],
+        /,
+        *,
+        init: bool = True,
+        repr: bool = True,
+        eq: bool = True,
+        order: bool = False,
+        unsafe_hash: bool = False,
+        frozen: bool = False,
+        match_args: bool = True,
+        kw_only: bool = False,
+        slots: bool = False,
+        weakref_slot: bool = False,
+    ) -> type[_T]: ...
+    @overload
+    def dataclass(
+        cls: None = ...,
+        /,
         *,
         init: bool = True,
         repr: bool = True,
@@ -78,6 +116,8 @@ if sys.version_info >= (3, 11):
 elif sys.version_info >= (3, 10):
     @overload
     def dataclass(
+        cls: type[_T],
+        /,
         *,
         init: bool = True,
         repr: bool = True,
@@ -88,18 +128,21 @@ elif sys.version_info >= (3, 10):
         match_args: bool = True,
         kw_only: bool = False,
         slots: bool = False,
-    ) -> Callable[[type[_T]], type[_T]]: ...
-
-else:
+    ) -> type[_T]: ...
     @overload
     def dataclass(
+        cls: None = ...,
+        /,
         *,
         init: bool = True,
         repr: bool = True,
         eq: bool = True,
         order: bool = False,
         unsafe_hash: bool = False,
         frozen: bool = False,
+        match_args: bool = True,
+        kw_only: bool = False,
+        slots: bool = False,
     ) -> Callable[[type[_T]], type[_T]]: ...
 
 # See https://github.com/python/mypy/issues/10750