Fix false positive on generic NamedTuple __new__

mypy/checker.py

@@ -8463,13 +8463,7 @@ def get_type_range_of_type(self, typ: Type) -> TypeRange | None:
             return TypeRange(item, is_upper_bound=True)
         if isinstance(typ, FunctionLike) and typ.is_type_obj():
             # If a type is generic, `isinstance` can only narrow its variables to Any.
-            any_parameterized = fill_typevars_with_any(typ.type_object())
-            # Tuples may have unattended type variables among their items
-            if isinstance(any_parameterized, TupleType):
-                erased_type = erase_typevars(any_parameterized)
-            else:
-                erased_type = any_parameterized
-            return TypeRange(erased_type, is_upper_bound=False)
+            return TypeRange(fill_typevars_with_any(typ.type_object()), is_upper_bound=False)
         if isinstance(typ, TypeType):
             # Type[A] means "any type that is a subtype of A" rather than "precisely type A"
             # we indicate this by setting is_upper_bound flag

mypy/typevars.py

@@ -70,7 +70,7 @@ def fill_typevars_with_any(typ: TypeInfo) -> Instance | TupleType:
     erased_tuple_type = erase_typevars(typ.tuple_type, {tv.id for tv in typ.defn.type_vars})
     assert isinstance(erased_tuple_type, ProperType)
     if isinstance(erased_tuple_type, TupleType):
-        return typ.tuple_type.copy_modified(fallback=inst)
+        return erased_tuple_type.copy_modified(fallback=inst)
     return inst
 
 

test-data/unit/check-namedtuple.test

@@ -875,7 +875,7 @@ def f(o: Base) -> None:
 [out]
 
 [case testNamedTupleNew]
-from typing import NamedTuple
+from typing import Generic, NamedTuple, TypeVar
 
 Base = NamedTuple('Base', [('param', int)])
 
@@ -885,6 +885,18 @@ class Child(Base):
 
 Base(param=10)
 Child(param=10)
+
+T = TypeVar("T")
+class GenericBase(NamedTuple, Generic[T]):
+    value: T
+
+class GenericChild(GenericBase[T]):
+    def __new__(cls, value: int) -> GenericChild[int]:
+        raise BaseException
+
+class BadChild(GenericBase[T]):
+    def __new__(cls, value: int) -> GenericBase[int]:  # E: Incompatible return type for "__new__" (returns "GenericBase[int]", but must return a subtype of "BadChild[Any]")
+        raise BaseException
 [builtins fixtures/tuple.pyi]
 
 [case testNamedTupleClassMethodWithGenericReturnValue]