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Previously BUILD instruction missed handling for `__slots__`

see handling in pickle code https://github.com/python/cpython/blob/c5b99f5c2c5347d66b9da362773969c531fb6c85/Lib/pickle.py#L1846-L1867

e.g.

```python
from dataclasses import dataclass

# Define the dataclass
dataclass
class MyDataClass:
    __slots__ = ["x", "y"]
    x: int
    y: str
# Create an instance of the dataclass
my_data = MyDataClass(x=2, y=3)
# Save the dataclass to a file
torch.save(my_data, "my_data.pt")
with torch.serialization.safe_globals([MyDataClass]):
    loaded_my_data = torch.load("my_data.pt", weights_only=True)
# AttributeError: 'MyDataClass' object has no attribute '__dict__'
```






[ghstack-poisoned]

Previously `BUILD` instruction missed handling for `__slots__`.

### Background
When does pickle serialize a `BUILD` instruction? When `state` is not `None` and `state_setter` is `None` [[link](https://github.com/python/cpython/blob/c5b99f5c2c5347d66b9da362773969c531fb6c85/Lib/pickle.py#L765)]

`__reduce__`/`__reduce_ex__` are expected to return tuples of length 2 to 6 where `state` is the 3rd argument.

Note the return type for [`__getstate__` ](https://docs.python.org/3/library/pickle.html#object.__getstate__)

- For a class that has no instance [`__dict__`](https://docs.python.org/3/reference/datamodel.html#object.__dict__) and no [`__slots__`](https://docs.python.org/3/reference/datamodel.html#object.__slots__), the default state is None.
- For a class that has an instance [`__dict__`](https://docs.python.org/3/reference/datamodel.html#object.__dict__) and no [`__slots__`](https://docs.python.org/3/reference/datamodel.html#object.__slots__), the default state is `self.__dict__`.
- For a class that has an instance [`__dict__`](https://docs.python.org/3/reference/datamodel.html#object.__dict__) and [`__slots__`](https://docs.python.org/3/reference/datamodel.html#object.__slots__), the default state is a tuple consisting of two dictionaries: `self.__dict__`, and a dictionary mapping slot names to slot values. Only slots that have a value are included in the latter.
- For a class that has [`__slots__`](https://docs.python.org/3/reference/datamodel.html#object.__slots__) and no instance [`__dict__`](https://docs.python.org/3/reference/datamodel.html#object.__dict__), the default state is a tuple whose first item is None and whose second item is a dictionary mapping slot names to slot values described in the previous bullet.

see handling in pickle code https://github.com/python/cpython/blob/c5b99f5c2c5347d66b9da362773969c531fb6c85/Lib/pickle.py#L1846-L1867

Before this PR, this would fail

```python
from dataclasses import dataclass

# Define the dataclass
dataclass
class MyDataClass:
    __slots__ = ["x", "y"]
    x: int
    y: str
# Create an instance of the dataclass
my_data = MyDataClass(x=2, y=3)
# Save the dataclass to a file
torch.save(my_data, "my_data.pt")
with torch.serialization.safe_globals([MyDataClass]):
    loaded_my_data = torch.load("my_data.pt", weights_only=True)
# AttributeError: 'MyDataClass' object has no attribute '__dict__'
```






[ghstack-poisoned]

…ed objects with __slots__"

Previously `BUILD` instruction missed handling for `__slots__`. **This only applies for things allowlisted via `add_safe_globals`/`safe_globals` that use slots.**

### Background
When does pickle serialize a `BUILD` instruction? When `state` is not `None` and `state_setter` is `None` [[link](https://github.com/python/cpython/blob/c5b99f5c2c5347d66b9da362773969c531fb6c85/Lib/pickle.py#L765)]. In this case, the docs tell us that either `__setstate__` or a `__dict__` update will be performed [[link](https://github.com/python/cpython/blob/3.13/Lib/pickletools.py#L1984)]

`__reduce__`/`__reduce_ex__` are expected to return tuples of length 2 to 6 where `state` is the 3rd argument. When user doesn't patch `__reduce__` but patches `__setstate__`/`__getstate__`, state will be what is yielded by `__getstate__`

Note the return type for [`__getstate__` ](https://docs.python.org/3/library/pickle.html#object.__getstate__)

- For a class that has no instance [`__dict__`](https://docs.python.org/3/reference/datamodel.html#object.__dict__) and no [`__slots__`](https://docs.python.org/3/reference/datamodel.html#object.__slots__), the default state is None.
- For a class that has an instance [`__dict__`](https://docs.python.org/3/reference/datamodel.html#object.__dict__) and no [`__slots__`](https://docs.python.org/3/reference/datamodel.html#object.__slots__), the default state is `self.__dict__`.
- For a class that has an instance [`__dict__`](https://docs.python.org/3/reference/datamodel.html#object.__dict__) and [`__slots__`](https://docs.python.org/3/reference/datamodel.html#object.__slots__), the default state is a tuple consisting of two dictionaries: `self.__dict__`, and a dictionary mapping slot names to slot values. Only slots that have a value are included in the latter.
- For a class that has [`__slots__`](https://docs.python.org/3/reference/datamodel.html#object.__slots__) and no instance [`__dict__`](https://docs.python.org/3/reference/datamodel.html#object.__dict__), the default state is a tuple whose first item is None and whose second item is a dictionary mapping slot names to slot values described in the previous bullet.

see handling in pickle code https://github.com/python/cpython/blob/c5b99f5c2c5347d66b9da362773969c531fb6c85/Lib/pickle.py#L1846-L1867

Before this PR, we didn't account for the fact that when `__setstate__` is not defined, `state` might be a tuple so this would fail

```python
from dataclasses import dataclass

# Define the dataclass
dataclass
class MyDataClass:
    __slots__ = ["x", "y"]
    x: int
    y: str
# Create an instance of the dataclass
my_data = MyDataClass(x=2, y=3)
# Save the dataclass to a file
torch.save(my_data, "my_data.pt")
with torch.serialization.safe_globals([MyDataClass]):
    loaded_my_data = torch.load("my_data.pt", weights_only=True)
# AttributeError: 'MyDataClass' object has no attribute '__dict__'
```






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