test_slots.py

# SPDX-License-Identifier: MIT

"""
Unit tests for slots-related functionality.
"""

import pickle
import sys
import types
import weakref

import pytest

import attr

from attr._compat import PYPY, just_warn, make_set_closure_cell


# Pympler doesn't work on PyPy.
try:
    from pympler.asizeof import asizeof

    has_pympler = True
except BaseException:  # Won't be an import error.
    has_pympler = False


@attr.s
class C1:
    x = attr.ib(validator=attr.validators.instance_of(int))
    y = attr.ib()

    def method(self):
        return self.x

    @classmethod
    def classmethod(cls):
        return "clsmethod"

    @staticmethod
    def staticmethod():
        return "staticmethod"

    def my_class(self):
        return __class__

    def my_super(self):
        """Just to test out the no-arg super."""
        return super().__repr__()


@attr.s(slots=True, hash=True)
class C1Slots:
    x = attr.ib(validator=attr.validators.instance_of(int))
    y = attr.ib()

    def method(self):
        return self.x

    @classmethod
    def classmethod(cls):
        return "clsmethod"

    @staticmethod
    def staticmethod():
        return "staticmethod"

    def my_class(self):
        return __class__

    def my_super(self):
        """Just to test out the no-arg super."""
        return super().__repr__()


def test_slots_being_used():
    """
    The class is really using __slots__.
    """
    non_slot_instance = C1(x=1, y="test")
    slot_instance = C1Slots(x=1, y="test")

    assert "__dict__" not in dir(slot_instance)
    assert "__slots__" in dir(slot_instance)

    assert "__dict__" in dir(non_slot_instance)
    assert "__slots__" not in dir(non_slot_instance)

    assert {"__weakref__", "x", "y"} == set(slot_instance.__slots__)

    if has_pympler:
        assert asizeof(slot_instance) < asizeof(non_slot_instance)

    non_slot_instance.t = "test"
    with pytest.raises(AttributeError):
        slot_instance.t = "test"

    assert 1 == non_slot_instance.method()
    assert 1 == slot_instance.method()

    assert attr.fields(C1Slots) == attr.fields(C1)
    assert attr.asdict(slot_instance) == attr.asdict(non_slot_instance)


def test_basic_attr_funcs():
    """
    Comparison, `__eq__`, `__hash__`, `__repr__`, `attrs.asdict` work.
    """
    a = C1Slots(x=1, y=2)
    b = C1Slots(x=1, y=3)
    a_ = C1Slots(x=1, y=2)

    # Comparison.
    assert b > a

    assert a_ == a

    # Hashing.
    hash(b)  # Just to assert it doesn't raise.

    # Repr.
    assert "C1Slots(x=1, y=2)" == repr(a)

    assert {"x": 1, "y": 2} == attr.asdict(a)


def test_inheritance_from_nonslots():
    """
    Inheritance from a non-slotted class works.

    Note that a slotted class inheriting from an ordinary class loses most of
    the benefits of slotted classes, but it should still work.
    """

    @attr.s(slots=True, hash=True)
    class C2Slots(C1):
        z = attr.ib()

    c2 = C2Slots(x=1, y=2, z="test")

    assert 1 == c2.x
    assert 2 == c2.y
    assert "test" == c2.z

    c2.t = "test"  # This will work, using the base class.

    assert "test" == c2.t

    assert 1 == c2.method()
    assert "clsmethod" == c2.classmethod()
    assert "staticmethod" == c2.staticmethod()

    assert {"z"} == set(C2Slots.__slots__)

    c3 = C2Slots(x=1, y=3, z="test")

    assert c3 > c2

    c2_ = C2Slots(x=1, y=2, z="test")

    assert c2 == c2_

    assert "C2Slots(x=1, y=2, z='test')" == repr(c2)

    hash(c2)  # Just to assert it doesn't raise.

    assert {"x": 1, "y": 2, "z": "test"} == attr.asdict(c2)


def test_nonslots_these():
    """
    Enhancing a dict class using 'these' works.

    This will actually *replace* the class with another one, using slots.
    """

    class SimpleOrdinaryClass:
        def __init__(self, x, y, z):
            self.x = x
            self.y = y
            self.z = z

        def method(self):
            return self.x

        @classmethod
        def classmethod(cls):
            return "clsmethod"

        @staticmethod
        def staticmethod():
            return "staticmethod"

    C2Slots = attr.s(
        these={"x": attr.ib(), "y": attr.ib(), "z": attr.ib()},
        init=False,
        slots=True,
        hash=True,
    )(SimpleOrdinaryClass)

    c2 = C2Slots(x=1, y=2, z="test")
    assert 1 == c2.x
    assert 2 == c2.y
    assert "test" == c2.z
    with pytest.raises(AttributeError):
        c2.t = "test"  # We have slots now.

    assert 1 == c2.method()
    assert "clsmethod" == c2.classmethod()
    assert "staticmethod" == c2.staticmethod()

    assert {"__weakref__", "x", "y", "z"} == set(C2Slots.__slots__)

    c3 = C2Slots(x=1, y=3, z="test")
    assert c3 > c2
    c2_ = C2Slots(x=1, y=2, z="test")
    assert c2 == c2_

    assert "SimpleOrdinaryClass(x=1, y=2, z='test')" == repr(c2)

    hash(c2)  # Just to assert it doesn't raise.

    assert {"x": 1, "y": 2, "z": "test"} == attr.asdict(c2)


def test_inheritance_from_slots():
    """
    Inheriting from an attrs slotted class works.
    """

    @attr.s(slots=True, hash=True)
    class C2Slots(C1Slots):
        z = attr.ib()

    @attr.s(slots=True, hash=True)
    class C2(C1):
        z = attr.ib()

    c2 = C2Slots(x=1, y=2, z="test")
    assert 1 == c2.x
    assert 2 == c2.y
    assert "test" == c2.z

    assert {"z"} == set(C2Slots.__slots__)

    assert 1 == c2.method()
    assert "clsmethod" == c2.classmethod()
    assert "staticmethod" == c2.staticmethod()

    with pytest.raises(AttributeError):
        c2.t = "test"

    non_slot_instance = C2(x=1, y=2, z="test")
    if has_pympler:
        assert asizeof(c2) < asizeof(non_slot_instance)

    c3 = C2Slots(x=1, y=3, z="test")
    assert c3 > c2
    c2_ = C2Slots(x=1, y=2, z="test")
    assert c2 == c2_

    assert "C2Slots(x=1, y=2, z='test')" == repr(c2)

    hash(c2)  # Just to assert it doesn't raise.

    assert {"x": 1, "y": 2, "z": "test"} == attr.asdict(c2)


def test_inheritance_from_slots_with_attribute_override():
    """
    Inheriting from a slotted class doesn't re-create existing slots
    """

    class HasXSlot:
        __slots__ = ("x",)

    @attr.s(slots=True, hash=True)
    class C2Slots(C1Slots):
        # y re-defined here but it shouldn't get a slot
        y = attr.ib()
        z = attr.ib()

    @attr.s(slots=True, hash=True)
    class NonAttrsChild(HasXSlot):
        # Parent class has slot for "x" already, so we skip it
        x = attr.ib()
        y = attr.ib()
        z = attr.ib()

    c2 = C2Slots(1, 2, "test")
    assert 1 == c2.x
    assert 2 == c2.y
    assert "test" == c2.z

    assert {"z"} == set(C2Slots.__slots__)

    na = NonAttrsChild(1, 2, "test")
    assert 1 == na.x
    assert 2 == na.y
    assert "test" == na.z

    assert {"__weakref__", "y", "z"} == set(NonAttrsChild.__slots__)


def test_inherited_slot_reuses_slot_descriptor():
    """
    We reuse slot descriptor for an attr.ib defined in a slotted attr.s
    """

    class HasXSlot:
        __slots__ = ("x",)

    class OverridesX(HasXSlot):
        @property
        def x(self):
            return None

    @attr.s(slots=True)
    class Child(OverridesX):
        x = attr.ib()

    assert Child.x is not OverridesX.x
    assert Child.x is HasXSlot.x

    c = Child(1)
    assert 1 == c.x
    assert set() == set(Child.__slots__)

    ox = OverridesX()
    assert ox.x is None


def test_bare_inheritance_from_slots():
    """
    Inheriting from a bare attrs slotted class works.
    """

    @attr.s(
        init=False, eq=False, order=False, hash=False, repr=False, slots=True
    )
    class C1BareSlots:
        x = attr.ib(validator=attr.validators.instance_of(int))
        y = attr.ib()

        def method(self):
            return self.x

        @classmethod
        def classmethod(cls):
            return "clsmethod"

        @staticmethod
        def staticmethod():
            return "staticmethod"

    @attr.s(init=False, eq=False, order=False, hash=False, repr=False)
    class C1Bare:
        x = attr.ib(validator=attr.validators.instance_of(int))
        y = attr.ib()

        def method(self):
            return self.x

        @classmethod
        def classmethod(cls):
            return "clsmethod"

        @staticmethod
        def staticmethod():
            return "staticmethod"

    @attr.s(slots=True, hash=True)
    class C2Slots(C1BareSlots):
        z = attr.ib()

    @attr.s(slots=True, hash=True)
    class C2(C1Bare):
        z = attr.ib()

    c2 = C2Slots(x=1, y=2, z="test")
    assert 1 == c2.x
    assert 2 == c2.y
    assert "test" == c2.z

    assert 1 == c2.method()
    assert "clsmethod" == c2.classmethod()
    assert "staticmethod" == c2.staticmethod()

    with pytest.raises(AttributeError):
        c2.t = "test"

    non_slot_instance = C2(x=1, y=2, z="test")
    if has_pympler:
        assert asizeof(c2) < asizeof(non_slot_instance)

    c3 = C2Slots(x=1, y=3, z="test")
    assert c3 > c2
    c2_ = C2Slots(x=1, y=2, z="test")
    assert c2 == c2_

    assert "C2Slots(x=1, y=2, z='test')" == repr(c2)

    hash(c2)  # Just to assert it doesn't raise.

    assert {"x": 1, "y": 2, "z": "test"} == attr.asdict(c2)


class TestClosureCellRewriting:
    def test_closure_cell_rewriting(self):
        """
        Slotted classes support proper closure cell rewriting.

        This affects features like `__class__` and the no-arg super().
        """
        non_slot_instance = C1(x=1, y="test")
        slot_instance = C1Slots(x=1, y="test")

        assert non_slot_instance.my_class() is C1
        assert slot_instance.my_class() is C1Slots

        # Just assert they return something, and not an exception.
        assert non_slot_instance.my_super()
        assert slot_instance.my_super()

    def test_inheritance(self):
        """
        Slotted classes support proper closure cell rewriting when inheriting.

        This affects features like `__class__` and the no-arg super().
        """

        @attr.s
        class C2(C1):
            def my_subclass(self):
                return __class__

        @attr.s
        class C2Slots(C1Slots):
            def my_subclass(self):
                return __class__

        non_slot_instance = C2(x=1, y="test")
        slot_instance = C2Slots(x=1, y="test")

        assert non_slot_instance.my_class() is C1
        assert slot_instance.my_class() is C1Slots

        # Just assert they return something, and not an exception.
        assert non_slot_instance.my_super()
        assert slot_instance.my_super()

        assert non_slot_instance.my_subclass() is C2
        assert slot_instance.my_subclass() is C2Slots

    @pytest.mark.parametrize("slots", [True, False])
    def test_cls_static(self, slots):
        """
        Slotted classes support proper closure cell rewriting for class- and
        static methods.
        """
        # Python can reuse closure cells, so we create new classes just for
        # this test.

        @attr.s(slots=slots)
        class C:
            @classmethod
            def clsmethod(cls):
                return __class__

        assert C.clsmethod() is C

        @attr.s(slots=slots)
        class D:
            @staticmethod
            def statmethod():
                return __class__

        assert D.statmethod() is D

    @pytest.mark.skipif(PYPY, reason="set_closure_cell always works on PyPy")
    @pytest.mark.skipif(
        sys.version_info >= (3, 8),
        reason="can't break CodeType.replace() via monkeypatch",
    )
    def test_code_hack_failure(self, monkeypatch):
        """
        Keeps working if function/code object introspection doesn't work
        on this (nonstandard) interpreter.

        A warning is emitted that points to the actual code.
        """
        # This is a pretty good approximation of the behavior of
        # the actual types.CodeType on Brython.
        monkeypatch.setattr(types, "CodeType", lambda: None)
        func = make_set_closure_cell()

        with pytest.warns(RuntimeWarning) as wr:
            func()

        w = wr.pop()
        assert __file__ == w.filename
        assert (
            "Running interpreter doesn't sufficiently support code object "
            "introspection.  Some features like bare super() or accessing "
            "__class__ will not work with slotted classes.",
        ) == w.message.args

        assert just_warn is func


@pytest.mark.skipif(PYPY, reason="__slots__ only block weakref on CPython")
def test_not_weakrefable():
    """
    Instance is not weak-referenceable when `weakref_slot=False` in CPython.
    """

    @attr.s(slots=True, weakref_slot=False)
    class C:
        pass

    c = C()

    with pytest.raises(TypeError):
        weakref.ref(c)


@pytest.mark.skipif(
    not PYPY, reason="slots without weakref_slot should only work on PyPy"
)
def test_implicitly_weakrefable():
    """
    Instance is weak-referenceable even when `weakref_slot=False` in PyPy.
    """

    @attr.s(slots=True, weakref_slot=False)
    class C:
        pass

    c = C()
    w = weakref.ref(c)

    assert c is w()


def test_weakrefable():
    """
    Instance is weak-referenceable when `weakref_slot=True`.
    """

    @attr.s(slots=True, weakref_slot=True)
    class C:
        pass

    c = C()
    w = weakref.ref(c)

    assert c is w()


def test_weakref_does_not_add_a_field():
    """
    `weakref_slot=True` does not add a field to the class.
    """

    @attr.s(slots=True, weakref_slot=True)
    class C:
        field = attr.ib()

    assert [f.name for f in attr.fields(C)] == ["field"]


def tests_weakref_does_not_add_when_inheriting_with_weakref():
    """
    `weakref_slot=True` does not add a new __weakref__ slot when inheriting
    one.
    """

    @attr.s(slots=True, weakref_slot=True)
    class C:
        pass

    @attr.s(slots=True, weakref_slot=True)
    class D(C):
        pass

    d = D()
    w = weakref.ref(d)

    assert d is w()


def tests_weakref_does_not_add_with_weakref_attribute():
    """
    `weakref_slot=True` does not add a new __weakref__ slot when an attribute
    of that name exists.
    """

    @attr.s(slots=True, weakref_slot=True)
    class C:
        __weakref__ = attr.ib(
            init=False, hash=False, repr=False, eq=False, order=False
        )

    c = C()
    w = weakref.ref(c)

    assert c is w()


def test_slots_empty_cell():
    """
    Tests that no `ValueError: Cell is empty` exception is raised when
    closure cells are present with no contents in a `slots=True` class.
    (issue https://github.com/python-attrs/attrs/issues/589)

    On Python 3, if a method mentions `__class__` or uses the no-arg `super()`,
    the compiler will bake a reference to the class in the method itself as
    `method.__closure__`. Since `attrs` replaces the class with a clone,
    `_ClassBuilder._create_slots_class(self)` will rewrite these references so
    it keeps working. This method was not properly covering the edge case where
    the closure cell was empty, we fixed it and this is the non-regression
    test.
    """

    @attr.s(slots=True)
    class C:
        field = attr.ib()

        def f(self, a):
            super(C, self).__init__()

    C(field=1)


@attr.s(getstate_setstate=True)
class C2:
    x = attr.ib()


@attr.s(slots=True, getstate_setstate=True)
class C2Slots:
    x = attr.ib()


class TestPickle:
    @pytest.mark.parametrize("protocol", range(pickle.HIGHEST_PROTOCOL))
    def test_pickleable_by_default(self, protocol):
        """
        If nothing else is passed, slotted classes can be pickled and
        unpickled with all supported protocols.
        """
        i1 = C1Slots(1, 2)
        i2 = pickle.loads(pickle.dumps(i1, protocol))

        assert i1 == i2
        assert i1 is not i2

    def test_no_getstate_setstate_for_dict_classes(self):
        """
        As long as getstate_setstate is None, nothing is done to dict
        classes.
        """
        i = C1(1, 2)

        assert None is getattr(i, "__getstate__", None)
        assert None is getattr(i, "__setstate__", None)

    def test_no_getstate_setstate_if_option_false(self):
        """
        Don't add getstate/setstate if getstate_setstate is False.
        """

        @attr.s(slots=True, getstate_setstate=False)
        class C:
            x = attr.ib()

        i = C(42)

        assert None is getattr(i, "__getstate__", None)
        assert None is getattr(i, "__setstate__", None)

    @pytest.mark.parametrize("cls", [C2(1), C2Slots(1)])
    def test_getstate_set_state_force_true(self, cls):
        """
        If getstate_setstate is True, add them unconditionally.
        """
        assert None is not getattr(cls, "__getstate__", None)
        assert None is not getattr(cls, "__setstate__", None)


def test_slots_super_property_get():
    """
    On Python 2/3: the `super(self.__class__, self)` works.
    """

    @attr.s(slots=True)
    class A:
        x = attr.ib()

        @property
        def f(self):
            return self.x

    @attr.s(slots=True)
    class B(A):
        @property
        def f(self):
            return super().f ** 2

    assert B(11).f == 121
    assert B(17).f == 289


def test_slots_super_property_get_shortcut():
    """
    On Python 3, the `super()` shortcut is allowed.
    """

    @attr.s(slots=True)
    class A:
        x = attr.ib()

        @property
        def f(self):
            return self.x

    @attr.s(slots=True)
    class B(A):
        @property
        def f(self):
            return super().f ** 2

    assert B(11).f == 121
    assert B(17).f == 289