Change __getstate__ and __setstate__ to use a dict (#1004) (#1009)

Co-authored-by: Nikola Dipanov <ndipanov@hudson-trading.com>

src/attr/_make.py

@@ -922,7 +922,7 @@ class _ClassBuilder:
             """
             Automatically created by attrs.
             """
-            return tuple(getattr(self, name) for name in state_attr_names)
+            return {name: getattr(self, name) for name in state_attr_names}
 
         hash_caching_enabled = self._cache_hash
 
@@ -931,8 +931,9 @@ class _ClassBuilder:
             Automatically created by attrs.
             """
             __bound_setattr = _obj_setattr.__get__(self)
-            for name, value in zip(state_attr_names, state):
-                __bound_setattr(name, value)
+            for name in state_attr_names:
+                if name in state:
+                    __bound_setattr(name, state[name])
 
             # The hash code cache is not included when the object is
             # serialized, but it still needs to be initialized to None to

tests/test_slots.py

@@ -9,6 +9,8 @@ import sys
 import types
 import weakref
 
+from unittest import mock
+
 import pytest
 
 import attr
@@ -743,3 +745,58 @@ def test_slots_super_property_get_shortcut():
 
     assert B(11).f == 121
     assert B(17).f == 289
+
+
+@attr.s(slots=True)
+class A:
+    x = attr.ib()
+    b = attr.ib()
+    c = attr.ib()
+
+
+@pytest.mark.parametrize("cls", [A])
+def test_slots_unpickle_after_attr_removed(cls):
+    """
+    We don't assign attributes we don't have anymore if the class has
+    removed it.
+    """
+    a = cls(1, 2, 3)
+    a_pickled = pickle.dumps(a)
+    a_unpickled = pickle.loads(a_pickled)
+    assert a_unpickled == a
+
+    @attr.s(slots=True)
+    class NEW_A:
+        x = attr.ib()
+        c = attr.ib()
+
+    with mock.patch(f"{__name__}.A", NEW_A):
+        new_a = pickle.loads(a_pickled)
+        assert new_a.x == 1
+        assert new_a.c == 3
+        assert not hasattr(new_a, "b")
+
+
+@pytest.mark.parametrize("cls", [A])
+def test_slots_unpickle_after_attr_added(cls):
+    """
+    We don't assign attribute we haven't had before if the class has one added.
+    """
+    a = cls(1, 2, 3)
+    a_pickled = pickle.dumps(a)
+    a_unpickled = pickle.loads(a_pickled)
+    assert a_unpickled == a
+
+    @attr.s(slots=True)
+    class NEW_A:
+        x = attr.ib()
+        b = attr.ib()
+        d = attr.ib()
+        c = attr.ib()
+
+    with mock.patch(f"{__name__}.A", NEW_A):
+        new_a = pickle.loads(a_pickled)
+        assert new_a.x == 1
+        assert new_a.b == 2
+        assert new_a.c == 3
+        assert not hasattr(new_a, "d")