gh-90562: Improve zero argument support for super() in dataclasses when slots=True

Lib/dataclasses.py

@@ -1222,11 +1222,6 @@ def _get_slots(cls):
 
 
 def _update_func_cell_for__class__(f, oldcls, newcls):
-    # Returns True if we update a cell, else False.
-    if f is None:
-        # f will be None in the case of a property where not all of
-        # fget, fset, and fdel are used.  Nothing to do in that case.
-        return False
     try:
         idx = f.__code__.co_freevars.index("__class__")
     except ValueError:
@@ -1235,13 +1230,38 @@ def _update_func_cell_for__class__(f, oldcls, newcls):
     # Fix the cell to point to the new class, if it's already pointing
     # at the old class.  I'm not convinced that the "is oldcls" test
     # is needed, but other than performance can't hurt.
-    closure = f.__closure__[idx]
-    if closure.cell_contents is oldcls:
-        closure.cell_contents = newcls
+    cell = f.__closure__[idx]
+    if cell.cell_contents is oldcls:
+        cell.cell_contents = newcls
         return True
     return False
 
 
+def _find_inner_functions(obj, _seen=None, _depth=0):
+    if _seen is None:
+        _seen = set()
+    if id(obj) in _seen:
+        return None
+    _seen.add(id(obj))
+
+    _depth += 1
+    # Normally just inspection of a descriptor object itself should be enough,
+    # and we should encounter the function as its attribute,
+    # but in case function was wrapped (e.g. functools.partition was used),
+    # we want to dive at least one level deeper.
+    if _depth > 2:
+        return None
+
+    for attr in dir(obj):
+        value = getattr(obj, attr, None)
+        if value is None:
+            continue
+        if isinstance(value, types.FunctionType):
+            yield inspect.unwrap(value)
+            return
+        yield from _find_inner_functions(value, _seen, _depth)
+
+
 def _create_slots(defined_fields, inherited_slots, field_names, weakref_slot):
     # The slots for our class.  Remove slots from our base classes.  Add
     # '__weakref__' if weakref_slot was given, unless it is already present.
@@ -1317,19 +1337,41 @@ def _add_slots(cls, is_frozen, weakref_slot, defined_fields):
     # (the newly created one, which we're returning) and not the
     # original class.  We can break out of this loop as soon as we
     # make an update, since all closures for a class will share a
-    # given cell.
+    # given cell.  First we try to find a pure function or a property,
+    # and then fallback to inspecting custom descriptors
+    # if no pure function or property is found.
+
+    custom_descriptors_to_check = []
     for member in newcls.__dict__.values():
         # If this is a wrapped function, unwrap it.
         member = inspect.unwrap(member)
 
         if isinstance(member, types.FunctionType):
             if _update_func_cell_for__class__(member, cls, newcls):
                 break
-        elif isinstance(member, property):
-            if (_update_func_cell_for__class__(member.fget, cls, newcls)
-                or _update_func_cell_for__class__(member.fset, cls, newcls)
-                or _update_func_cell_for__class__(member.fdel, cls, newcls)):
-                break
+        elif isinstance(member, property) and (
+            any(
+                # Unwrap once more in case function
+                # was wrapped before it became property.
+                _update_func_cell_for__class__(inspect.unwrap(f), cls, newcls)
+                for f in (member.fget, member.fset, member.fdel)
+                if f is not None
+            )
+        ):
+            break
+        elif hasattr(member, "__get__") and not inspect.ismemberdescriptor(
+            member
+        ):
+            # We don't want to inspect custom descriptors just yet
+            # there's still a chance we'll encounter a pure function
+            # or a property and won't have to use slower recursive search.
+            custom_descriptors_to_check.append(member)
+    else:
+        # Now let's ensure custom descriptors won't be left out.
+        for descriptor in custom_descriptors_to_check:
+            for f in _find_inner_functions(descriptor):
+                if _update_func_cell_for__class__(f, cls, newcls):
+                    break
 
     return newcls
 

Lib/test/test_dataclasses/__init__.py

@@ -13,6 +13,8 @@
 import weakref
 import traceback
 import unittest
+from functools import partial
+from functools import update_wrapper
 from unittest.mock import Mock
 from typing import ClassVar, Any, List, Union, Tuple, Dict, Generic, TypeVar, Optional, Protocol, DefaultDict
 from typing import get_type_hints
@@ -5031,6 +5033,201 @@ def foo(self):
 
         A().foo()
 
+    def test_wrapped_property(self):
+        def mydecorator(f):
+            @wraps(f)
+            def wrapper(*args, **kwargs):
+                return f(*args, **kwargs)
+            return wrapper
+
+        class B:
+            @property
+            def foo(self):
+                return "bar"
+
+        @dataclass(slots=True)
+        class A(B):
+            @property
+            @mydecorator
+            def foo(self):
+                return super().foo
+
+        self.assertEqual(A().foo, "bar")
+
+    def test_custom_descriptor(self):
+        class CustomDescriptor:
+            def __init__(self, f):
+                self._f = f
+
+            def __get__(self, instance, owner):
+                return self._f(instance)
+
+        class B:
+            def foo(self):
+                return "bar"
+
+        @dataclass(slots=True)
+        class A(B):
+            @CustomDescriptor
+            def foo(cls):
+                return super().foo()
+
+        self.assertEqual(A().foo, "bar")
+
+    def test_custom_descriptor_wrapped(self):
+        class CustomDescriptor:
+            def __init__(self, f):
+                self._f = update_wrapper(lambda *args, **kwargs: f(*args, **kwargs), f)
+
+            def __get__(self, instance, owner):
+                return self._f(instance)
+
+        class B:
+            def foo(self):
+                return "bar"
+
+        @dataclass(slots=True)
+        class A(B):
+            @CustomDescriptor
+            def foo(cls):
+                return super().foo()
+
+        self.assertEqual(A().foo, "bar")
+
+    def test_custom_nested_descriptor(self):
+        class CustomFunctionWrapper:
+            def __init__(self, f):
+                self._f = f
+
+            def __call__(self, *args, **kwargs):
+                return self._f(*args, **kwargs)
+
+        class CustomDescriptor:
+            def __init__(self, f):
+                self._wrapper = CustomFunctionWrapper(f)
+
+            def __get__(self, instance, owner):
+                return self._wrapper(instance)
+
+        class B:
+            def foo(self):
+                return "bar"
+
+        @dataclass(slots=True)
+        class A(B):
+            @CustomDescriptor
+            def foo(cls):
+                return super().foo()
+
+        self.assertEqual(A().foo, "bar")
+
+    def test_custom_nested_descriptor_with_partial(self):
+        class CustomDescriptor:
+            def __init__(self, f):
+                self._wrapper = partial(f, value="bar")
+
+            def __get__(self, instance, owner):
+                return self._wrapper(instance)
+
+        class B:
+            def foo(self, value):
+                return value
+
+        @dataclass(slots=True)
+        class A(B):
+            @CustomDescriptor
+            def foo(self, value):
+                return super().foo(value)
+
+        self.assertEqual(A().foo, "bar")
+
+    def test_pure_functions_preferred_to_custom_descriptors(self):
+        class CustomDescriptor:
+            def __init__(self, f):
+                self._wrapper = partial(f, value="bar")
+
+            def __get__(self, instance, owner):
+                return self._wrapper(instance)
+
+            def __dir__(self):
+                raise RuntimeError("Never should be accessed")
+
+        class B:
+            def foo(self, value):
+                return value
+
+        with self.assertRaises(RuntimeError) as context:
+            @dataclass(slots=True)
+            class A(B):
+                @CustomDescriptor
+                def foo(self, value): ...
+
+        self.assertEqual(context.exception.args, ("Never should be accessed",))
+
+        @dataclass(slots=True)
+        class A(B):
+            @CustomDescriptor
+            def foo(self, value):
+                return super().foo(value)
+
+            @property
+            def bar(self):
+                return super()
+
+        self.assertEqual(A().foo, "bar")
+
+        @dataclass(slots=True)
+        class A(B):
+            @CustomDescriptor
+            def foo(self, value):
+                return super().foo(value)
+
+            def bar(self):
+                return super()
+
+        self.assertEqual(A().foo, "bar")
+
+    def test_custom_too_nested_descriptor(self):
+        class UnnecessaryNestedWrapper:
+            def __init__(self, wrapper):
+                self._wrapper = wrapper
+
+            def __call__(self, *args, **kwargs):
+                return self._wrapper(*args, **kwargs)
+
+        class CustomFunctionWrapper:
+            def __init__(self, f):
+                self._f = f
+
+            def __call__(self, *args, **kwargs):
+                return self._f(*args, **kwargs)
+
+        class CustomDescriptor:
+            def __init__(self, f):
+                self._wrapper = UnnecessaryNestedWrapper(CustomFunctionWrapper(f))
+
+            def __get__(self, instance, owner):
+                return self._wrapper(instance)
+
+        class B:
+            def foo(self):
+                return "bar"
+
+        @dataclass(slots=True)
+        class A(B):
+            @CustomDescriptor
+            def foo(cls):
+                return super().foo()
+
+        with self.assertRaises(TypeError) as context:
+            A().foo
+
+        expected_error_message = (
+            'super(type, obj): obj (instance of A) is not '
+            'an instance or subtype of type (A).'
+        )
+        self.assertEqual(context.exception.args, (expected_error_message,))
+
     def test_remembered_class(self):
         # Apply the dataclass decorator manually (not when the class
         # is created), so that we can keep a reference to the

Misc/NEWS.d/next/Library/2024-09-27-19-50-30.gh-issue-90562.HeL_JA.rst

@@ -0,0 +1,2 @@
+Modify dataclasses to enable zero argument support for ``super()``  when ``slots=True`` is
+specified and custom descriptor is used or ``property`` function is wrapped.