bpo-43176: Fix processing of empty dataclasses (GH-24484)
When a dataclass inherits from an empty base, all immutability checks are omitted. This PR fixes this and adds tests for it.
Automerge-Triggered-By: GH:ericvsmith
diff --git a/Lib/dataclasses.py b/Lib/dataclasses.py
index 3de2ec0..afc4b82 100644
--- a/Lib/dataclasses.py
+++ b/Lib/dataclasses.py
@@ -860,7 +860,7 @@ def _process_class(cls, init, repr, eq, order, unsafe_hash, frozen):
# Only process classes that have been processed by our
# decorator. That is, they have a _FIELDS attribute.
base_fields = getattr(b, _FIELDS, None)
- if base_fields:
+ if base_fields is not None:
has_dataclass_bases = True
for f in base_fields.values():
fields[f.name] = f
diff --git a/Lib/test/test_dataclasses.py b/Lib/test/test_dataclasses.py
index 5515ca4..12c1918 100644
--- a/Lib/test/test_dataclasses.py
+++ b/Lib/test/test_dataclasses.py
@@ -2594,6 +2594,30 @@ class D(C):
self.assertEqual(d.i, 0)
self.assertEqual(d.j, 10)
+ def test_inherit_nonfrozen_from_empty_frozen(self):
+ @dataclass(frozen=True)
+ class C:
+ pass
+
+ with self.assertRaisesRegex(TypeError,
+ 'cannot inherit non-frozen dataclass from a frozen one'):
+ @dataclass
+ class D(C):
+ j: int
+
+ def test_inherit_nonfrozen_from_empty(self):
+ @dataclass
+ class C:
+ pass
+
+ @dataclass
+ class D(C):
+ j: int
+
+ d = D(3)
+ self.assertEqual(d.j, 3)
+ self.assertIsInstance(d, C)
+
# Test both ways: with an intermediate normal (non-dataclass)
# class and without an intermediate class.
def test_inherit_nonfrozen_from_frozen(self):
diff --git a/Misc/NEWS.d/next/Library/2021-02-09-07-24-29.bpo-43176.bocNQn.rst b/Misc/NEWS.d/next/Library/2021-02-09-07-24-29.bpo-43176.bocNQn.rst
new file mode 100644
index 0000000..66a175d
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-02-09-07-24-29.bpo-43176.bocNQn.rst
@@ -0,0 +1 @@
+Fixed processing of empty dataclasses.
\ No newline at end of file