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