gh-160665: Recognize dataclass markers deferred by lazy imports

Author: LarryHu0217

Lib/dataclasses.py

@@ -854,6 +854,9 @@ def _get_field(cls, a_name, a_type, default_kw_only):
     # For the complete discussion, see https://bugs.python.org/issue33453
     if isinstance(a_type, str):
         a_type_annotation = _get_type_from_annotation(a_type, cls)
+    elif isinstance(a_type, annotationlib.ForwardRef):
+        # An unresolved lazy import can defer the whole annotation.
+        a_type_annotation = _get_type_from_annotation(a_type.__forward_arg__, cls)
     else:
         a_type_annotation = a_type
 

Lib/test/test_dataclasses/__init__.py

@@ -4530,6 +4530,32 @@ def test_lazy_import_annotations(self):
         self.assertEqual([f.name for f in fields(m.C)], ['x', 'y'])
         self.assertNotIsInstance(vars(m)['t'], types.LazyImportType)
 
+    def test_lazy_import_forwardref_annotations(self):
+        m = import_helper.import_fresh_module(
+            'test.test_dataclasses.dataclass_lazy_initvar',
+            fresh=['test.test_dataclasses.dataclass_lazy_initvar_other'],
+        )
+        self.assertIsNotNone(m)
+        value = m.A()
+        for cls in (m.DirectInitVar, m.QualifiedInitVar, m.AliasedInitVar):
+            with self.subTest(cls=cls):
+                instance = cls(value)
+                self.assertIs(instance.received, value)
+                self.assertEqual(fields(cls), ())
+                self.assertNotIn('value', vars(instance))
+                self.assertIsInstance(cls.__dataclass_fields__['value'].type,
+                                      annotationlib.ForwardRef)
+
+        with self.subTest(cls=m.DeferredClassVar):
+            self.assertEqual(fields(m.DeferredClassVar), ())
+            self.assertEqual(vars(m.DeferredClassVar()), {})
+
+        with self.subTest(cls=m.DeferredField):
+            self.assertEqual([f.name for f in fields(m.DeferredField)], ['value'])
+            self.assertIs(m.DeferredField(value).value, value)
+            self.assertIsInstance(fields(m.DeferredField)[0].type,
+                                  annotationlib.ForwardRef)
+
     def test_text_annotations(self):
         from test.test_dataclasses import dataclass_textanno
 

Lib/test/test_dataclasses/dataclass_lazy_initvar.py

@@ -0,0 +1,16 @@
+from dataclasses import dataclass
+
+from test.test_dataclasses.dataclass_lazy_initvar_other import (
+    AliasedInitVar, DeferredClassVar, DeferredField, DirectInitVar,
+    QualifiedInitVar,
+)
+
+__all__ = [
+    'A', 'AliasedInitVar', 'DeferredClassVar', 'DeferredField',
+    'DirectInitVar', 'QualifiedInitVar',
+]
+
+
+@dataclass
+class A:
+    pass

Lib/test/test_dataclasses/dataclass_lazy_initvar_other.py

@@ -0,0 +1,40 @@
+from dataclasses import dataclass, InitVar
+from dataclasses import InitVar as IV
+from typing import ClassVar
+import dataclasses
+
+lazy from test.test_dataclasses.dataclass_lazy_initvar import A
+
+
+@dataclass
+class DirectInitVar:
+    value: InitVar[A]
+
+    def __post_init__(self, value):
+        self.received = value
+
+
+@dataclass
+class QualifiedInitVar:
+    value: dataclasses.InitVar[A]
+
+    def __post_init__(self, value):
+        self.received = value
+
+
+@dataclass
+class AliasedInitVar:
+    value: IV[A]
+
+    def __post_init__(self, value):
+        self.received = value
+
+
+@dataclass
+class DeferredClassVar:
+    value: ClassVar[A] = None
+
+
+@dataclass
+class DeferredField:
+    value: A

Misc/NEWS.d/next/Library/2026-10-25-10-12-00.gh-issue-160665.3jLz8x.rst

@@ -0,0 +1,3 @@
+Fix :func:`dataclasses.dataclass` handling of :class:`~dataclasses.InitVar` and
+:data:`~typing.ClassVar` annotations when a lazy import cannot yet be resolved
+during a circular import.