From 7f5a264f31d5bb45d0a45b0ecd00a99709374624 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dani=C3=ABl=20van=20Noord?=
 <13665637+DanielNoord@users.noreply.github.com>
Date: Tue, 28 Jul 2026 21:09:20 +0200
Subject: [PATCH] Fix `default_factory` for inherited dataclass

---
 mypyc/irbuild/classdef.py         |  4 ++--
 mypyc/test-data/run-python37.test | 12 +++++++++++-
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/mypyc/irbuild/classdef.py b/mypyc/irbuild/classdef.py
index 4fd9a2e2cc748..61587b46161f7 100644
--- a/mypyc/irbuild/classdef.py
+++ b/mypyc/irbuild/classdef.py
@@ -760,7 +760,6 @@ def find_attr_initializers(
     if cls.builtin_base:
         return set(), []
 
-    cls_type = dataclass_type(cdef)
     attrs_with_defaults: set[str] = set()
     default_assignments: list[tuple[AssignmentStmt, str]] = []
 
@@ -774,10 +773,11 @@ def find_attr_initializers(
         info_ir = builder.mapper.type_to_ir.get(info)
         if info_ir is None:
             continue
+        info_cls_type = dataclass_type(info.defn)
         for stmt in info.defn.defs.body:
             if not isinstance(stmt, AssignmentStmt):
                 continue
-            name = default_attr_name(stmt, info_ir, cls_type)
+            name = default_attr_name(stmt, info_ir, info_cls_type)
             if name is None:
                 continue
             attrs_with_defaults.add(name)
diff --git a/mypyc/test-data/run-python37.test b/mypyc/test-data/run-python37.test
index 61d428c17a441..1245ad516a2d9 100644
--- a/mypyc/test-data/run-python37.test
+++ b/mypyc/test-data/run-python37.test
@@ -74,8 +74,15 @@ class Person5:
     friends: Set[str] = field(default_factory=set)
     parents: FrozenSet[str] = frozenset()
 
+@dataclass
+class HasFactoryDefault:
+    x: dict[str, int] = field(default_factory=dict)
+
+class InheritsDataclassInit(HasFactoryDefault):
+    pass
+
 [file other.py]
-from native import Person1, Person1b, Person2, Person3, Person4, Person5, testBool
+from native import Person1, Person1b, Person2, Person3, Person4, Person5, testBool, InheritsDataclassInit
 i1 = Person1(age = 5, name = 'robot')
 assert i1.age == 5
 assert i1.name == 'robot'
@@ -125,6 +132,9 @@ assert Person1.__annotations__ == {'age': int, 'name': str}
 assert Person2.__annotations__ == {'age': int, 'name': str}
 assert Person5.__annotations__ == {'weight': float, 'friends': set,
                                        'parents': frozenset}
+v = InheritsDataclassInit()
+assert isinstance(v.x, dict)
+assert v.x == {}
 
 [file driver.py]
 import sys