From c0f25e93e4a9d0a7d3cdb4ed3d2ad6fe5ed78b21 Mon Sep 17 00:00:00 2001
From: Tristan Simas <tristan.simas@mail.mcgill.ca>
Date: Sat, 3 Oct 2026 20:56:33 -0400
Subject: [PATCH] Keep authored nominal subtypes in clean nested source (#1)

---
 src/pycodify/formatters.py |  6 +++++-
 tests/test_core.py         | 32 +++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/src/pycodify/formatters.py b/src/pycodify/formatters.py
index fb90c68..b58290a 100644
--- a/src/pycodify/formatters.py
+++ b/src/pycodify/formatters.py
@@ -328,7 +328,11 @@ def _format_dataclass_expression(
                 current_value,
                 field_ctx,
             )
-            if context.clean_mode and not nested_has_fields:
+            if (
+                context.clean_mode
+                and not nested_has_fields
+                and type(current_value) is type(default_value)
+            ):
                 continue
             imports |= nested_imports
             lines.append(f"{field_name}={nested_code}")
diff --git a/tests/test_core.py b/tests/test_core.py
index 31a8e1f..e703a4e 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -1,7 +1,7 @@
 """Tests for pycodify.core module."""
 
 import pytest
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from enum import Enum
 from types import MappingProxyType
 
@@ -29,6 +29,36 @@ class SimpleConfig:
     enabled: bool = True
 
 
+@dataclass
+class VolumeConfig(SimpleConfig):
+    depth: int = 60
+
+
+@dataclass
+class NominalConfig(SimpleConfig):
+    pass
+
+
+@dataclass
+class NestedConfig:
+    image: SimpleConfig = field(default_factory=SimpleConfig)
+
+
+@pytest.mark.parametrize("image_type", [VolumeConfig, NominalConfig])
+def test_clean_nested_defaults_preserve_authored_nominal_owner(image_type):
+    config = NestedConfig(image=image_type())
+    source = generate_python_source(Assignment("config", config), clean_mode=True)
+    namespace = {}
+    exec(source, namespace)
+    assert type(namespace["config"].image) is image_type
+    assert namespace["config"] == config
+
+
+def test_clean_nested_unchanged_default_remains_omitted():
+    source = generate_python_source(Assignment("config", NestedConfig()), clean_mode=True)
+    assert "image=" not in source
+
+
 class ExtensionProbe:
     pass