fix(inheritance): ensure field inheritance does not mutate parent class

src/trame_dataclass/v2.py

@@ -139,12 +139,15 @@ def _setup_class_fields(owner):
         "CLIENT_ONLY_NAMES",
         "CLIENT_DEEP_REACTIVE",
     ]:
-        if not hasattr(owner, key):
-            setattr(owner, key, set())
+        if key not in owner.__dict__:
+            parent_set = getattr(owner, key, set())
+            setattr(owner, key, set(parent_set))
+
     # dict
     for key in ["ENCODERS", "TYPE_CHECKING"]:
-        if not hasattr(owner, key):
-            setattr(owner, key, {})
+        if key not in owner.__dict__:
+            parent_dict = getattr(owner, key, {})
+            setattr(owner, key, dict(parent_dict))
 
 
 def check_forward_ref(ref_name):

tests/test_inheritance_v2.py

@@ -0,0 +1,67 @@
+from trame_dataclass.v2 import (
+    StateDataModel,
+    Sync,
+)
+
+
+def test_inheritance_field_names():
+    class Simple(StateDataModel):
+        a = Sync(int, 1)
+        b = Sync(int, 2)
+
+    class Complex(Simple):
+        c = Sync(int, 3)
+
+    assert "a" in Complex.FIELD_NAMES
+    assert "b" in Complex.FIELD_NAMES
+    assert "c" in Complex.FIELD_NAMES
+
+    assert "c" not in Simple.FIELD_NAMES
+
+
+def test_inheritance_runtime_behavior():
+    class Simple(StateDataModel):
+        a = Sync(int, 10)
+
+    class Complex(Simple):
+        b = Sync(int, 20)
+
+    simple_obj = Simple()
+    assert isinstance(simple_obj, Simple)
+    assert not isinstance(simple_obj, Complex)
+
+    complex_obj = Complex()
+    assert isinstance(complex_obj, Simple)
+    assert isinstance(complex_obj, Complex)
+
+    assert simple_obj.a == 10
+    assert complex_obj.a == 10
+    assert complex_obj.b == 20
+
+    simple_obj.a = 15
+    complex_obj.a = 5
+    complex_obj.b = 25
+
+    assert simple_obj.a == 15
+    assert complex_obj.a == 5
+    assert complex_obj.b == 25
+
+
+def test_inheritance_field_isolation():
+    class A(StateDataModel):
+        x = Sync(int, 1)
+
+    class B(A):
+        y = Sync(int, 2)
+
+    class C(A):
+        z = Sync(int, 3)
+
+    # B and C should not share mutations
+    assert "y" in B.FIELD_NAMES
+    assert "y" not in A.FIELD_NAMES
+    assert "y" not in C.FIELD_NAMES
+
+    assert "z" in C.FIELD_NAMES
+    assert "z" not in A.FIELD_NAMES
+    assert "z" not in B.FIELD_NAMES