Bugfix - prevent Prefab and get_attributes from converting subclasses downwards to Attributes

Author: DavidCEllis

src/ducktools/classbuilder/__init__.py

@@ -1139,13 +1139,16 @@ def field_annotation_gatherer(cls_or_ns, *, cls_annotations=None):
                 if isinstance(attrib, field_type):
                     kw_only = attrib.kw_only or kw_flag
 
-                    attrib = field_type.from_field(attrib, type=v, kw_only=kw_only)
+                    # Don't try to down convert subclass instances
+                    attrib_type = type(attrib)
+                    attrib = attrib_type.from_field(attrib, type=v, kw_only=kw_only)
 
                     if attrib.default is not NOTHING and leave_default_values:
                         modifications[k] = attrib.default
                     else:
                         # NOTHING sentinel indicates a value should be removed
                         modifications[k] = NOTHING
+
                 elif not isinstance(attrib, _MemberDescriptorType):
                     attrib = field_type(default=attrib, type=v, kw_only=kw_flag)
                     if not leave_default_values:

src/ducktools/classbuilder/prefab.py

@@ -73,9 +73,10 @@ def get_attributes(cls, *, local=False):
     """
     attributes = get_fields(cls, local=local)
 
-    if any(type(obj) is not Attribute for obj in attributes.values()):
+    if any(type(obj) is Field for obj in attributes.values()):
         attributes = {
-            k: Attribute.from_field(v) for k, v in attributes.items()
+            k: Attribute.from_field(v) if type(v) is Field else v
+            for k, v in attributes.items()
         }
 
     return attributes

tests/prefab/test_get_methods.py

@@ -2,15 +2,54 @@
 from textwrap import indent
 from unittest.mock import patch
 
-from ducktools.classbuilder import get_methods, get_generated_code, print_generated_code, INTERNALS_DICT
-from ducktools.classbuilder.prefab import Prefab
+from ducktools.classbuilder import (
+    get_methods,
+    get_generated_code,
+    print_generated_code,
+    slotclass,
+    SlotFields,
+    INTERNALS_DICT,
+)
+from ducktools.classbuilder.prefab import attribute, get_attributes, Attribute, Prefab
 
 
 class Example(Prefab):
     a: int = 42
     b: str = "Life the Universe and Everything"
 
 
+def test_get_attributes():
+    expected = {
+        "a": attribute(default=42, type=int),
+        "b": attribute(default="Life the Universe and Everything", type=str),
+    }
+    assert get_attributes(Example) == expected
+
+def test_get_attributes_converts_upward():
+    expected = {
+        "a": attribute(default=42),
+    }
+    @slotclass
+    class HasFields:
+        __slots__ = SlotFields(a=42)
+
+    assert get_attributes(HasFields) == expected
+
+
+def test_get_attributes_not_converting_downward():
+    class NewAttribute(Attribute):
+        new_arg: int = 42
+
+    class HasNewAttribute(Prefab):
+        a: str = NewAttribute(default="Oh dear not again")
+
+    expected = {
+        "a": NewAttribute(default="Oh dear not again", type=str)
+    }
+
+    assert get_attributes(HasNewAttribute) == expected
+
+
 def test_get_generated_code_keys():
     assert get_methods(Example).keys() == get_generated_code(Example).keys()