Apply attrs' converter to default before omit_if_default check

src/cattrs/gen/__init__.py

@@ -4,7 +4,7 @@
 from collections.abc import Callable, Iterable, Mapping
 from typing import TYPE_CHECKING, Any, Final, Literal, TypeVar
 
-from attrs import NOTHING, Attribute, Factory
+from attrs import NOTHING, Attribute, Converter, Factory
 from typing_extensions import NoDefault
 
 from .._compat import (
@@ -177,16 +177,27 @@ def make_dict_unstructure_fn_from_attrs(
             if isinstance(d, Factory):
                 globs[def_name] = d.factory
                 internal_arg_parts[def_name] = d.factory
-                if d.takes_self:
-                    lines.append(f"  if instance.{attr_name} != {def_name}(instance):")
-                else:
-                    lines.append(f"  if instance.{attr_name} != {def_name}():")
-                lines.append(f"    res['{kn}'] = {invoke}")
+                def_str = f"{def_name}(instance)" if d.takes_self else f"{def_name}()"
             else:
                 globs[def_name] = d
                 internal_arg_parts[def_name] = d
-                lines.append(f"  if instance.{attr_name} != {def_name}:")
-                lines.append(f"    res['{kn}'] = {invoke}")
+                def_str = def_name
+
+            c = a.converter
+            if c is not None:
+                conv_name = f"__c_conv_{attr_name}"
+                globs[conv_name] = c
+                internal_arg_parts[conv_name] = c
+                if isinstance(c, Converter):
+                    field_name = f"__c_field_{attr_name}"
+                    globs[field_name] = a
+                    internal_arg_parts[field_name] = a
+                    def_str = f"{conv_name}({def_str}, instance, {field_name})"
+                else:
+                    def_str = f"{conv_name}({def_str})"
+
+            lines.append(f"  if instance.{attr_name} != {def_str}:")
+            lines.append(f"    res['{kn}'] = {invoke}")
 
         else:
             # No default or no override.

tests/test_converter.py

@@ -16,6 +16,7 @@
     Union,
 )
 
+import attrs
 import pytest
 from attrs import Factory, define, field, fields, has, make_class
 from hypothesis import assume, given
@@ -339,6 +340,31 @@ class C:
     assert inst == converter.structure(unstructured, C)
 
 
+@given(simple_typed_classes(defaults="always", allow_nan=False))
+def test_omit_default_with_attrs_converter_roundtrip(cl_and_vals):
+    """
+    Omit default with attrs' converter on the converter works.
+    """
+    converter = Converter(omit_if_default=True)
+    cl, vals, kwargs = cl_and_vals
+
+    @define
+    class C:
+        a1: int = field(default="1", converter=int)
+        a2: int = field(default="1", converter=attrs.Converter(int))
+        c: cl = Factory(lambda: cl(*vals, **kwargs))
+
+    inst = C()
+    unstructured = converter.unstructure(inst)
+    assert unstructured == {}
+    assert inst == converter.structure(unstructured, C)
+
+    inst = C(0, 0)
+    unstructured = converter.unstructure(inst)
+    assert unstructured == {"a1": 0, "a2": 0}
+    assert inst == converter.structure(unstructured, C)
+
+
 def test_dict_roundtrip_with_alias():
     """
     A class with an aliased attribute can be unstructured and structured.