Honor dict_factory in generated unstructure hooks

HISTORY.md

@@ -13,6 +13,8 @@ Our backwards-compatibility policy can be found [here](https://github.com/python
 
 ## NEXT
 
+- The generated unstructure hooks now honor the converter's `dict_factory` (for example `Converter(dict_factory=OrderedDict)`), like `BaseConverter.unstructure_attrs_asdict` already did.
+  ([#228](https://github.com/python-attrs/cattrs/issues/228))
 - Fix the msgspec converter passing typed deques directly to the encoder, which cannot serialize them. Deques are now unstructured into lists, including when nested in attrs classes or dataclasses.
   ([#818](https://github.com/python-attrs/cattrs/issues/818) [#819](https://github.com/python-attrs/cattrs/pull/819))
 

src/cattrs/gen/__init__.py

@@ -227,22 +227,39 @@ def make_dict_unstructure_fn_from_attrs(
 
         else:
             # No default or no override.
-            invocation_lines.append(f"{kn!r}: {invoke},")
+            invocation_lines.append((kn, invoke))
+
+    # If the converter has a custom dict factory, the result must be built
+    # using it (like `BaseConverter.unstructure_attrs_asdict` does) instead
+    # of a plain dict literal.
+    use_dict_factory = converter._dict_factory is not dict
+    if use_dict_factory:
+        globs["__c_dict_factory"] = converter._dict_factory
+        internal_arg_parts["__c_dict_factory"] = converter._dict_factory
 
     internal_arg_line = ", ".join([f"{i}={i}" for i in internal_arg_parts])
     if internal_arg_line:
         internal_arg_line = f", {internal_arg_line}"
     for k, v in internal_arg_parts.items():
         globs[k] = v
 
-    total_lines = (
-        [f"def {fn_name}(instance{internal_arg_line}):"]
-        + ["  res = {"]
-        + [f"    {line}" for line in invocation_lines]
-        + ["  }"]
-        + lines
-        + ["  return res"]
-    )
+    if use_dict_factory:
+        total_lines = (
+            [f"def {fn_name}(instance{internal_arg_line}):"]
+            + ["  res = __c_dict_factory()"]
+            + [f"  res[{kn!r}] = {invoke}" for kn, invoke in invocation_lines]
+            + lines
+            + ["  return res"]
+        )
+    else:
+        total_lines = (
+            [f"def {fn_name}(instance{internal_arg_line}):"]
+            + ["  res = {"]
+            + [f"    {kn!r}: {invoke}," for kn, invoke in invocation_lines]
+            + ["  }"]
+            + lines
+            + ["  return res"]
+        )
     script = "\n".join(total_lines)
     fname = generate_unique_filename(
         cl, "unstructure", lines=total_lines if _cattrs_use_linecache else []

tests/test_gen_dict.py

@@ -1,5 +1,6 @@
 """Tests for generated dict functions."""
 
+from collections import OrderedDict
 from dataclasses import dataclass
 from math import ceil
 from typing import Annotated, Dict, Literal, Type, Union
@@ -794,3 +795,36 @@ def test_fields_exception():
     """fields() raises on a non-attrs, non-dataclass class."""
     with pytest.raises(Exception):  # noqa: B017
         fields(int)
+
+
+def test_dict_factory_used_by_generated_hooks():
+    """Generated unstructure hooks honor the converter's `dict_factory`.
+
+    Regression test for https://github.com/python-attrs/cattrs/issues/228
+    """
+
+    @define
+    class Inner:
+        x: int
+
+    @define
+    class Outer:
+        inner: Inner
+        a: int = 1
+
+    converter = Converter(dict_factory=OrderedDict)
+
+    res = converter.unstructure(Outer(Inner(2)))
+    assert isinstance(res, OrderedDict)
+    assert isinstance(res["inner"], OrderedDict)
+    assert res == {"inner": {"x": 2}, "a": 1}
+
+    # Also through an explicitly generated hook.
+    hook = make_dict_unstructure_fn(Outer, converter)
+    assert isinstance(hook(Outer(Inner(2))), OrderedDict)
+
+    # And with a converter omitting defaults.
+    omitting = Converter(dict_factory=OrderedDict, omit_if_default=True)
+    res = omitting.unstructure(Outer(Inner(2)))
+    assert isinstance(res, OrderedDict)
+    assert res == {"inner": {"x": 2}}