Fix nested dataclass with init=False not working correctly (#650)

CHANGELOG.rst

@@ -22,6 +22,8 @@ Fixed
 - Adding ``attrs.define`` dataclasses with nested dataclasses that are marked with
   ``attrs.field`` (such as for a default factory) are not parsed correctly (`#643
   <https://github.com/omni-us/jsonargparse/pull/643>`__)
+- Nested dataclass with ``init=False`` not working correctly (`#650
+  <https://github.com/omni-us/jsonargparse/pull/650>`__).
 
 
 v4.35.0 (2024-12-16)

jsonargparse/_signatures.py

@@ -122,6 +122,10 @@ def add_class_arguments(
                 defaults = default.lazy_get_init_args().as_dict()
             elif is_dataclass_like(default.__class__):
                 defaults = dataclass_to_dict(default)
+                args = set(k[len(prefix) :] for k in added_args)
+                skip_not_added = [k for k in defaults if k not in args]
+                if skip_not_added:
+                    skip.update(skip_not_added)  # skip init=False
             elif isinstance(default, Namespace):
                 defaults = default.as_dict()
             if defaults:
@@ -428,9 +432,10 @@ def _add_signature_parameter(
                 kwargs.update(sub_add_kwargs)
             with ActionTypeHint.allow_default_instance_context():
                 action = container.add_argument(*args, **kwargs)
-            action.sub_add_kwargs = sub_add_kwargs
-            if is_subclass_typehint and len(subclass_skip) > 0:
-                action.sub_add_kwargs["skip"] = subclass_skip
+            if action is not None:  # None when class without any parameters
+                action.sub_add_kwargs = sub_add_kwargs
+                if is_subclass_typehint and len(subclass_skip) > 0:
+                    action.sub_add_kwargs["skip"] = subclass_skip
             added_args.append(dest)
         elif is_required and fail_untyped:
             raise ValueError(

jsonargparse_tests/test_dataclass_like.py

@@ -255,6 +255,27 @@ def test_dataclass_field_init_false(parser):
     assert isinstance(init.data, DataInitFalse)
 
 
+@dataclasses.dataclass
+class NestedDataInitFalse:
+    x: bool = dataclasses.field(default=False, init=False)
+
+
+@dataclasses.dataclass
+class ParentDataInitFalse:
+    y: NestedDataInitFalse = dataclasses.field(default_factory=NestedDataInitFalse)
+
+
+def test_nested_dataclass_field_init_false(parser):
+    parser.add_class_arguments(ParentDataInitFalse, "data")
+    assert parser.get_defaults() == Namespace()
+    cfg = parser.parse_args([])
+    assert cfg == Namespace()
+    init = parser.instantiate_classes(cfg)
+    assert isinstance(init.data, ParentDataInitFalse)
+    assert isinstance(init.data.y, NestedDataInitFalse)
+    assert init.data.y.x is False
+
+
 @dataclasses.dataclass
 class DataFieldFactory:
     a1: List[int] = dataclasses.field(default_factory=lambda: [1, 2, 3])