Fixed nested generic dataclasses not working correctly (#709)

Author: mauvilsa

CHANGELOG.rst

@@ -36,6 +36,8 @@ Fixed
 ^^^^^
 - ``ActionParser`` not updating ``dest`` of groups for instantiation (`#707
   <https://github.com/omni-us/jsonargparse/pull/707>`__).
+- Nested generic dataclasses not working correctly (`#709
+  <https://github.com/omni-us/jsonargparse/pull/709>`__).
 
 
 v4.38.0 (2025-03-26)

jsonargparse/_signatures.py

@@ -537,7 +537,7 @@ def _create_group_if_requested(
                     doc_group = str(obj[0])
                 else:
                     doc_group = str(obj)
-            name = obj.__name__ if nested_key is None else nested_key
+            name = get_object_name(obj) if nested_key is None else nested_key
             group = self.add_argument_group(strip_title(doc_group), name=name)
             if config_load and nested_key is not None:
                 group.add_argument("--" + nested_key, action=_ActionConfigLoad(basetype=config_load_type))
@@ -548,6 +548,12 @@ def _create_group_if_requested(
         return group
 
 
+def get_object_name(obj) -> str:
+    if hasattr(obj, "__name__"):
+        return obj.__name__
+    return str(obj).split(".")[-1].replace("[", "_").replace("]", "")
+
+
 def group_instantiate_class(group, cfg):
     try:
         value, parent, key = cfg.get_value_and_parent(group.dest)

jsonargparse/_typehints.py

@@ -644,7 +644,7 @@ def get_class_parser(val_class, sub_add_kwargs=None, skip_args=0):
         parser = parent_parser.get()
         parser = type(parser)(exit_on_error=False, logger=parser.logger, parser_mode=parser.parser_mode)
         remove_actions(parser, (ActionConfigFile, _ActionPrintConfig))
-        if inspect.isclass(val_class):
+        if inspect.isclass(val_class) or inspect.isclass(get_typehint_origin(val_class)):
             parser.add_class_arguments(val_class, **kwargs)
         else:
             kwargs = {k: v for k, v in kwargs.items() if k != "instantiate"}

jsonargparse_tests/test_dataclass_like.py

@@ -2,6 +2,7 @@
 
 import dataclasses
 import json
+import sys
 from typing import Any, Dict, Generic, List, Literal, Optional, Tuple, TypeVar, Union
 from unittest.mock import patch
 
@@ -539,6 +540,31 @@ def test_nested_generic_dataclass(parser):
     assert "--x.y.g4 g4          (required, type: dict[str, union[float, bool]])" in help_str
 
 
+if sys.version_info >= (3, 9):
+    V = TypeVar("V")
+
+    @dataclasses.dataclass(frozen=True)
+    class GenericChild(Generic[V]):
+        value: V
+
+    @dataclasses.dataclass(frozen=True)
+    class GenericBase(Generic[V]):
+        children: tuple[GenericChild[V], ...]
+
+    @dataclasses.dataclass(frozen=True)
+    class GenericSubclass(GenericBase[str]):
+        children: tuple[GenericChild[str], ...]
+
+    def test_generic_dataclass_subclass(parser):
+        parser.add_class_arguments(GenericSubclass, "x")
+        cfg = parser.parse_args(['--x.children=[{"value": "a"}, {"value": "b"}]'])
+        init = parser.instantiate_classes(cfg)
+        assert cfg.x.children == (Namespace(value="a"), Namespace(value="b"))
+        assert isinstance(init.x, GenericSubclass)
+        assert isinstance(init.x.children[0], GenericChild)
+        assert isinstance(init.x.children[1], GenericChild)
+
+
 # union mixture tests