Fix default_config_files making parse fail for subcommands and nested subclass types

CHANGELOG.rst

@@ -31,6 +31,9 @@ Fixed
 - ``dump`` failing when a link target requires serialization and
   ``skip_link_targets=False`` (`#542
   <https://github.com/omni-us/jsonargparse/pull/542>`__).
+- ``default_config_files`` making parse fail for subcommands and nested subclass
+  types (`lightning-forums#5963
+  <https://lightning.ai/forums/t/problem-lightningcli-with-default-config-files/5963>`__).
 - Import path of inherited classmethod not resolving correctly (`lightning#19863
   comment
   <https://github.com/Lightning-AI/pytorch-lightning/discussions/19863#discussioncomment-10010226>`__).

jsonargparse/_actions.py

@@ -580,12 +580,12 @@ def add_prefix(key):
 @contextmanager
 def parent_parsers_context(key, parser):
     prev = parent_parsers.get()
-    curr = prev + [(key, parser)]
-    t = parent_parsers.set(curr)
+    curr = [] if parser is None else prev + [(key, parser)]
+    token = parent_parsers.set(curr)
     try:
         yield
     finally:
-        parent_parsers.reset(t)
+        parent_parsers.reset(token)
 
 
 class _ActionSubCommands(_SubParsersAction):

jsonargparse/_typehints.py

@@ -39,6 +39,7 @@
     _find_action,
     _find_parent_action,
     _is_action_value_list,
+    parent_parsers_context,
     remove_actions,
 )
 from ._common import (
@@ -453,7 +454,7 @@ def skip_sub_defaults_apply(v):
                 or (isinstance(v, dict) and any(is_subclass_spec(e) for e in v.values()))
             )
 
-        with ActionTypeHint.sub_defaults_context():
+        with ActionTypeHint.sub_defaults_context(), parent_parsers_context(None, None):
             parser._apply_actions(cfg, skip_fn=skip_sub_defaults_apply)
 
     @staticmethod

jsonargparse_tests/test_subcommands.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import json
 import os
 import warnings
 from pathlib import Path
@@ -255,6 +256,46 @@ def test_subcommand_required_arg_in_default_config(parser, subparser, tmp_cwd):
     assert strip_meta(cfg) == Namespace(output="test", prepare=Namespace(media="test"), subcommand="prepare")
 
 
+class SubModel:
+    def __init__(self, p1: int, p2: str = "-"):
+        pass
+
+
+class Model:
+    def __init__(self, submodel: SubModel):
+        self.submodel = submodel
+
+
+def test_subcommand_default_config_add_subdefaults(parser, subparser, tmp_cwd):
+    config = {
+        "fit": {
+            "model": {
+                "class_path": f"{__name__}.Model",
+                "init_args": {
+                    "submodel": {
+                        "class_path": f"{__name__}.SubModel",
+                        "init_args": {"p1": 1},
+                    }
+                },
+            }
+        }
+    }
+    Path("config.json").write_text(json.dumps(config))
+    parser.default_config_files = ["config.json"]
+    subcommands = parser.add_subcommands()
+    subparser = ArgumentParser()
+    subparser.add_argument("--model", type=Model, required=True)
+    subcommands.add_subcommand("fit", subparser)
+    cfg = parser.parse_args([])
+    assert cfg.fit.model.class_path == f"{__name__}.Model"
+    assert list(cfg.fit.model.init_args.__dict__.keys()) == ["submodel"]
+    assert cfg.fit.model.init_args.submodel.class_path == f"{__name__}.SubModel"
+    assert cfg.fit.model.init_args.submodel.init_args == Namespace(p1=1, p2="-")
+    init = parser.instantiate_classes(cfg)
+    assert isinstance(init.fit.model, Model)
+    assert isinstance(init.fit.model.submodel, SubModel)
+
+
 def test_subsubcommands_parse_args(subtests):
     parser_s1_a = ArgumentParser(exit_on_error=False)
     parser_s1_a.add_argument("--os1a", default="os1a_def")