Subclass types no longer allow class instance to be set as default (l…

…ightning#18731).

CHANGELOG.rst

@@ -26,6 +26,12 @@ Fixed
 - Failures with subcommands and default_config_files when keys are repeated
   (`#160 <https://github.com/omni-us/jsonargparse/issues/160>`__).
 
+Changed
+^^^^^^^
+- Subclass types no longer allow class instance to be set as default
+  (`lightning#18731
+  <https://github.com/Lightning-AI/lightning/issues/18731>`__).
+
 
 v4.25.0 (2023-09-25)
 --------------------

jsonargparse/_core.py

@@ -884,10 +884,9 @@ def set_defaults(self, *args: Dict[str, Any], **kwargs: Any) -> None:
                         raise KeyError(f'No action for destination key "{dest}" to set its default.')
                     elif isinstance(action, ActionConfigFile):
                         ActionConfigFile.set_default_error()
-                    action.default = default
                     if isinstance(action, ActionTypeHint):
-                        action.normalize_default()
-                    self._defaults[dest] = action.default
+                        default = action.normalize_default(default)
+                    self._defaults[dest] = action.default = default
         if kwargs:
             self.set_defaults(kwargs)
 

jsonargparse/_signatures.py

@@ -373,7 +373,8 @@ def _add_signature_parameter(
             }
             if is_dataclass_like_typehint:
                 kwargs.update(sub_add_kwargs)
-            action = group.add_argument(*args, **kwargs)
+            with ActionTypeHint.allow_default_instance_context():
+                action = group.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

jsonargparse/_typehints.py

@@ -146,6 +146,7 @@
     literal_types.add(__import__("typing").Literal)
 
 subclass_arg_parser: ContextVar = ContextVar("subclass_arg_parser")
+allow_default_instance: ContextVar = ContextVar("allow_default_instance", default=False)
 sub_defaults: ContextVar = ContextVar("sub_defaults", default=False)
 
 
@@ -187,23 +188,26 @@ def __init__(self, typehint: Optional[Type] = None, enable_path: bool = False, *
                 kwargs["metavar"] = typehint_metavar(self._typehint)
             super().__init__(**kwargs)
             self._supports_append = self.supports_append(self._typehint)
-            self.normalize_default()
+            self.default = self.normalize_default(self.default)
 
-    def normalize_default(self):
-        default = self.default
+    def normalize_default(self, default):
+        is_subclass_type = self.is_subclass_typehint(self._typehint, all_subtypes=False)
         if isinstance(default, LazyInitBaseClass):
-            self.default = default.lazy_get_init_data()
-        elif (
-            self.is_subclass_typehint(self._typehint, all_subtypes=False)
-            and isinstance(default, dict)
-            and "class_path" in default
-        ):
-            self.default = subclass_spec_as_namespace(default)
-            self.default.class_path = normalize_import_path(self.default.class_path, self._typehint)
+            default = default.lazy_get_init_data()
+        elif is_subclass_type and isinstance(default, dict) and "class_path" in default:
+            default = subclass_spec_as_namespace(default)
+            default.class_path = normalize_import_path(default.class_path, self._typehint)
         elif is_enum_type(self._typehint) and isinstance(default, Enum):
-            self.default = default.name
+            default = default.name
         elif is_callable_type(self._typehint) and callable(default) and not inspect.isclass(default):
-            self.default = get_import_path(default)
+            default = get_import_path(default)
+        elif is_subclass_type and not allow_default_instance.get():
+            from ._parameter_resolvers import UnknownDefault
+
+            default_type = type(default)
+            if not is_subclass(default_type, UnknownDefault) and self.is_subclass_typehint(default_type):
+                raise ValueError("Subclass types require as default either a dict with class_path or a lazy instance.")
+        return default
 
     @staticmethod
     def prepare_add_argument(args, kwargs, enable_path, container, logger, sub_add_kwargs=None):
@@ -356,6 +360,15 @@ def subclass_arg_context(parser):
         subclass_arg_parser.set(parser)
         yield
 
+    @staticmethod
+    @contextmanager
+    def allow_default_instance_context():
+        token = allow_default_instance.set(True)
+        try:
+            yield
+        finally:
+            allow_default_instance.reset(token)
+
     @staticmethod
     @contextmanager
     def sub_defaults_context():
@@ -1200,15 +1213,8 @@ def typehint_metavar(typehint):
 
 
 def serialize_class_instance(val):
-    type_val = type(val)
-    val = str(val)
-    warning(
-        f"""
-        Not possible to serialize an instance of {type_val}. It will be
-        represented as the string {val}. If this was set as a default, consider
-        using lazy_instance.
-    """
-    )
+    val = f"Unable to serialize instance {val}"
+    warning(val)
     return val
 
 

jsonargparse_tests/test_subclasses.py

@@ -29,6 +29,7 @@
     get_parse_args_stderr,
     get_parse_args_stdout,
     get_parser_help,
+    source_unavailable,
 )
 
 
@@ -1209,19 +1210,6 @@ def test_add_subclass_lazy_default(parser):
     assert "'init_args': {'firstweekday': 5}" in help_str
 
 
-def test_add_subclass_instance_default(parser):
-    parser.add_subclass_arguments(Calendar, "cal")
-    parser.set_defaults({"cal": Calendar(firstweekday=2)})
-    cfg = parser.parse_args([])
-    assert isinstance(cfg["cal"], Calendar)
-    init = parser.instantiate_classes(cfg)
-    assert init["cal"] is cfg["cal"]
-    with warnings.catch_warnings(record=True) as w:
-        dump = parser.dump(cfg)
-    assert "Not possible to serialize an instance of" in str(w[0].message)
-    assert "cal: <calendar.Calendar object at " in dump
-
-
 class TupleBaseA:
     def __init__(self, a1: int = 1, a2: float = 2.3):
         self.a1 = a1
@@ -1267,6 +1255,40 @@ def test_add_subclass_not_required_group(parser):
     assert init == Namespace()
 
 
+# instance defaults tests
+
+
+def test_add_subclass_set_defaults_instance_default(parser):
+    parser.add_subclass_arguments(Calendar, "cal")
+    with pytest.raises(ValueError) as ctx:
+        parser.set_defaults({"cal": Calendar(firstweekday=2)})
+    ctx.match("Subclass types require as default either a dict with class_path or a lazy instance")
+
+
+def test_add_argument_subclass_instance_default(parser):
+    with pytest.raises(ValueError) as ctx:
+        parser.add_argument("--cal", type=Calendar, default=Calendar(firstweekday=2))
+    ctx.match("Subclass types require as default either a dict with class_path or a lazy instance")
+
+
+class InstanceDefault:
+    def __init__(self, cal: Calendar = Calendar(firstweekday=2)):
+        pass
+
+
+def test_subclass_signature_instance_default(parser):
+    with source_unavailable():
+        parser.add_class_arguments(InstanceDefault)
+    cfg = parser.parse_args([])
+    assert isinstance(cfg["cal"], Calendar)
+    init = parser.instantiate_classes(cfg)
+    assert init["cal"] is cfg["cal"]
+    with warnings.catch_warnings(record=True) as w:
+        dump = parser.dump(cfg)
+    assert "Unable to serialize instance" in str(w[0].message)
+    assert "cal: Unable to serialize instance <calendar.Calendar " in dump
+
+
 # parameter skip tests