Fix add_class_arguments with dashes in the nested_key fail to instantiate

CHANGELOG.rst

@@ -12,6 +12,15 @@ The semantic versioning only considers the public API as described in
 paths are considered internals and can change in minor and patch releases.
 
 
+v4.37.1 (2025-02-??)
+--------------------
+
+Fixed
+^^^^^
+- ``add_class_arguments`` with dashes in the ``nested_key`` fail to instantiate
+  (`#679 <https://github.com/omni-us/jsonargparse/pull/679>`__).
+
+
 v4.37.0 (2025-02-14)
 --------------------
 

jsonargparse/_signatures.py

@@ -546,7 +546,7 @@ def _create_group_if_requested(
             if config_load and nested_key is not None:
                 group.add_argument("--" + nested_key, action=_ActionConfigLoad(basetype=config_load_type))
             if inspect.isclass(obj) and nested_key is not None and instantiate:
-                group.dest = nested_key
+                group.dest = nested_key.replace("-", "_")
                 group.group_class = obj
                 group.instantiate_class = group_instantiate_class
         return group

jsonargparse_tests/test_signatures.py

@@ -243,7 +243,18 @@ def test_add_class_implemented_with_new(parser):
 
 class RequiredParams:
     def __init__(self, n: int, m: float):
-        pass
+        self.n = n
+        self.m = m
+
+
+def test_add_class_group_name_dash_required_parameters(parser):
+    parser.add_class_arguments(RequiredParams, "required-params")
+    assert "required-params" in parser.groups
+    cfg = parser.parse_args(["--required-params.n=6", "--required-params.m=0.9"])
+    init = parser.instantiate_classes(cfg)
+    assert isinstance(init.required_params, RequiredParams)
+    assert init.required_params.n == 6
+    assert init.required_params.m == 0.9
 
 
 def test_add_class_with_required_parameters(parser):