Allow adding settings to existing groups

Calling add_group or add_persistent_group twice will add any new
settings defined.

Raise a ValueError if add_group or add_persistent_group is called during
a call to add_group or add_persistent_group.

settngs.py

@@ -150,6 +150,11 @@ class Setting:
     def __repr__(self) -> str:  # pragma: no cover
         return self.__str__()
 
+    def __eq__(self, other: object) -> bool:
+        if not isinstance(other, Setting):
+            return NotImplemented
+        return self.__dict__ == other.__dict__
+
     def get_dest(self, prefix: str, names: Sequence[str], dest: str | None) -> tuple[str, str, bool]:
         dest_name = None
         flag = False
@@ -496,13 +501,15 @@ class Manager:
 
     def add_group(self, name: str, group: Callable[[Manager], None], exclusive_group: bool = False) -> None:
         """
-        The primary way to add define options on this class
+        The primary way to add define options on this class.
 
         Args:
             name: The name of the group to define
             group: A function that registers individual options using :meth:`add_setting`
             exclusive_group: If this group is an argparse exclusive group
         """
+        if self.current_group_name != '':
+            raise ValueError('Sub groups are not allowed')
         self.current_group_name = name
         self.exclusive_group = exclusive_group
         group(self)
@@ -511,15 +518,22 @@ class Manager:
 
     def add_persistent_group(self, name: str, group: Callable[[Manager], None], exclusive_group: bool = False) -> None:
         """
-        The primary way to add define options on this class
+        The primary way to add define options on this class.
+        This group allows existing values to persist even if there is no corresponding setting defined for it.
 
         Args:
             name: The name of the group to define
             group: A function that registers individual options using :meth:`add_setting`
             exclusive_group: If this group is an argparse exclusive group
         """
+        if self.current_group_name != '':
+            raise ValueError('Sub groups are not allowed')
         self.current_group_name = name
         self.exclusive_group = exclusive_group
+        if self.current_group_name in self.definitions:
+            if not self.definitions[self.current_group_name].persistent:
+                raise ValueError('Group already existis and is not persistent')
+        else:
             self.definitions[self.current_group_name] = Group(True, {})
         group(self)
         self.current_group_name = ''

tests/settngs_test.py

@@ -2,6 +2,7 @@ from __future__ import annotations
 
 import argparse
 import json
+from collections import defaultdict
 
 import pytest
 
@@ -141,7 +142,7 @@ def test_clean_config(settngs_manager):
     assert cleaned['persistent']['hello'] == 'success'
 
 
-def test_parse_cmdline(settngs_manager, tmp_path):
+def test_parse_cmdline(settngs_manager):
     settngs_manager.add_group('tst', lambda parser: parser.add_setting('--test', default='hello', cmdline=True))
 
     normalized, _ = settngs_manager.parse_cmdline(['--test', 'success'])
@@ -150,7 +151,7 @@ def test_parse_cmdline(settngs_manager, tmp_path):
     assert normalized['tst']['test'] == 'success'
 
 
-def test_parse_cmdline_with_namespace(settngs_manager, tmp_path):
+def test_parse_cmdline_with_namespace(settngs_manager):
     settngs_manager.add_group('tst', lambda parser: parser.add_setting('--test', default='hello', cmdline=True))
 
     normalized, _ = settngs_manager.parse_cmdline(
@@ -286,6 +287,42 @@ def test_cli_explicit_default(settngs_manager, tmp_path):
     assert normalized['tst']['test'] == 'success'
 
 
+def test_adding_to_existing_group(settngs_manager, tmp_path):
+    def default_to_regular(d):
+        if isinstance(d, defaultdict):
+            d = {k: default_to_regular(v) for k, v in d.items()}
+        return d
+    settngs_manager.add_group('tst', lambda parser: parser.add_setting('--test', default='success'))
+    settngs_manager.add_group('tst', lambda parser: parser.add_setting('--test2', default='success'))
+
+    def tst(parser):
+        parser.add_setting('--test', default='success')
+        parser.add_setting('--test2', default='success')
+
+    settngs_manager2 = settngs.Manager()
+    settngs_manager2.add_group('tst', tst)
+
+    assert default_to_regular(settngs_manager.definitions) == default_to_regular(settngs_manager2.definitions)
+
+
+def test_adding_to_existing_persistent_group(settngs_manager, tmp_path):
+    def default_to_regular(d):
+        if isinstance(d, defaultdict):
+            d = {k: default_to_regular(v) for k, v in d.items()}
+        return d
+    settngs_manager.add_persistent_group('tst', lambda parser: parser.add_setting('--test', default='success'))
+    settngs_manager.add_persistent_group('tst', lambda parser: parser.add_setting('--test2', default='success'))
+
+    def tst(parser):
+        parser.add_setting('--test', default='success')
+        parser.add_setting('--test2', default='success')
+
+    settngs_manager2 = settngs.Manager()
+    settngs_manager2.add_persistent_group('tst', tst)
+
+    assert default_to_regular(settngs_manager.definitions) == default_to_regular(settngs_manager2.definitions)
+
+
 def test_example(capsys, tmp_path, monkeypatch):
     monkeypatch.chdir(tmp_path)
     settings_file = tmp_path / 'settings.json'