diffsettings leaves out custom default settings

[orlnub123]

If you've manually configured the settings with default settings that differ from the default they won't show up if you run the diffsettings command. This is only observable on master as before 49b6793 the settings were forcefully setup, replacing the manually configured settings.

The reason this happens is because module_to_dict reads the settings from the __dict__. If you haven't manually configured your settings this is fine because the default wrapped settings object preassigns all settings to the __dict__. Since UserSettingsHolder, the class that wraps manually configured settings, relies on the __dir__ + __getattr__ pattern which allows the underlying default settings object to be dynamic it doesn't store settings from the default settings in its __dict__.

[Simon Charette]

Marking as master release blocker since it's a regression introduced by 49b679371fe9beddcd23a93b5fdbadea914f37f8 (#29236).

[Tim Graham <timograham@…>]

In 573f44d6:

Fixed #30057 -- Fixed diffsettings ignoring custom configured settings.

Regression in 49b679371fe9beddcd23a93b5fdbadea914f37f8.

[orlnub123]

Reopening with a ​PR for some follow up.

[Tim Graham]

The PR seems to be about additional test coverage which can be added without an open ticket.

[Tim Graham <timograham@…>]

In 2c0fda7f:

Refs #30057 -- Added more diffsettings tests.

The test in 573f44d62fe1e87e2c20a74eba5e20ca9ff0ed85 doesn't act as a
regression test.