New helper plugin_settings_for_settings_plugin, to use from cli hooks and internally

src/octoprint/plugin/__init__.py

@@ -161,6 +161,34 @@ def plugin_settings(plugin_key, defaults=None, get_preprocessors=None, set_prepr
 	                      set_preprocessors=set_preprocessors)
 
 
+def plugin_settings_for_settings_plugin(plugin_key, instance, settings=None):
+	"""
+	Factory method for creating a :class:`PluginSettings` instance for a given :class:`SettingsPlugin` instance.
+
+	Will return `None` if the provided `instance` is not a :class:`SettingsPlugin` instance.
+
+	Arguments:
+	    plugin_key (string): The plugin identifier for which to create the settings instance.
+	    implementation (octoprint.plugin.SettingsPlugin): The :class:`SettingsPlugin` instance.
+	    settings (octoprint.settings.Settings): The settings instance to use. Defaults to the global OctoPrint settings.
+
+	Returns:
+	    PluginSettings or None: A fully initialized :class:`PluginSettings` instance to be used to access the plugin's
+	        settings, or `None` if the provided `instance` was not a class:`SettingsPlugin`
+	"""
+	if not isinstance(instance, SettingsPlugin):
+		return None
+
+	try:
+		defaults = instance.get_settings_defaults()
+		get_preprocessors, set_preprocessors = instance.get_settings_preprocessors()
+	except:
+		logging.getLogger(__name__).exception("Error while retrieving defaults or preprocessors for plugin {}".format(plugin_key))
+		return None
+
+	return plugin_settings(plugin_key, defaults=defaults, get_preprocessors=get_preprocessors, set_preprocessors=set_preprocessors, settings=settings)
+
+
 def call_plugin(types, method, args=None, kwargs=None, callback=None, error_callback=None, sorting_context=None):
 	"""
 	Helper method to invoke the indicated ``method`` on all registered plugin implementations implementing the

src/octoprint/server/__init__.py

@@ -215,14 +215,10 @@ class Server():
 			)
 
 		def settings_plugin_inject_factory(name, implementation):
-			if not isinstance(implementation, octoprint.plugin.SettingsPlugin):
-				return None
-			default_settings = implementation.get_settings_defaults()
-			get_preprocessors, set_preprocessors = implementation.get_settings_preprocessors()
-			plugin_settings = octoprint.plugin.plugin_settings(name,
-			                                                   defaults=default_settings,
-			                                                   get_preprocessors=get_preprocessors,
-			                                                   set_preprocessors=set_preprocessors)
+			plugin_settings = octoprint.plugin.plugin_settings_for_settings_plugin(name, implementation)
+			if plugin_settings is None:
+				return
+
 			return dict(settings=plugin_settings)
 
 		def settings_plugin_config_migration_and_cleanup(name, implementation):