added IBasePlugin.get_default_config()

src/shore/core/plugins.py

@@ -139,6 +139,11 @@ class IBasePlugin(Interface):
   Config = staticattr(None)
   config = attr(default=None)
 
+  @default
+  @classmethod
+  def get_default_config(cls):
+    return cls.Config()
+
   @default
   @classmethod
   def new_instance(cls, config: 'Config') -> 'IBasePlugin':
@@ -149,9 +154,12 @@ class IBasePlugin(Interface):
     if cls.Config is None and config is not None:
       raise ValueError('{} does not expect a config, got {}'.format(
         cls.__name__, type(config).__name__))
-    elif cls.Config and not isinstance(config, cls.Config):
-      raise ValueError('{} expects a config of type {}, got {}'.format(
-        cls.__name__, cls.Config.__name__, type(config).__name__))
+    elif cls.Config is not None:
+      if config is None:
+        config = cls.get_default_config()
+      elif not isinstance(config, cls.Config):
+        raise ValueError('{} expects a config of type {}, got {}'.format(
+          cls.__name__, cls.Config.__name__, type(config).__name__))
 
     instance = cls()
     instance.config = config

src/shore/model.py

@@ -357,18 +357,19 @@ class PluginConfig(Struct):
   def _deserialize(cls, mapper, node):
     if isinstance(node.value, str):
       plugin_name = node.value
-      config = {}
+      config = None
     elif isinstance(node.value, dict):
-      if len(node.value) != 1:
-        raise ValueError('expected only one key')
-      plugin_name, config = next(iter(node.value.items()))
+      if 'type' not in node.value:
+        node.value_error('missing "type" key')
+      config = node.value.copy()
+      plugin_name = config.pop('type')
     else:
       raise TypeError('expected str or dict')
     try:
       plugin_cls = load_plugin(plugin_name)
     except PluginNotFound as exc:
       raise ValueError('plugin "{}" not found'.format(exc))
-    if plugin_cls.Config is not None:
+    if plugin_cls.Config is not None and config is not None:
       config = mapper.deserialize_node(node.make_child(plugin_name, plugin_cls.Config, config))
     elif plugin_cls.Config is None and config:
       raise TypeError('plugin {} expects no configuration'.format(plugin_name))