config: Add ExtensionConfigSchema.

mopidy/utils/config.py

@@ -209,3 +209,17 @@ class ConfigSchema(object):
         if errors:
             raise exceptions.ConfigError(errors)
         return values
+
+
+class ExtensionConfigSchema(ConfigSchema):
+    """Sub-classed ConfigSchema for use in extensions.
+
+    Ensures that `enabled` config value is present and that section name is
+    prefixed with ext.
+    """
+    def __init__(self):
+        super(ExtensionConfigSchema, self).__init__()
+        self['enabled'] = Boolean()
+
+    def format(self, name, values):
+        return super(ExtensionConfigSchema, self).format('ext.%s' % name, values)

tests/utils/config_test.py

@@ -320,3 +320,13 @@ class ConfigSchemaTest(unittest.TestCase):
         self.assertNotIn('foo', cm.exception)
         self.assertIn('failure', cm.exception['bar'])
         self.assertIn('not found', cm.exception['baz'])
+
+
+class ExtensionConfigSchemaTest(unittest.TestCase):
+    def test_schema_includes_enabled(self):
+        schema = config.ExtensionConfigSchema()
+        self.assertIsInstance(schema['enabled'], config.Boolean)
+
+    def test_section_name_is_prefixed(self):
+        schema = config.ExtensionConfigSchema()
+        self.assertEqual('[ext.foo]', schema.format('foo', {}))