webassets now requires us to implement __contains__. This fixes a

problem in which existing Flask config values could be overridden with
their Flask-Assets defaults.

src/flaskext/assets.py

@@ -16,6 +16,9 @@ def _transform_key(self, key):
         else:
             return key.upper()
 
+    def __contains__(self, key):
+        return self._transform_key(key) in self.env.app.config
+
     def __getitem__(self, key):
         return self.env.app.config[self._transform_key(key)]
 

tests/test_config.py

@@ -35,3 +35,13 @@ def test_custom_values(self):
         """
         self.app.config['LESS_PATH'] = '/usr/bin/less'
         assert self.env.config['LESS_PATH'] == '/usr/bin/less'
+
+    def test_no_override(self):
+        """Ensure that the webassets defaults do not override existing
+        Flask config values.
+        """
+        app = Flask(__name__)
+        app.config['ASSETS_UPDATER'] = 'MOO'
+        env = Environment(app)
+        assert env.updater == 'MOO'
+        assert app.config['ASSETS_UPDATER'] == 'MOO'