Restore compatibility with Settings.overrides while still deprecating it

scrapy/settings/__init__.py

@@ -1,8 +1,10 @@
 import six
 import json
+import warnings
 from importlib import import_module
 
 from scrapy.utils.deprecate import create_deprecated_class
+from scrapy.exceptions import ScrapyDeprecationWarning
 
 from . import default_settings
 
@@ -108,6 +110,22 @@ class Settings(object):
             if key.isupper():
                 self.set(key, getattr(module, key), priority)
 
+    @property
+    def overrides(self):
+        warnings.warn("`Settings.overrides` attribute is deprecated and won't "
+                      "be supported in Scrapy 0.26, use "
+                      "`Settings.set(name, value, priority='cmdline')` instead",
+                      category=ScrapyDeprecationWarning, stacklevel=2)
+        try:
+            o = self._overrides
+        except AttributeError:
+            class _DictProxy(dict):
+                def __setitem__(this, key, value):
+                    super(_DictProxy, this).__setitem__(key, value)
+                    self.set(key, value, priority='cmdline')
+            self._overrides = o = _DictProxy()
+        return o
+
 
 class CrawlerSettings(Settings):
 

scrapy/tests/test_settings/__init__.py

@@ -1,5 +1,6 @@
 import six
 import unittest
+import warnings
 try:
     from unittest import mock
 except ImportError:
@@ -189,7 +190,15 @@ class SettingsTest(unittest.TestCase):
         self.assertEqual(settings.getdict('TEST_DICT3', {'key1': 5}), {'key1': 5})
         self.assertRaises(ValueError, settings.getdict, 'TEST_LIST1')
 
+    def test_deprecated_attribute(self):
+        self.settings.set('BAR', 'fuz', priority='cmdline')
+        with warnings.catch_warnings(record=True) as w:
+            self.settings.overrides['BAR'] = 'foo'
+            self.assertIn("Settings.overrides", str(w[0].message))
+            self.assertEqual(self.settings.get('BAR'), 'foo')
+            self.assertEqual(self.settings.overrides.get('BAR'), 'foo')
+            self.assertIn('BAR', self.settings.overrides)
+
 
 if __name__ == "__main__":
     unittest.main()
-