Config file warning

src/pydocstyle/config.py

@@ -256,10 +256,17 @@ def _get_config(self, node):
                 raise IllegalConfiguration('Configuration file {!r} specified '
                                            'via --config was not found.'
                                            .format(self._run_conf.config))
+
             if None in self._cache:
                 return self._cache[None]
             options, _ = self._read_configuration_file(self._run_conf.config)
-            config = self._create_check_config(options)
+
+            if options is None:
+                log.warning('Configuration file does not contain a '
+                            'pydocstyle section. Using default configuration.')
+                config = self._create_check_config(self._options)
+            else:
+                config = self._create_check_config(options)
 
         # Make the CLI always win
         final_config = {}

src/tests/test_integration.py

@@ -251,6 +251,17 @@ def foo():
     assert 'D103' not in err
 
 
+def test_sectionless_config_file(env):
+    """Test that config files without a valid section name issue a warning."""
+    with env.open('config.ini', 'wt') as conf:
+        conf.write('[pdcstl]')
+        config_path = conf.name
+
+    _, err, code = env.invoke('--config={}'.format(config_path))
+    assert code == 0
+    assert 'Configuration file does not contain a pydocstyle section' in err
+
+
 def test_config_path(env):
     """Test that options are correctly loaded from a specific config file.