change keyword_arguments_for so it does not modify and return

src/flake8/checker.py

@@ -340,13 +340,15 @@ class FileChecker:
         LOG.debug("Running %r with %r", plugin, arguments)
         assert self.processor is not None
         try:
-            self.processor.keyword_arguments_for(plugin.parameters, arguments)
+            params = self.processor.keyword_arguments_for(
+                plugin.parameters, arguments
+            )
         except AttributeError as ae:
             raise exceptions.PluginRequestedUnknownParameters(
                 plugin_name=plugin.display_name, exception=ae
             )
         try:
-            return plugin.obj(**arguments)
+            return plugin.obj(**arguments, **params)
         except Exception as all_exc:
             LOG.critical(
                 "Plugin %s raised an unexpected exception",

src/flake8/processor.py

@@ -241,16 +241,15 @@ class FileProcessor:
     def keyword_arguments_for(
         self,
         parameters: Dict[str, bool],
-        arguments: Optional[Dict[str, Any]] = None,
+        arguments: Dict[str, Any],
     ) -> Dict[str, Any]:
         """Generate the keyword arguments for a list of parameters."""
-        if arguments is None:
+        ret = {}
-            arguments = {}
         for param, required in parameters.items():
             if param in arguments:
                 continue
             try:
-                arguments[param] = getattr(self, param)
+                ret[param] = getattr(self, param)
             except AttributeError:
                 if required:
                     raise
@@ -260,7 +259,7 @@ class FileProcessor:
                         "but this is not an available parameter.",
                         param,
                     )
-        return arguments
+        return ret
 
     def generate_tokens(self) -> Generator[tokenize.TokenInfo, None, None]:
         """Tokenize the file and yield the tokens."""

tests/unit/test_file_processor.py

@@ -209,21 +209,21 @@ def test_next_line(default_options):
     [
         (
             {"blank_before": True, "blank_lines": True},
-            None,
+            {},
             {"blank_before": 0, "blank_lines": 0},
         ),
         (
             {"noqa": True, "fake": True},
             {"fake": "foo"},
-            {"noqa": False, "fake": "foo"},
+            {"noqa": False},
         ),
         (
             {"blank_before": True, "blank_lines": True, "noqa": True},
             {"blank_before": 10, "blank_lines": 5, "noqa": True},
-            {"blank_before": 10, "blank_lines": 5, "noqa": True},
+            {},
         ),
-        ({}, {"fake": "foo"}, {"fake": "foo"}),
+        ({}, {"fake": "foo"}, {}),
-        ({"non-existent": False}, {"fake": "foo"}, {"fake": "foo"}),
+        ({"non-existent": False}, {"fake": "foo"}, {}),
     ],
 )
 def test_keyword_arguments_for(params, args, expected_kwargs, default_options):
@@ -235,9 +235,9 @@ def test_keyword_arguments_for(params, args, expected_kwargs, default_options):
             "Line 1",
         ],
     )
-    kwargs_for = file_processor.keyword_arguments_for
+    ret = file_processor.keyword_arguments_for(params, args)
 
-    assert kwargs_for(params, args) == expected_kwargs
+    assert ret == expected_kwargs
 
 
 def test_keyword_arguments_for_does_not_handle_attribute_errors(
@@ -253,7 +253,7 @@ def test_keyword_arguments_for_does_not_handle_attribute_errors(
     )
 
     with pytest.raises(AttributeError):
-        file_processor.keyword_arguments_for({"fake": True})
+        file_processor.keyword_arguments_for({"fake": True}, {})
 
 
 def test_processor_split_line(default_options):