Add check for name-is-parameter-and-nonlocal

Author: ramonsaraiva

doc/user_guide/checkers/features.rst

@@ -65,6 +65,8 @@ Basic checker Messages
   Emitted when a name is used prior a global declaration, which results in an
   error since Python 3.6. This message can't be emitted when using Python <
   3.6.
+:name-is-parameter-and-nonlocal (E0134): *Name %r is parameter and nonlocal*
+  Emitted when a nonlocal variable is also a parameter.
 :return-outside-function (E0104): *Return outside function*
   Used when a "return" statement is found outside a function or method.
 :return-arg-in-generator (E0106): *Return with argument inside generator*

doc/user_guide/messages/messages_overview.rst

@@ -120,6 +120,7 @@ All messages in the error category:
    error/mixed-format-string
    error/modified-iterating-dict
    error/modified-iterating-set
+   error/name-is-parameter-and-nolocal
    error/no-member
    error/no-method-argument
    error/no-name-in-module

doc/whatsnew/fragments/6882.new_check

@@ -0,0 +1,3 @@
+Added ``name-is-parameter-and-nonlocal`` which flags when a nonlocal variable is also a paremeter.
+
+Closes #6682

pylint/checkers/base/basic_error_checker.py

@@ -204,6 +204,11 @@ class BasicErrorChecker(_BasicChecker):
             "which results in an error since Python 3.6.",
             {"minversion": (3, 6)},
         ),
+        "E0134": (
+            "Name %r is parameter and nonlocal",
+            "name-is-parameter-and-nonlocal",
+            "Emitted when a nonlocal variable is also a parameter.",
+        ),
     }
 
     def open(self) -> None:
@@ -267,6 +272,7 @@ def visit_starred(self, node: nodes.Starred) -> None:
     )
     def visit_functiondef(self, node: nodes.FunctionDef) -> None:
         self._check_nonlocal_and_global(node)
+        self._check_nonlocal_and_parameter(node)
         self._check_name_used_prior_global(node)
         if not redefined_by_decorator(
             node
@@ -327,6 +333,14 @@ def _check_name_used_prior_global(self, node: nodes.FunctionDef) -> None:
                     "used-prior-global-declaration", node=node_name, args=(name,)
                 )
 
+    def _check_nonlocal_and_parameter(self, node: nodes.FunctionDef) -> None:
+        """Check that a name is both parameter and nonlocal."""
+        node_arg_names = {arg.name for arg in node.args.args}
+        for body_node in node.nodes_of_class(nodes.Nonlocal):
+            for non_local_name in body_node.names:
+                if non_local_name in node_arg_names:
+                    self.add_message("name-is-parameter-and-nonlocal", node=body_node)
+
     def _check_nonlocal_and_global(self, node: nodes.FunctionDef) -> None:
         """Check that a name is both nonlocal and global."""
 

tests/functional/n/name/name_is_parameter_and_nonlocal.py

@@ -0,0 +1,5 @@
+# pylint: disable=missing-docstring,invalid-name,nonlocal-without-binding
+
+
+def tomato(is_tasty: bool = True):
+    nonlocal is_tasty # [name-is-parameter-and-nonlocal]

tests/functional/n/name/name_is_parameter_and_nonlocal.txt

@@ -0,0 +1 @@
+name-is-parameter-and-nonlocal:5:4:5:21:tomato:Name %r is parameter and nonlocal:UNDEFINED