Introduce A006 for lambda shadowing

CHANGES.rst

@@ -3,10 +3,11 @@
 Changelog
 =========
 
-2.3.1 (unreleased)
+2.3.1 (2024-04-01)
 ------------------
 
-- Nothing changed yet.
+- Add rule for lambda argument shadowing (`A006`).
+  [cielavenir]
 
 
 2.3.0 (2024-03-29)

README.rst

@@ -104,6 +104,9 @@ A004:
 A005:
   A module is shadowing a Python builtin module (e.g: `logging` or `socket`)
 
+A006:
+  A lambda argument is shadowing a Python builtin.
+
 License
 -------
 GPL 2.0

flake8_builtins.py

@@ -15,6 +15,7 @@ class BuiltinsChecker:
     class_attribute_msg = 'A003 class attribute "{0}" is shadowing a Python builtin'
     import_msg = 'A004 import statement "{0}" is shadowing a Python builtin'
     module_name_msg = 'A005 the module is shadowing a Python builtin module "{0}"'
+    lambda_argument_msg = 'A006 lambda argument "{0}" is shadowing a Python builtin'
 
     names = []
     ignore_list = {
@@ -113,6 +114,9 @@ def run(self):
             elif isinstance(statement, function_nodes):
                 value = self.check_function_definition(statement)
 
+            elif isinstance(statement, ast.Lambda):
+                value = self.check_lambda_definition(statement)
+
             elif isinstance(statement, for_nodes):
                 value = self.check_for_loop(statement)
 
@@ -181,6 +185,20 @@ def check_function_definition(self, statement):
                     variable=arg.arg,
                 )
 
+    def check_lambda_definition(self, statement):
+        all_arguments = []
+        all_arguments.extend(statement.args.args)
+        all_arguments.extend(getattr(statement.args, 'kwonlyargs', []))
+        all_arguments.extend(getattr(statement.args, 'posonlyargs', []))
+
+        for arg in all_arguments:
+            if isinstance(arg, ast.arg) and arg.arg in self.names:
+                yield self.error(
+                    arg,
+                    message=self.lambda_argument_msg,
+                    variable=arg.arg,
+                )
+
     def check_for_loop(self, statement):
         stack = [statement.target]
         while stack:

run_tests.py

@@ -156,6 +156,11 @@ def bla(list):
     check_code(source, 'A002')
 
 
+def test_lambda_argument_message():
+    source = 'takefirst = lambda list: list[0]'
+    check_code(source, 'A006')
+
+
 def test_keyword_argument_message():
     source = """
     def bla(dict=3):
@@ -182,6 +187,15 @@ def bla(list, /):
     """
     check_code(source, 'A002')
 
+@pytest.mark.skipif(
+    sys.version_info < (3, 8),
+    reason='This syntax is only valid in Python 3.8+',
+)
+def test_lambda_posonly_argument_message():
+    source = """
+    takefirst = lambda list, /: list[0]
+    """
+    check_code(source, 'A006')
 
 def test_no_error():
     source = """def bla(first):\n    b = 4"""