Fix a false negative for duplicate-argument-name

doc/user_guide/checkers/features.rst

@@ -65,7 +65,7 @@ Basic checker Messages
   methods and is instantiated.
 :star-needs-assignment-target (E0114): *Can use starred expression only in assignment target*
   Emitted when a star expression is not used in an assignment target.
-:duplicate-argument-name (E0108): *Duplicate argument name %s in function definition*
+:duplicate-argument-name (E0108): *Duplicate argument name %r in function definition*
   Duplicate argument names in function definitions are syntax errors.
 :return-in-init (E0101): *Explicit return in __init__*
   Used when the special class method __init__ has an explicit return value.

doc/whatsnew/fragments/9669.false_negative

@@ -0,0 +1,3 @@
+Fix a false negative for ``duplicate-argument-name`` by including ``positional-only``, ``*args`` and ``**kwargs`` arguments in the check.
+
+Closes #9669

pylint/checkers/base/basic_error_checker.py

@@ -145,7 +145,7 @@ class BasicErrorChecker(_BasicChecker):
             "pre-decrement operator -- and ++, which doesn't exist in Python.",
         ),
         "E0108": (
-            "Duplicate argument name %s in function definition",
+            "Duplicate argument name %r in function definition",
             "duplicate-argument-name",
             "Duplicate argument names in function definitions are syntax errors.",
         ),
@@ -285,8 +285,8 @@ def visit_functiondef(self, node: nodes.FunctionDef) -> None:
                     self.add_message("return-in-init", node=node)
         # Check for duplicate names by clustering args with same name for detailed report
         arg_clusters = {}
-        arguments: Iterator[Any] = filter(None, [node.args.args, node.args.kwonlyargs])
-        for arg in itertools.chain.from_iterable(arguments):
+        arguments: Iterator[Any] = node.args.arguments
+        for arg in arguments:
             if arg.name in arg_clusters:
                 self.add_message(
                     "duplicate-argument-name",

tests/functional/a/async_functions.txt

@@ -5,6 +5,6 @@ too-many-arguments:26:0:26:26:complex_function:Too many arguments (10/5):UNDEFIN
 too-many-branches:26:0:26:26:complex_function:Too many branches (13/12):UNDEFINED
 too-many-return-statements:26:0:26:26:complex_function:Too many return statements (10/6):UNDEFINED
 dangerous-default-value:59:0:59:14:func:Dangerous default value [] as argument:UNDEFINED
-duplicate-argument-name:59:18:59:19:func:Duplicate argument name a in function definition:HIGH
+duplicate-argument-name:59:18:59:19:func:Duplicate argument name 'a' in function definition:HIGH
 disallowed-name:64:0:64:13:foo:"Disallowed name ""foo""":HIGH
 empty-docstring:64:0:64:13:foo:Empty function docstring:HIGH

tests/functional/d/duplicate/duplicate_argument_name.py

@@ -1,14 +1,23 @@
 """Check for duplicate function arguments."""
 
+# pylint: disable=missing-docstring, line-too-long
+
 
 def foo1(_, _): # [duplicate-argument-name]
-    """Function with duplicate argument name."""
+    ...
 
 def foo2(_abc, *, _abc): # [duplicate-argument-name]
-    """Function with duplicate argument name."""
+    ...
 
 def foo3(_, _=3): # [duplicate-argument-name]
-    """Function with duplicate argument name."""
+    ...
 
 def foo4(_, *, _): # [duplicate-argument-name]
-    """Function with duplicate argument name."""
+    ...
+
+def foo5(_, *_, _=3): # [duplicate-argument-name, duplicate-argument-name]
+    ...
+
+# +1: [duplicate-argument-name, duplicate-argument-name, duplicate-argument-name, duplicate-argument-name]
+def foo6(_, /, _, *_, _="_", **_):
+    ...

tests/functional/d/duplicate/duplicate_argument_name.txt

@@ -1,4 +1,10 @@
-duplicate-argument-name:4:12:4:13:foo1:Duplicate argument name _ in function definition:HIGH
-duplicate-argument-name:7:18:7:22:foo2:Duplicate argument name _abc in function definition:HIGH
-duplicate-argument-name:10:12:10:13:foo3:Duplicate argument name _ in function definition:HIGH
-duplicate-argument-name:13:15:13:16:foo4:Duplicate argument name _ in function definition:HIGH
+duplicate-argument-name:6:12:6:13:foo1:Duplicate argument name '_' in function definition:HIGH
+duplicate-argument-name:9:18:9:22:foo2:Duplicate argument name '_abc' in function definition:HIGH
+duplicate-argument-name:12:12:12:13:foo3:Duplicate argument name '_' in function definition:HIGH
+duplicate-argument-name:15:15:15:16:foo4:Duplicate argument name '_' in function definition:HIGH
+duplicate-argument-name:18:13:18:14:foo5:Duplicate argument name '_' in function definition:HIGH
+duplicate-argument-name:18:16:18:17:foo5:Duplicate argument name '_' in function definition:HIGH
+duplicate-argument-name:22:15:22:16:foo6:Duplicate argument name '_' in function definition:HIGH
+duplicate-argument-name:22:19:22:20:foo6:Duplicate argument name '_' in function definition:HIGH
+duplicate-argument-name:22:22:22:23:foo6:Duplicate argument name '_' in function definition:HIGH
+duplicate-argument-name:22:31:22:32:foo6:Duplicate argument name '_' in function definition:HIGH