Fix #5371: Correctly count arguments to static methods missing @staticmethod decorator (#5412)

* Fix #5371: Correctly count arguments to static methods missing @staticmethod decorator

* Implementations of MapReduceMixin.reduce_map_data were actually not classmethods

7 files changed, 39 insertions, 12 deletions

diff --git a/ChangeLog b/ChangeLog
index f946dbbc5..f77b7e870 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -23,6 +23,11 @@ Release date: TBA
 
   Closes #5323
 
+* Fixed detection of ``arguments-differ`` when superclass static
+  methods lacked a ``@staticmethod`` decorator.
+
+  Closes #5371
+
 ..
   Insert your changelog randomly, it will reduce merge conflicts
   (Ie. not necessarily at the end)
diff --git a/pylint/checkers/classes.py b/pylint/checkers/classes.py
index 2d63b8bbd..4bbc45f20 100644
--- a/pylint/checkers/classes.py
+++ b/pylint/checkers/classes.py
@@ -177,7 +177,7 @@ def _definition_equivalent_to_call(definition, call):
 
 def _positional_parameters(method):
     positional = method.args.args
-    if method.type in {"classmethod", "method"}:
+    if method.is_bound() and method.type in {"classmethod", "method"}:
         positional = positional[1:]
     return positional
 
diff --git a/pylint/checkers/mapreduce_checker.py b/pylint/checkers/mapreduce_checker.py
index cb76decf9..9b90c634a 100644
--- a/pylint/checkers/mapreduce_checker.py
+++ b/pylint/checkers/mapreduce_checker.py
@@ -14,7 +14,6 @@ class MapReduceMixin(metaclass=abc.ABCMeta):
     def get_map_data(self):
         """Returns mergable/reducible data that will be examined"""
 
-    @classmethod
     @abc.abstractmethod
-    def reduce_map_data(cls, linter, data):
+    def reduce_map_data(self, linter, data):
         """For a given Checker, receives data for all mapped runs"""
diff --git a/tests/functional/a/arguments_differ.py b/tests/functional/a/arguments_differ.py
index b5b43505a..d6689d920 100644
--- a/tests/functional/a/arguments_differ.py
+++ b/tests/functional/a/arguments_differ.py
@@ -141,7 +141,7 @@ class PropertySetter(Property):
 

 class StaticmethodChild2(Staticmethod):

 

-    def func(self, data):

+    def func(self, data):  # [arguments-differ]

         super().func(data)

 

 

@@ -151,15 +151,23 @@ class SuperClass(object):
     def impl(arg1, arg2, **kwargs):

         return arg1 + arg2

 

+    def should_have_been_decorated_as_static(arg1, arg2):  # pylint: disable=no-self-argument

+        return arg1 + arg2

+

 

 class MyClass(SuperClass):

 

-    def impl(self, *args, **kwargs):

+    @staticmethod

+    def impl(*args, **kwargs):

         """

         Acceptable use of vararg in subclass because it does not violate LSP.

         """

         super().impl(*args, **kwargs)

 

+    @staticmethod

+    def should_have_been_decorated_as_static(arg1, arg2):

+        return arg1 + arg2

+

 

 class FirstHasArgs(object):

 

diff --git a/tests/functional/a/arguments_differ.txt b/tests/functional/a/arguments_differ.txt
index ea0b74dfa..5cce378e2 100644
--- a/tests/functional/a/arguments_differ.txt
+++ b/tests/functional/a/arguments_differ.txt
@@ -3,9 +3,10 @@ arguments-differ:23:4:24:12:ChildDefaults.test:Number of parameters was 3 in 'Pa
 arguments-differ:41:4:42:12:ClassmethodChild.func:Number of parameters was 2 in 'Classmethod.func' and is now 0 in overridden 'ClassmethodChild.func' method:UNDEFINED
 arguments-differ:68:4:69:64:VarargsChild.has_kwargs:Variadics removed in overridden 'VarargsChild.has_kwargs' method:UNDEFINED
 arguments-renamed:71:4:72:89:VarargsChild.no_kwargs:Parameter 'args' has been renamed to 'arg' in overridden 'VarargsChild.no_kwargs' method:UNDEFINED
-arguments-differ:172:4:173:12:SecondChangesArgs.test:Number of parameters was 2 in 'FirstHasArgs.test' and is now 4 in overridden 'SecondChangesArgs.test' method:UNDEFINED
-arguments-differ:298:4:299:60:Foo.kwonly_1:Number of parameters was 4 in 'AbstractFoo.kwonly_1' and is now 3 in overridden 'Foo.kwonly_1' method:UNDEFINED
-arguments-differ:301:4:302:82:Foo.kwonly_2:Number of parameters was 3 in 'AbstractFoo.kwonly_2' and is now 2 in overridden 'Foo.kwonly_2' method:UNDEFINED
-arguments-differ:304:4:305:32:Foo.kwonly_3:Number of parameters was 3 in 'AbstractFoo.kwonly_3' and is now 3 in overridden 'Foo.kwonly_3' method:UNDEFINED
-arguments-differ:307:4:308:32:Foo.kwonly_4:Number of parameters was 3 in 'AbstractFoo.kwonly_4' and is now 3 in overridden 'Foo.kwonly_4' method:UNDEFINED
-arguments-differ:310:4:311:41:Foo.kwonly_5:Variadics removed in overridden 'Foo.kwonly_5' method:UNDEFINED
+arguments-differ:144:4:145:26:StaticmethodChild2.func:Number of parameters was 1 in 'Staticmethod.func' and is now 2 in overridden 'StaticmethodChild2.func' method:UNDEFINED
+arguments-differ:180:4:181:12:SecondChangesArgs.test:Number of parameters was 2 in 'FirstHasArgs.test' and is now 4 in overridden 'SecondChangesArgs.test' method:UNDEFINED
+arguments-differ:306:4:307:60:Foo.kwonly_1:Number of parameters was 4 in 'AbstractFoo.kwonly_1' and is now 3 in overridden 'Foo.kwonly_1' method:UNDEFINED
+arguments-differ:309:4:310:82:Foo.kwonly_2:Number of parameters was 3 in 'AbstractFoo.kwonly_2' and is now 2 in overridden 'Foo.kwonly_2' method:UNDEFINED
+arguments-differ:312:4:313:32:Foo.kwonly_3:Number of parameters was 3 in 'AbstractFoo.kwonly_3' and is now 3 in overridden 'Foo.kwonly_3' method:UNDEFINED
+arguments-differ:315:4:316:32:Foo.kwonly_4:Number of parameters was 3 in 'AbstractFoo.kwonly_4' and is now 3 in overridden 'Foo.kwonly_4' method:UNDEFINED
+arguments-differ:318:4:319:41:Foo.kwonly_5:Variadics removed in overridden 'Foo.kwonly_5' method:UNDEFINED
diff --git a/tests/functional/a/arguments_differ_issue5371.py b/tests/functional/a/arguments_differ_issue5371.py
new file mode 100644
index 000000000..a0cd39613
--- /dev/null
+++ b/tests/functional/a/arguments_differ_issue5371.py
@@ -0,0 +1,13 @@
+"""https://github.com/PyCQA/pylint/issues/5371"""
+from enum import Enum
+
+
+class MyEnum(Enum):
+    """
+    Enum._generate_next_value_() in the stdlib currently lacks a
+    @staticmethod decorator.
+    """
+
+    @staticmethod
+    def _generate_next_value_(name: str, start: int, count: int, last_values: list):
+        return 42
diff --git a/tests/test_check_parallel.py b/tests/test_check_parallel.py
index df493ccb2..d1b5a6489 100644
--- a/tests/test_check_parallel.py
+++ b/tests/test_check_parallel.py
@@ -20,6 +20,7 @@ from astroid import nodes
 import pylint.interfaces
 import pylint.lint.parallel
 from pylint.checkers.base_checker import BaseChecker
+from pylint.checkers.mapreduce_checker import MapReduceMixin
 from pylint.lint import PyLinter
 from pylint.lint.parallel import _worker_check_single_file as worker_check_single_file
 from pylint.lint.parallel import _worker_initialize as worker_initialize
@@ -73,7 +74,7 @@ class SequentialTestChecker(BaseChecker):
         self.data.append(record)
 
 
-class ParallelTestChecker(BaseChecker):
+class ParallelTestChecker(BaseChecker, MapReduceMixin):
     """A checker that does need to consolidate data.
 
     To simulate the need to consolidate data, this checker only