fix(4756): fix false positive unused-private-member for private met…

…hods (#5345)

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>
Co-authored-by: Daniël van Noord <13665637+DanielNoord@users.noreply.github.com>

ChangeLog

@@ -582,6 +582,10 @@ Release date: 2021-11-24
 
   Closes #4412 #5287
 
+* Fix ``unused-private-member`` false positive when accessing private methods through ``property``.
+
+  Closes #4756
+
 * Fix ``install graphiz`` message which isn't needed for puml output format.
 
 * ``MessageTest`` of the unittest ``testutil`` now requires the ``confidence`` attribute

doc/whatsnew/2.13.rst

@@ -153,6 +153,10 @@ Other Changes
 
   Closes #5722
 
+* Fix ``unused-private-member`` false positive when accessing private methods through ``property``.
+
+  Closes #4756
+
 * Fixed crash from ``arguments-differ`` and ``arguments-renamed`` when methods were
   defined outside the top level of a class.
 

pylint/checkers/classes/class_checker.py

@@ -900,29 +900,35 @@ def _check_unused_private_functions(self, node: nodes.ClassDef) -> None:
                     n.name for n in parent_scope.nodes_of_class(nodes.Name)
                 ):
                     continue
-            for attribute in node.nodes_of_class(nodes.Attribute):
-                if (
-                    attribute.attrname != function_def.name
-                    or attribute.scope() == function_def  # We ignore recursive calls
-                ):
-                    continue
-                if isinstance(attribute.expr, nodes.Name) and attribute.expr.name in (
-                    "self",
-                    "cls",
-                    node.name,
-                ):
-                    # self.__attrname
-                    # cls.__attrname
-                    # node_name.__attrname
+            for child in node.nodes_of_class((nodes.Name, nodes.Attribute)):
+                # Check for cases where the functions are used as a variable instead of as a method call
+                if isinstance(child, nodes.Name) and child.name == function_def.name:
                     break
-                if isinstance(attribute.expr, nodes.Call):
-                    # type(self).__attrname
-                    inferred = safe_infer(attribute.expr)
+                if isinstance(child, nodes.Attribute):
+                    # Ignore recursive calls
                     if (
-                        isinstance(inferred, nodes.ClassDef)
-                        and inferred.name == node.name
+                        child.attrname != function_def.name
+                        or child.scope() == function_def
                     ):
+                        continue
+
+                    # Check self.__attrname, cls.__attrname, node_name.__attrname
+                    if isinstance(child.expr, nodes.Name) and child.expr.name in {
+                        "self",
+                        "cls",
+                        node.name,
+                    }:
+
                         break
+
+                    # Check type(self).__attrname
+                    if isinstance(child.expr, nodes.Call):
+                        inferred = safe_infer(child.expr)
+                        if (
+                            isinstance(inferred, nodes.ClassDef)
+                            and inferred.name == node.name
+                        ):
+                            break
             else:
                 name_stack = []
                 curr = parent_scope

tests/functional/u/unused/unused_private_member.py

@@ -1,4 +1,6 @@
 # pylint: disable=missing-docstring, invalid-name, too-few-public-methods, no-self-use, line-too-long, unused-argument, protected-access
+from functools import partialmethod
+
 
 class AnotherClass():
     def __test(self):  # [unused-private-member]
@@ -311,6 +313,29 @@ def method(self):
         print(self.__class__.__ham)
 
 
+# https://github.com/PyCQA/pylint/issues/4756
+# Check for false positives emitted when private functions are not referenced in the class body
+# with standard calls but passed as arguments to other functions.
+class FalsePositive4756a:
+    def __bar(self, x):
+        print(x)
+    fizz = partialmethod(__bar, 'fizz')
+foo = FalsePositive4756a()
+foo.fizz()
+
+class FalsePositive4756b:
+    def __get_prop(self):
+        pass
+
+    def __set_prop(self, value):
+        pass
+
+    def __del_prop(self):
+        pass
+
+    prop = property(__get_prop, __set_prop, __del_prop)
+
+
 class TypeSelfCallInMethod:
     """Regression test for issue 5569"""
     @classmethod

tests/functional/u/unused/unused_private_member.txt

@@ -1,20 +1,20 @@
-unused-private-member:4:4:4:14:AnotherClass.__test:Unused private member `AnotherClass.__test(self)`:UNDEFINED
-unused-private-member:8:4:8:15:HasUnusedInClass:Unused private member `HasUnusedInClass.__my_secret`:UNDEFINED
-unused-private-member:12:4:12:37:HasUnusedInClass.__private_class_method_unused:Unused private member `HasUnusedInClass.__private_class_method_unused(cls)`:UNDEFINED
-unused-private-member:20:4:20:38:HasUnusedInClass.__private_static_method_unused:Unused private member `HasUnusedInClass.__private_static_method_unused()`:UNDEFINED
-unused-private-member:28:8:28:30:HasUnusedInClass.__init__:Unused private member `HasUnusedInClass.__instance_secret`:UNDEFINED
-unused-private-member:34:4:34:14:HasUnusedInClass.__test:Unused private member `HasUnusedInClass.__test(self, x, y, z)`:UNDEFINED
-unused-private-member:55:4:55:24:HasUnusedInClass.__test_recursive:Unused private member `HasUnusedInClass.__test_recursive(self)`:UNDEFINED
-unused-private-member:133:8:133:21:FalsePositive4657.__init__:Unused private member `FalsePositive4657.__attr_c`:UNDEFINED
-undefined-variable:138:15:138:18:FalsePositive4657.attr_c:Undefined variable 'cls':UNDEFINED
-unused-private-member:157:8:157:26:FalsePositive4668.__new__:Unused private member `FalsePositive4668.__unused`:UNDEFINED
-unused-private-member:181:8:181:27:FalsePositive4673.do_thing.__true_positive:Unused private member `FalsePositive4673.do_thing.__true_positive(in_thing)`:UNDEFINED
-unused-private-member:201:8:201:21:FalsePositive4673.complicated_example.__inner_4:Unused private member `FalsePositive4673.complicated_example.__inner_4()`:UNDEFINED
-unused-private-member:212:8:212:23:Crash4755Context.__init__:Unused private member `Crash4755Context.__messages`:UNDEFINED
-unused-private-member:229:4:229:24:FalsePositive4681:Unused private member `FalsePositive4681.__should_cause_error`:UNDEFINED
-unused-private-member:239:12:239:50:FalsePositive4681.__init__:Unused private member `FalsePositive4681.__should_cause_error`:UNDEFINED
-unused-private-member:243:12:243:50:FalsePositive4681.__init__:Unused private member `FalsePositive4681.__should_cause_error`:UNDEFINED
-unused-private-member:274:4:274:31:FalsePositive4849.__unused_private_method:Unused private member `FalsePositive4849.__unused_private_method()`:UNDEFINED
-unused-private-member:291:4:291:23:Pony.__init_defaults:Unused private member `Pony.__init_defaults(self)`:UNDEFINED
-unused-private-member:296:4:296:23:Pony.__get_fur_color:Unused private member `Pony.__get_fur_color(self)`:UNDEFINED
-unused-private-member:318:8:318:15:TypeSelfCallInMethod.b:Unused private member `TypeSelfCallInMethod.__a`:UNDEFINED
+unused-private-member:6:4:6:14:AnotherClass.__test:Unused private member `AnotherClass.__test(self)`:UNDEFINED
+unused-private-member:10:4:10:15:HasUnusedInClass:Unused private member `HasUnusedInClass.__my_secret`:UNDEFINED
+unused-private-member:14:4:14:37:HasUnusedInClass.__private_class_method_unused:Unused private member `HasUnusedInClass.__private_class_method_unused(cls)`:UNDEFINED
+unused-private-member:22:4:22:38:HasUnusedInClass.__private_static_method_unused:Unused private member `HasUnusedInClass.__private_static_method_unused()`:UNDEFINED
+unused-private-member:30:8:30:30:HasUnusedInClass.__init__:Unused private member `HasUnusedInClass.__instance_secret`:UNDEFINED
+unused-private-member:36:4:36:14:HasUnusedInClass.__test:Unused private member `HasUnusedInClass.__test(self, x, y, z)`:UNDEFINED
+unused-private-member:57:4:57:24:HasUnusedInClass.__test_recursive:Unused private member `HasUnusedInClass.__test_recursive(self)`:UNDEFINED
+unused-private-member:135:8:135:21:FalsePositive4657.__init__:Unused private member `FalsePositive4657.__attr_c`:UNDEFINED
+undefined-variable:140:15:140:18:FalsePositive4657.attr_c:Undefined variable 'cls':UNDEFINED
+unused-private-member:159:8:159:26:FalsePositive4668.__new__:Unused private member `FalsePositive4668.__unused`:UNDEFINED
+unused-private-member:183:8:183:27:FalsePositive4673.do_thing.__true_positive:Unused private member `FalsePositive4673.do_thing.__true_positive(in_thing)`:UNDEFINED
+unused-private-member:203:8:203:21:FalsePositive4673.complicated_example.__inner_4:Unused private member `FalsePositive4673.complicated_example.__inner_4()`:UNDEFINED
+unused-private-member:214:8:214:23:Crash4755Context.__init__:Unused private member `Crash4755Context.__messages`:UNDEFINED
+unused-private-member:231:4:231:24:FalsePositive4681:Unused private member `FalsePositive4681.__should_cause_error`:UNDEFINED
+unused-private-member:241:12:241:50:FalsePositive4681.__init__:Unused private member `FalsePositive4681.__should_cause_error`:UNDEFINED
+unused-private-member:245:12:245:50:FalsePositive4681.__init__:Unused private member `FalsePositive4681.__should_cause_error`:UNDEFINED
+unused-private-member:276:4:276:31:FalsePositive4849.__unused_private_method:Unused private member `FalsePositive4849.__unused_private_method()`:UNDEFINED
+unused-private-member:293:4:293:23:Pony.__init_defaults:Unused private member `Pony.__init_defaults(self)`:UNDEFINED
+unused-private-member:298:4:298:23:Pony.__get_fur_color:Unused private member `Pony.__get_fur_color(self)`:UNDEFINED
+unused-private-member:343:8:343:15:TypeSelfCallInMethod.b:Unused private member `TypeSelfCallInMethod.__a`:UNDEFINED