[unused-private-member] add logic for checking nested functions

ChangeLog

@@ -14,7 +14,7 @@ Release date: TBA
 
 * pyreverse: Show class has-a relationships inferred from the type-hint
 
-Closes #4744
+  Closes #4744
 
 * Added ``ignored-parents`` option to the design checker to ignore specific
   classes from the ``too-many-ancestors`` check (R0901).
@@ -56,6 +56,10 @@ Closes #4744
 
   Closes #3692
 
+* Fix false-positive of ``unused-private-member`` when using nested functions in a class
+
+  Closes #4673
+
 
 What's New in Pylint 2.9.6?
 ===========================

pylint/checkers/classes.py

@@ -909,6 +909,13 @@ def _check_unused_private_functions(self, node: astroid.ClassDef) -> None:
             function_def = cast(astroid.FunctionDef, function_def)
             if not is_attr_private(function_def.name):
                 continue
+            parent_scope = function_def.parent.scope()
+            if isinstance(parent_scope, astroid.FunctionDef):
+                # Handle nested functions
+                if function_def.name in (
+                    n.name for n in parent_scope.nodes_of_class(astroid.Name)
+                ):
+                    continue
             for attribute in node.nodes_of_class(astroid.Attribute):
                 attribute = cast(astroid.Attribute, attribute)
                 if (
@@ -931,11 +938,19 @@ def _check_unused_private_functions(self, node: astroid.ClassDef) -> None:
                     ):
                         break
             else:
-                function_repr = f"{function_def.name}({function_def.args.as_string()})"
+                name_stack = []
+                curr = parent_scope
+                # Generate proper names for nested functions
+                while curr != node:
+                    name_stack.append(curr.name)
+                    curr = curr.parent.scope()
+
+                outer_level_names = f"{'.'.join(reversed(name_stack))}"
+                function_repr = f"{outer_level_names}.{function_def.name}({function_def.args.as_string()})"
                 self.add_message(
                     "unused-private-member",
                     node=function_def,
-                    args=(node.name, function_repr),
+                    args=(node.name, function_repr.lstrip(".")),
                 )
 
     def _check_unused_private_variables(self, node: astroid.ClassDef) -> None:

tests/functional/u/unused/unused_private_member.py

@@ -160,3 +160,44 @@ def __new__(cls, func, *args):
     def exec(self):
         print(self.__secret_bool)
         return self.func(*self.__args)
+
+
+# Test cases for false-positive reported in #4673
+# https://github.com/PyCQA/pylint/issues/4673
+class FalsePositive4673:
+    """ The testing class """
+
+    def __init__(self, in_thing):
+        self.thing = False
+        self.do_thing(in_thing)
+
+    def do_thing(self, in_thing):
+        """ Checks the false-positive condition, sets a property. """
+        def __false_positive(in_thing):
+            print(in_thing)
+
+        def __true_positive(in_thing):  # [unused-private-member]
+            print(in_thing)
+
+        __false_positive(in_thing)
+        self.thing = True
+
+    def undo_thing(self):
+        """ Unsets a property. """
+        self.thing = False
+
+    def complicated_example(self, flag):
+        def __inner_1():
+            pass
+
+        def __inner_2():
+            pass
+
+        def __inner_3(fn):
+            return fn
+
+        def __inner_4():  # [unused-private-member]
+            pass
+
+        fn_to_return = __inner_1 if flag else __inner_3(__inner_2)
+        return fn_to_return

tests/functional/u/unused/unused_private_member.txt

@@ -7,3 +7,5 @@ unused-private-member:34:4:HasUnusedInClass.__test:Unused private member `HasUnu
 unused-private-member:55:4:HasUnusedInClass.__test_recursive:Unused private member `HasUnusedInClass.__test_recursive(self)`:HIGH
 unused-private-member:132:8:FalsePositive4657.__init__:Unused private member `FalsePositive4657.__attr_c`:HIGH
 undefined-variable:137:15:FalsePositive4657.attr_c:Undefined variable 'cls':HIGH
+unused-private-member:179:8:FalsePositive4673.do_thing.__true_positive:Unused private member `FalsePositive4673.do_thing.__true_positive(in_thing)`:HIGH
+unused-private-member:199:8:FalsePositive4673.complicated_example.__inner_4:Unused private member `FalsePositive4673.complicated_example.__inner_4()`:HIGH