Fix ``protected-access`` for attributes and methods of nested classes (#5232)

* Fix access to private function in inner class on protected-access bug

* Add functional test for protected-access from inner class

* Add Ikraduya to CONTRIBUTORS file

* Add if statement to avoid potential bug

* Fix ``protected-access`` for attributes and methods of nested classes
This closes #3066

Co-authored-by: ikraduya <ikraduya@gmail.com>
Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

7 files changed, 123 insertions, 16 deletions

diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index b4bab0120..cc8393996 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -570,3 +570,5 @@ contributors:
 * Takahide Nojima: contributor
 
 * Tushar Sadhwani (tusharsadhwani): contributor
+
+* Ikraduya Edian: contributor
diff --git a/ChangeLog b/ChangeLog
index 8b1e97508..b35606e4b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -30,6 +30,10 @@ Release date: TBA
 
   Closes #3197
 
+* Fixed ``protected-access`` for accessing of attributes and methods of inner classes
+
+  Closes #3066
+
 * Added support for ``ModuleNotFoundError`` (``import-error`` and ``no-name-in-module``).
   ``ModuleNotFoundError`` inherits from ``ImportError`` and was added in Python ``3.6``
 
diff --git a/doc/whatsnew/2.12.rst b/doc/whatsnew/2.12.rst
index 627a5eb07..98008e109 100644
--- a/doc/whatsnew/2.12.rst
+++ b/doc/whatsnew/2.12.rst
@@ -78,6 +78,10 @@ Other Changes
   ``use-implicit-booleaness-not-len`` in order to be consistent with
   ``use-implicit-booleaness-not-comparison``.
 
+* Fixed ``protected-access`` for accessing of attributes and methods of inner classes
+
+  Closes #3066
+
 * Update ``literal-comparison``` checker to ignore tuple literals
 
   Closes #3031
diff --git a/pylint/checkers/classes.py b/pylint/checkers/classes.py
index f6db8a73f..730f2e659 100644
--- a/pylint/checkers/classes.py
+++ b/pylint/checkers/classes.py
@@ -63,6 +63,7 @@ from pylint.checkers.utils import (
     class_is_abstract,
     decorated_with,
     decorated_with_property,
+    get_outer_class,
     has_known_bases,
     is_attr_private,
     is_attr_protected,
@@ -1606,9 +1607,22 @@ a metaclass class method.",
             if self._is_type_self_call(node.expr):
                 return
 
+            # Check if we are inside the scope of a class or nested inner class
+            inside_klass = True
+            outer_klass = klass
+            parents_callee = callee.split(".")
+            parents_callee.reverse()
+            for callee in parents_callee:
+                if callee != outer_klass.name:
+                    inside_klass = False
+                    break
+
+                # Move up one level within the nested classes
+                outer_klass = get_outer_class(outer_klass)
+
             # We are in a class, one remaining valid cases, Klass._attr inside
             # Klass
-            if not (callee == klass.name or callee in klass.basenames):
+            if not (inside_klass or callee in klass.basenames):
                 # Detect property assignments in the body of the class.
                 # This is acceptable:
                 #
diff --git a/pylint/checkers/utils.py b/pylint/checkers/utils.py
index 3361eef8a..f5b4f42a5 100644
--- a/pylint/checkers/utils.py
+++ b/pylint/checkers/utils.py
@@ -673,6 +673,13 @@ def node_frame_class(node: nodes.NodeNG) -> Optional[nodes.ClassDef]:
     return klass
 
 
+def get_outer_class(class_node: astroid.ClassDef) -> Optional[astroid.ClassDef]:
+    """Return the class that is the outer class of given (nested) class_node"""
+    parent_klass = class_node.parent.frame()
+
+    return parent_klass if isinstance(parent_klass, astroid.ClassDef) else None
+
+
 def is_attr_private(attrname: str) -> Optional[Match[str]]:
     """Check that attribute name is private (at least two leading underscores,
     at most one trailing underscore)
diff --git a/tests/functional/a/access/access_to_protected_members.py b/tests/functional/a/access/access_to_protected_members.py
index ffbfabf15..7d732dcc5 100644
--- a/tests/functional/a/access/access_to_protected_members.py
+++ b/tests/functional/a/access/access_to_protected_members.py
@@ -211,3 +211,67 @@ class Issue1159Subclass(Issue1159):
         instance = Issue1159OtherClass()
         instance._bar = 3  # [protected-access]
         _ = instance._foo  # [protected-access]
+
+
+class Issue3066:
+    """Test for GitHub issue 3066
+    Accessing of attributes/methods of inner and outer classes
+    https://github.com/PyCQA/pylint/issues/3066"""
+
+    attr = 0
+    _attr = 1
+
+    @staticmethod
+    def _bar(i):
+        """Docstring."""
+
+    @staticmethod
+    def foobar(i):
+        """Test access from outer class"""
+        Issue3066._attr = 2
+        Issue3066.Aclass._attr = "y"  # [protected-access]
+        Issue3066.Aclass.Bclass._attr = "b"  # [protected-access]
+
+        Issue3066._bar(i)
+        Issue3066.Aclass._bar(i)  # [protected-access]
+        Issue3066.Aclass.Bclass._bar(i)  # [protected-access]
+
+    class Aclass:
+        """Inner class for GitHub issue 3066"""
+
+        _attr = "x"
+
+        @staticmethod
+        def foobar(i):
+            """Test access from inner class"""
+            Issue3066._attr = 2  # [protected-access]
+            Issue3066.Aclass._attr = "y"
+            Issue3066.Aclass.Bclass._attr = "b"  # [protected-access]
+
+            Issue3066._bar(i)  # [protected-access]
+            Issue3066.Aclass._bar(i)
+            Issue3066.Aclass.Bclass._bar(i)  # [protected-access]
+
+        @staticmethod
+        def _bar(i):
+            """Docstring."""
+
+        class Bclass:
+            """Inner inner class for GitHub issue 3066"""
+
+            _attr = "a"
+
+            @staticmethod
+            def foobar(i):
+                """Test access from inner inner class"""
+                Issue3066._attr = 2  # [protected-access]
+                Issue3066.Aclass._attr = "y"  # [protected-access]
+                Issue3066.Aclass.Bclass._attr = "b"
+
+                Issue3066._bar(i)  # [protected-access]
+                Issue3066.Aclass._bar(i)  # [protected-access]
+                Issue3066.Aclass.Bclass._bar(i)
+
+            @staticmethod
+            def _bar(i):
+                """Docstring."""
diff --git a/tests/functional/a/access/access_to_protected_members.txt b/tests/functional/a/access/access_to_protected_members.txt
index 1b93683db..3f127f70c 100644
--- a/tests/functional/a/access/access_to_protected_members.txt
+++ b/tests/functional/a/access/access_to_protected_members.txt
@@ -1,16 +1,28 @@
-protected-access:19:14:MyClass.test:Access to a protected member _haha of a client class
-protected-access:41:0::Access to a protected member _protected of a client class
-protected-access:42:6::Access to a protected member _protected of a client class
-protected-access:43:0::Access to a protected member _cls_protected of a client class
-protected-access:44:6::Access to a protected member _cls_protected of a client class
-protected-access:58:19:Issue1031.incorrect_access:Access to a protected member _protected of a client class
-protected-access:72:48:Issue1802.__eq__:Access to a protected member __private of a client class
-protected-access:80:32:Issue1802.not_in_special:Access to a protected member _foo of a client class
-protected-access:100:32:Issue1802.__fake_special__:Access to a protected member _foo of a client class
-protected-access:162:8:Issue1159.access_other_attr:Access to a protected member _bar of a client class
-protected-access:163:12:Issue1159.access_other_attr:Access to a protected member _foo of a client class
+protected-access:19:14:MyClass.test:Access to a protected member _haha of a client class:HIGH
+protected-access:41:0::Access to a protected member _protected of a client class:HIGH
+protected-access:42:6::Access to a protected member _protected of a client class:HIGH
+protected-access:43:0::Access to a protected member _cls_protected of a client class:HIGH
+protected-access:44:6::Access to a protected member _cls_protected of a client class:HIGH
+protected-access:58:19:Issue1031.incorrect_access:Access to a protected member _protected of a client class:HIGH
+protected-access:72:48:Issue1802.__eq__:Access to a protected member __private of a client class:HIGH
+protected-access:80:32:Issue1802.not_in_special:Access to a protected member _foo of a client class:HIGH
+protected-access:100:32:Issue1802.__fake_special__:Access to a protected member _foo of a client class:HIGH
+protected-access:162:8:Issue1159.access_other_attr:Access to a protected member _bar of a client class:HIGH
+protected-access:163:12:Issue1159.access_other_attr:Access to a protected member _foo of a client class:HIGH
 no-member:194:12:Issue1159Subclass.access_missing_member:Instance of 'Issue1159Subclass' has no '_baz' member; maybe '_bar'?:INFERENCE
-protected-access:194:12:Issue1159Subclass.access_missing_member:Access to a protected member _baz of a client class
-attribute-defined-outside-init:203:8:Issue1159Subclass.assign_missing_member:Attribute '_qux' defined outside __init__
-protected-access:212:8:Issue1159Subclass.access_other_attr:Access to a protected member _bar of a client class
-protected-access:213:12:Issue1159Subclass.access_other_attr:Access to a protected member _foo of a client class
+protected-access:194:12:Issue1159Subclass.access_missing_member:Access to a protected member _baz of a client class:HIGH
+attribute-defined-outside-init:203:8:Issue1159Subclass.assign_missing_member:Attribute '_qux' defined outside __init__:HIGH
+protected-access:212:8:Issue1159Subclass.access_other_attr:Access to a protected member _bar of a client class:HIGH
+protected-access:213:12:Issue1159Subclass.access_other_attr:Access to a protected member _foo of a client class:HIGH
+protected-access:232:8:Issue3066.foobar:Access to a protected member _attr of a client class:HIGH
+protected-access:233:8:Issue3066.foobar:Access to a protected member _attr of a client class:HIGH
+protected-access:236:8:Issue3066.foobar:Access to a protected member _bar of a client class:HIGH
+protected-access:237:8:Issue3066.foobar:Access to a protected member _bar of a client class:HIGH
+protected-access:247:12:Issue3066.Aclass.foobar:Access to a protected member _attr of a client class:HIGH
+protected-access:249:12:Issue3066.Aclass.foobar:Access to a protected member _attr of a client class:HIGH
+protected-access:251:12:Issue3066.Aclass.foobar:Access to a protected member _bar of a client class:HIGH
+protected-access:253:12:Issue3066.Aclass.foobar:Access to a protected member _bar of a client class:HIGH
+protected-access:267:16:Issue3066.Aclass.Bclass.foobar:Access to a protected member _attr of a client class:HIGH
+protected-access:268:16:Issue3066.Aclass.Bclass.foobar:Access to a protected member _attr of a client class:HIGH
+protected-access:271:16:Issue3066.Aclass.Bclass.foobar:Access to a protected member _bar of a client class:HIGH
+protected-access:272:16:Issue3066.Aclass.Bclass.foobar:Access to a protected member _bar of a client class:HIGH