From 0f87c0e5eb03b97ef4095ba3c93b705a3b04d967 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dani=C3=ABl=20van=20Noord?=
 <13665637+DanielNoord@users.noreply.github.com>
Date: Mon, 18 Oct 2021 17:45:51 +0200
Subject: [PATCH] Make ``used-before-assignment`` consider classes in method
 annotation and defaults This closes #3771

---
 ChangeLog                                     |  5 ++++
 doc/whatsnew/2.12.rst                         |  5 ++++
 pylint/checkers/variables.py                  | 30 +++++++++++++++++++
 .../u/use/used_before_assignement.py          | 20 ++++++++++++-
 .../u/use/used_before_assignement.txt         |  6 ++--
 5 files changed, 63 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index f26007d1e4..c19d95c54b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -31,6 +31,11 @@ Release date: TBA
 
   Closes #4031
 
+* ``used-before-assignment`` now correctly considers references to classes as type annotation
+  or default values in first-level methods
+
+  Closes #3771
+
 * Fix bug with importing namespace packages with relative imports
 
   Closes #2967 and #5131
diff --git a/doc/whatsnew/2.12.rst b/doc/whatsnew/2.12.rst
index be1e5245c4..94772a77b8 100644
--- a/doc/whatsnew/2.12.rst
+++ b/doc/whatsnew/2.12.rst
@@ -74,3 +74,8 @@ Other Changes
   used in metaclass declarations
 
   Closes #4031
+
+* ``used-before-assignment`` now correctly considers references to classes as type annotation
+  or default values in first-level methods
+
+  Closes #3771
diff --git a/pylint/checkers/variables.py b/pylint/checkers/variables.py
index 1d78184c81..8ab167485d 100644
--- a/pylint/checkers/variables.py
+++ b/pylint/checkers/variables.py
@@ -1195,6 +1195,11 @@ def visit_name(self, node: nodes.Name) -> None:
                             )
                 elif self._is_only_type_assignment(node, defstmt):
                     self.add_message("undefined-variable", node=node, args=node.name)
+                elif self._is_first_level_self_referring_annotation(node, defstmt):
+                    self.add_message(
+                        "used-before-assignment", node=node, args=node.name
+                    )
+                    break
 
             current_consumer.mark_as_consumed(node.name, found_nodes)
             # check it's not a loop variable used outside the loop
@@ -1569,6 +1574,31 @@ def _is_only_type_assignment(node: nodes.Name, defstmt: nodes.Statement) -> bool
                     return False
         return True
 
+    @staticmethod
+    def _is_first_level_self_referring_annotation(
+        node: nodes.Name, defstmt: nodes.Statement
+    ) -> bool:
+        """Check if a method annotation refers to its own class on the first level.
+        This schould be done with quotes:
+            def MyClass():
+                def method(parameter: "MyClass"):
+                    pass
+                def other_method(self) -> bool:
+                    def inner_method(self, other: MyClass) -> bool:
+                        pass
+                    pass
+        """
+        if isinstance(defstmt, nodes.ClassDef) and node.frame().parent == defstmt:
+            # Check if used as type annotation
+            if isinstance(node.parent, nodes.Arguments):
+                return True
+            # Check if used as default value by calling the class
+            if isinstance(node.parent, nodes.Call) and isinstance(
+                node.parent.parent, nodes.Arguments
+            ):
+                return True
+        return False
+
     def _ignore_class_scope(self, node):
         """
         Return True if the node is in a local class scope, as an assignment.
diff --git a/tests/functional/u/use/used_before_assignement.py b/tests/functional/u/use/used_before_assignement.py
index 285f3d180d..cffddb9b94 100644
--- a/tests/functional/u/use/used_before_assignement.py
+++ b/tests/functional/u/use/used_before_assignement.py
@@ -1,8 +1,26 @@
 """pylint doesn't see the NameError in this module"""
-#pylint: disable=consider-using-f-string
+#pylint: disable=consider-using-f-string, missing-function-docstring
 __revision__ = None
 
 MSG = "hello %s" % MSG  # [used-before-assignment]
 
 MSG2 = ("hello %s" %
         MSG2) # [used-before-assignment]
+
+
+class MyClass:
+    """Type annotation or default values for first level methods can't refer to their own class"""
+    def incorrect_method(self, other: MyClass) -> bool:  # [used-before-assignment]
+        return self == other
+
+    def second_incorrect_method(self, other = MyClass()) -> bool:  # [used-before-assignment]
+        return self == other
+
+    def correct_method(self, other: "MyClass") -> bool:
+        return self == other
+
+    def second_correct_method(self) -> bool:
+        def inner_method(self, other: MyClass) -> bool:
+            return self == other
+
+        return inner_method(self, MyClass())
diff --git a/tests/functional/u/use/used_before_assignement.txt b/tests/functional/u/use/used_before_assignement.txt
index d19fe322ac..708880ac03 100644
--- a/tests/functional/u/use/used_before_assignement.txt
+++ b/tests/functional/u/use/used_before_assignement.txt
@@ -1,2 +1,4 @@
-used-before-assignment:5:19::Using variable 'MSG' before assignment
-used-before-assignment:8:8::Using variable 'MSG2' before assignment
+used-before-assignment:5:19::Using variable 'MSG' before assignment:HIGH
+used-before-assignment:8:8::Using variable 'MSG2' before assignment:HIGH
+used-before-assignment:13:38:MyClass.incorrect_method:Using variable 'MyClass' before assignment:HIGH
+used-before-assignment:16:46:MyClass.second_incorrect_method:Using variable 'MyClass' before assignment:HIGH