Make used-before-assignment consider classes in method annotation and defaults

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

doc/whatsnew/2.12.rst

@@ -75,6 +75,11 @@ Other Changes
 
   Closes #4031
 
+* ``used-before-assignment`` now correctly considers references to classes as type annotation
+  or default values in first-level methods
+
+  Closes #3771
+
 * Fix double emitting of ``not-callable`` on inferrable ``properties``
 
   Closes #4426

pylint/checkers/variables.py

@@ -1195,6 +1195,17 @@ 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_type_annotation_reference(node, defstmt):
+                    if not utils.is_postponed_evaluation_enabled(node):
+                        self.add_message(
+                            "used-before-assignment", node=node, args=node.name
+                        )
+                    break
+                elif self._is_first_level_default_reference(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 +1580,33 @@ def _is_only_type_assignment(node: nodes.Name, defstmt: nodes.Statement) -> bool
                     return False
         return True
 
+    @staticmethod
+    def _is_first_level_type_annotation_reference(
+        node: nodes.Name, defstmt: nodes.Statement
+    ) -> bool:
+        """Check if a first level method's annotation refers to its own class.
+        See tests/functional/u/use/used_before_assignement.py for additional examples.
+        """
+        if isinstance(defstmt, nodes.ClassDef) and node.frame().parent == defstmt:
+            # Check if used as type annotation
+            if isinstance(node.parent, nodes.Arguments):
+                return True
+        return False
+
+    @staticmethod
+    def _is_first_level_default_reference(
+        node: nodes.Name, defstmt: nodes.Statement
+    ) -> bool:
+        """Check if a first level method's default value refers to its own class.
+        See tests/functional/u/use/used_before_assignement.py for additional examples.
+        """
+        if isinstance(defstmt, nodes.ClassDef) and node.frame().parent == defstmt:
+            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.

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())

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

tests/functional/u/use/used_before_assignment_py37.py

@@ -0,0 +1,24 @@
+"""Tests for used-before-assignment with functions added in python 3.7"""
+# pylint: disable=missing-function-docstring
+from __future__ import annotations
+
+
+class MyClass:
+    """With the future import only default values can't refer to the base class"""
+
+    def incorrect_method(self, other: MyClass) -> bool:
+        return self == other
+
+    def second_incorrect_method(
+        self, other=MyClass() # [used-before-assignment]
+    ) -> bool:
+        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())

tests/functional/u/use/used_before_assignment_py37.rc

@@ -0,0 +1,2 @@
+[testoptions]
+min_pyver=3.7

tests/functional/u/use/used_before_assignment_py37.txt

@@ -0,0 +1 @@
+used-before-assignment:13:20:MyClass.second_incorrect_method:Using variable 'MyClass' before assignment:HIGH