Fix possibly-used-before-assignment false negative for type-annotated assignment

doc/whatsnew/fragments/10421.false_negative

@@ -0,0 +1,4 @@
+Fix a false negative for `possibly-used-before-assignment` when a variable is conditionally defined
+and later assigned to a type-annotated variable.
+
+Closes #10421

pylint/checkers/variables.py

@@ -2541,12 +2541,13 @@ def _is_never_evaluated(
         return False
 
     @staticmethod
-    def _is_variable_annotation_in_function(node: nodes.NodeNG) -> bool:
-        is_annotation = utils.get_node_first_ancestor_of_type(node, nodes.AnnAssign)
+    def _is_variable_annotation_in_function(node: nodes.Name) -> bool:
+        ann_assign = utils.get_node_first_ancestor_of_type(node, nodes.AnnAssign)
         return (
-            is_annotation
+            ann_assign
+            and (node is ann_assign.annotation or ann_assign.annotation.parent_of(node))
             and utils.get_node_first_ancestor_of_type(  # type: ignore[return-value]
-                is_annotation, nodes.FunctionDef
+                ann_assign, nodes.FunctionDef
             )
         )
 

tests/functional/u/used/used_before_assignment_scoping.py

@@ -16,3 +16,10 @@ def func():
     first = datetime.now()  # [used-before-assignment]
     second = datetime.now()
     return first, second
+
+
+def annotated_declaration_with_type_subscript():
+    dt_list: list[datetime]
+    dt_list = [datetime.now(), datetime.now()]  # [used-before-assignment]
+
+    return dt_list

tests/functional/u/used/used_before_assignment_scoping.txt

@@ -1,2 +1,3 @@
 used-before-assignment:10:13:10:21:func_two:Using variable 'datetime' before assignment:INFERENCE
 used-before-assignment:16:12:16:20:func:Using variable 'datetime' before assignment:INFERENCE
+used-before-assignment:23:15:23:23:annotated_declaration_with_type_subscript:Using variable 'datetime' before assignment:INFERENCE

tests/functional/u/used/used_before_assignment_type_annotations.py

@@ -88,3 +88,22 @@ def my_method(self) -> Coords:
             pass
 
     print(MyObject)
+
+
+def conditional_annotated_assignment():
+    """Variable is conditionally defined but later used in a type-annotated assignment."""
+    if object() is None:
+        data={"cat": "harf"}
+    token: str = data.get("cat")  # [possibly-used-before-assignment]
+    print(token)
+
+
+def loop_conditional_annotated_assignment():
+    """Variable is conditionally defined inside a for-loop but later used
+    in a type-annotated assignment.
+    """
+    for _ in range(3):
+        if object() is None:
+            data={"cat": "harf"}
+    token: str = data.get("cat")  # [possibly-used-before-assignment]
+    print(token)

tests/functional/u/used/used_before_assignment_type_annotations.txt

@@ -1,3 +1,5 @@
 used-before-assignment:15:10:15:18:only_type_assignment:Using variable 'variable' before assignment:HIGH
 used-before-assignment:28:10:28:18:value_assignment_after_access:Using variable 'variable' before assignment:HIGH
 undefined-variable:62:14:62:17:decorator_returning_incorrect_function.wrapper_with_type_and_no_value:Undefined variable 'var':HIGH
+possibly-used-before-assignment:97:17:97:21:conditional_annotated_assignment:Possibly using variable 'data' before assignment:CONTROL_FLOW
+possibly-used-before-assignment:108:17:108:21:loop_conditional_annotated_assignment:Possibly using variable 'data' before assignment:CONTROL_FLOW