Emit used-before-assignment when calling nested functions before assignment

doc/whatsnew/2/2.15/index.rst

@@ -46,6 +46,10 @@ False negatives fixed
 
   Closes #5653
 
+* Emit ``used-before-assignment`` when calling nested functions before assignment.
+
+  Closes #6812
+
 * Emit ``used-before-assignment`` for self-referencing assignments under if conditions.
 
   Closes #6643

pylint/checkers/variables.py

@@ -204,11 +204,12 @@ class C: ...
         return False
     if isinstance(frame, nodes.FunctionDef):
         # If the parent of the current node is a
-        # function, then it can be under its scope
-        # (defined in, which doesn't concern us) or
+        # function, then it can be under its scope (defined in); or
         # the `->` part of annotations. The same goes
         # for annotations of function arguments, they'll have
         # their parent the Arguments node.
+        if frame.parent_of(defframe):
+            return node.lineno < defframe.lineno
         if not isinstance(node.parent, (nodes.FunctionDef, nodes.Arguments)):
             return False
     elif any(

tests/functional/u/used/used_before_assignment.py

@@ -6,3 +6,10 @@
 MSG = "hello %s" % MSG  # [used-before-assignment]
 
 MSG2 = "hello %s" % MSG2  # [used-before-assignment]
+
+def outer():
+    inner()  # [used-before-assignment]
+    def inner():
+        pass
+
+outer()

tests/functional/u/used/used_before_assignment.txt

@@ -1,2 +1,3 @@
 used-before-assignment:6:19:6:22::Using variable 'MSG' before assignment:HIGH
 used-before-assignment:8:20:8:24::Using variable 'MSG2' before assignment:HIGH
+used-before-assignment:11:4:11:9:outer:Using variable 'inner' before assignment:HIGH