Add tests for nonlocal checks

Author: zenlyj

tests/functional/u/used/used_before_assignment_nonlocal.py

@@ -106,3 +106,30 @@ def inner():
         print(args)
     inner()
     print(args)
+
+
+def nonlocal_in_outer_frame_fail():
+    """nonlocal declared in outer frame, bad usage and assignation in inner frame"""
+    num = 1
+    def outer():
+        nonlocal num
+        def inner():
+            print(num)  # [used-before-assignment]
+            num = 2
+        inner()
+    outer()
+
+
+def nonlocal_in_outer_frame_ok(callback, condition_a, condition_b):
+    """nonlocal declared in outer frame, usage and definition in different frames"""
+    def outer():
+        nonlocal callback
+        if condition_a:
+            def inner():
+                callback()  # should not emit possibly-used-before-assignment
+            inner()
+        else:
+            if condition_b:
+                def callback():
+                    pass
+    outer()

tests/functional/u/used/used_before_assignment_nonlocal.txt

@@ -6,3 +6,4 @@ used-before-assignment:33:44:33:53:test_fail4:Using variable 'undefined' before
 used-before-assignment:39:18:39:28:test_fail5:Using variable 'undefined1' before assignment:HIGH
 used-before-assignment:90:10:90:18:type_annotation_never_gets_value_despite_nonlocal:Using variable 'some_num' before assignment:HIGH
 used-before-assignment:96:14:96:18:inner_function_lacks_access_to_outer_args.inner:Using variable 'args' before assignment:HIGH
+used-before-assignment:117:18:117:21:nonlocal_in_outer_frame_fail.outer.inner:Using variable 'num' before assignment:HIGH