Prevent `used-before-assignment` for assignment via nonlocal after type annotation (#6185)

5 files changed, 56 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index e477660c4..602ac4113 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -40,6 +40,11 @@ Release date: TBA
   * functions & classes which contain both a docstring and an ellipsis.
   * A body which contains an ellipsis ``nodes.Expr`` node & at least one other statement.
 
+* Fix false positive for ``used-before-assignment`` for assignments taking place via
+  nonlocal declarations after an earlier type annotation.
+
+  Closes #5394
+
 * Fix crash for ``redefined-slots-in-subclass`` when the type of the slot is not a const or a string.
 
   Closes #6100
diff --git a/doc/whatsnew/2.13.rst b/doc/whatsnew/2.13.rst
index d8d105f3c..73e898d24 100644
--- a/doc/whatsnew/2.13.rst
+++ b/doc/whatsnew/2.13.rst
@@ -576,6 +576,11 @@ Other Changes
 
   Closes #5803
 
+* Fix false positive for ``used-before-assignment`` for assignments taking place via
+  nonlocal declarations after an earlier type annotation.
+
+  Closes #5394
+
 * Fix false positive for 'nonexistent-operator' when repeated '-' are
   separated (e.g. by parens).
 
diff --git a/pylint/checkers/variables.py b/pylint/checkers/variables.py
index dcd59b39b..be30c0579 100644
--- a/pylint/checkers/variables.py
+++ b/pylint/checkers/variables.py
@@ -2074,6 +2074,20 @@ class VariablesChecker(BaseChecker):
         parent = node
         while parent is not defstmt_frame.parent:
             parent_scope = parent.scope()
+
+            # Find out if any nonlocals receive values in nested functions
+            for inner_func in parent_scope.nodes_of_class(nodes.FunctionDef):
+                if inner_func is parent_scope:
+                    continue
+                if any(
+                    node.name in nl.names
+                    for nl in inner_func.nodes_of_class(nodes.Nonlocal)
+                ) and any(
+                    node.name == an.name
+                    for an in inner_func.nodes_of_class(nodes.AssignName)
+                ):
+                    return False
+
             local_refs = parent_scope.locals.get(node.name, [])
             for ref_node in local_refs:
                 # If local ref is in the same frame as our node, but on a later lineno
diff --git a/tests/functional/u/used/used_before_assignment_nonlocal.py b/tests/functional/u/used/used_before_assignment_nonlocal.py
index 5cbdd510c..aa0b654b7 100644
--- a/tests/functional/u/used/used_before_assignment_nonlocal.py
+++ b/tests/functional/u/used/used_before_assignment_nonlocal.py
@@ -58,3 +58,34 @@ def nonlocal_in_ifexp():
     on_click(True)

 

 nonlocal_in_ifexp()

+

+

+def type_annotation_only_gets_value_via_nonlocal():

+    """https://github.com/PyCQA/pylint/issues/5394"""

+    some_num: int

+    def inner():

+        nonlocal some_num

+        some_num = 5

+    inner()

+    print(some_num)

+

+

+def type_annotation_only_gets_value_via_nonlocal_nested():

+    """Similar, with nesting"""

+    some_num: int

+    def inner():

+        def inner2():

+            nonlocal some_num

+            some_num = 5

+        inner2()

+    inner()

+    print(some_num)

+

+

+def type_annotation_never_gets_value_despite_nonlocal():

+    """Type annotation lacks a value despite nonlocal declaration"""

+    some_num: int

+    def inner():

+        nonlocal some_num

+    inner()

+    print(some_num)  # [used-before-assignment]

diff --git a/tests/functional/u/used/used_before_assignment_nonlocal.txt b/tests/functional/u/used/used_before_assignment_nonlocal.txt
index 90525457e..f3e873315 100644
--- a/tests/functional/u/used/used_before_assignment_nonlocal.txt
+++ b/tests/functional/u/used/used_before_assignment_nonlocal.txt
@@ -4,3 +4,4 @@ used-before-assignment:30:20:30:30:test_fail3:Using variable 'test_fail4' before
 used-before-assignment:34:22:34:32:test_fail4:Using variable 'test_fail5' before assignment:HIGH
 used-before-assignment:34:44:34:53:test_fail4:Using variable 'undefined' before assignment:HIGH
 used-before-assignment:40:18:40:28:test_fail5:Using variable 'undefined1' before assignment:HIGH
+used-before-assignment:91:10:91:18:type_annotation_never_gets_value_despite_nonlocal:Using variable 'some_num' before assignment:HIGH