Fix SystemError when nested function has annotation on positional-only argument (GH-17826)

Lib/test/test_positional_only_arg.py

@@ -15,6 +15,10 @@ def global_pos_only_and_normal(a, /, b):
 def global_pos_only_defaults(a=1, /, b=2):
     return a, b
 
+def global_inner_has_pos_only():
+    def f(x: int, /): ...
+    return f
+
 
 class PositionalOnlyTestCase(unittest.TestCase):
 
@@ -412,6 +416,9 @@ def method(self, /):
 
         self.assertEqual(C().method(), sentinel)
 
+    def test_annotations(self):
+        assert global_inner_has_pos_only().__annotations__ == {'x': int}
+
 
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Core and Builtins/2020-01-04-17-25-34.bpo-39215.xiqiIz.rst

@@ -0,0 +1,2 @@
+Fix ``SystemError`` when nested function has annotation on positional-only
+argument - by Anthony Sottile.

Python/symtable.c

@@ -1717,6 +1717,8 @@ static int
 symtable_visit_annotations(struct symtable *st, stmt_ty s,
                            arguments_ty a, expr_ty returns)
 {
+    if (a->posonlyargs && !symtable_visit_argannotations(st, a->posonlyargs))
+        return 0;
     if (a->args && !symtable_visit_argannotations(st, a->args))
         return 0;
     if (a->vararg && a->vararg->annotation)