bpo-40726: handle uninitalized end_lineno on ast.increment_lineno

Author: isidentical

Lib/ast.py

@@ -229,8 +229,11 @@ def increment_lineno(node, n=1):
     for child in walk(node):
         if 'lineno' in child._attributes:
             child.lineno = getattr(child, 'lineno', 0) + n
-        if 'end_lineno' in child._attributes:
-            child.end_lineno = getattr(child, 'end_lineno', 0) + n
+        if (
+            "end_lineno" in child._attributes
+            and (end_lineno := getattr(child, "end_lineno", 0)) is not None
+        ):
+            child.end_lineno = end_lineno + n
     return node
 
 

Lib/test/test_ast.py

@@ -830,6 +830,11 @@ def test_increment_lineno(self):
             'lineno=4, col_offset=4, end_lineno=4, end_col_offset=5), lineno=4, '
             'col_offset=0, end_lineno=4, end_col_offset=5))'
         )
+        src = ast.Call(
+            func=ast.Name("test", ast.Load()), args=[], keywords=[], lineno=1
+        )
+        self.assertEqual(ast.increment_lineno(src).lineno, 2)
+        self.assertIsNone(ast.increment_lineno(src).end_lineno)
 
     def test_iter_fields(self):
         node = ast.parse('foo()', mode='eval')

Misc/NEWS.d/next/Library/2020-05-22-12-45-58.bpo-40726.7oBdMw.rst

@@ -0,0 +1,2 @@
+Handle cases where the ``end_lineno`` is ``None`` on
+:func:`ast.increment_lineno`.