bpo-40726: handle uninitalized end_lineno on ast.increment_lineno (GH-20312)

(cherry picked from commit 8f4380d2f5839a321475104765221a7394a9d649)

Co-authored-by: Batuhan Taskaya <batuhanosmantaskaya@gmail.com>

2 files changed, 21 insertions, 3 deletions

diff --git a/Lib/ast.py b/Lib/ast.py
index 6a5b39e..65ebd01 100644
--- a/Lib/ast.py
+++ b/Lib/ast.py
@@ -180,7 +180,11 @@ def copy_location(new_node, old_node):
     for attr in 'lineno', 'col_offset', 'end_lineno', 'end_col_offset':
         if attr in old_node._attributes and attr in new_node._attributes:
             value = getattr(old_node, attr, None)
-            if value is not None:
+            # end_lineno and end_col_offset are optional attributes, and they
+            # should be copied whether the value is None or not.
+            if value is not None or (
+                hasattr(old_node, attr) and attr.startswith("end_")
+            ):
                 setattr(new_node, attr, value)
     return new_node
 
@@ -229,8 +233,11 @@ 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
 
 
diff --git a/Lib/test/test_ast.py b/Lib/test/test_ast.py
index 78e4a56..f5aef61 100644
--- a/Lib/test/test_ast.py
+++ b/Lib/test/test_ast.py
@@ -812,6 +812,12 @@ Module(
             'lineno=1, col_offset=4, end_lineno=1, end_col_offset=5), lineno=1, '
             'col_offset=0, end_lineno=1, end_col_offset=5))'
         )
+        src = ast.Call(col_offset=1, lineno=1, end_lineno=1, end_col_offset=1)
+        new = ast.copy_location(src, ast.Call(col_offset=None, lineno=None))
+        self.assertIsNone(new.end_lineno)
+        self.assertIsNone(new.end_col_offset)
+        self.assertEqual(new.lineno, 1)
+        self.assertEqual(new.col_offset, 1)
 
     def test_fix_missing_locations(self):
         src = ast.parse('write("spam")')
@@ -851,6 +857,11 @@ Module(
             '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')