Keep variation stack in bound during PGN parsing

chess/pgn.py

@@ -593,9 +593,11 @@ def read_game(handle):
 
                 in_variation = False
             elif token == ")":
-                # Found a close variation token.
-                variation_stack.pop()
-                board_stack.pop()
+                # Found a close variation token. Always leave at least the
+                # root node on the stack.
+                if len(variation_stack) > 1:
+                    variation_stack.pop()
+                    board_stack.pop()
             elif token in ["1-0", "0-1", "1/2-1/2", "*"] and len(variation_stack) == 1:
                 # Found a result token.
                 found_content = True

test.py

@@ -986,6 +986,12 @@ def test_comment_at_eol(self):
         self.assertTrue(5 in node.variation(1).nags)
         self.assertEqual(node.variation(1).comment, "/\\ Ne7, c6")
 
+    def test_variation_stack(self):
+        pgn = StringIO("1. e4 (1. d4))) !? *")
+        game = chess.pgn.read_game(pgn)
+        self.assertEqual(game.variation(0).move, chess.Move.from_uci("e2e4"))
+        self.assertEqual(game.variation(1).move, chess.Move.from_uci("d2d4"))
+
     def test_annotation_symbols(self):
         pgn = StringIO("1. b4?! g6 2. Bb2 Nc6? 3. Bxh8!!")
         game = chess.pgn.read_game(pgn)