gh-118877: Fix AssertionError crash in pyrepl

A crash of the new pyrepl was triggered by pressing up arrow when tab completion menu was displayed.
python · pablogsal · Jan 21, 2025 · May 10, 2024 · May 11, 2024 · May 12, 2024
commit dc98b552a99e59cf1cf56e985d3c5d74942cd143
@@ -245,7 +245,7 @@ def do(self) -> None:
            x, y = r.pos2xy()
            new_y = y - 1

-            if new_y < 0:
+            if r.bol() == 0:
                if r.historyi > 0:
                    r.select_item(r.historyi - 1)
                    return

diff --git a/Lib/test/test_pyrepl.py b/Lib/test/test_pyrepl.py
@@ -607,6 +607,30 @@ def test_global_namespace_completion(self):
        output = multiline_input(reader, namespace)
        self.assertEqual(output, "python")

+    def test_updown_arrow_with_completion_menu(self):
+        """Up arrow in the middle of unfinished tab completion when the menu is displayed
+        should work and trigger going back in history. Down arrow should subsequently
+        get us back to the incomplete command."""
+        code = "import os\nos.\t\t"
+        namespace = {"os": os}
+
+        events = itertools.chain(
+            code_to_events(code),
+            [
+                Event(evt='key', data='up', raw=bytearray(b'\x1bOA')),
+                Event(evt="key", data="down", raw=bytearray(b"\x1bOB")),
+            ],
+            code_to_events("\n")
+        )
+        reader = self.prepare_reader(events, namespace=namespace)
+        output = multiline_input(reader, namespace)
+        # This is the first line, nothing to see here
+        self.assertEqual(output, "import os")
+        # This is the second line. We pressed up and down arrows
+        # so we should end up where we were when we initiated tab completion.
+        output = multiline_input(reader, namespace)
+        self.assertEqual(output, "os.")
+

 @patch("_pyrepl.curses.tigetstr", lambda x: b"")
 class TestUnivEventQueue(TestCase):
@@ -1001,6 +1025,5 @@ def test_up_arrow_after_ctrl_r(self):
        reader, _ = handle_all_events(events)
        self.assert_screen_equals(reader, "")

-
 if __name__ == '__main__':
    unittest.main()