Fix async_alert to respect allow_style setting for 3.x branch

cmd2/cmd2.py

@@ -5744,6 +5744,8 @@ def async_alert(self, alert_msg: str, new_prompt: str | None = None) -> None:  #
             update_terminal = False
 
             if alert_msg:
+                if self.allow_style == ru.AllowStyle.NEVER:
+                    alert_msg = su.strip_style(alert_msg)
                 alert_msg += '\n'
                 update_terminal = True
 

tests/test_async_alert.py

@@ -0,0 +1,50 @@
+import unittest
+from unittest.mock import MagicMock, patch
+
+import cmd2
+import cmd2.cmd2  # to patch vt100_support
+from cmd2 import rich_utils as ru
+
+
+class TestAsyncAlert(unittest.TestCase):
+    def test_async_alert_strips_ansi_when_allow_style_is_never(self):
+        app = cmd2.Cmd()
+
+        # Patch vt100_support to True
+        with patch('cmd2.cmd2.vt100_support', True):
+            # Patch threading functions
+            mock_current_thread = MagicMock()
+            mock_current_thread.name = "NotMainThread"
+
+            with (
+                patch('threading.current_thread', return_value=mock_current_thread),
+                patch('threading.main_thread', return_value=MagicMock()),
+                patch('cmd2.cmd2.rl_get_display_prompt', return_value='(Cmd) '),
+                patch('cmd2.cmd2.readline.get_line_buffer', return_value=''),
+                patch('cmd2.cmd2.rl_get_point', return_value=0),
+                patch('cmd2.cmd2.rl_force_redisplay'),
+                patch('sys.stdout', new_callable=MagicMock) as mock_stdout,
+            ):
+                # Set allow_style to NEVER
+                app.allow_style = ru.AllowStyle.NEVER
+
+                # Styled message
+                msg = "\033[31mError\033[0m"
+
+                # Call async_alert
+                app.async_alert(msg)
+
+                # Capture calls to write
+                # mock_stdout.write.call_args_list -> [call(str), call(str)...]
+                # We look at all written strings
+                written_content = "".join([call.args[0] for call in mock_stdout.write.call_args_list])
+
+                # Check that ANSI codes for color are NOT present
+                if "\033[31m" in written_content:
+                    raise AssertionError(f"Found ANSI color code in output: {written_content!r}")
+                if "Error" not in written_content:
+                    raise AssertionError(f"Message 'Error' not found in output: {written_content!r}")
+
+
+if __name__ == '__main__':
+    unittest.main()