fix connect/ disconnect without arguments (#14877)

src/lightning_app/CHANGELOG.md

@@ -22,7 +22,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 ### Fixed
 
--
+- CLI usage without arguments errors ([#14877](https://github.com/Lightning-AI/lightning/pull/14877))
 
 
 ## [0.6.2] - 2022-09-21

src/lightning_app/cli/lightning_cli.py

@@ -50,7 +50,7 @@ def get_app_url(runtime_type: RuntimeType, *args: Any, need_credits: bool = Fals
 
 def main() -> None:
     # 1: Handle connection to a Lightning App.
-    if sys.argv[1] in ("connect", "disconnect"):
+    if len(sys.argv) > 1 and sys.argv[1] in ("connect", "disconnect"):
         _main()
     else:
         # 2: Collect the connection a Lightning App.

tests/tests_app/cli/test_cli.py

@@ -49,6 +49,18 @@ def test_commands(command):
     assert result.exit_code == 0
 
 
+def test_main_lightning_cli_no_arguments():
+    """Validate the Lightning CLI without args."""
+    res = os.popen("python -m lightning").read()
+    assert "login   " in res
+    assert "logout  " in res
+    assert "run     " in res
+    assert "list    " in res
+    assert "delete  " in res
+    assert "create  " in res
+    assert "show    " in res
+
+
 def test_main_lightning_cli_help():
     """Validate the Lightning CLI."""
     res = os.popen("python -m lightning --help").read()