fix: warn user when first argument to session.run is a list (#786)

nox/sessions.py

@@ -379,6 +379,10 @@ def run(
         if not args:
             raise ValueError("At least one argument required to run().")
 
+        if len(args) == 1 and isinstance(args[0], (list, tuple)):
+            msg = "First argument to `session.run` is a list. Did you mean to use `session.run(*args)`?"
+            raise ValueError(msg)
+
         if self._runner.global_config.install_only:
             logger.info(f"Skipping {args[0]} run, as --install-only is set.")
             return None

tests/test_sessions.py

@@ -842,6 +842,12 @@ def test___dict__(self):
         expected = {name: getattr(session, name) for name in session.__slots__}
         assert session.__dict__ == expected
 
+    def test_first_arg_list(self):
+        session, _ = self.make_session_and_runner()
+
+        with pytest.raises(ValueError):
+            session.run(["ls", "-al"])
+
 
 class TestSessionRunner:
     def make_runner(self):