Add --namespace argument to launch command.

launch_ros/test/test_cli_namespace.py

@@ -0,0 +1,62 @@
+#!/usr/bin/env python3
+
+# Copyright 2025 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import unittest
+import subprocess
+
+class TestNamespaceArgument(unittest.TestCase):
+    """Test the --namespace command line argument for ros2 launch."""
+
+    def test_namespace_argument(self):
+        """Test that the --namespace argument correctly namespaces topics."""
+        try:
+            # Start the talker_listener launch file with namespace argument
+            launch_proc_remapped = subprocess.Popen(
+                ['ros2', 'launch', 'demo_nodes_cpp', 'talker_listener_launch.py', 
+                 '--namespace', 'test_namespace'],
+                stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE
+            )
+
+            # Run ros2 topic list to get the remapped topics
+            result = subprocess.run(['ros2', 'topic', 'list'], 
+                                  stdout=subprocess.PIPE, 
+                                  stderr=subprocess.PIPE, 
+                                  text=True, 
+                                  check=True)
+            remapped_topics = result.stdout.strip().split('\n')
+
+            # Verify /chatter is NOT in the list
+            self.assertNotIn('/chatter', remapped_topics, 
+                           f"Did not expect to find /chatter after remapping. Topics: {remapped_topics}")
+
+            # Verify /test_namespace/chatter IS in the list
+            self.assertIn('/test_namespace/chatter', remapped_topics, 
+                        f"Expected to find /test_namespace/chatter after remapping. Topics: {remapped_topics}")
+
+        finally:
+            # Clean up
+            if 'launch_proc_remapped' in locals():
+                launch_proc_remapped.terminate()
+                try:
+                    launch_proc_remapped.wait(timeout=5)
+                except subprocess.TimeoutExpired:
+                    launch_proc_remapped.kill()
+                    launch_proc_remapped.wait()
+
+
+if __name__ == '__main__':
+    unittest.main() 

ros2launch/ros2launch/api/api.py

@@ -25,6 +25,7 @@
 import launch
 from launch.frontend import Parser
 from launch.launch_description_sources import get_launch_description_from_any_launch_file
+from launch_ros.actions import PushROSNamespace
 
 
 class MultipleLaunchFilesError(Exception):
@@ -145,7 +146,8 @@ def launch_a_launch_file(
     noninteractive=False,
     args=None,
     option_extensions={},
-    debug=False
+    debug=False,
+    namespace=None
 ):
     """Launch a given launch file (by path) and pass it the given launch file arguments."""
     for name in sorted(option_extensions.keys()):
@@ -167,14 +169,17 @@ def launch_a_launch_file(
     parsed_launch_arguments = parse_launch_arguments(launch_file_arguments)
     # Include the user provided launch file using IncludeLaunchDescription so that the
     # location of the current launch file is set.
-    launch_description = launch.LaunchDescription([
+    launch_description = launch.LaunchDescription()
+    if namespace is not None:
+        launch_description.add_action(PushROSNamespace(namespace))
+    launch_description.add_action(
         launch.actions.IncludeLaunchDescription(
             launch.launch_description_sources.AnyLaunchDescriptionSource(
                 launch_file_path
             ),
             launch_arguments=parsed_launch_arguments,
-        ),
-    ])
+        )
+    )
     for name in sorted(option_extensions.keys()):
         result = option_extensions[name].prelaunch(
             launch_description,

ros2launch/ros2launch/command/launch.py

@@ -102,6 +102,10 @@ def add_arguments(self, parser, cli_name):
             help=('Regex pattern for filtering which executables the --launch-prefix is applied '
                   'to by matching the executable name.')
         )
+        parser.add_argument(
+            '--namespace',
+            help=('A namespace to push to the actions/nodes started by the launch file.')
+        )
         arg = parser.add_argument(
             'package_name',
             help='Name of the ROS package which contains the launch file')
@@ -175,5 +179,6 @@ def main(self, *, parser, args):
                 noninteractive=args.noninteractive,
                 args=args,
                 option_extensions=self._option_extensions,
-                debug=args.debug
+                debug=args.debug,
+                namespace=args.namespace
             )