Add simple ROS Launch support.

[tervay-bdai]

Addresses #214, as it's important for us.

This is a simple implementation of ROS launch support. It creates an executable Python script that parses the given launch file and calls LaunchService().run() with it.

This does not support Python-based launch files, only XML and YAML, because I am not familiar enough with Python launch files to support that. (But would be happy to learn if pointed in the right direction.)

I am relatively new to custom Bazel rules/macros so there may be a better way you already had planned, and I'm happy to use that method if desired.

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This change is 

[adityapande-1995]

Since we're running a sample launch file, it'd be nice to add some nontrivial nodes and check that everything is working. Lets include a talker and listener demo if possible ?

I'd like to make sure all the environment variables are inherited and work together.

[tervay-bdai]

Thanks for the tip; this uncovered issues I didn't catch with the previous log launches. It seems like there are some environment issues that I am not sure how to solve, since I don't thoroughly understand how the rules here work.

11:01 | ~/workspace/drake-ros/ros2_example_bazel_installed | $ bazel run //ros2_example_apps:example_launch_yaml
DEBUG: Rule 'ros2' indicated that a canonical reproducible form can be obtained by modifying arguments sha256 = "7bd08a17ad5846c9b890c43f051ce61b6b353e4a2d444c62be8c533ddcd4b6aa"
DEBUG: Repository ros2 instantiated at:
  /home/jtervay/workspace/drake-ros/ros2_example_bazel_installed/WORKSPACE:78:13: in <toplevel>
Repository rule ros2_archive defined at:
  /home/jtervay/.cache/bazel/_bazel_jtervay/d46afbf710ac2d6d6949df3dfa5228cb/external/bazel_ros2_rules/ros2/defs.bzl:317:31: in <toplevel>
INFO: Analyzed target //ros2_example_apps:example_launch_yaml (44 packages loaded, 706 targets configured).
INFO: Found 1 target...
Target //ros2_example_apps:example_launch_yaml up-to-date:
  bazel-bin/ros2_example_apps/_example_launch_yaml_shim.py
  bazel-bin/ros2_example_apps/example_launch_yaml
INFO: Elapsed time: 55.473s, Critical Path: 0.01s
INFO: 2 processes: 1 internal, 1 linux-sandbox.
INFO: Build completed successfully, 2 total actions
INFO: Running command line: bazel-bin/ros2_example_apps/example_launch_yaml
Traceback (most recent call last):
  File "/home/jtervay/.cache/bazel/_bazel_jtervay/d46afbf710ac2d6d6949df3dfa5228cb/execroot/ros2_example_bazel_installed/bazel-out/k8-opt/bin/ros2_example_apps/example_launch_yaml.runfiles/ros2_example_bazel_installed/ros2_example_apps/example_launch_yaml_launch_script.py", line 9, in <module>
    ld = parser.parse_description(re)
  File "/home/jtervay/.cache/bazel/_bazel_jtervay/d46afbf710ac2d6d6949df3dfa5228cb/execroot/ros2_example_bazel_installed/bazel-out/k8-opt/bin/ros2_example_apps/example_launch_yaml.runfiles/ros2/archive/launch/lib/python3.10/site-packages/launch/frontend/parser.py", line 133, in parse_description
    actions = [self.parse_action(child) for child in entity.children]
  File "/home/jtervay/.cache/bazel/_bazel_jtervay/d46afbf710ac2d6d6949df3dfa5228cb/execroot/ros2_example_bazel_installed/bazel-out/k8-opt/bin/ros2_example_apps/example_launch_yaml.runfiles/ros2/archive/launch/lib/python3.10/site-packages/launch/frontend/parser.py", line 133, in <listcomp>
    actions = [self.parse_action(child) for child in entity.children]
  File "/home/jtervay/.cache/bazel/_bazel_jtervay/d46afbf710ac2d6d6949df3dfa5228cb/execroot/ros2_example_bazel_installed/bazel-out/k8-opt/bin/ros2_example_apps/example_launch_yaml.runfiles/ros2/archive/launch/lib/python3.10/site-packages/launch/frontend/parser.py", line 110, in parse_action
    return instantiate_action(entity, self)
  File "/home/jtervay/.cache/bazel/_bazel_jtervay/d46afbf710ac2d6d6949df3dfa5228cb/execroot/ros2_example_bazel_installed/bazel-out/k8-opt/bin/ros2_example_apps/example_launch_yaml.runfiles/ros2/archive/launch/lib/python3.10/site-packages/launch/frontend/expose.py", line 38, in instantiate_action
    raise RuntimeError('Unrecognized entity of the type: {}'.format(entity.type_name))
RuntimeError: Unrecognized entity of the type: node

If I run source /opt/ros/humble/setup.bash on a local ROS installation, it works, although I have no idea why:

11:02 | ~/workspace/drake-ros/ros2_example_bazel_installed | $ source /opt/ros/humble/setup.bash
11:04 | ~/workspace/drake-ros/ros2_example_bazel_installed | $ bazel run //ros2_example_apps:example_launch_yaml
INFO: Analyzed target //ros2_example_apps:example_launch_yaml (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //ros2_example_apps:example_launch_yaml up-to-date:
  bazel-bin/ros2_example_apps/_example_launch_yaml_shim.py
  bazel-bin/ros2_example_apps/example_launch_yaml
INFO: Elapsed time: 0.061s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action
INFO: Running command line: bazel-bin/ros2_example_apps/example_launch_yaml
[INFO] [launch]: All log files can be found below /home/jtervay/.ros/log/2023-07-12-11-04-30-531282-jtervay-LT-768482
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [talker-1]: process started with pid [768745]
[INFO] [listener-2]: process started with pid [768747]
[talker-1] [INFO] [1689174271.563178985] [talker]: Publishing: 'Hello World: 1'
[listener-2] [INFO] [1689174271.564104305] [listener]: I heard: [Hello World: 1]

Guidance would be appreciated here.

Although, now that I think about it, this is probably an issue with the python script we are running to run the launch files, not with any of the rules themselves.

[adityapande-1995]

@tervay-bdai are you seeing the same error for both yaml and xml launch files ?

[tervay-bdai]

Yes

[adityapande-1995]

Another point to note is that the yaml and xml "frontends" to ros launch internally use the python launch style, so ideally if you support yaml/xml ros launch, the python style should work as well.

[adityapande-1995]

Looks like we are missing python dependencies. I'm discussing how to add ros launch in a simpler way here : #214. Fixing the PYTHONPATH in the shim for ros2 command would solve most of our problems.

[tervay-bdai]

Closing since it seems like upstream is working on this and doing it better than I would.