Add support for ros_launch() rules (#298)

Co-authored-by: Eric Cousineau <[email protected]>

bazel_ros2_rules/ros2/README.md

@@ -91,6 +91,10 @@ equivalent to the native `py_binary` and `py_test` rules, ensure these binaries
 run in an environment that is tightly coupled with the underlying ROS 2
 workspace install space.
 
+To generate a Python or XML launch target, `ros_launch` is available in the
+`ros_py.bzl` file. Note that there are some nuances; pelase see the Launch
+Files section below.
+
 To generate and build ROS 2 interfaces, a `rosidl_interfaces_group` rule is
 available in the `rosidl.bzl` file. This rule generates C++ and Python code
 for the given ROS 2 interface definition files and builds them using what is
@@ -103,6 +107,21 @@ the same file. By default, these naming conventions allow downstream
 `rosidl_interfaces_group` rules to depend on upstream `rosidl_interface_group`
 rules.
 
+#### Launch Files
+
+An example of the `ros_launch` macro can be found under `ros2_example_apps`.
+Please note the following limitations:
+
+- Exposing a Bazel package as a ROS package has not yet been done. Once that is
+  done, `launch_ros.actions.Node` / `<node/>` can be used.
+- For Python launch files, it is best to use `Rlocation` (as shown in the example)
+  so that the launch file can be run via `bazel run`, `bazel test`, and
+  `./bazel-bin` (directly).
+- For XML launch files, we need to (somehow) expose either ROS packages or
+  `Rlocation`. This needs to be done in a way that can be discovered by
+  [`Parser.load_launch_extensions`](https://github.com/ros2/launch/blob/698e979382877242621a0d633750fe96ff0c2bca/launch/launch/frontend/parser.py#L72-L87),
+  which may require care to do so correctly in Bazel.
+
 ### Tools
 
 The `rmw_isolation` subpackage provides C++ and Python `isolate_rmw_by_path`
@@ -192,5 +211,8 @@ From the above two examples (at present), the following features are in
 The other repos, however, have the following that `bazel_ros2_rules` is
 missing:
 
-- Affordances for `ros2 launch`
 - Launching from containers (Docker, Apptainer)
+
+Some common features might be:
+
+- Bazel affordances for `ros2 launch`

bazel_ros2_rules/ros2/resources/bazel_ros_env/bazel_ros_env.py

@@ -64,7 +64,10 @@ def _runfiles():
 
 
 def Rlocation(path):
-    return _runfiles().Rlocation(path)
+    result = _runfiles().Rlocation(path)
+    if result is None:
+        raise RuntimeError(f"Unable to find Rlocation({repr(path)})")
+    return result
 
 
 def make_bazel_runfiles_env():

bazel_ros2_rules/ros2/ros_py.bzl

@@ -130,6 +130,102 @@ def ros_py_binary(
     )
     py_binary_rule(name = name, **kwargs)
 
+def _add_deps(existing, new):
+    deps = list(existing)
+    for dep in new:
+        if dep not in deps:
+            deps.append(dep)
+    return deps
+
+def _generate_file_impl(ctx):
+    out = ctx.actions.declare_file(ctx.label.name)
+    ctx.actions.write(out, ctx.attr.content, ctx.attr.is_executable)
+    return [DefaultInfo(
+        files = depset([out]),
+        data_runfiles = ctx.runfiles(files = [out]),
+    )]
+
+_generate_file = rule(
+    attrs = {
+        "content": attr.string(mandatory = True),
+        "is_executable": attr.bool(default = False),
+    },
+    output_to_genfiles = True,
+    implementation = _generate_file_impl,
+)
+
+_LAUNCH_PY_TEMPLATE = """
+import os
+import sys
+
+from bazel_ros_env import Rlocation
+
+assert __name__ == "__main__"
+launch_file = Rlocation({launch_respath})
+ros2_bin = Rlocation("ros2/ros2")
+args = [ros2_bin, "launch", launch_file] + sys.argv[1:]
+os.execv(ros2_bin, args)
+"""
+
+def _make_respath(relpath, workspace_name):
+    repo = native.repository_name()
+    if repo == "@":
+        if workspace_name == None:
+            fail(
+                "Please provide `ros_launch(*, workspace_name)` so that " +
+                "paths can be resolved properly",
+            )
+        repo = workspace_name
+    pkg = native.package_name()
+    if pkg != "":
+        pieces = [repo, pkg, relpath]
+    else:
+        pieces = [repo, relpath]
+    return "/".join(pieces)
+
+def ros_launch(
+        name,
+        launch_file,
+        args = [],
+        data = [],
+        deps = [],
+        visibility = None,
+        # TODO(eric.cousineau): Remove this once Bazel provides a way to tell
+        # runfiles.py to use "this repository" in a way that doesn't require
+        # bespoke information.
+        workspace_name = None,
+        **kwargs):
+    main = "{}_roslaunch_main.py".format(name)
+    launch_respath = _make_respath(launch_file, workspace_name)
+
+    content = _LAUNCH_PY_TEMPLATE.format(
+        launch_respath = repr(launch_respath),
+    )
+    _generate_file(
+        name = main,
+        content = content,
+        visibility = ["//visibility:private"],
+    )
+
+    deps = _add_deps(
+        deps,
+        [
+            "@ros2//:ros2",
+            "@ros2//resources/bazel_ros_env:bazel_ros_env_py",
+        ],
+    )
+    data = data + [launch_file]
+
+    ros_py_binary(
+        name = name,
+        main = main,
+        deps = deps,
+        srcs = [main],
+        data = data,
+        visibility = visibility,
+        **kwargs
+    )
+
 def ros_py_test(
         name,
         rmw_implementation = None,

ros2_example_bazel_installed/ros2_example_apps/BUILD.bazel

@@ -2,7 +2,7 @@
 # vi: set ft=python :
 
 load("@ros2//:ros_cc.bzl", "ros_cc_binary", "ros_cc_test")
-load("@ros2//:ros_py.bzl", "ros_py_binary", "ros_py_test")
+load("@ros2//:ros_py.bzl", "ros_launch", "ros_py_binary", "ros_py_test")
 load("@ros2//:rosidl.bzl", "rosidl_interfaces_group")
 load("//tools:cmd_test.bzl", "cmd_test")
 
@@ -201,6 +201,67 @@ ros_py_binary(
     ],
 )
 
+# ROS launch example.
+ros_py_binary(
+    name = "eg_talker",
+    srcs = ["roslaunch_eg_nodes/eg_talker.py"],
+    data = ["@ros2//:rmw_cyclonedds_cpp_cc"],
+    deps = [
+        "@ros2//:rclpy_py",
+        "@ros2//:std_msgs_py",
+    ],
+)
+
+ros_cc_binary(
+    name = "eg_listener",
+    srcs = ["roslaunch_eg_nodes/eg_listener.cpp"],
+    data = ["@ros2//:rmw_cyclonedds_cpp_cc"],
+    deps = [
+        "@ros2//:rclcpp_cc",
+        "@ros2//:std_msgs_cc",
+    ],
+)
+
+# See bazel_ros2_rules/ros2/README.md, Launch Files, for notes on
+# features and limitations.
+
+# Uses a python launch file to spawn the talker and listener.
+workspace_name = "ros2_example_bazel_installed"
+
+ros_launch(
+    name = "roslaunch_eg_py",
+    data = [
+        ":eg_listener",
+        ":eg_talker",
+    ],
+    launch_file = "eg_launch.py",
+    workspace_name = workspace_name,
+)
+
+# Uses an xml launch file to spawn the talker and listener.
+ros_launch(
+    name = "roslaunch_eg_xml",
+    data = [
+        ":eg_listener",
+        ":eg_talker",
+    ],
+    launch_file = "eg_launch.xml",
+    workspace_name = workspace_name,
+)
+
+ros_py_test(
+    name = "roslaunch_eg_test",
+    srcs = ["test/roslaunch_eg_test.py"],
+    data = [
+        ":roslaunch_eg_py",
+        ":roslaunch_eg_xml",
+    ],
+    main = "test/roslaunch_eg_test.py",
+    deps = [
+        "@ros2//resources/bazel_ros_env:bazel_ros_env_py",
+    ],
+)
+
 ros_py_test(
     name = "custom_message_rosbag_test",
     srcs = ["test/custom_message_rosbag_test.py"],

ros2_example_bazel_installed/ros2_example_apps/README.md

@@ -16,3 +16,27 @@ bazel run //ros2_example_apps:oracle_py
 ```sh
 bazel run //ros2_example_apps:inquirer_cc
 ```
+
+### Example Launch Files
+
+See `bazel_ros2_rules/ros2/README.md`, Launch Files, for notes on
+features and limitations.
+
+Example Python launch file:
+
+```sh
+bazel run //ros2_example_apps:roslaunch_eg_py
+
+# Or
+bazel build //ros2_example_apps:roslaunch_eg_py
+./bazel-bin/ros2_example_apps/roslaunch_eg_py
+```
+
+Example XML launch file:
+
+```sh
+bazel run //ros2_example_apps:roslaunch_eg_xml
+```
+
+WARNING: Per notes in `bazel_ros2_rules/ros2/README.md`, the XML launch file
+will not resolve paths correctly.

ros2_example_bazel_installed/ros2_example_apps/eg_launch.py

@@ -0,0 +1,18 @@
+from bazel_ros_env import Rlocation
+from launch import LaunchDescription
+from launch.actions import ExecuteProcess
+
+
+def generate_launch_description():
+    # See bazel_ros2_rules/ros2/README.md, Launch Files, for notes on
+    # features and limitations.
+    prefix = "ros2_example_bazel_installed/ros2_example_apps"
+    talker_bin = Rlocation(f"{prefix}/eg_talker")
+    listener_bin = Rlocation(f"{prefix}/eg_listener")
+
+    return LaunchDescription([
+        # Running a talker written in python.
+        ExecuteProcess(cmd=[talker_bin]),
+        # Running a listener written in cpp.
+        ExecuteProcess(cmd=[listener_bin]),
+    ])

ros2_example_bazel_installed/ros2_example_apps/eg_launch.xml

@@ -0,0 +1,8 @@
+<launch>
+  <!--
+  See bazel_ros2_rules/ros2/README.md, Launch Files, for notes on
+  features and limitations.
+  -->
+  <executable cmd="ros2_example_apps/eg_talker" output="screen"/>
+  <executable cmd="ros2_example_apps/eg_listener" output="screen"/>
+</launch>

ros2_example_bazel_installed/ros2_example_apps/roslaunch_eg_nodes/eg_listener.cpp

@@ -0,0 +1,48 @@
+#include <chrono>
+#include <memory>
+
+#include "rclcpp/rclcpp.hpp"
+#include "std_msgs/msg/string.hpp"
+using std::placeholders::_1;
+
+class MinimalSubscriber : public rclcpp::Node
+{
+  public:
+    MinimalSubscriber(int max_count = 10)
+    : Node("minimal_subscriber"), max_count_(max_count)
+    {
+      subscription_ = this->create_subscription<std_msgs::msg::String>(
+      "topic", 10, std::bind(&MinimalSubscriber::topic_callback, this, _1));
+    }
+
+    bool is_done() const { return count_ >= max_count_; }
+
+  private:
+    void topic_callback(const std_msgs::msg::String::SharedPtr msg)
+    {
+      RCLCPP_INFO(this->get_logger(), "I heard: '%s'", msg->data.c_str());
+      ++count_;
+    }
+    rclcpp::Subscription<std_msgs::msg::String>::SharedPtr subscription_;
+
+    int max_count_{};
+    int count_{};
+};
+
+int main(int argc, char * argv[])
+{
+  rclcpp::init(argc, argv);
+
+  // Use explicit `spin_some` so we can manually check for completion.
+  auto node = std::make_shared<MinimalSubscriber>();
+  rclcpp::executors::SingleThreadedExecutor executor;
+  executor.add_node(node);
+  // Use large enough non-zero max duration to ensure we do not block.
+  const std::chrono::microseconds spin_max_duration{50};
+
+  while (rclcpp::ok() && !node->is_done()) {
+    executor.spin_some(spin_max_duration);
+  }
+
+  return 0;
+}

ros2_example_bazel_installed/ros2_example_apps/roslaunch_eg_nodes/eg_talker.py

@@ -0,0 +1,42 @@
+import rclpy
+from rclpy.executors import SingleThreadedExecutor
+from rclpy.node import Node
+
+from std_msgs.msg import String
+
+
+class MinimalPublisher(Node):
+
+    def __init__(self, *, max_count = 10):
+        super().__init__("node")
+        self.publisher = self.create_publisher(String, "topic", 10)
+        timer_period = 0.1  # seconds
+        self.timer = self.create_timer(timer_period, self.timer_callback)
+        self.count = 0
+        self.max_count = max_count
+
+    def timer_callback(self):
+        msg = String()
+        msg.data = f"Hello World: {self.count}"
+        self.publisher.publish(msg)
+        self.get_logger().info(f"Publishing: '{msg.data}'")
+        self.count += 1
+
+    def is_done(self):
+        return self.count >= self.max_count
+
+
+def main():
+    rclpy.init()
+
+    node = MinimalPublisher()
+
+    # Use explicit `spin_once` so we can manually check for completion.
+    executor = SingleThreadedExecutor()
+    executor.add_node(node)
+    while rclpy.ok() and not node.is_done():
+        executor.spin_once(timeout_sec=1e-3)
+
+
+if __name__ == "__main__":
+    main()