Add Bazel build support for macOS

[srmainwaring]

Desired behaviour

Build the ignition libraries with Bazel on macOS.

Alternatives considered

Not applicable

Implementation suggestion

Prototype changes to Bazel build files in the following forks - these are macOS only at present.

• https://github.com/srmainwaring/ign-bazel/tree/bazel-macos
• https://github.com/srmainwaring/ign-common/tree/bazel-macos/ign-common3
• https://github.com/srmainwaring/ign-math/tree/bazel-macos/ign-math6
• https://github.com/srmainwaring/ign-plugin/tree/bazel-macos/ign-plugin1
• https://github.com/srmainwaring/ign-transport/tree/bazel-macos/ign-transport9
• https://github.com/srmainwaring/ign-tools/tree/bazel-macos/ign-tools1

The Bazel build for these libraries do not require changes

• https://github.com/ignitionrobotics/ign-msgs
• https://github.com/ignitionrobotics/ign-physics
• https://github.com/ignitionrobotics/ign-utils
• https://github.com/ignitionrobotics/sdformat

The libraries will build up to ignition-physics. To build ign-rendering and the libraries that depend on it needs a larger number of changes to the Bazel build files for ogre2, and to be useful this will need to be updated to ogrev2.2 with Metal support.

Additional context

See https://community.gazebosim.org/t/python-bindings-for-gazebo-ignition/360/12?u=srmainwaring

[srmainwaring]

Hi @mjcarroll, bindings for publishing using ign-transport are working (on macOS) on this branch https://github.com/srmainwaring/python-ignition/tree/bazel-macos/python-ignition.

For example the publisher from the ign-transport Messages tutorial looks like this in Python:

import time

from ignition.msgs.stringmsg_pb2 import StringMsg

from python_ignition.ignition_transport import AdvertiseMessageOptions
from python_ignition.ignition_transport import Node
from python_ignition.ignition_transport import Publisher

def main():
    # Create a transport node and advertise a topic
    node = Node()
    topic = "/foo"
    msg_type_name = StringMsg.DESCRIPTOR.full_name
    pub_options = AdvertiseMessageOptions()
    pub = node.advertise(topic, msg_type_name, pub_options)
    if pub.valid():
        print("Advertising {} on topic[{}]".format(msg_type_name, topic))
    else:
        print("Error advertising topic [{}]".format(topic))

    # Prepare the message
    msg = StringMsg()
    msg.data = "hello"

    try:
        while True:
          if not pub.publish(msg):
              break

          print("Publishing hello on topic[{}]".format(topic))
          time.sleep(1.0)

    except KeyboardInterrupt:
        pass

if __name__ == "__main__":
    main()

It's a bit fiddly to assemble at present because I have not updated the bazel.repos file which is required from macOS. On Ubuntu you should only need the external build file ign-msgs9.BUILD, but I have not tested on that platform.

The message build files need a clean up and macros to generate the protobuf binding rules, but at this stage I'm trying to scope the tasks to get the other libraries working and finish the transport bindings, so will get back to that later on.