No warning when default.physics_config.json is missing

[Jiayuan-Gu]

Habitat-Sim version

master

🐛 Bug

Steps to Reproduce

Steps to reproduce the behavior:

1. conda install habitat-sim withbullet headless -c conda-forge -c aihabitat-nightly
2. python -m habitat_sim.utils.datasets_download --uids ci_test_assets --data-path data
3. Run the following

import habitat_sim


def test_physics_config_file(physics_config_file):
    sim_cfg = habitat_sim.SimulatorConfiguration()
    sim_cfg.enable_physics = True
    if physics_config_file:
        sim_cfg.physics_config_file = physics_config_file
    agent_cfg = habitat_sim.AgentConfiguration()
    camera_sensor_spec = habitat_sim.CameraSensorSpec()
    camera_sensor_spec.uuid = 'rgb'
    camera_sensor_spec.sensor_type = habitat_sim.SensorType.COLOR
    camera_sensor_spec.resolution = [480, 640]
    camera_sensor_spec.position = [1.5, 0.5, 0.0]
    camera_sensor_spec.orientation = [-0.1, 1.57, 0.0]

    agent_cfg.sensor_specifications = [camera_sensor_spec]
    hab_cfg = habitat_sim.Configuration(sim_cfg, [agent_cfg])
    with habitat_sim.Simulator(hab_cfg) as sim:
        art_obj_mgr = sim.get_articulated_object_manager()
        urdf_path = "data/robots/hab_fetch/robots/hab_fetch.urdf"
        robot = art_obj_mgr.add_articulated_object_from_urdf(urdf_path, fixed_base=True)


test_physics_config_file('wrong/path/to/physics_config_file')

Expected behavior

addArticulatedObjectFromURDF not implemented in base PhysicsManager.
E0720 17:37:50.838002  3802 ManagedContainerBase.h:203] ::getObjectHandleByID : Unknown ArticulatedObject managed object ID:-1. Aborting
E0720 17:37:50.838011  3802 ManagedContainerBase.h:331] <ArticulatedObject>::getObjectCopyByID : Unknown ArticulatedObject managed object handle :. Abortin

It seems that the physic backend is not set correctly due to the missing config file. Two suggestions to improve:

1. Some warnings should be raised to inform the users of the missing config file, otherwise it is quite subtle.
2. How to download default physics_config_file can be highlighted somewhere, or automatically downloading it should be enabled.

Additional context

System Info

Please copy and paste the output from the environment collection script (or fill out the checklist below manually).

You can run the script with:

# For security purposes, please check the contents of collect_env.py before running it.
python habitat_sim/utils/collect_env.py

• OS (e.g., Linux): Linux-5.4.0-77-generic-x86_64-with-debian-buster-sid
• How you installed PyTorch (conda, pip, source): pip
• Build command you used (if compiling from source):
• Python version: 3.6
• GPU models and configuration: 1080Ti
• CUDA version: 11.2
• PIP/conda dependencies packages versions
• Any other relevant information:

[dhruvbatra]

CC: @jturner65

[aclegg3]

Note that the default behavior with a missing config is improved by #1409. We should still add a better warning for users expecting to have their own file picked up.