[Mac OS] Default --device to cpu on macOS

source/isaaclab/changelog.d/antoiner-feat-macos-cpu-device-default.changed.rst

@@ -0,0 +1,2 @@
+* Changed :func:`~isaaclab.app.launch_simulation` to warn when it runs on the CPU because ``--device`` was not
+  given on macOS.

source/isaaclab/isaaclab/app/sim_launcher.py

@@ -594,6 +594,9 @@ def launch_simulation(
 
     # Resolve the device before any launcher or physics init: --device, else this rank's GPU, else the config's.
     _resolve_distributed_device(args)
+    if sys.platform == "darwin" and args.get("device") == "cpu" and not args.get("device_explicit", False):
+        # the --device default on macOS, which has no CUDA
+        logger.warning("No --device given; using 'cpu' because macOS has no CUDA.")
     if sim_cfg is not None:
         args["device"] = args.get("device") or sim_cfg.device
         # Decide the visualizers once, into the SimulationCfg.

source/isaaclab_physx/changelog.d/antoiner-feat-macos-cpu-device-default.changed.rst

@@ -0,0 +1,2 @@
+* Changed the ``--device`` default to ``cpu`` on macOS, which has no CUDA, so commands run without passing
+  ``--device cpu``. Other platforms still default to ``cuda:0``.

source/isaaclab_physx/isaaclab_physx/app/kit_launcher.py

@@ -82,8 +82,8 @@ def _sanitize_sys_argv_for_kit(argv: list[str]) -> list[str]:
 class _StoreAndMarkExplicit(argparse.Action):
     """Store the value and set ``<dest>_explicit``, for options whose default must stay a real value.
 
-    ``--device`` defaults to ``"cuda:0"`` because scripts read ``args_cli.device`` before launch, yet XR
-    needs to know whether it was passed (see :meth:`KitLauncher._resolve_device_settings`).
+    ``--device`` defaults to ``"cuda:0"`` (``"cpu"`` on macOS) because scripts read ``args_cli.device`` before
+    launch, yet XR needs to know whether it was passed (see :meth:`KitLauncher._resolve_device_settings`).
     """
 
     def __call__(self, parser, namespace, values, option_string=None):
@@ -358,8 +358,12 @@ def add_launcher_args(parser: argparse.ArgumentParser) -> None:
             "--device",
             type=str,
             action=_StoreAndMarkExplicit,
-            default="cuda:0",
-            help='The device to run the simulation on. Can be "cpu", "cuda", "cuda:N", where N is the device ID',
+            # macOS has no CUDA; checked without importing torch, which must load after Kit
+            default="cpu" if sys.platform == "darwin" else "cuda:0",
+            help=(
+                'The device to run the simulation on. Can be "cpu", "cuda", "cuda:N", where N is the device ID.'
+                ' Defaults to "cuda:0", or "cpu" on macOS.'
+            ),
         )
         arg_group.add_argument(
             "--visualizer",