[Bug Report] JointPositionToLimitsAction does not preserve order on edge case

[ian-chuang]

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Describe the bug

I want to preserve the order of the joint names in EMAJointPositionToLimitsActionCfg except when I use the config below it doesn't preserve the order.

joint_pos = mdp.EMAJointPositionToLimitsActionCfg(
    asset_name="robot",
    joint_names=[f"joint_{i}" for i in range(16)],
    alpha=0.95,
    rescale_to_limits=True,
    preserve_order=True,
)

I found the bug here:

IsaacLab/source/isaaclab/isaaclab/envs/mdp/actions/joint_actions_to_limits.py

Line 71 in 37ddf62

self._joint_ids = slice(None)

Basically if the length of joint_names matches the number of joints in the asset the joint_id needed for preserving order are overwritten.

I believe if we just confirm that self.cfg.joint_names is set beforehand then we shouldn't overwrite self._joint_ids

Steps to reproduce

Set joint_names to match the number of joints in the asset.