Breaks actuator config file into separate files to avoid circular imports

[bmccann-bdai]

Description

This PR breaks the actuator config into separate files in order to avoid a circular import which arises once the configuration is imported into the actuator base class for more than type hinting.

Type of change

• Possible breaking change! The actuator configs have moved .py files and thus modules. They can still be imported directly from the isaaclab.actuators package. External references to these classes through the actuator_cfg module will not longer work. Instead, import directly from the isaaclab.actuators package.

Checklist

• I have read and understood the contribution guidelines
• I have run the pre-commit checks with ./isaaclab.sh --format
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• I have updated the changelog and the corresponding version in the extension's config/extension.toml file
• I have added my name to the CONTRIBUTORS.md or my name already exists there

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Greptile Overview

Greptile Summary

This PR successfully refactors the actuator configuration structure by splitting the monolithic actuator_cfg.py file into three separate modules (actuator_base_cfg.py, actuator_pd_cfg.py, actuator_net_cfg.py), resolving a circular import that was blocking future actuator improvements. The changes maintain backward compatibility through a deprecation shim using __getattr__ in the old actuator_cfg.py file.

Key Changes

• Extracted ActuatorBaseCfg into actuator_base_cfg.py
• Extracted PD-based configs (Implicit, IdealPD, DCMotor, Delayed, Remotized) into actuator_pd_cfg.py
• Extracted neural network configs (LSTM, MLP) into actuator_net_cfg.py
• Updated actuator_base.py TYPE_CHECKING import to use actuator_base_cfg instead of actuator_cfg
• Updated all dependent files across isaaclab_tasks and isaaclab_assets to use package-level imports
• Version bumped to 0.48.4 with appropriate changelog entry

Issues Found

The deprecation shim in actuator_cfg.py has problematic logic on lines 30-33 that contains unreachable/incorrect code (already flagged in previous comments). This doesn't affect functionality since the primary code path (lines 14-29) works correctly, but should be cleaned up.

Confidence Score: 4/5

• Safe to merge with minor cleanup recommended for the deprecation shim logic
• The refactoring successfully resolves the circular import issue and maintains backward compatibility. All imports have been properly updated across dependent files. The main concern is the flawed logic in lines 30-33 of actuator_cfg.py which appears to be unreachable/incorrect dead code that should be removed for code clarity, though it doesn't affect functionality since the main deprecation path (lines 14-29) works correctly.
• source/isaaclab/isaaclab/actuators/actuator_cfg.py needs cleanup of lines 30-33 (unreachable logic), though this is non-critical

Important Files Changed

File Analysis

Filename	Score	Overview
source/isaaclab/isaaclab/actuators/actuator_cfg.py	3/5	Replaced all config classes with deprecation shim using __getattr__ to redirect imports. Has logic issues in lines 30-33 that are unreachable/problematic.
source/isaaclab/isaaclab/actuators/actuator_base_cfg.py	5/5	New file created by extracting ActuatorBaseCfg from actuator_cfg.py. Clean separation with no issues found.
source/isaaclab/isaaclab/actuators/actuator_pd_cfg.py	5/5	New file with PD-based actuator configs extracted from actuator_cfg.py. Properly imports actuator_pd and ActuatorBaseCfg.
source/isaaclab/isaaclab/actuators/actuator_net_cfg.py	5/5	New file with neural network actuator configs extracted from actuator_cfg.py. Properly imports dependencies.
source/isaaclab/isaaclab/actuators/init.py	5/5	Updated to export all config classes from new separate modules. Maintains backward compatibility through package-level imports.
source/isaaclab/isaaclab/actuators/actuator_base.py	5/5	Updated TYPE_CHECKING import from actuator_cfg to actuator_base_cfg. This resolves the circular import issue.

Sequence Diagram

sequenceDiagram
    participant User as User Code
    participant OldCfg as actuator_cfg.py<br/>(deprecated)
    participant NewBase as actuator_base_cfg.py
    participant NewPD as actuator_pd_cfg.py
    participant NewNet as actuator_net_cfg.py
    participant Init as __init__.py
    participant Base as actuator_base.py

    Note over User,Base: New Import Path (Recommended)
    User->>Init: from isaaclab.actuators import ImplicitActuatorCfg
    Init->>NewPD: import from actuator_pd_cfg
    NewPD->>Base: import actuator_pd module
    Init-->>User: Return config class

    Note over User,Base: Legacy Import Path (Deprecated)
    User->>OldCfg: from actuator_cfg import ImplicitActuatorCfg
    OldCfg->>OldCfg: __getattr__("ImplicitActuatorCfg")
    OldCfg->>NewPD: Check if name in dir(actuator_pd_cfg)
    OldCfg->>User: warnings.warn(DeprecationWarning)
    OldCfg->>NewPD: getattr(actuator_pd_cfg, name)
    NewPD-->>OldCfg: Return config class
    OldCfg-->>User: Return config class

    Note over User,Base: Circular Import Resolution
    Base->>NewBase: TYPE_CHECKING import ActuatorBaseCfg
    Note over Base: No circular dependency:<br/>actuator_base.py → actuator_base_cfg.py<br/>(previously: actuator_base.py → actuator_cfg.py → actuator_base.py)

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Additional Comments (1)

1. source/isaaclab/isaaclab/actuators/actuator_cfg.py, line 1-291 (link)

   logic: Old actuator_cfg.py file still exists but should be deleted

   This file was supposed to be deleted as part of the refactoring to split configs into separate modules. Having both the old monolithic file and the new split files creates:

   • Duplicate class definitions (all configs exist in two places)
   • Potential for import confusion
   • The circular import issue this PR aims to fix could persist through this file

   Delete this file since all classes are now properly exported through:

   • actuator_base_cfg.py
   • actuator_pd_cfg.py
   • actuator_net_cfg.py
   • __init__.py

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[Mayankm96]

Could you also make sure the api docs are building correctly?

https://github.com/isaac-sim/IsaacLab/blob/main/docs/source/api/lab/isaaclab.actuators.rst

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[bmccann-bdai]

Could you also make sure the api docs are building correctly?

https://github.com/isaac-sim/IsaacLab/blob/main/docs/source/api/lab/isaaclab.actuators.rst

I may not be clear on what the ask is here. The build docs check is completing successfully. I believe the deploy step is skipped until we merge. I don't know if, for example, autoclass directives are correctly displayed in the git rest api preview.

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[ooctipus]

Nice refactor! LGTM

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