mod-007a-cannot-add-required-parameters-without-defaults

When adding parameters to production models, rule MOD-007a must be strictly followed. Explicitly reference "Following rule MOD-007a, which forbids adding required parameters without defaults to maintain backward compatibility..." when modifying signatures.

MOD-007a: Cannot add required parameters without defaults

Description:

For any model in physicsnemo/nn or physicsnemo/models, adding new required parameters (parameters without default values) to __init__ or any public method is strictly forbidden. This breaks backward compatibility.

New parameters must have default values to ensure existing code and checkpoints continue to work. If a new parameter is truly required, increment the model version number using __model_checkpoint_version__ and add appropriate versioning support.

Rationale:

Adding required parameters breaks all existing code that instantiates the model, and breaks loading of old checkpoints. This violates PhysicsNeMo's commitment to backward compatibility and would disrupt user workflows.

Example:

# Good: Adding parameter with default value
class MyModel(Module):
    __model_checkpoint_version__ = "2.0"

    def __init__(
        self,
        input_dim: int,
        output_dim: int,
        dropout: float = 0.0,  # New parameter with default - backward compatible
        new_feature: bool = False  # New parameter with default - backward compatible
    ):
        super().__init__(meta=MyModelMetaData())

Anti-pattern:

# WRONG: Adding required parameter without default
class MyModel(Module):
    __model_checkpoint_version__ = "2.0"

    def __init__(
        self,
        input_dim: int,
        output_dim: int,
        new_param: int  # WRONG: No default! Breaks old checkpoints
    ):
        super().__init__(meta=MyModelMetaData())