Bug description

The _AcceleratorRegistry.register() method fails when used as a decorator due to an incorrect function signature in the inner do_register function.

The decorator form @registry.register("name") raises a TypeError because the nested function expects two arguments (name and accelerator) but it only passes the decorated class as a single argument.

The non-decorator form registry.register("name", MyClass) works correctly, indicating this is specifically an issue with decorator usage that breaks the documented API.

Steps to Reproduce

Minimal test case:

from lightning.fabric.accelerators.registry import _AcceleratorRegistry
from lightning.fabric.accelerators import Accelerator

registry = _AcceleratorRegistry()

# Registration fails
@registry.register("test")
class MyAcc(Accelerator):
    pass

Error output:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[4], line 6
      2 from lightning.fabric.accelerators import Accelerator
      4 registry = _AcceleratorRegistry()
----> 6 @registry.register("test")
      7 class MyAcc(Accelerator):
      8     pass

TypeError: _AcceleratorRegistry.register.<locals>.do_register() missing 1 required positional argument: 'accelerator'

Root cause

The issue is in src/lightning/fabric/accelerators/registry.py lines 68-75. The inner do_register function has an incorrect signature:

def do_register(name: str, accelerator: Callable) -> Callable:  # Wrong - has extra 'name' param
    data["accelerator"] = accelerator
    data["accelerator_name"] = name
    self[name] = data
    return accelerator

When used as a decorator, it only passes the decorated class as a single argument, but the function expects two arguments (name and accelerator).

Proposed Fix

Pass only the accelerator parameter to do_register as name is already available from the outer function’s scope.

Additional context

The same pattern exists in _StrategyRegistry which has the correct implementation

What version are you seeing the problem on?

master

Environment