After the changes in D7674, solid pretty much subsumes the functionality of lambda_solid. To preserve backcompat, preserve the decorator as a simple wrapper over the @solid machinery.
i dont know if we need a deprecation warning - but we can probably communicate something to that effect here since there is like no need for this anymore thanks to the changes in @solid
There's no situation where we'd expect a user to use it, right? If so, IMO we should document it as deprecated.
On whether to have a deprecation warning, my instinct is no. I don't think there's any rush to actually remove it, given how small its footprint is.
@schrockn might have opinions.