Currently, we call quite a lot of pop methods in the get_builder_from_protocol() methods to remove inputs which are not necessary for the underlying work chain, for example:

I was thinking it would be good to be able to simply add this removal of inputs to the .yaml files. I.e. replace:

with

default_inputs:
    bands_kpoints_distance: 0.025
    clean_workdir: True
    nbands_factor: 3.0
    relax:
        structure: null
        clean_workdir: null
        base_final_scf: null
    scf:
        pw:
            structure: null
<...>

I think this would be cleaner since you can see the inputs that are added/updated/removed in one place: the .yaml file. I especially noticed this when working on the PdosWorkChain protocol (see this PR in case you're just too curious and already want to have a look and maybe review it, @sphuber 😁 ). There are several inputs which need to be removed from the default values for the nscf PwBaseWorkChain, and I think it would cleaner and more readable to do this in the PwBaseWorkChain.

There are other advantages to adding the possibility of being able to remove inputs by setting the overrides value to None. @flavianojs was trying to switch to using the kpoints input (i.e. providing a KpointsData) instead of the kpoints_distance input. This is currently not possible by providing the correct overrides. Of course, it's possible to adjust this after obtaining the builder, but I think it should be possible to change all inputs with the overrides. This will also make it easier in the future for people to define their own protocols - which can touch every input - by writing .yaml files.

I'm not entirely sure yet how to implement this. We have to be careful not to just pop the None already in the ProtocolMixin.get_protocol_inputs() method, since then it will already be popped at a higher level work chain. Perhaps we should only pop here the highest level inputs, with the sole exception of the PwBaseWorkChain, since this is sort of the end of the line for all work chains. I'll come up with a working solution and open a PR, but I already wanted to see if anyone has comments on this.