param selections requires all selections in one stage

[jllanfranchi]

See issue #306 for more discussion

[LeanderFischer]

what? bye :wave:

[thehrh]

I just tested by slightly modifying an example pipeline, and also went through the code, and this issue is still relevant.

It also serves as a (in fact, afaict, the sole) reminder of what the parameter selection mechanism currently (but definitely unintentionally) does internally for a Pipeline and DistributionMaker. This might for some reason have proven satisfactory for all use cases so far, but the intricacies and the (possibly) desirable behaviour outlined in the mentioned discussion are valuable for eventually fixing this mechanism or making it more powerful.

I'm reopening this issue for that reason. Sorry!