The facet dependencies system should get ported to d8 as well.
Currently, there are 3 facet depencies that are available with a basic install of facetapi + facetapi_bonus. Of those 3 (roles, bundles, another facet) only 1 is actually worth porting to d8 imho. I think roles and bundles shouldn't be configured on the facet-level but should be configured on the display level (block / panel / ...). Another facet as a dependency is a good use-case though and needs to be ported.
Port the "another facet" facet dependency.
- Unit test
- Integration test