External grid modules in the DUNE module tree.
We have a number of external grid modules and the way they are inserted in the DUNE module tree differs, e.g. some like dune-alugrid or dune-spgrid depend on dune-grid and are then suggested by other modules and others, such as dune-uggrid, are a suggestion to dune-grid and thereby explicitly assuming the existence of dune-grid. While the first approach is clear in terms of the dependency of the grid implementations on the dune-grid module the second approach somehow has the hen-egg problem but avoids the necessity to add suggestions in various downstream modules.
Question: How should we deal with this in the future?