Split Data.Generics.Labels into generic-lens-labels

[phadej]

While looking at generic-optics stuff (where generic-optics cannot have IsLabel instance ,as opticsdefine one itself), it occurred to me:

As we are splitting packages, let's split Data.Generics.Labels out of generic-lens into own package, e.g. generic-lens-labels.

Then it would be very easy to see if some library "accidentally" uses the IsLabel ((->) ...), as the fact is visible from package dependency graph.

[kcsongor]

In principle I agree with this idea. There is already a library with that name, https://hackage.haskell.org/package/generic-lens-labels which does exactly that, but it doesn't seem to be maintained and it's for an older version of generic-lens.

@duog, would you be open to transferring the maintainership of generic-lens-labels so we could keep it up to date with the upstream library?

[michaelpj]

We could move it into an additional public library, perhaps.