[Nix-dev] lens 4 transition plan?

[Gergely Risko]

Hi,

Peter: I saw that you started to upgrade stuff to lens 4, e.g. linear
1.6 requires it and in nixpkgs lens is now correctly overridden to
version 4 for that package.

However I wanted to ask for your transition plan/timeframe regarding
this change?  Do you plan to switch over to lens4 as default sometime
and provide overrides for the not forward compatible packages?

Should we provide patches in nixpkgs where needed to upgrade everything
to lens4 until they're fixed upstream?

Asking this, because having both lens3 and lens4 can cause some
instances to be provided multiple times and that causes some pain.  I
just ignored linear for now in my system, but I really would like to
minimize the timespan of the situation where half my packages depend on
lens3 and the other half on lens4. :)

As always: thanks for maintaining Haskell in nixpkgs, great job!

Cheers,
Gergely