Sebastian Graf authored Sep 28, 2020 and Marge Bot committed Oct 01, 2020

Because the generated `KindRep`s don't have an unfolding, !3230 did not
actually stop to compute, attach and serialise unnecessary CPR
signatures for them. As already said in
`Note [CPR for data structures]`, that leads to bloated interface
files which is ultimately quadratic for Nested CPR.

So we don't attach any CPR signature to bindings that

  * Are not thunks (because thunks are not in WHNF)
  * Have arity 0 (which means the top-level constructor is not a lambda)

If the data structure has an unfolding, we continue to look through it.
If not (as is the case for `KindRep`s), we look at the unchanged CPR
signature and see `topCprType`, as expected.