haddock: Make explicit the support window policy for haddock-library
From Haddock's README:
haddock-library
: is concerned with the parsing and processing of the Haddock markup language. Unlike the other packages, it is expected to build on a fairly wide range of GHC versions.
However this is under-specified. We ought to make very explicit the number of releases that we support.
Cabal supports five years' worth of minor releases (at the time of writing, 9.10.1, 9.8.2, 9.6.4, 9.4.8, 9.2.8, 9.0.2, 8.10.7, 8.8.4, 8.6.5).
Maybe this is too much for us, as we have fewer consumers of this library. I have no doubt that adopting a shifting window will help with removing CPP and help dust the codebase.
In any case, I'm interested in your opinion @haddock (and others).