Hi, Oleg Grenrus and everybody. I solved my problem. I. e. I wrote the second tool from this letter: https://mail.haskell.org/pipermail/haskell-cafe/2021-May/134018.html . Result is in commit https://git.sr.ht/~safinaskar/check-cfg-ambiguity/commit/2ef843a42e51848608f... (it is possible that I will break everything in future commits, so here I refer to this particular commit). Here is fragment of my check-cfg-ambiguity.cabal: ---------------- library exposed-modules: CheckCFGAmbiguity -- base 4.13 removed Monad.fail, so "before base 4.13 there was nothing" build-depends: -- CI-BOUNDS-BEGIN base >= 4.13.0.0 && <= 4.15.0.0, containers >= 0.6.2.1 && <= 0.6.4.1 -- CI-BOUNDS-END default-language: Haskell2010 ---------------- My CI script .build.yml parses this cabal file using ad-hoc regexes and sed (markers "CI-BOUNDS-BEGIN" and "CI-BOUNDS-END" help here; well, I have shell/sed addiction, and shell/sed [not haskell!] are still more convenient to me for such tasks) and extracts version info from this cabal file. Thus I don't have to repeat version numbers in CI script, i. e. I don't have DRY violation. Then CI script uses this info to build and test my package two times: for lower versions (with corresponding ghc version!) and for higher versions. Here is resulting CI log: https://builds.sr.ht/~safinaskar/job/516259 . Also: it was hard to find proper way to integrate cabal and doctest. Internet is full of misleading information. For example, https://hackage.haskell.org/package/cabal-doctest says that this package will become obsolete when command "cabal doctest" arrives and gives link https://github.com/haskell/cabal/issues/2327 to track progress. Link https://github.com/haskell/cabal/issues/2327 says that "cabal doctest" is implemented, so it seems that cabal-doctest is really deprecated and one should use "cabal doctest". But both https://hackage.haskell.org/package/cabal-doctest and https://github.com/haskell/cabal/issues/2327 don't say that "cabal doctest" not only ADDED, but also REMOVED: https://github.com/haskell/cabal/pull/7167/ . (Well, they didn't say this until today.) After lots of searching internet I chose current approach, see lots of comments about this in check-cfg-ambiguity.cabal . Of course, all my heroic efforts would be useless, if I did this for single package. I plan to publish more packages, and thus I did all this research == Askar Safin http://safinaskar.com https://sr.ht/~safinaskar https://github.com/safinaskar