Build failure in a released version when using an older version of 'containers'

[chris-martin]

I tried to build relude-1.0.0.1 with containers-0.5.7.1 using GHC 8.8.4 and got a compile error:

src/Relude/Nub.hs:62:1: error:
Error:     Could not load module ‘Data.Containers.ListUtils’
    It is a member of the hidden package ‘containers-0.6.2.1’.
    Perhaps you need to add ‘containers’ to the build-depends in your .cabal file.
    Use -v (or `:set -v` in ghci) to see a list of the files searched for.
   |
62 | import qualified Data.Containers.ListUtils as Containers
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This module was added in containers-0.6.0.1, so I'm thinking maybe it was a mistake for containers-0.5.7.1 to be in bounds?

[chshersh]

containers is a boot library so old GHC versions will use older versions of containers library. The earliest GHC version supported by Relude is 8.2.2 and this GHC versions ships with containers-0.5.10.2.

So, bumping up the lower bound from 0.5.7 to 0.5.10.2 is the correct thing to do nevertheless. But it won't solve your issue as 0.5.10.2 still doesn't have the Data.Containers.ListUtils module. However, I don't think this is a problem as Relude uses CPP to support older containers versions:

relude/src/Relude/Nub.hs

Lines 80 to 85 in fcb3225

	ordNub :: forall a . (Ord a) => [a] -> [a]
	#if __GLASGOW_HASKELL__ > 804
	ordNub = Containers.nubOrd
	{-# INLINE ordNub #-}
	#else
	ordNub = go Set.empty

It's more surprising to me how you're using GHC with different versions of boot libraries instead of shipped one 🤔 But I guess it never was the expectation from relude to support "non-standard" combinations of GHC and boot library versions. I personally wasn't aware this is possible or supported.

You could try to bump up the lower bound for containers to 0.6 and see how the CI goes and whether it still works with old GHC versions. And if yes, CPP can be removed and the code will become cleaner 🧹 🙂

[sjakobi]

Even though containers is a boot library, cabal or stack aren't forced to use the version bundled with GHC.

Only the builtin subset of the boot libraries is non-upgradeable, e.g. base, template-haskell and the ghc* packages.

So the CPP on ordNub should refer to the containers version instead to the GHC version.