Breaking changes to the base library

[Harendra Kumar]

I see the following errors when compiling with ghc head version:

$ ghc-stage2 --version
The Glorious Glasgow Haskell Compilation System, version 9.3.20210608

$ cabal build --with-compiler ghc-stage2 --allow-newer

Data/Colour/CIE.hs:80:12: error:
    Ambiguous occurrence ‘sum’
    It could refer to
       either ‘Prelude.sum’,
              imported from ‘Prelude’ at Data/Colour/CIE.hs:25:8-22
              (and originally defined in ‘Data.Foldable’)
           or ‘Data.List.sum’,
              imported from ‘Data.List’ at Data/Colour/CIE.hs:41:1-16
              (and originally defined in ‘GHC.List’)
   |
80 |    total = sum $ map fst l
   |            ^^^

Can someone briefly describe this change and what's the recommended way of
fixing this? Just hide the Data.List definition? I do not see this
mentioned in the release notes of 9.2/9.4 here:
https://ghc.gitlab.haskell.org/ghc/doc/users_guide/9.2.1-notes.html

-harendra
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