union-find-0.2 does not build with GHC 9.4

[andreasabel]

In base-4.17, the MonadFail instance for ST was removed:

$ cabal build
Build profile: -w ghc-9.4.4 -O1
In order, the following will be built (use -v for more details):
 - union-find-0.2 (lib:union-find) (first run)
...
src/Data/UnionFind/ST.hs:133:5: error:
    • No instance for (MonadFail (ST s))
        arising from a do statement
        with the failable pattern ‘Info info_ref1’
    • In a stmt of a 'do' block: Info info_ref1 <- readSTRef link_ref1
      In the second argument of ‘($)’, namely
        ‘do Info info_ref1 <- readSTRef link_ref1
            Info info_ref2 <- readSTRef link_ref2
            MkInfo w1 d1 <- readSTRef info_ref1
            MkInfo w2 d2 <- readSTRef info_ref2
            ....’
      In a stmt of a 'do' block:
        when (point1 /= point2)
          $ do Info info_ref1 <- readSTRef link_ref1
               Info info_ref2 <- readSTRef link_ref2
               MkInfo w1 d1 <- readSTRef info_ref1
               MkInfo w2 d2 <- readSTRef info_ref2
               ....

Lifted from:

• union-find fails to compile commercialhaskell/stackage#6770

In my role as Hackage Trustee, I revised base to <4.17: https://hackage.haskell.org/package/union-find-0.2/revisions/

[andreasabel]

[bergmark]

I'm getting a different error:

src/Ignore/Types.hs:30:10: error:
    • No instance for (Semigroup FileIgnoredChecker)
        arising from the superclasses of an instance declaration
    • In the instance declaration for ‘Monoid FileIgnoredChecker’
   |
30 | instance Monoid FileIgnoredChecker where
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^

[andreasabel]

The steps to the error I see are:

cabal get union-find
cd union-find-2.0
cabal build -w ghc-9.4.4 --allow-newer=union-find:base