Bug 700982 – dev-haskell/cabal-1.24.2.0 with ghc-8.6.5: Ambiguous occurrence ‘<>’

• Status: CONFIRMED
• Product: Gentoo Linux

[Description Martin Bays 2019-11-23 11:58:26 UTC]

After installing ghc-8.6.5, building cabal fails with the error:
```
Distribution/System.hs:186:39: error:
    Ambiguous occurrence ‘<>’
    It could refer to either ‘Prelude.<>’,
                             imported from ‘Prelude’ at Distribution/System.hs:19:8-26
                             (and originally defined in ‘GHC.Base’)
                          or ‘Text.PrettyPrint.<>’,
                             imported from ‘Text.PrettyPrint’ at Distribution/System.hs:51:26-29
                             (and originally defined in ‘Text.PrettyPrint.HughesPJ’)
    |
186 |   disp (Platform arch os) = disp arch <> Disp.char '-' <> disp os
    |                                       ^^
```

(full build log attached)

[Comment 1 Martin Bays 2019-11-23 11:59:12 UTC]

Created attachment 597148 [details]
dev-haskell:cabal-1.24.2.0:20191123-100436.log

build log

[Comment 2 Martin Bays 2019-11-23 12:01:51 UTC]

Created attachment 597150 [details]
emerge-info

emerge --info

[Comment 3 Sergei Trofimovich (RETIRED) 2019-11-23 16:10:18 UTC]

For ghc-8.6.5 we'll need to add cabal-2.4.01 from ::haskell overlay.