GHC 9.10: Pattern match has inaccessible right hand side

[locallycompact]

       > src/Polysemy/Internal/Union.hs:298:1: warning: [8;;https://errors.haskell.org/messages/GHC-94210GHC-942108;;] [-Woverlapping-patterns]
       >     Pattern match has inaccessible right hand side
       >     In an equation for ‘absurdU’: absurdU (Union _ _) = ...
       >     |
       > 298 | absurdU (Union _ _) = error "Unsafe use of UnsafeMkElemOf"

https://gitlab.horizon-haskell.net/package-sets/horizon-advance/-/jobs/1417118#L185

[m4dc4p]

I also see errors related to TH changes:

[17 of 44] Compiling Polysemy.Internal.TH.Effect ( src/Polysemy/Internal/TH/Effect.hs, dist/build/Polysemy/Internal/TH/Effect.o, dist/build/Polysemy/Internal/TH/Effect.dyn_o )
src/Polysemy/Internal/TH/Effect.hs:140:28: error: [8;;https://errors.haskell.org/messages/GHC-83865GHC-838658;;]
    • Couldn't match type ‘Name -> Dec’ with ‘Dec’
      Expected: Fixity -> NamespaceSpecifier -> Dec
        Actual: Fixity -> NamespaceSpecifier -> Name -> Dec
    • Probable cause: ‘InfixD’ is applied to too few arguments
      In the first argument of ‘flip’, namely ‘InfixD’
      In the second argument of ‘(.)’, namely
        ‘flip InfixD (cliFunName cli)’
      In the second argument of ‘maybe’, namely
        ‘(pure . flip InfixD (cliFunName cli))’
    |
140 |   =  maybe [] (pure . flip InfixD (cliFunName cli)) (cliFunFixity cli)
    |                            ^^^^^^

[m4dc4p]

The fix for the error above is really simple:

diff --git a/vendor/polysemy/src/Polysemy/Internal/TH/Effect.hs b/vendor/polysemy/src/Polysemy/Internal/TH/Effect.hs
index c4df68da3..bb8051326 100644
--- a/vendor/polysemy/src/Polysemy/Internal/TH/Effect.hs
+++ b/vendor/polysemy/src/Polysemy/Internal/TH/Effect.hs
@@ -137,7 +137,11 @@ genFreer should_mk_sigs type_name = do
 -- its body on effect's data constructor.
 genSig :: ConLiftInfo -> [Dec]
 genSig cli
-  =  maybe [] (pure . flip InfixD (cliFunName cli)) (cliFunFixity cli)
+#if __GLASGOW_HASKELL__ >= 910
+  =  maybe [] (\fixity -> pure $ InfixD fixity NoNamespaceSpecifier (cliFunName cli)) (cliFunFixity cli)
+#else
+  =  maybe [] (\fixity -> pure $ InfixD fixity (cliFunName cli)) (cliFunFixity cli)
+#endif
   ++ [ SigD (cliFunName cli) $ quantifyType
        $ ForallT [] (member_cxt : cliFunCxt cli)
        $ foldArrowTs sem

I didn't look into the warning, but that will get the library compiling at least.

[tek]

I think that warning has always been there, hasn't it? Gotta research which GHC versions need that match.

Anyway, I added the TH fix, but I don't have 9.10 available, so someone's gotta test this.

[locallycompact]

You can get a 9.10.1 shell for polysemy directly from horizon by doing:

nix develop 'git
+https://gitlab.horizon-haskell.net/package-sets/horizon-advance#polysemy.env'

Run ghc-pkg list to see what it pulled.

[tek]

thanks. I'm getting

conflict: ghc-tcplugins-extra => ghc>=7.10 && <9.10

although I saw that there's a patch in the repo that's supposed to jailbreak this

[tek]

added some CPP for the warning as well

[m4dc4p]

I would be happy to test but I can't tell what branch or commit I should use. I don't see a linked PR ...

[tek]

@m4dc4p it's in master

[m4dc4p]

Can confirm this builds with 9.10.1!

[tek]

alright, uploaded a release!