No instance nor default method for class operation put (cereal 0.5)

[JPMoresmau]

I run ghc-mod at the root of a haskell project, I get:

ghc-mod: Language/Haskell/GhcMod/Types.hs:404:10-39: No instance nor default method for class operation put

I have 5.4
ghc-mod --version
ghc-mod version 5.4.0.0 compiled by GHC 7.10.1

I have another 5.4.0.0 install in another directory (same ghc, different sandbox) that works. The one that works has cereal 0.4.1.1 installed, the one that doesn't cereal-0.5.0.0. I realize this is a very recent version uploaded yesterday, is ghc-mod not compatible with it?

[cnd]

what if we will

instance Serialize CabalHelper.Programs where
  put = ... and I don't know what here :)

really please help me with that

[DanielG]

Serialize has default instances via GHC.Generics, IIRC you just need to add a deriving clause for that:

deriving instance Generic Whatever

[cnd]

It feels more complicated since CabalHelper.Programs already deriving Generic

[DanielG]

Looking at the diff cereal-0.4.1.1..cereal-0.5.0.0, I can't see any changes to relevant class instances so I'm not sure what's going on.

[chamini2]

I'm getting this issue using atom-haskell/haskell-ghc-mod

[ciez]

ghc-mod list
throws
ghc-mod: Language/Haskell/GhcMod/Types.hs:404:10-39: No instance nor default method for class operation get

[DanielG]

Please reinstall ghc-mod after running cabal update, I uploaded updated cabal metadata that includes a version constraint for cereal.

[ciez]

just did
cabal update
cabal --no-require-sandbox --reinstall install ghc-mod

ghc-mod-5.4.0.0 (reinstall) (changes: async-2.0.2 added)

same error:
ghc-mod: Language/Haskell/GhcMod/Types.hs:404:10-39: No instance nor default method for class operation get

[DanielG]

How about what I suggested here: #680 (comment) ?

[ciez]

0.5.0.0 cereal is installed..

[DanielG]

Argh looks like I got the constraint wrong: https://github.com/kazu-yamamoto/ghc-mod/blob/master/ghc-mod.cabal#L150 I'll upload another cabal metadata revision later.

[DanielG]

@ciez what do you mean it's not installed?

[ciez]

I was checking from a sandboxed dir where there is no cereal.

.cabal dir where ghc-mod is installed does show cereal 5.0.0
reinstalling ghc-mod with cereal constraint worked.

ta, Daniel

[DanielG]

I've uploaded the updated metadata now so it should work for now. I would appreciate if anyone would look into what's really going on here though.

[DanielG]

I've replaced cereal with binary now, really should've been doing this from the beginning since it comes with GHC. Anyways this should be fixed now. Just remember to rm -r dist/ || rm -r .stack-work since the caches won't get invalidated in the git version because the version number hasn't changed yet.

[DanielG]

Can you guys please test and confirm this actually works so I can close this issue?

[JPMoresmau]

Done a clean build on a new install, no issue. No cereal in the dependency list, so I guess we're good!

[DanielG]

Well yeah cereal is gone but you never know if I broke something while I was ripping that out ;)