What is causing the "Unrecognized field abi" warning?

[Edward Z. Yang]

Hello Sven,

Recent versions of Cabal output an 'abi' field to the installed package
database which records what the abi hash of the package is.  Old
versions GHC (or more specifically, ghc-pkg) are not able to interpret
this, so they print an error; however, the error is harmless.

If the messages are bothersome, we could setup Cabal to not print out
fields if it knows that GHC doesn't support them.

Edward

Excerpts from Sven Panne's message of 2015-11-29 12:39:58 -0800:
> This shows up in more recent builds of my packages on Travis CI, e.g.
> https://travis-ci.org/haskell-opengl/OpenGL/jobs/93814917#L296, but I don't
> have a clue what's causing it (GHC? cabal? Something else?), if I should
> ignore it or if I should somehow act on that. :-/ My gut feeling is that
> it's GHC, but I might be wrong...
> 
> Cheers,
>    S.