[Haskell-cafe] Travis builds failing with spurious errors

[Francesco Mazzoli]

Hi all,

Apologies if this is not the right space to ask this question.

We set up CI for Agda with Travis: <https://travis-ci.org/agda/agda>.

The problem is that we're having trouble with older versions of GHC.
For example, with GHC 7.4.2, the build complains that
ScopedTypeVariables is not enabled, even if it is.  You can check the
build failure here:
<https://travis-ci.org/agda/agda/jobs/39834738#L795>, and the relevant
file here: <https://github.com/agda/agda/blob/9a82afaf7657a97e85e7e31ea23f6386f99acd35/src/full/Agda/TypeChecking/Serialise.hs>.
As you can see from the pragmas ScopedTypeVariables is enabled, and in
fact when building locally I have no problems.

We also got some spurious messages regarding syntax.

Has anybody encountered similar problems?  I don't know if it's
something depending on Travis or some configuration mistakes, but I'm
a bit at loss on how to research this.  Moving the OPTIONS_GHC pragma
after the LANGUAGE pragmas seems to fix the issue but I'd like to know
what's going on.

Thanks,
Francesco