HEADS-UP: diagrams does not compile with HEAD (regressions)

[Gabor Greif]

Devs,

as of recently GHC HEAD stopped building the diagrams library. Several
prerequisite libs also fail to compile. A specific error message
appears in an attoparsec issue
<https://github.com/bos/attoparsec/issues/67>, for which I have
submitted a workaround. But as Herbert cautiously points out, this
could be a recent GHC bug surfacing.

The symptoms of the bug seem to be that GHC complains about the usage
of (~) type equality operation, but there is no reference to that type
operator in the source code. To work around the problem it suffices to
add -XGADTs or -XTypeFamilies.

Does this ring any bells? Can automatized tests catch such things in the future?

Cheers,

    Gabor