Support GHC 8.0

[ndmitchell]

In RC1 I hit https://ghc.haskell.org/trac/ghc/ticket/11379 and https://ghc.haskell.org/trac/ghc/ticket/11458, both of which got fixed for RC2.

RC2 gave us haskell/directory#42 which is now fixed. I'm currently running into into https://ghc.haskell.org/trac/ghc/ticket/11555.

[ndmitchell]

Now the fact that fclabels doesn't support GHC 8.0 is my current bottleneck (since I test the shake-language-c project), so test suite and compilation all seem fine.

[kaoskorobase]

Hi Neil, FWIW eventually I'd like to switch shake-language-c to lens again, not sure if that would help. Can't give an ETA at the moment unfortunately.

[ndmitchell]

@kaoskorobase - doesn't make much odds to me either way, no real rush on this, since I know the real bits of Shake all work.

[ndmitchell]

I raised the fclabels issue at sebastiaanvisser/fclabels#31, and they seem to have a few fixes circulating, e.g. sebastiaanvisser/fclabels#32.

[hesselink]

Yes, sebastiaanvisser/fclabels#32 is the full fix. There's currently a a transformers issue, but if you really need it, I could release without that. That will probably mean the test suite will break again with RC3.

[ndmitchell]

@hesselink - thanks for the offer, but no real need - I'm happy to wait until after RC3. I've got the fundamental Shake test suite working so I'm happy to wait a bit.

[ndmitchell]

fclabels is in, I've turned back on the full test suite for 8.0 and it passes. Only remaining issue is https://ghc.haskell.org/trac/ghc/ticket/11555.

[ndmitchell]

Another GHC bug - https://ghc.haskell.org/trac/ghc/ticket/11830. Seems -I0 is buggy in the later RC variants.

[ndmitchell]

I think we're now fully working with GHC 8.0 rc4 - mostly because GHC keeps fixing the bugs, which is great. Backing out the GHC 11555 tweaks then closing this ticket.

[ndmitchell]

Backed out the 11555 fixes. Shake works out of the box with GHC 8.2 so all happy.