Allow building with transformers 0.5 (on GHC 8 RC)

[cnd]

No description provided.

[23Skidoo]

+1. Would be also nice if the upper bound was bumped for the released version on Hackage.

[HuwCampbell]

Hi, thanks.
Not sure if this is correct however, as there's a requirement for transformers-compat in the 0.4 branch that transformers is < 0.5. So this probably won't resolve the way you're expecting.
Ed is preparing for a new version over there (ekmett/transformers-compat@4a29c5c).
Once that gets pushed through I'll bump it all up.

[cnd]

@HuwCampbell to be honest I don't see actual problem with transformers-compat, I used to install it and used it to build another application...

[HuwCampbell]

The problem is that optparse depends on transformers-compat, which currently requires transformers to be < 0.5 (although this will change very soon with Ed's changes).
So one still can't use transformers 0.5 after this change. To demonstrate, I can set transformers == 0.5.* – then I get a conflict:

trying: optparse-applicative-0.12.0.0 (user goal)
next goal: transformers (dependency of optparse-applicative-0.12.0.0)
rejecting: transformers-0.3.0.0/installed-645... (conflict:
optparse-applicative => transformers==0.5.*)
trying: transformers-0.5.0.0
trying: transformers-compat-0.4.0.4 (dependency of
optparse-applicative-0.12.0.0)
trying: transformers-compat-0.4.0.4:-two
rejecting: transformers-compat-0.4.0.4:-three (conflict:
transformers==0.5.0.0, transformers-compat-0.4.0.4:three =>
transformers>=0.4.1 && <0.5)
rejecting: transformers-compat-0.4.0.4:+three (manual flag can only be changed
explicitly)
Dependency tree exhaustively searched.

[cnd]

@HuwCampbell oh right it's just bumped so transformers-compat should be < 0.6 either, I was making this PR before version bump

[HuwCampbell]

Merged a similar PR, thanks!