packages in GHC should have different versions from hackage if the packages differ
I try to compile a package with many dependencies using GHC-7.5.20120426 in order to check whether #5970 (closed) is resolved. This turns out to be difficult because this temporary GHC version seems to use packages with the same version as their counterparts on Hackage but different content.
For example GHC-7.5.20120426 is bundled with unix-188.8.131.52 and bytestring-0.10.0.0. However the unix-184.108.40.206 on Hackage excludes bytestring-0.10.0.0. Thus cabal-install refuses to install something that depends on unix-220.127.116.11.
Another example: Both GHC-7.4.1 and GHC-7.5.20120426 are bundled with base-18.104.22.168. However in GHC-7.5, Num is no longer superclass of Bits. I think such a change requires a version bump to base-4.6.