I have been messing around a little bit with building GHC from source on Windows, and found the msys2 wikipage quite useful, but somewhat outdated. Quite a few steps in those instructions are no longer necessary and can be omitted. I am working on cleaning up that wikipage right now and should be done in a day or two.

I've found a recent email in the middle of updating the wikipage about other people planning to do the same, so I thought I'd shoot an email to make sure that work is not being duplicated.

msys2 seems to be in good shape and should probably be promoted to the primary suggested method to build ghc on Windows. Let's look into that once the new build instructions have been proofread and verified.
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Gintautas Miliauskas