So I spent my weekend in the jungles Windows compatibility layers. I'll spare you the details as they are gruesome but here's a brief summary, * There are a few nasty bugs currently in msys2 which affect the GHC testsuite driver: * Mingw Python packages are terribly broken (#12554) * Msys Python packages are also broken, but differently and only with msys2-runtime >= 2.5.1 (#12660) * Both of these issues manifest as a failure to remove test directories; unfortunately this error is hidden by the testsuite driver and you will likely instead see an error of the form, [Error 183] Cannot create a file when that file already exists: ... from os.makedirs. This issue appears to happen more often when threading is enabled in the testsuite driver (e.g. `make test THREADS=4` after disable the check disabling it in runtests.py), but can also happen in single-threaded mode. * If you see this issue do the following, * Check #12554 for comments suggesting that the issue has been fixed upstream. If so, update msys2. * Run `pacman -Q msys2-runtime` and verify that you are running a 2.5-series runtime * If you are running a 2.5-series runtime, you can simply downgrade to the last-known-good version, 2.5.0, by running, $ wget http://repo.msys2.org/msys/x86_64/msys2-runtime-2.5.0.17080.65c939c-1-x86_64... $ pacman -U msys2-runtime-2.5.0.17080.65c939c-1-x86_64.pkg.tar.xz * If you are running any other runtime version then sadly you will need to reinstall msys2. This base tarball, http://repo.msys2.org/distrib/x86_64/msys2-base-x86_64-20160719.tar.xz, is known to work. * After you have an msys installation with function runtime, you'll need to ensure that the testsuite driver runs with the msys python interpreter (located in /usr/bin/python), not the mingw interpreter (located in /mingw*/bin/python). This can be accomplished with `make test PYTHON=/usr/bin/python`. Unfortunately there's no easy way of doing this with `./validate`. The easiest (but terrible) hack is, $ cp /usr/bin/python /mingw64/bin/python * Armed with this knowledge, I should soon be able to bring the Windows build bot back online. * At some point someone is going to need to track down these bugs in CPython and/or msys2 if Windows support is going to remain viable. If you have time and interest in a challenge please get let me know. Now to go drown my sorrows. Cheers, - Ben