Hi all, A few minutes ago I merged !7448 and the associated MRs, moving GHC to use the msys2 Clang64 toolchain on Windows. This work improves compilation time, maintainability, and fixes a numerous long-standing bugs affecting Windows and other platforms. However, as a result you may find that in an existing tree `configure` will fail with an error complaining that `clang` can not be found. This is due to the fact that the toolchain tarballs are stale and be fixed with: rm -R _build inplace/mingw win32-tarballs ./boot ./configure --enable-tarballs-autodownload Do let me know if you see any other issues; I'm a bit under the weather at the moment but I'll try to keep an eye on email. Cheers, - Ben