Hadrian fails if build root is absolute path
If --build-root is an absolute path, Hadrian fails when running deriveConstants with the error No mode given. This happens because of the following lines in Settings.Builders.DeriveConstants:
[ mconcat $ flip fmap deriveConstantsPairs $ \(fileName, flag) ->
output ("**/" ++ fileName) ? arg flag
According to Shake’s documentation, using ** as a FilePattern does not match absolute path prefixes, so it never matches if output is an absolute path, and no mode argument is added.