DiazCarrete, Interesting: it seems that #GHC is moving towards typechecking desugared expressions in some cases, instead of typechecking the surface syntax.
The tricky part is not making the error messages worse.
https://youtu.be/LFIL0myeOlo?list=PLyrlk8Xaylp5ahGXwF_NvYEhVOnedRIAs&t=469