Can't refer to `UserId` in an `Id` field

[parsonsmatt]

This QQ breaks with an error that UserId is not in scope.

share [ mkPersist sqlSettings ] [persistLowerCase|

User
    name    String

Profile
    Id      UserId
    email   String
|]

However, using UserId is usually fine in other contexts. So why isn't this working?

[parsonsmatt]

I think I figured out what's going on here

There's a type SqlTypeExp that, when lifted into a Q Exp, will either splice in the SqlType directly, or, if it's a SqlTypeExp FieldType, will translate the FieldType into a Template Haskell Type, and then splice a call like [| sqlType (Proxy :: Proxy $(fieldTypeToType fieldType) ) |].

There's a bunch of other tricks, and I guess what's happening is that we're trying to lookup a UserId before the alias is defined.