From 9729cd9d153b51cfed7c05d66422e69f65ce204c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Manuel=20G=C3=B3mez?= <targen@gmail.com>
Date: Fri, 12 Sep 2014 13:18:51 +0000
Subject: [PATCH] Default type instance for AuthEntity

`AuthEntity` is now a type family associated to the `YesodAuthPersist`
class, so its old type alias definition has now become its default type
instance, which allows recovering the old behavior with minimal
boilerplate: an empty instance declaration for `YesodAuthPersist` makes
a Yesod application written with Persistent work just like before.

Unfortunately, this requires enabling `UndecidableInstances` in the
`Yesod.Auth` module since there is now a nested type family application
(as `AuthEntity` is now itself a type family).

This was tested with the scaffolded application with PostgreSQL, and it
works (given another small change to make it work with Persistent 2 due
to how `SqlPersistT` is now defined).
---
 yesod-auth/Yesod/Auth.hs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/yesod-auth/Yesod/Auth.hs b/yesod-auth/Yesod/Auth.hs
index f2ea0ab0..78b2d734 100644
--- a/yesod-auth/Yesod/Auth.hs
+++ b/yesod-auth/Yesod/Auth.hs
@@ -9,6 +9,7 @@
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE UndecidableInstances #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 module Yesod.Auth
     ( -- * Subsite
@@ -392,6 +393,7 @@ class (YesodAuth master, YesodPersist master) => YesodAuthPersist master where
     --
     -- Since 1.2.0
     type AuthEntity master :: *
+    type instance AuthEntity master = KeyEntity (AuthId master)
 
     getAuthEntity :: AuthId master -> HandlerT master IO (Maybe (AuthEntity master))