From 570353a7dd402ac954e53d1bbcdbef3951f9c7a9 Mon Sep 17 00:00:00 2001
From: Nickolay Kudasov <nickolay.kudasov@gmail.com>
Date: Wed, 31 Aug 2016 03:18:19 +0300
Subject: [PATCH] Add placeholder instance to the otherwise empty type family
 (fix GHC 7 builds)

---
 src/Web/Internal/FormUrlEncoded.hs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/Web/Internal/FormUrlEncoded.hs b/src/Web/Internal/FormUrlEncoded.hs
index 7386774..ddde3a9 100644
--- a/src/Web/Internal/FormUrlEncoded.hs
+++ b/src/Web/Internal/FormUrlEncoded.hs
@@ -255,6 +255,8 @@ data Proxy3 a b c = Proxy3
 
 type family NotSupported (cls :: k1) (a :: k2) (reason :: Symbol) :: Constraint where
 #if __GLASGOW_HASKELL__ < 800
+  -- this is just a placeholder case for older GHCs to not freak out on an empty closed type family
+  NotSupported cls a "this type family is actually empty" = ()
 #else
   NotSupported cls a reason = TypeError
     ( 'Text "Cannot derive a Generic-based " ':<>: 'ShowType cls ':<>: 'Text " instance for " ':<>: 'ShowType a ':<>: 'Text "." ':$$: