nix: Add a tool for checking Haskell imports and exports (#1768)

src/PostgREST/Config.hs

@@ -16,6 +16,7 @@ Other hardcoded options such as the minimum version number also belong here.
 {-# LANGUAGE FlexibleInstances     #-}
 {-# LANGUAGE LambdaCase            #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE QuasiQuotes           #-}
 {-# LANGUAGE ScopedTypeVariables   #-}
 {-# LANGUAGE TemplateHaskell       #-}
 {-# OPTIONS_GHC -fno-warn-type-defaults #-}

src/PostgREST/Private/QueryFragment.hs

@@ -1,4 +1,5 @@
-{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE LambdaCase  #-}
+{-# LANGUAGE QuasiQuotes #-}
 {-|
 Module      : PostgREST.Private.QueryFragment
 Description : Helper functions for PostgREST.QueryBuilder.

src/PostgREST/Statements.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE QuasiQuotes #-}
 {-|
 Module      : PostgREST.Statements
 Description : PostgREST single SQL statements.