7.10 changes

.travis.yml

@@ -1,11 +1,19 @@
 language: haskell
 
-ghc:
-  - 7.8
+env:
+  - CABALVER=1.18 GHCVER=7.8.4
+  - CABALVER=1.22 GHCVER=7.10.1
+
+before_install:
+ - travis_retry sudo add-apt-repository -y ppa:hvr/ghc
+ - travis_retry sudo apt-get update
+ - travis_retry sudo apt-get install cabal-install-$CABALVER ghc-$GHCVER
+ - export PATH=/opt/ghc/$GHCVER/bin:/opt/cabal/$CABALVER/bin:$PATH
+ - travis_retry cabal update
 
 install:
-  - ghc --version
-  - cabal --version
+ - echo "$(ghc --version) [$(ghc --print-project-git-commit-id 2> /dev/null || echo '?')]"
+ - cabal --version
 
 script:
   - ./scripts/test-all.sh

scripts/shell.nix

@@ -2,12 +2,17 @@
 # Also a good way of running the tests for all packages
 with (import <nixpkgs> {}).pkgs;
 let modifiedHaskellPackages = haskellngPackages.override {
-      overrides = self: super: {
-        servant = self.callPackage ../servant {};
-        servant-server = self.callPackage ../servant-server {};
-        servant-client = self.callPackage ../servant-client {};
-        servant-jquery = self.callPackage ../servant-jquery {};
-        servant-docs   = self.callPackage ../servant-docs {};
+      overrides = with haskell-ng.lib ; self: super: {
+        servant = appendConfigureFlag ( self.callPackage ../servant {} )
+            "--ghc-options=-Werror";
+        servant-server = appendConfigureFlag (self.callPackage
+                ../servant-server {}) "--ghc-options=-Werror";
+        servant-client = appendConfigureFlag (self.callPackage
+            ../servant-client {}) "--ghc-options=-Werror";
+        servant-jquery = appendConfigureFlag (self.callPackage
+            ../servant-jquery {}) "--ghc-options=-Werror";
+        servant-docs   = appendConfigureFlag (self.callPackage ../servant-docs
+            {}) "--ghc-options=-Werror";
       };
     };
 in modifiedHaskellPackages.ghcWithPackages ( p : with p ; [

scripts/test-all.sh

@@ -17,15 +17,16 @@ set -o errexit
 DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
 GHC_FLAGS="-Werror"
 SOURCES_TXT="$( dirname $DIR)/sources.txt"
+CABAL=${CABAL:-cabal}
 
 declare -a SOURCES
 readarray -t SOURCES < "$SOURCES_TXT"
 
 
 prepare_sandbox () {
-    cabal sandbox init
+    $CABAL sandbox init
     for s in ${SOURCES[@]} ; do
-        (cd "$s" && cabal sandbox init --sandbox=../ && cabal sandbox add-source .)
+        (cd "$s" && $CABAL sandbox init --sandbox=../ && $CABAL sandbox add-source .)
     done
 }
 
@@ -33,10 +34,10 @@ test_each () {
     for s in ${SOURCES[@]} ; do
         echo "Testing $s..."
         cd "$s"
-        cabal install --only-dependencies --enable-tests
-        cabal configure --enable-tests --ghc-options="$GHC_FLAGS"
-        cabal build
-        cabal test
+        $CABAL install --only-dependencies --enable-tests
+        $CABAL configure --enable-tests --ghc-options="$GHC_FLAGS"
+        $CABAL build
+        $CABAL test
         cd ..
     done
 }

servant-client/src/Servant/Client.hs

@@ -1,12 +1,15 @@
-{-# LANGUAGE DataKinds #-}
-{-# LANGUAGE InstanceSigs #-}
-{-# LANGUAGE TypeFamilies #-}
-{-# LANGUAGE TypeOperators #-}
-{-# LANGUAGE FlexibleContexts #-}
-{-# LANGUAGE FlexibleInstances #-}
-{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE CPP                  #-}
+{-# LANGUAGE DataKinds            #-}
+{-# LANGUAGE FlexibleContexts     #-}
+{-# LANGUAGE FlexibleInstances    #-}
+{-# LANGUAGE InstanceSigs         #-}
+{-# LANGUAGE OverloadedStrings    #-}
+{-# LANGUAGE ScopedTypeVariables  #-}
+{-# LANGUAGE TypeFamilies         #-}
+{-# LANGUAGE TypeOperators        #-}
+#if !MIN_VERSION_base(4,8,0)
 {-# LANGUAGE OverlappingInstances #-}
-{-# LANGUAGE ScopedTypeVariables #-}
+#endif
 -- | This module provides 'client' which can automatically generate
 -- querying functions for each endpoint just from the type representing your
 -- API.
@@ -18,21 +21,21 @@ module Servant.Client
   , module Servant.Common.BaseUrl
   ) where
 
-import Control.Monad
-import Control.Monad.Trans.Either
-import Data.ByteString.Lazy (ByteString)
-import Data.List
-import Data.Proxy
-import Data.String.Conversions
-import Data.Text (unpack)
-import GHC.TypeLits
-import Network.HTTP.Client (Response)
-import Network.HTTP.Media
-import qualified Network.HTTP.Types as H
-import Servant.API
-import Servant.API.ContentTypes
-import Servant.Common.BaseUrl
-import Servant.Common.Req
+import           Control.Monad
+import           Control.Monad.Trans.Either
+import           Data.ByteString.Lazy       (ByteString)
+import           Data.List
+import           Data.Proxy
+import           Data.String.Conversions
+import           Data.Text                  (unpack)
+import           GHC.TypeLits
+import           Network.HTTP.Client        (Response)
+import           Network.HTTP.Media
+import qualified Network.HTTP.Types         as H
+import           Servant.API
+import           Servant.API.ContentTypes
+import           Servant.Common.BaseUrl
+import           Servant.Common.Req
 
 -- * Accessing APIs as a Client
 
@@ -123,14 +126,22 @@ instance HasClient Delete where
 -- side querying function that is created when calling 'client'
 -- will just require an argument that specifies the scheme, host
 -- and port to send the request to.
-instance (MimeUnrender ct result) => HasClient (Get (ct ': cts) result) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPABLE #-}
+#endif
+  (MimeUnrender ct result) => HasClient (Get (ct ': cts) result) where
   type Client' (Get (ct ': cts) result) = BaseUrl -> EitherT ServantError IO result
   clientWithRoute Proxy req host =
     performRequestCT (Proxy :: Proxy ct) H.methodGet req [200, 203] host
 
 -- | If you have a 'Get xs ()' endpoint, the client expects a 204 No Content
 -- HTTP header.
-instance HasClient (Get (ct ': cts) ()) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+  HasClient (Get (ct ': cts) ()) where
   type Client' (Get (ct ': cts) ()) = BaseUrl -> EitherT ServantError IO ()
   clientWithRoute Proxy req host =
     performRequestNoBody H.methodGet req [204] host
@@ -176,7 +187,11 @@ instance (KnownSymbol sym, ToText a, HasClient sublayout)
 -- side querying function that is created when calling 'client'
 -- will just require an argument that specifies the scheme, host
 -- and port to send the request to.
-instance (MimeUnrender ct a) => HasClient (Post (ct ': cts) a) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPABLE #-}
+#endif
+  (MimeUnrender ct a) => HasClient (Post (ct ': cts) a) where
   type Client' (Post (ct ': cts) a) = BaseUrl -> EitherT ServantError IO a
 
   clientWithRoute Proxy req uri =
@@ -184,7 +199,11 @@ instance (MimeUnrender ct a) => HasClient (Post (ct ': cts) a) where
 
 -- | If you have a 'Post xs ()' endpoint, the client expects a 204 No Content
 -- HTTP header.
-instance HasClient (Post (ct ': cts) ()) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+  HasClient (Post (ct ': cts) ()) where
   type Client' (Post (ct ': cts) ()) = BaseUrl -> EitherT ServantError IO ()
   clientWithRoute Proxy req host =
     void $ performRequestNoBody H.methodPost req [204] host
@@ -193,7 +212,11 @@ instance HasClient (Post (ct ': cts) ()) where
 -- side querying function that is created when calling 'client'
 -- will just require an argument that specifies the scheme, host
 -- and port to send the request to.
-instance (MimeUnrender ct a) => HasClient (Put (ct ': cts) a) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPABLE #-}
+#endif
+  (MimeUnrender ct a) => HasClient (Put (ct ': cts) a) where
   type Client' (Put (ct ': cts) a) = BaseUrl -> EitherT ServantError IO a
 
   clientWithRoute Proxy req host =
@@ -201,7 +224,11 @@ instance (MimeUnrender ct a) => HasClient (Put (ct ': cts) a) where
 
 -- | If you have a 'Put xs ()' endpoint, the client expects a 204 No Content
 -- HTTP header.
-instance HasClient (Put (ct ': cts) ()) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+  HasClient (Put (ct ': cts) ()) where
   type Client' (Put (ct ': cts) ()) = BaseUrl -> EitherT ServantError IO ()
   clientWithRoute Proxy req host =
     void $ performRequestNoBody H.methodPut req [204] host
@@ -210,7 +237,11 @@ instance HasClient (Put (ct ': cts) ()) where
 -- side querying function that is created when calling 'client'
 -- will just require an argument that specifies the scheme, host
 -- and port to send the request to.
-instance (MimeUnrender ct a) => HasClient (Patch (ct ': cts) a) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPABLE #-}
+#endif
+  (MimeUnrender ct a) => HasClient (Patch (ct ': cts) a) where
   type Client' (Patch (ct ': cts) a) = BaseUrl -> EitherT ServantError IO a
 
   clientWithRoute Proxy req host =
@@ -218,7 +249,11 @@ instance (MimeUnrender ct a) => HasClient (Patch (ct ': cts) a) where
 
 -- | If you have a 'Patch xs ()' endpoint, the client expects a 204 No Content
 -- HTTP header.
-instance HasClient (Patch (ct ': cts) ()) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+  HasClient (Patch (ct ': cts) ()) where
   type Client' (Patch (ct ': cts) ()) = BaseUrl -> EitherT ServantError IO ()
   clientWithRoute Proxy req host =
     void $ performRequestNoBody H.methodPatch req [204] host

servant-client/src/Servant/Common/Req.hs

@@ -1,8 +1,11 @@
-{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE CPP                 #-}
+{-# LANGUAGE OverloadedStrings   #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 module Servant.Common.Req where
 
+#if !MIN_VERSION_base(4,8,0)
 import Control.Applicative
+#endif
 import Control.Exception
 import Control.Monad
 import Control.Monad.Catch (MonadThrow)

servant-client/test/Servant/ClientSpec.hs

@@ -340,6 +340,6 @@ pathGen :: Gen (NonEmptyList Char)
 pathGen = fmap NonEmpty path
  where
   path = listOf1 $ elements $
-    filter (not . (`elem` "?%[]/#;")) $
+    filter (not . (`elem` ("?%[]/#;" :: String))) $
     filter isPrint $
     map chr [0..127]

servant-client/test/Servant/Common/BaseUrlSpec.hs

@@ -1,7 +1,10 @@
+{-# LANGUAGE CPP                  #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 module Servant.Common.BaseUrlSpec where
 
+#if !MIN_VERSION_base(4,8,0)
 import Control.Applicative
+#endif
 import Control.DeepSeq
 import Test.Hspec
 import Test.QuickCheck

servant-docs/src/Servant/Docs/Internal.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                  #-}
 {-# LANGUAGE ConstraintKinds      #-}
 {-# LANGUAGE DataKinds            #-}
 {-# LANGUAGE DeriveGeneric        #-}
@@ -13,7 +14,9 @@
 {-# LANGUAGE UndecidableInstances #-}
 module Servant.Docs.Internal where
 
+#if !MIN_VERSION_base(4,8,0)
 import           Control.Applicative
+#endif
 import           Control.Lens
 import           Data.ByteString.Lazy.Char8 (ByteString)
 import           Data.Hashable

servant-jquery/src/Servant/JQuery/Internal.hs

@@ -1,15 +1,18 @@
-{-# LANGUAGE DataKinds #-}
-{-# LANGUAGE TypeFamilies #-}
-{-# LANGUAGE TypeOperators #-}
-{-# LANGUAGE ConstraintKinds #-}
-{-# LANGUAGE TemplateHaskell #-}
-{-# LANGUAGE FlexibleContexts #-}
-{-# LANGUAGE FlexibleInstances #-}
-{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE CPP                  #-}
+{-# LANGUAGE ConstraintKinds      #-}
+{-# LANGUAGE DataKinds            #-}
+{-# LANGUAGE FlexibleContexts     #-}
+{-# LANGUAGE FlexibleInstances    #-}
+{-# LANGUAGE ScopedTypeVariables  #-}
+{-# LANGUAGE TemplateHaskell      #-}
+{-# LANGUAGE TypeFamilies         #-}
+{-# LANGUAGE TypeOperators        #-}
 {-# LANGUAGE UndecidableInstances #-}
 module Servant.JQuery.Internal where
 
+#if !MIN_VERSION_base(4,8,0)
 import Control.Applicative
+#endif
 import Control.Lens
 import Data.Char (toLower)
 import qualified Data.CharSet as Set

servant-server/src/Servant/Server/Internal.hs

@@ -1,12 +1,15 @@
+{-# LANGUAGE CPP                  #-}
 {-# LANGUAGE DataKinds            #-}
 {-# LANGUAGE FlexibleContexts     #-}
 {-# LANGUAGE FlexibleInstances    #-}
-{-# LANGUAGE OverlappingInstances #-}
 {-# LANGUAGE OverloadedStrings    #-}
 {-# LANGUAGE PolyKinds            #-}
 {-# LANGUAGE ScopedTypeVariables  #-}
 {-# LANGUAGE TypeFamilies         #-}
 {-# LANGUAGE TypeOperators        #-}
+#if !MIN_VERSION_base(4,8,0)
+{-# LANGUAGE OverlappingInstances #-}
+#endif
 module Servant.Server.Internal where
 
 import           Control.Applicative         ((<$>))
@@ -280,8 +283,11 @@ instance HasServer Delete where
 -- (returning a status code of 200). If there was no @Accept@ header or it
 -- was @*/*@, we return encode using the first @Content-Type@ type on the
 -- list.
-instance ( AllCTRender ctypes a
-         ) => HasServer (Get ctypes a) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPABLE #-}
+#endif
+         ( AllCTRender ctypes a ) => HasServer (Get ctypes a) where
 
   type ServerT' (Get ctypes a) m = m a
 
@@ -302,8 +308,14 @@ instance ( AllCTRender ctypes a
     | otherwise = respond $ failWith NotFound
 
 -- '()' ==> 204 No Content
-instance HasServer (Get ctypes ()) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+          HasServer (Get ctypes ()) where
+
   type ServerT' (Get ctypes ()) m = m ()
+
   route Proxy action request respond
     | pathIsEmpty request && requestMethod request == methodGet = do
         e <- runEitherT action
@@ -316,8 +328,14 @@ instance HasServer (Get ctypes ()) where
     | otherwise = respond $ failWith NotFound
 
 -- Add response headers
-instance ( AllCTRender ctypes v ) => HasServer (Get ctypes (Headers h v)) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+          ( AllCTRender ctypes v ) => HasServer (Get ctypes (Headers h v)) where
+
   type ServerT' (Get ctypes (Headers h v)) m = m (Headers h v)
+
   route Proxy action request respond
     | pathIsEmpty request && requestMethod request == methodGet = do
       e <- runEitherT action
@@ -380,7 +398,11 @@ instance (KnownSymbol sym, FromText a, HasServer sublayout)
 -- (returning a status code of 201). If there was no @Accept@ header or it
 -- was @*/*@, we return encode using the first @Content-Type@ type on the
 -- list.
-instance ( AllCTRender ctypes a
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPABLE #-}
+#endif
+         ( AllCTRender ctypes a
          ) => HasServer (Post ctypes a) where
 
   type ServerT' (Post ctypes a) m = m a
@@ -401,8 +423,14 @@ instance ( AllCTRender ctypes a
         respond $ failWith WrongMethod
     | otherwise = respond $ failWith NotFound
 
-instance HasServer (Post ctypes ()) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+         HasServer (Post ctypes ()) where
+
   type ServerT' (Post ctypes ()) m = m ()
+
   route Proxy action request respond
     | pathIsEmpty request && requestMethod request == methodPost = do
         e <- runEitherT action
@@ -415,8 +443,14 @@ instance HasServer (Post ctypes ()) where
     | otherwise = respond $ failWith NotFound
 
 -- Add response headers
-instance ( AllCTRender ctypes v ) => HasServer (Post ctypes (Headers h v)) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+         ( AllCTRender ctypes v ) => HasServer (Post ctypes (Headers h v)) where
+
   type ServerT' (Post ctypes (Headers h v)) m = m (Headers h v)
+
   route Proxy action request respond
     | pathIsEmpty request && requestMethod request == methodPost = do
       e <- runEitherT action
@@ -447,8 +481,11 @@ instance ( AllCTRender ctypes v ) => HasServer (Post ctypes (Headers h v)) where
 -- (returning a status code of 200). If there was no @Accept@ header or it
 -- was @*/*@, we return encode using the first @Content-Type@ type on the
 -- list.
-instance ( AllCTRender ctypes a
-         ) => HasServer (Put ctypes a) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPABLE #-}
+#endif
+         ( AllCTRender ctypes a) => HasServer (Put ctypes a) where
 
   type ServerT' (Put ctypes a) m = m a
 
@@ -468,8 +505,14 @@ instance ( AllCTRender ctypes a
         respond $ failWith WrongMethod
     | otherwise = respond $ failWith NotFound
 
-instance HasServer (Put ctypes ()) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+         HasServer (Put ctypes ()) where
+
   type ServerT' (Put ctypes ()) m = m ()
+
   route Proxy action request respond
     | pathIsEmpty request && requestMethod request == methodPut = do
         e <- runEitherT action
@@ -482,8 +525,14 @@ instance HasServer (Put ctypes ()) where
     | otherwise = respond $ failWith NotFound
 
 -- Add response headers
-instance ( AllCTRender ctypes v ) => HasServer (Put ctypes (Headers h v)) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+         ( AllCTRender ctypes v ) => HasServer (Put ctypes (Headers h v)) where
+
   type ServerT' (Put ctypes (Headers h v)) m = m (Headers h v)
+
   route Proxy action request respond
     | pathIsEmpty request && requestMethod request == methodPut = do
       e <- runEitherT action
@@ -512,8 +561,12 @@ instance ( AllCTRender ctypes v ) => HasServer (Put ctypes (Headers h v)) where
 -- If successfully returning a value, we just require that its type has
 -- a 'ToJSON' instance and servant takes care of encoding it for you,
 -- yielding status code 200 along the way.
-instance ( AllCTRender ctypes a
-         ) => HasServer (Patch ctypes a) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPABLE #-}
+#endif
+         ( AllCTRender ctypes a) => HasServer (Patch ctypes a) where
+
   type ServerT' (Patch ctypes a) m = m a
 
   route Proxy action request respond
@@ -532,8 +585,14 @@ instance ( AllCTRender ctypes a
         respond $ failWith WrongMethod
     | otherwise = respond $ failWith NotFound
 
-instance HasServer (Patch ctypes ()) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+          HasServer (Patch ctypes ()) where
+
   type ServerT' (Patch ctypes ()) m = m ()
+
   route Proxy action request respond
     | pathIsEmpty request && requestMethod request == methodPatch = do
         e <- runEitherT action
@@ -546,8 +605,14 @@ instance HasServer (Patch ctypes ()) where
     | otherwise = respond $ failWith NotFound
 
 -- Add response headers
-instance ( AllCTRender ctypes v ) => HasServer (Patch ctypes (Headers h v)) where
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+         ( AllCTRender ctypes v ) => HasServer (Patch ctypes (Headers h v)) where
+
   type ServerT' (Patch ctypes (Headers h v)) m = m (Headers h v)
+
   route Proxy action request respond
     | pathIsEmpty request && requestMethod request == methodPatch = do
       e <- runEitherT action

servant/servant.cabal

@@ -59,7 +59,8 @@ library
     , network-uri >= 2.6
   hs-source-dirs: src
   default-language: Haskell2010
-  other-extensions: ConstraintKinds
+  other-extensions: CPP
+                  , ConstraintKinds
                   , DataKinds
                   , DeriveDataTypeable
                   , FlexibleInstances

servant/src/Servant/API/Alternative.hs

@@ -1,8 +1,11 @@
+{-# LANGUAGE CPP                #-}
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE TypeOperators      #-}
 module Servant.API.Alternative ((:<|>)(..)) where
 
+#if !MIN_VERSION_base(4,8,0)
 import           Data.Monoid   (Monoid (..))
+#endif
 import           Data.Typeable (Typeable)
 -- | Union of two APIs, first takes precedence in case of overlap.
 --

servant/src/Servant/API/ContentTypes.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                   #-}
 {-# LANGUAGE ConstraintKinds       #-}
 {-# LANGUAGE DataKinds             #-}
 {-# LANGUAGE DeriveDataTypeable    #-}
@@ -63,7 +64,9 @@ module Servant.API.ContentTypes
     , eitherDecodeLenient
     ) where
 
+#if !MIN_VERSION_base(4,8,0)
 import           Control.Applicative        ((<*))
+#endif
 import           Control.Arrow              (left)
 import           Control.Monad
 import           Data.Aeson                 (FromJSON, ToJSON, Value,

servant/src/Servant/API/ResponseHeaders.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                    #-}
 {-# LANGUAGE DataKinds              #-}
 {-# LANGUAGE DeriveFunctor          #-}
 {-# LANGUAGE FlexibleContexts       #-}
@@ -6,11 +7,13 @@
 {-# LANGUAGE GADTs                  #-}
 {-# LANGUAGE KindSignatures         #-}
 {-# LANGUAGE MultiParamTypeClasses  #-}
-{-# LANGUAGE OverlappingInstances   #-}
 {-# LANGUAGE PolyKinds              #-}
 {-# LANGUAGE ScopedTypeVariables    #-}
 {-# LANGUAGE TypeOperators          #-}
 {-# LANGUAGE UndecidableInstances   #-}
+#if !MIN_VERSION_base(4,8,0)
+{-# LANGUAGE OverlappingInstances   #-}
+#endif
 
 -- | This module provides facilities for adding headers to a response.
 --
@@ -50,13 +53,21 @@ class AddHeader h v orig new
     | h v orig -> new, new -> h, new -> v, new -> orig where
   addHeader :: v -> orig -> new
 
-instance ( KnownSymbol h, ToByteString v
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPING #-}
+#endif
+         ( KnownSymbol h, ToByteString v
          ) => AddHeader h v (Headers (fst ': rest)  a) (Headers (Header h v ': fst ': rest) a) where
     addHeader a (Headers resp heads) = Headers resp ((headerName, toByteString' a) : heads)
       where
         headerName = CI.mk . pack $ symbolVal (Proxy :: Proxy h)
 
-instance ( KnownSymbol h, ToByteString v
+instance
+#if MIN_VERSION_base(4,8,0)
+         {-# OVERLAPPABLE #-}
+#endif
+         ( KnownSymbol h, ToByteString v
          , new ~ (Headers '[Header h v] a)
          ) => AddHeader h v a new where
     addHeader a resp = Headers resp [(headerName, toByteString' a)]

servant/src/Servant/Common/Text.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                  #-}
 {-# LANGUAGE FlexibleInstances    #-}
 {-# LANGUAGE OverloadedStrings    #-}
 {-# LANGUAGE TypeSynonymInstances #-}
@@ -6,12 +7,18 @@ module Servant.Common.Text
   , ToText(..)
   ) where
 
+#if !MIN_VERSION_base(4,8,0)
 import           Control.Applicative     ((<$>))
+#endif
 import           Data.Int                (Int16, Int32, Int64, Int8)
 import           Data.String.Conversions (cs)
 import           Data.Text               (Text)
 import           Data.Text.Read          (Reader, decimal, rational, signed)
-import           Data.Word               (Word, Word16, Word32, Word64, Word8)
+import           Data.Word               (Word16, Word32, Word64, Word8
+#if !MIN_VERSION_base(4,8,0)
+        , Word
+#endif
+        )
 
 -- | For getting values from url captures and query string parameters
 -- Instances should obey:

servant/src/Servant/Utils/Links.hs

@@ -1,13 +1,13 @@
-{-# LANGUAGE PolyKinds #-}
-{-# LANGUAGE ConstraintKinds #-}
-{-# LANGUAGE DataKinds #-}
-{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE CPP                    #-}
+{-# LANGUAGE ConstraintKinds        #-}
+{-# LANGUAGE DataKinds              #-}
+{-# LANGUAGE FlexibleInstances      #-}
 {-# LANGUAGE FunctionalDependencies #-}
-{-# LANGUAGE PolyKinds #-}
-{-# LANGUAGE ScopedTypeVariables #-}
-{-# LANGUAGE TypeFamilies #-}
-{-# LANGUAGE TypeOperators #-}
-{-# LANGUAGE UndecidableInstances #-}
+{-# LANGUAGE PolyKinds              #-}
+{-# LANGUAGE ScopedTypeVariables    #-}
+{-# LANGUAGE TypeFamilies           #-}
+{-# LANGUAGE TypeOperators          #-}
+{-# LANGUAGE UndecidableInstances   #-}
 
 -- | Type safe generation of internal links.
 --
@@ -104,7 +104,11 @@ module Servant.Utils.Links (
 import Data.List
 import Data.Proxy ( Proxy(..) )
 import Data.Text (Text, unpack)
+#if !MIN_VERSION_base(4,8,0)
 import Data.Monoid ( Monoid(..), (<>) )
+#else
+import Data.Monoid ( (<>) )
+#endif
 import Network.URI ( URI(..), escapeURIString, isUnreserved )
 import GHC.TypeLits ( KnownSymbol, symbolVal )
 import GHC.Exts(Constraint)

servant/test/Servant/API/ContentTypesSpec.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                   #-}
 {-# LANGUAGE DataKinds             #-}
 {-# LANGUAGE DeriveGeneric         #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
@@ -5,7 +6,9 @@
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 module Servant.API.ContentTypesSpec where
 
+#if !MIN_VERSION_base(4,8,0)
 import           Control.Applicative
+#endif
 import           Control.Arrow
 import           Data.Aeson
 import           Data.Aeson.Parser          (jstring)

servant/test/Servant/Common/TextSpec.hs

@@ -1,8 +1,13 @@
+{-# LANGUAGE CPP #-}
 module Servant.Common.TextSpec where
 
 import           Data.Int                  (Int16, Int32, Int64, Int8)
 import           Data.Text                 (Text)
-import           Data.Word                 (Word, Word16, Word32, Word64, Word8)
+import           Data.Word                 (Word16, Word32, Word64, Word8
+#if !MIN_VERSION_base(4,8,0)
+                 , Word
+#endif
+                 )
 import           Servant.Common.Text
 import           Test.Hspec
 import           Test.QuickCheck