Make servant buildable with cabal new-build

.gitignore

@@ -1,4 +1,5 @@
 **/*/dist
+dist-newstyle
 /bin
 /lib
 /share

cabal.project

@@ -0,0 +1,7 @@
+packages:
+  servant/
+  servant-client/
+  servant-docs/
+  servant-foreign/
+  servant-server/
+  doc/tutorial/

doc/tutorial/tutorial.cabal

@@ -47,6 +47,7 @@ library
                      , http-client
   default-language:    Haskell2010
   ghc-options:         -Wall -pgmL markdown-unlit
+  build-tool-depends: markdown-unlit:markdown-unlit
 
 test-suite spec
   type: exitcode-stdio-1.0

servant-server/Setup.hs

@@ -1,2 +0,0 @@
-import           Distribution.Simple
-main = defaultMain

servant-server/Setup.lhs

@@ -0,0 +1,165 @@
+\begin{code}
+{-# LANGUAGE CPP #-}
+#ifndef MIN_VERSION_Cabal
+#define MIN_VERSION_Cabal(x,y,z) 0
+#endif
+#ifndef MIN_VERSION_directory
+#define MIN_VERSION_directory(x,y,z) 0
+#endif
+#if MIN_VERSION_Cabal(1,24,0)
+#define InstalledPackageId UnitId
+#endif
+module Main (main) where
+
+import Control.Monad ( when )
+import Data.List ( nub )
+import Distribution.Package ( InstalledPackageId )
+import Distribution.Package ( PackageId, Package (..), packageVersion )
+import Distribution.PackageDescription ( PackageDescription(), TestSuite(..) , Library (..), BuildInfo (..))
+import Distribution.Simple ( defaultMainWithHooks, UserHooks(..), simpleUserHooks )
+import Distribution.Simple.Utils ( rewriteFile, createDirectoryIfMissingVerbose )
+import Distribution.Simple.BuildPaths ( autogenModulesDir )
+import Distribution.Simple.Setup ( BuildFlags(buildDistPref, buildVerbosity), fromFlag)
+import Distribution.Simple.LocalBuildInfo ( withPackageDB, withLibLBI, withTestLBI, LocalBuildInfo(), ComponentLocalBuildInfo(componentPackageDeps), compiler )
+import Distribution.Simple.Compiler ( showCompilerId , PackageDB (..))
+import Distribution.Text ( display , simpleParse )
+import System.FilePath ( (</>) )
+
+#if MIN_VERSION_Cabal(1,25,0)
+import Distribution.Simple.BuildPaths ( autogenComponentModulesDir )
+#endif
+
+#if MIN_VERSION_directory(1,2,2)
+import System.Directory (makeAbsolute)
+#else
+import System.Directory (getCurrentDirectory)
+import System.FilePath (isAbsolute)
+
+makeAbsolute :: FilePath -> IO FilePath
+makeAbsolute p | isAbsolute p = return p
+               | otherwise    = do
+    cwd <- getCurrentDirectory
+    return $ cwd </> p
+#endif
+
+main :: IO ()
+main = defaultMainWithHooks simpleUserHooks
+  { buildHook = \pkg lbi hooks flags -> do
+     generateBuildModule flags pkg lbi
+     buildHook simpleUserHooks pkg lbi hooks flags
+  }
+
+generateBuildModule :: BuildFlags -> PackageDescription -> LocalBuildInfo -> IO ()
+generateBuildModule flags pkg lbi = do
+  let verbosity = fromFlag (buildVerbosity flags)
+  let distPref = fromFlag (buildDistPref flags)
+
+  -- Package DBs
+  let dbStack = withPackageDB lbi ++ [ SpecificPackageDB $ distPref </> "package.conf.inplace" ]
+  let dbFlags = "-hide-all-packages" : packageDbArgs dbStack
+
+  withLibLBI pkg lbi $ \lib libcfg -> do
+    let libBI = libBuildInfo lib
+
+    -- modules
+    let modules = exposedModules lib ++ otherModules libBI
+    -- it seems that doctest is happy to take in module names, not actual files!
+    let module_sources = modules
+
+    -- We need the directory with library's cabal_macros.h!
+#if MIN_VERSION_Cabal(1,25,0)
+    let libAutogenDir = autogenComponentModulesDir lbi libcfg
+#else
+    let libAutogenDir = autogenModulesDir lbi
+#endif
+
+    -- Lib sources and includes
+    iArgs <- mapM (fmap ("-i"++) . makeAbsolute) $ libAutogenDir : hsSourceDirs libBI
+    includeArgs <- mapM (fmap ("-I"++) . makeAbsolute) $ includeDirs libBI
+
+    -- CPP includes, i.e. include cabal_macros.h
+    let cppFlags = map ("-optP"++) $
+            [ "-include", libAutogenDir ++ "/cabal_macros.h" ]
+            ++ cppOptions libBI
+
+    -- Actually we need to check whether testName suite == "doctests"
+    -- pending https://github.com/haskell/cabal/pull/4229 getting into GHC HEAD tree
+    withTestLBI pkg lbi $ \suite suitecfg -> when (testName suite == "doctests") $ do
+
+      -- get and create autogen dir
+#if MIN_VERSION_Cabal(1,25,0)
+      let testAutogenDir = autogenComponentModulesDir lbi suitecfg
+#else
+      let testAutogenDir = autogenModulesDir lbi
+#endif
+      createDirectoryIfMissingVerbose verbosity True testAutogenDir
+
+      -- write autogen'd file
+      rewriteFile (testAutogenDir </> "Build_doctests.hs") $ unlines
+        [ "module Build_doctests where"
+        , ""
+        -- -package-id etc. flags
+        , "pkgs :: [String]"
+        , "pkgs = " ++ (show $ formatDeps $ testDeps libcfg suitecfg)
+        , ""
+        , "flags :: [String]"
+        , "flags = " ++ show (iArgs ++ includeArgs ++ dbFlags ++ cppFlags)
+        , ""
+        , "module_sources :: [String]"
+        , "module_sources = " ++ show (map display module_sources)
+        ]
+  where
+    -- we do this check in Setup, as then doctests don't need to depend on Cabal
+    isOldCompiler = maybe False id $ do
+      a <- simpleParse $ showCompilerId $ compiler lbi
+      b <- simpleParse "7.5"
+      return $ packageVersion (a :: PackageId) < b
+
+    formatDeps = map formatOne
+    formatOne (installedPkgId, pkgId)
+      -- The problem is how different cabal executables handle package databases
+      -- when doctests depend on the library
+      | packageId pkg == pkgId = "-package=" ++ display pkgId
+      | otherwise              = "-package-id=" ++ display installedPkgId
+
+    -- From Distribution.Simple.Program.GHC
+    packageDbArgs :: [PackageDB] -> [String]
+    packageDbArgs | isOldCompiler = packageDbArgsConf
+                  | otherwise     = packageDbArgsDb
+
+    -- GHC <7.6 uses '-package-conf' instead of '-package-db'.
+    packageDbArgsConf :: [PackageDB] -> [String]
+    packageDbArgsConf dbstack = case dbstack of
+      (GlobalPackageDB:UserPackageDB:dbs) -> concatMap specific dbs
+      (GlobalPackageDB:dbs)               -> ("-no-user-package-conf")
+                                           : concatMap specific dbs
+      _ -> ierror
+      where
+        specific (SpecificPackageDB db) = [ "-package-conf=" ++ db ]
+        specific _                      = ierror
+        ierror = error $ "internal error: unexpected package db stack: "
+                      ++ show dbstack
+
+    -- GHC >= 7.6 uses the '-package-db' flag. See
+    -- https://ghc.haskell.org/trac/ghc/ticket/5977.
+    packageDbArgsDb :: [PackageDB] -> [String]
+    -- special cases to make arguments prettier in common scenarios
+    packageDbArgsDb dbstack = case dbstack of
+      (GlobalPackageDB:UserPackageDB:dbs)
+        | all isSpecific dbs              -> concatMap single dbs
+      (GlobalPackageDB:dbs)
+        | all isSpecific dbs              -> "-no-user-package-db"
+                                           : concatMap single dbs
+      dbs                                 -> "-clear-package-db"
+                                           : concatMap single dbs
+     where
+       single (SpecificPackageDB db) = [ "-package-db=" ++ db ]
+       single GlobalPackageDB        = [ "-global-package-db" ]
+       single UserPackageDB          = [ "-user-package-db" ]
+       isSpecific (SpecificPackageDB _) = True
+       isSpecific _                     = False
+
+testDeps :: ComponentLocalBuildInfo -> ComponentLocalBuildInfo -> [(InstalledPackageId, PackageId)]
+testDeps xs ys = nub $ componentPackageDeps xs ++ componentPackageDeps ys
+
+\end{code}

servant-server/servant-server.cabal

@@ -19,7 +19,7 @@ author:              Servant Contributors
 maintainer:          haskell-servant-maintainers@googlegroups.com
 copyright:           2014-2016 Zalora South East Asia Pte Ltd, Servant Contributors
 category:            Web
-build-type:          Simple
+build-type:          Custom
 cabal-version:       >=1.10
 tested-with:         GHC >= 7.8
 extra-source-files:
@@ -31,6 +31,9 @@ source-repository head
   type: git
   location: http://github.com/haskell-servant/servant.git
 
+custom-setup
+  setup-depends:
+     Cabal >=1.14, base, filepath, directory
 
 library
   exposed-modules:
@@ -144,7 +147,7 @@ test-suite doctests
               , directory
               , filepath
  type: exitcode-stdio-1.0
- main-is: test/Doctests.hs
+ main-is: test/doctests.hs
  buildable: True
  default-language: Haskell2010
  ghc-options: -Wall -threaded

servant-server/test/Doctests.hs

@@ -1,41 +0,0 @@
-module Main where
-
-import           Data.List            (isPrefixOf)
-import           System.Directory
-import           System.FilePath
-import           System.FilePath.Find
-import           Test.DocTest
-
-main :: IO ()
-main = do
-    files <- find always (extension ==? ".hs") "src"
-    mCabalMacrosFile <- getCabalMacrosFile
-    doctest $ "-isrc" : "-Iinclude" :
-              (maybe [] (\ f -> ["-optP-include", "-optP" ++ f]) mCabalMacrosFile) ++
-              "-XOverloadedStrings" :
-              "-XFlexibleInstances" :
-              "-XMultiParamTypeClasses" :
-              "-XDataKinds" :
-              "-XTypeOperators" :
-              files
-
-getCabalMacrosFile :: IO (Maybe FilePath)
-getCabalMacrosFile = do
-  exists <- doesDirectoryExist "dist"
-  if exists
-    then do
-      contents <- getDirectoryContents "dist"
-      let rest = "build" </> "autogen" </> "cabal_macros.h"
-      whenExists $ case filter ("dist-sandbox-" `isPrefixOf`) contents of
-        [x] -> "dist" </> x </> rest
-        [] -> "dist" </> rest
-        xs -> error $ "ran doctests with multiple dist/dist-sandbox-xxxxx's: \n"
-                    ++ show xs ++ "\nTry cabal clean"
-    else return Nothing
- where
-  whenExists :: FilePath -> IO (Maybe FilePath)
-  whenExists file = do
-    exists <- doesFileExist file
-    return $ if exists
-      then Just file
-      else Nothing

servant-server/test/doctests.hsc

@@ -0,0 +1,61 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE ForeignFunctionInterface #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Main (doctests)
+-- Copyright   :  (C) 2012-14 Edward Kmett
+-- License     :  BSD-style (see the file LICENSE)
+-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- This module provides doctests for a project based on the actual versions
+-- of the packages it was built with. It requires a corresponding Setup.lhs
+-- to be added to the project
+-----------------------------------------------------------------------------
+module Main where
+
+import Build_doctests (flags, pkgs, module_sources)
+import Data.Foldable (traverse_)
+import Test.DocTest
+
+##if defined(mingw32_HOST_OS)
+##if defined(i386_HOST_ARCH)
+##define USE_CP
+import Control.Applicative
+import Control.Exception
+import Foreign.C.Types
+foreign import stdcall "windows.h SetConsoleCP" c_SetConsoleCP :: CUInt -> IO Bool
+foreign import stdcall "windows.h GetConsoleCP" c_GetConsoleCP :: IO CUInt
+##elif defined(x86_64_HOST_ARCH)
+##define USE_CP
+import Control.Applicative
+import Control.Exception
+import Foreign.C.Types
+foreign import ccall "windows.h SetConsoleCP" c_SetConsoleCP :: CUInt -> IO Bool
+foreign import ccall "windows.h GetConsoleCP" c_GetConsoleCP :: IO CUInt
+##endif
+##endif
+
+-- | Run in a modified codepage where we can print UTF-8 values on Windows.
+withUnicode :: IO a -> IO a
+##ifdef USE_CP
+withUnicode m = do
+  cp <- c_GetConsoleCP
+  (c_SetConsoleCP 65001 >> m) `finally` c_SetConsoleCP cp
+##else
+withUnicode m = m
+##endif
+
+main :: IO ()
+main = withUnicode $ do
+    traverse_ putStrLn args
+    doctest args
+  where
+    args = 
+      "-XOverloadedStrings" :
+      "-XFlexibleInstances" :
+      "-XMultiParamTypeClasses" :
+      "-XDataKinds" :
+      "-XTypeOperators" :
+      flags ++ pkgs ++ module_sources

servant/Setup.hs

@@ -1,2 +0,0 @@
-import           Distribution.Simple
-main = defaultMain

servant/Setup.lhs

@@ -0,0 +1,165 @@
+\begin{code}
+{-# LANGUAGE CPP #-}
+#ifndef MIN_VERSION_Cabal
+#define MIN_VERSION_Cabal(x,y,z) 0
+#endif
+#ifndef MIN_VERSION_directory
+#define MIN_VERSION_directory(x,y,z) 0
+#endif
+#if MIN_VERSION_Cabal(1,24,0)
+#define InstalledPackageId UnitId
+#endif
+module Main (main) where
+
+import Control.Monad ( when )
+import Data.List ( nub )
+import Distribution.Package ( InstalledPackageId )
+import Distribution.Package ( PackageId, Package (..), packageVersion )
+import Distribution.PackageDescription ( PackageDescription(), TestSuite(..) , Library (..), BuildInfo (..))
+import Distribution.Simple ( defaultMainWithHooks, UserHooks(..), simpleUserHooks )
+import Distribution.Simple.Utils ( rewriteFile, createDirectoryIfMissingVerbose )
+import Distribution.Simple.BuildPaths ( autogenModulesDir )
+import Distribution.Simple.Setup ( BuildFlags(buildDistPref, buildVerbosity), fromFlag)
+import Distribution.Simple.LocalBuildInfo ( withPackageDB, withLibLBI, withTestLBI, LocalBuildInfo(), ComponentLocalBuildInfo(componentPackageDeps), compiler )
+import Distribution.Simple.Compiler ( showCompilerId , PackageDB (..))
+import Distribution.Text ( display , simpleParse )
+import System.FilePath ( (</>) )
+
+#if MIN_VERSION_Cabal(1,25,0)
+import Distribution.Simple.BuildPaths ( autogenComponentModulesDir )
+#endif
+
+#if MIN_VERSION_directory(1,2,2)
+import System.Directory (makeAbsolute)
+#else
+import System.Directory (getCurrentDirectory)
+import System.FilePath (isAbsolute)
+
+makeAbsolute :: FilePath -> IO FilePath
+makeAbsolute p | isAbsolute p = return p
+               | otherwise    = do
+    cwd <- getCurrentDirectory
+    return $ cwd </> p
+#endif
+
+main :: IO ()
+main = defaultMainWithHooks simpleUserHooks
+  { buildHook = \pkg lbi hooks flags -> do
+     generateBuildModule flags pkg lbi
+     buildHook simpleUserHooks pkg lbi hooks flags
+  }
+
+generateBuildModule :: BuildFlags -> PackageDescription -> LocalBuildInfo -> IO ()
+generateBuildModule flags pkg lbi = do
+  let verbosity = fromFlag (buildVerbosity flags)
+  let distPref = fromFlag (buildDistPref flags)
+
+  -- Package DBs
+  let dbStack = withPackageDB lbi ++ [ SpecificPackageDB $ distPref </> "package.conf.inplace" ]
+  let dbFlags = "-hide-all-packages" : packageDbArgs dbStack
+
+  withLibLBI pkg lbi $ \lib libcfg -> do
+    let libBI = libBuildInfo lib
+
+    -- modules
+    let modules = exposedModules lib ++ otherModules libBI
+    -- it seems that doctest is happy to take in module names, not actual files!
+    let module_sources = modules
+
+    -- We need the directory with library's cabal_macros.h!
+#if MIN_VERSION_Cabal(1,25,0)
+    let libAutogenDir = autogenComponentModulesDir lbi libcfg
+#else
+    let libAutogenDir = autogenModulesDir lbi
+#endif
+
+    -- Lib sources and includes
+    iArgs <- mapM (fmap ("-i"++) . makeAbsolute) $ libAutogenDir : hsSourceDirs libBI
+    includeArgs <- mapM (fmap ("-I"++) . makeAbsolute) $ includeDirs libBI
+
+    -- CPP includes, i.e. include cabal_macros.h
+    let cppFlags = map ("-optP"++) $
+            [ "-include", libAutogenDir ++ "/cabal_macros.h" ]
+            ++ cppOptions libBI
+
+    -- Actually we need to check whether testName suite == "doctests"
+    -- pending https://github.com/haskell/cabal/pull/4229 getting into GHC HEAD tree
+    withTestLBI pkg lbi $ \suite suitecfg -> when (testName suite == "doctests") $ do
+
+      -- get and create autogen dir
+#if MIN_VERSION_Cabal(1,25,0)
+      let testAutogenDir = autogenComponentModulesDir lbi suitecfg
+#else
+      let testAutogenDir = autogenModulesDir lbi
+#endif
+      createDirectoryIfMissingVerbose verbosity True testAutogenDir
+
+      -- write autogen'd file
+      rewriteFile (testAutogenDir </> "Build_doctests.hs") $ unlines
+        [ "module Build_doctests where"
+        , ""
+        -- -package-id etc. flags
+        , "pkgs :: [String]"
+        , "pkgs = " ++ (show $ formatDeps $ testDeps libcfg suitecfg)
+        , ""
+        , "flags :: [String]"
+        , "flags = " ++ show (iArgs ++ includeArgs ++ dbFlags ++ cppFlags)
+        , ""
+        , "module_sources :: [String]"
+        , "module_sources = " ++ show (map display module_sources)
+        ]
+  where
+    -- we do this check in Setup, as then doctests don't need to depend on Cabal
+    isOldCompiler = maybe False id $ do
+      a <- simpleParse $ showCompilerId $ compiler lbi
+      b <- simpleParse "7.5"
+      return $ packageVersion (a :: PackageId) < b
+
+    formatDeps = map formatOne
+    formatOne (installedPkgId, pkgId)
+      -- The problem is how different cabal executables handle package databases
+      -- when doctests depend on the library
+      | packageId pkg == pkgId = "-package=" ++ display pkgId
+      | otherwise              = "-package-id=" ++ display installedPkgId
+
+    -- From Distribution.Simple.Program.GHC
+    packageDbArgs :: [PackageDB] -> [String]
+    packageDbArgs | isOldCompiler = packageDbArgsConf
+                  | otherwise     = packageDbArgsDb
+
+    -- GHC <7.6 uses '-package-conf' instead of '-package-db'.
+    packageDbArgsConf :: [PackageDB] -> [String]
+    packageDbArgsConf dbstack = case dbstack of
+      (GlobalPackageDB:UserPackageDB:dbs) -> concatMap specific dbs
+      (GlobalPackageDB:dbs)               -> ("-no-user-package-conf")
+                                           : concatMap specific dbs
+      _ -> ierror
+      where
+        specific (SpecificPackageDB db) = [ "-package-conf=" ++ db ]
+        specific _                      = ierror
+        ierror = error $ "internal error: unexpected package db stack: "
+                      ++ show dbstack
+
+    -- GHC >= 7.6 uses the '-package-db' flag. See
+    -- https://ghc.haskell.org/trac/ghc/ticket/5977.
+    packageDbArgsDb :: [PackageDB] -> [String]
+    -- special cases to make arguments prettier in common scenarios
+    packageDbArgsDb dbstack = case dbstack of
+      (GlobalPackageDB:UserPackageDB:dbs)
+        | all isSpecific dbs              -> concatMap single dbs
+      (GlobalPackageDB:dbs)
+        | all isSpecific dbs              -> "-no-user-package-db"
+                                           : concatMap single dbs
+      dbs                                 -> "-clear-package-db"
+                                           : concatMap single dbs
+     where
+       single (SpecificPackageDB db) = [ "-package-db=" ++ db ]
+       single GlobalPackageDB        = [ "-global-package-db" ]
+       single UserPackageDB          = [ "-user-package-db" ]
+       isSpecific (SpecificPackageDB _) = True
+       isSpecific _                     = False
+
+testDeps :: ComponentLocalBuildInfo -> ComponentLocalBuildInfo -> [(InstalledPackageId, PackageId)]
+testDeps xs ys = nub $ componentPackageDeps xs ++ componentPackageDeps ys
+
+\end{code}

servant/servant.cabal

@@ -15,7 +15,7 @@ author:              Servant Contributors
 maintainer:          haskell-servant-maintainers@googlegroups.com
 copyright:           2014-2016 Zalora South East Asia Pte Ltd, Servant Contributors
 category:            Web
-build-type:          Simple
+build-type:          Custom
 cabal-version:       >=1.10
 tested-with:         GHC >= 7.8
 extra-source-files:
@@ -25,6 +25,10 @@ source-repository head
   type: git
   location: http://github.com/haskell-servant/servant.git
 
+custom-setup
+  setup-depends:
+     Cabal >=1.14, base, filepath, directory
+
 library
   exposed-modules:
     Servant.API
@@ -134,8 +138,9 @@ test-suite doctests
               , directory
               , filepath
  type: exitcode-stdio-1.0
- main-is: test/Doctests.hs
+ main-is: test/doctests.hs
  buildable: True
  default-language: Haskell2010
  ghc-options: -Wall -threaded
+ build-tools: hsc2hs
  include-dirs: include

servant/test/Doctests.hs

@@ -1,40 +0,0 @@
-module Main where
-
-import           Data.List            (isPrefixOf)
-import           System.Directory
-import           System.FilePath
-import           System.FilePath.Find
-import           Test.DocTest
-
-main :: IO ()
-main = do
-    files <- find always (extension ==? ".hs") "src"
-    tfiles <- find always (extension ==? ".hs") "test/Servant"
-    mCabalMacrosFile <- getCabalMacrosFile
-    doctest $ "-isrc" : "-Iinclude" :
-              (maybe [] (\ f -> ["-optP-include", "-optP" ++ f]) mCabalMacrosFile) ++
-              "-XOverloadedStrings" :
-              "-XFlexibleInstances" :
-              "-XMultiParamTypeClasses" :
-              (files ++ tfiles)
-
-getCabalMacrosFile :: IO (Maybe FilePath)
-getCabalMacrosFile = do
-  exists <- doesDirectoryExist "dist"
-  if exists
-    then do
-      contents <- getDirectoryContents "dist"
-      let rest = "build" </> "autogen" </> "cabal_macros.h"
-      whenExists $ case filter ("dist-sandbox-" `isPrefixOf`) contents of
-        [x] -> "dist" </> x </> rest
-        [] -> "dist" </> rest
-        xs -> error $ "ran doctests with multiple dist/dist-sandbox-xxxxx's: \n"
-                    ++ show xs ++ "\nTry cabal clean"
-    else return Nothing
- where
-  whenExists :: FilePath -> IO (Maybe FilePath)
-  whenExists file = do
-    exists <- doesFileExist file
-    return $ if exists
-      then Just file
-      else Nothing

servant/test/doctests.hsc

@@ -0,0 +1,59 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE ForeignFunctionInterface #-}
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  Main (doctests)
+-- Copyright   :  (C) 2012-14 Edward Kmett
+-- License     :  BSD-style (see the file LICENSE)
+-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
+-- Stability   :  provisional
+-- Portability :  portable
+--
+-- This module provides doctests for a project based on the actual versions
+-- of the packages it was built with. It requires a corresponding Setup.lhs
+-- to be added to the project
+-----------------------------------------------------------------------------
+module Main where
+
+import Build_doctests (flags, pkgs, module_sources)
+import Data.Foldable (traverse_)
+import Test.DocTest
+
+##if defined(mingw32_HOST_OS)
+##if defined(i386_HOST_ARCH)
+##define USE_CP
+import Control.Applicative
+import Control.Exception
+import Foreign.C.Types
+foreign import stdcall "windows.h SetConsoleCP" c_SetConsoleCP :: CUInt -> IO Bool
+foreign import stdcall "windows.h GetConsoleCP" c_GetConsoleCP :: IO CUInt
+##elif defined(x86_64_HOST_ARCH)
+##define USE_CP
+import Control.Applicative
+import Control.Exception
+import Foreign.C.Types
+foreign import ccall "windows.h SetConsoleCP" c_SetConsoleCP :: CUInt -> IO Bool
+foreign import ccall "windows.h GetConsoleCP" c_GetConsoleCP :: IO CUInt
+##endif
+##endif
+
+-- | Run in a modified codepage where we can print UTF-8 values on Windows.
+withUnicode :: IO a -> IO a
+##ifdef USE_CP
+withUnicode m = do
+  cp <- c_GetConsoleCP
+  (c_SetConsoleCP 65001 >> m) `finally` c_SetConsoleCP cp
+##else
+withUnicode m = m
+##endif
+
+main :: IO ()
+main = withUnicode $ do
+    traverse_ putStrLn args
+    doctest args
+  where
+    args = 
+      "-XOverloadedStrings" :
+      "-XFlexibleInstances" :
+      "-XMultiParamTypeClasses" :
+      flags ++ pkgs ++ module_sources