cabal init: add support for default-language field

cabal-install/Distribution/Client/Init.hs

@@ -63,6 +63,7 @@ import Distribution.ModuleName
 import Distribution.InstalledPackageInfo
   ( InstalledPackageInfo, sourcePackageId, exposed )
 import qualified Distribution.Package as P
+import Language.Haskell.Extension ( Language(..) )
 
 import Distribution.Client.Init.Types
   ( InitFlags(..), PackageType(..), Category(..) )
@@ -127,6 +128,7 @@ extendFlags pkgIx =
   >=> getSynopsis
   >=> getCategory
   >=> getLibOrExec
+  >=> getLanguage
   >=> getGenComments
   >=> getSrcDir
   >=> getModulesBuildToolsAndDeps pkgIx
@@ -242,7 +244,24 @@ getLibOrExec flags = do
 
   return $ flags { packageType = maybeToFlag isLib }
 
--- | Ask whether to generate explanitory comments.
+-- | Ask for the base language of the package.
+getLanguage :: InitFlags -> IO InitFlags
+getLanguage flags = do
+  lang <-     return (flagToMaybe $ language flags)
+          ?>> maybePrompt flags
+                (either UnknownLanguage id `fmap`
+                  (promptList "What base language is the package written in"
+                    [Haskell2010, Haskell98]
+                    (Just Haskell2010)
+                    display
+                    True
+                  )
+                )
+          ?>> return (Just Haskell2010)
+
+  return $ flags { language = maybeToFlag lang }
+
+-- | Ask whether to generate explanatory comments.
 getGenComments :: InitFlags -> IO InitFlags
 getGenComments flags = do
   genComments <-     return (not <$> (flagToMaybe $ noComments flags))
@@ -678,6 +697,10 @@ generateCabalFile fileName c =
      , fieldS "build-tools" (listFieldS (buildTools c'))
               (Just "Extra tools (e.g. alex, hsc2hs, ...) needed to build the source.")
               False
+
+     , field  "default-language" (language c')
+              (Just "Base language which the package is written in.")
+              True
      ]
 
    listField :: Text s => Maybe [s] -> Flag String

cabal-install/Distribution/Client/Init/Types.hs

@@ -22,6 +22,7 @@ import Distribution.Verbosity
 import qualified Distribution.Package as P
 import Distribution.License
 import Distribution.ModuleName
+import Language.Haskell.Extension ( Language(..) )
 
 import qualified Text.PrettyPrint as Disp
 import qualified Distribution.Compat.ReadP as Parse
@@ -53,6 +54,7 @@ data InitFlags =
               , category     :: Flag (Either String Category)
 
               , packageType  :: Flag PackageType
+              , language     :: Flag Language
 
               , exposedModules :: Maybe [ModuleName]
               , otherModules   :: Maybe [ModuleName]
@@ -90,6 +92,7 @@ instance Monoid InitFlags where
     , synopsis       = mempty
     , category       = mempty
     , packageType    = mempty
+    , language       = mempty
     , exposedModules = mempty
     , otherModules   = mempty
     , dependencies   = mempty
@@ -114,6 +117,7 @@ instance Monoid InitFlags where
     , synopsis       = combine synopsis
     , category       = combine category
     , packageType    = combine packageType
+    , language       = combine language
     , exposedModules = combine exposedModules
     , otherModules   = combine otherModules
     , dependencies   = combine dependencies

cabal-install/Distribution/Client/Setup.hs

@@ -1052,6 +1052,14 @@ initCommand = CommandUI {
         (\v flags -> flags { IT.packageType = v })
         (noArg (Flag IT.Executable))
 
+      , option [] ["language"]
+        "Specify the default language."
+        IT.language
+        (\v flags -> flags { IT.language = v })
+        (reqArg "LANGUAGE" (readP_to_E ("Cannot parse language: "++)
+                                       (toFlag `fmap` parse))
+                          (flagToList . fmap display))
+
       , option ['o'] ["expose-module"]
         "Export a module from the package."
         IT.exposedModules