Fix issue with disappearing GADT kind signatures (#381)

Author: lukasz-golebiewski

lib/Language/Haskell/Stylish/Step/Data.hs

@@ -38,7 +38,7 @@ import           GHC.Hs.Types                     (ConDeclField (..),
                                                    HsConDetails (..), HsContext,
                                                    HsImplicitBndrs (..),
                                                    HsTyVarBndr (..),
-                                                   HsType (..), LHsQTyVars (..))
+                                                   HsType (..), LHsQTyVars (..), LHsKind)
 import           RdrName                          (RdrName)
 import           SrcLoc                           (GenLocated (..), Located,
                                                    RealLocated)
@@ -312,9 +312,11 @@ putName decl@MkDataDecl{..} =
     putRdrName dataDeclName
     space
     forM_ secondTvar putOutputable
+    maybePutKindSig
   else do
     putRdrName dataDeclName
     forM_ (hsq_explicit dataTypeVars) (\t -> space >> putOutputable t)
+    maybePutKindSig
 
   where
     firstTvar :: Maybe (Located (HsTyVarBndr GhcPs))
@@ -330,6 +332,12 @@ putName decl@MkDataDecl{..} =
       & drop 1
       & listToMaybe
 
+    maybePutKindSig :: Printer ()
+    maybePutKindSig = forM_ maybeKindSig (\k -> space >> putText "::" >> space >> putOutputable k)
+
+    maybeKindSig :: Maybe (LHsKind GhcPs)
+    maybeKindSig = dd_kindSig dataDefn
+
 putConstructor :: Config -> Int -> Located (ConDecl GhcPs) -> P ()
 putConstructor cfg consIndent (L _ cons) = case cons of
   ConDeclGADT{..} -> do

tests/Language/Haskell/Stylish/Step/Data/Tests.hs

@@ -75,6 +75,7 @@ tests = testGroup "Language.Haskell.Stylish.Step.Data.Tests"
     , testCase "case 60" case60
     , testCase "case 61 (issue 282)" case61
     , testCase "case 62 (issue 273)" case62
+    , testCase "case 63 (issue 338)" case63
     ]
 
 case00 :: Assertion
@@ -1377,6 +1378,17 @@ case62 = expected @=? testStep (step sameIndentStyle) input
       , "             }"
       ]
 
+case63 :: Assertion
+case63 = expected @=? testStep (step indentIndentStyle) input
+  where
+    input = unlines
+      [ "module Herp where"
+      , ""
+      , "data Foo :: * -> * where"
+      , "  Bar :: () -> Foo ()"
+      ]
+    expected = input
+
 sameSameStyle :: Config
 sameSameStyle = Config SameLine SameLine 2 2 False True SameLine False True NoMaxColumns