Deriving alignment for enums (#424)

* Failing test added

* Haddoc comment added

* Deriving alignment behavior changed & tests updated

* Test data name changed (just to look prettier)

Author: Lev135

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

@@ -196,8 +196,9 @@ putDataDecl cfg@Config {..} decl = do
     let derivingComments = deepAnnComments (GHC.dd_derivs defn)
 
     when (hasDeriving decl) do
-        if onelineEnum && null derivingComments then
-            space
+        if onelineEnum && null derivingComments then do
+            newline
+            spaces cDeriving
         else do
             forM_ derivingComments $ \lc -> do
                 newline

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

@@ -78,6 +78,7 @@ tests = testGroup "Language.Haskell.Stylish.Step.Data.Tests"
     , testCase "case 63 (issue #338)" case63
     , testCase "case 64" case64
     , testCase "case 65" case65
+    , testCase "case 66 (issue #411)" case66
     ]
 
 case00 :: Assertion
@@ -424,7 +425,8 @@ case20 = assertSnippet (step indentIndentStyle) input input
     input =
        [ "module Herp where"
        , ""
-       , "data Tag = Title | Text deriving (Eq, Show)"
+       , "data Tag = Title | Text"
+       , "  deriving (Eq, Show)"
        ]
 
 case21 :: Assertion
@@ -1161,7 +1163,8 @@ case55 :: Assertion
 case55 = assertSnippet (step sameSameNoSortStyle) input expected
   where
     input =
-       [ "data Foo = Foo deriving (Z, Y, X, Bar, Abcd)"
+       [ "data Foo = Foo"
+       , "  deriving (Z, Y, X, Bar, Abcd)"
        ]
 
     expected = input
@@ -1367,6 +1370,17 @@ case65 = assertSnippet (step indentIndentStyle) input input
         , "  deriving (Show)"
         ]
 
+-- | Deriving alignment for enums
+--
+-- Regression test for https://github.com/haskell/stylish-haskell/issues/411
+case66 :: Assertion
+case66 = assertSnippet (step indentIndentStyle) input input
+  where
+    input =
+      [ "data Foo = A | B | C"
+      , "  deriving (Eq, Show)"
+      ]
+
 sameSameStyle :: Config
 sameSameStyle = Config SameLine SameLine 2 2 False True SameLine False True NoMaxColumns