Add break_newtypes flag. (haskell#342)

Default behavior remains the same, but when you set `break_newtypes` to
`false` newtypes will be formatted on a single line.

Author: imuli

data/stylish-haskell.yaml

@@ -90,6 +90,11 @@ steps:
   #     # Default: false
   #     break_enums: false
   #
+  #     # Whether or not to break newtype types before `=` sign
+  #     #
+  #     # Default: true
+  #     break_newtypes: true
+  #
   #     # Whether or not to break single constructor data types before `=` sign
   #     #
   #     # Default: true

lib/Language/Haskell/Stylish/Config.hs

@@ -251,6 +251,7 @@ parseRecords c o = Data.step
         <*> (o A..: "field_comment")
         <*> (o A..: "deriving")
         <*> (o A..:? "break_enums" A..!= False)
+        <*> (o A..:? "break_newtypes" A..!= True)
         <*> (o A..:? "break_single_constructors" A..!= True)
         <*> (o A..: "via" >>= parseIndent)
         <*> (o A..:? "curried_context" A..!= False)

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

@@ -60,6 +60,8 @@ data Config = Config
       -- ^ Indent before @deriving@ lines (measured from column 0)
     , cBreakEnums              :: !Bool
       -- ^ Break enums by newlines and follow the above rules
+    , cBreakNewtypes           :: !Bool
+      -- ^ Break newtypes by newlines and follow the above rules
     , cBreakSingleConstructors :: !Bool
       -- ^ Break single constructors when enabled, e.g. @Indent 2@ will not cause newline after @=@
     , cVia                     :: !Indent
@@ -79,6 +81,7 @@ defaultConfig = Config
     , cFieldComment    = 2
     , cDeriving        = 4
     , cBreakEnums      = True
+    , cBreakNewtypes   = True
     , cBreakSingleConstructors = False
     , cVia             = Indent 4
     , cSortDeriving    = True
@@ -155,6 +158,7 @@ putDataDecl cfg@Config {..} decl = do
     when (hasConstructors decl) do
         case (cEquals, cFirstField) of
             (_, Indent x) | isEnum decl && cBreakEnums -> newline >> spaces x
+            (_, _) | if isNewtype decl then not cBreakNewtypes else singleConstructor decl && not cBreakSingleConstructors -> space
             (_, _)
                 | not (isNewtype decl)
                 , singleConstructor decl && not cBreakSingleConstructors ->

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

@@ -1382,19 +1382,19 @@ case66 = assertSnippet (step indentIndentStyle) input input
       ]
 
 sameSameStyle :: Config
-sameSameStyle = Config SameLine SameLine 2 2 False True SameLine False True NoMaxColumns
+sameSameStyle = Config SameLine SameLine 2 2 False True True SameLine False True NoMaxColumns
 
 sameIndentStyle :: Config
-sameIndentStyle = Config SameLine (Indent 2) 2 2 False True SameLine False True NoMaxColumns
+sameIndentStyle = Config SameLine (Indent 2) 2 2 False True True SameLine False True NoMaxColumns
 
 indentSameStyle :: Config
-indentSameStyle = Config (Indent 2) SameLine 2 2 False True SameLine False True NoMaxColumns
+indentSameStyle = Config (Indent 2) SameLine 2 2 False True True SameLine False True NoMaxColumns
 
 indentIndentStyle :: Config
-indentIndentStyle = Config (Indent 2) (Indent 2) 2 2 False True SameLine False True NoMaxColumns
+indentIndentStyle = Config (Indent 2) (Indent 2) 2 2 False True True SameLine False True NoMaxColumns
 
 indentIndentStyle4 :: Config
-indentIndentStyle4 = Config (Indent 4) (Indent 4) 4 4 False True SameLine False True NoMaxColumns
+indentIndentStyle4 = Config (Indent 4) (Indent 4) 4 4 False True True SameLine False True NoMaxColumns
 
 sameSameNoSortStyle :: Config
-sameSameNoSortStyle = Config SameLine SameLine 2 2 False True SameLine False False NoMaxColumns
+sameSameNoSortStyle = Config SameLine SameLine 2 2 False True True SameLine False False NoMaxColumns