Special setting for empty import lists

2 files changed, 29 insertions, 7 deletions

diff --git a/lib/Language/Haskell/Stylish/Config.hs b/lib/Language/Haskell/Stylish/Config.hs
index d14e1be..e551d71 100644
--- a/lib/Language/Haskell/Stylish/Config.hs
+++ b/lib/Language/Haskell/Stylish/Config.hs
@@ -187,6 +187,8 @@ parseImports config o = Imports.step
         <*> (o A..:? "long_list_align"
             >>= parseEnum longListAligns Imports.Inline)
         -- Note that padding has to be at least 1. Default is 4.
+        <*> (o A..:? "empty_list_align"
+            >>= parseEnum emptyListAligns Imports.Inherit)
         <*> (maybe 4 (max 1) <$> o A..:? "list_padding")
         <*> o A..:? "separate_lists" A..!= True)
   where
@@ -210,6 +212,11 @@ parseImports config o = Imports.step
         , ("multiline",          Imports.Multiline)
         ]
 
+    emptyListAligns =
+        [ ("inherit", Imports.Inherit)
+        , ("right_after", Imports.RightAfter)
+        ]
+
 
 --------------------------------------------------------------------------------
 parseLanguagePragmas :: Config -> A.Object -> A.Parser Step
diff --git a/lib/Language/Haskell/Stylish/Step/Imports.hs b/lib/Language/Haskell/Stylish/Step/Imports.hs
index ac84933..00ca9b7 100644
--- a/lib/Language/Haskell/Stylish/Step/Imports.hs
+++ b/lib/Language/Haskell/Stylish/Step/Imports.hs
@@ -5,12 +5,14 @@ module Language.Haskell.Stylish.Step.Imports
     , ImportAlign (..)
     , ListAlign (..)
     , LongListAlign (..)
+    , EmptyListAlign (..)
     , step
     ) where
 
 
 --------------------------------------------------------------------------------
 import           Control.Arrow                   ((&&&))
+import           Control.Monad                   (void)
 import           Data.Char                       (toLower)
 import           Data.List                       (intercalate, sortBy)
 import           Data.Maybe                      (isJust, maybeToList)
@@ -26,11 +28,12 @@ import           Language.Haskell.Stylish.Util
 
 --------------------------------------------------------------------------------
 data Align = Align
-    { importAlign   :: ImportAlign
-    , listAlign     :: ListAlign
-    , longListAlign :: LongListAlign
-    , listPadding   :: Int
-    , separateLists :: Bool
+    { importAlign    :: ImportAlign
+    , listAlign      :: ListAlign
+    , longListAlign  :: LongListAlign
+    , emptyListAlign :: EmptyListAlign
+    , listPadding    :: Int
+    , separateLists  :: Bool
     }
     deriving (Eq, Show)
 
@@ -47,6 +50,11 @@ data ListAlign
     | AfterAlias
     deriving (Eq, Show)
 
+data EmptyListAlign
+    = Inherit
+    | RightAfter
+    deriving (Eq, Show)
+
 data LongListAlign
     = Inline
     | InlineWithBreak
@@ -136,13 +144,16 @@ prettyImportSpec separate = prettyImportSpec'
 --------------------------------------------------------------------------------
 prettyImport :: (Ord l, Show l) =>
     Int -> Align -> Bool -> Bool -> Int -> H.ImportDecl l -> [String]
-prettyImport columns Align{..} padQualified padName longest imp =
-    case longListAlign of
+prettyImport columns Align{..} padQualified padName longest imp
+    | (void `fmap` H.importSpecs imp) == emptyImportSpec = emptyWrap
+    | otherwise = case longListAlign of
         Inline            -> inlineWrap
         InlineWithBreak   -> longListWrapper inlineWrap inlineWithBreakWrap
         InlineToMultiline -> longListWrapper inlineWrap inlineToMultilineWrap
         Multiline         -> longListWrapper inlineWrap multilineWrap
   where
+    emptyImportSpec = Just (H.ImportSpecList () False [])
+
     longListWrapper shortWrap longWrap
         | listAlign == NewLine
         || length shortWrap > 1
@@ -150,6 +161,10 @@ prettyImport columns Align{..} padQualified padName longest imp =
             = longWrap
         | otherwise = shortWrap
 
+    emptyWrap = case emptyListAlign of
+        Inherit -> inlineWrap
+        RightAfter -> [paddedNoSpecBase ++ " ()"]
+
     inlineWrap = inlineWrapper
         $ mapSpecs
         $ withInit (++ ",")