Introduce nicer style for records (#266)

1 files changed, 67 insertions, 21 deletions

diff --git a/lib/Language/Haskell/Stylish/Step/Data.hs b/lib/Language/Haskell/Stylish/Step/Data.hs
index 681c7c8..1f7732b 100644
--- a/lib/Language/Haskell/Stylish/Step/Data.hs
+++ b/lib/Language/Haskell/Stylish/Step/Data.hs
@@ -1,7 +1,9 @@
+{-# LANGUAGE RecordWildCards #-}
+
 module Language.Haskell.Stylish.Step.Data where
 
 import           Data.List                       (find, intercalate)
-import           Data.Maybe                      (maybeToList)
+import           Data.Maybe                      (fromMaybe, maybeToList)
 import qualified Language.Haskell.Exts           as H
 import           Language.Haskell.Exts.Comments
 import           Language.Haskell.Stylish.Block
@@ -10,20 +12,36 @@ import           Language.Haskell.Stylish.Step
 import           Language.Haskell.Stylish.Util
 import           Prelude                         hiding (init)
 
+data Indent
+    = SameLine
+    | Indent !Int
+  deriving (Show)
+
+data Config = Config
+    { cEquals           :: !Indent
+      -- ^ Indent between type constructor and @=@ sign (measured from column 0)
+    , cFirstField       :: !Indent
+      -- ^ Indent between data constructor and @{@ line (measured from column with data constructor name)
+    , cFieldComment     :: !Int
+      -- ^ Indent between column with @{@ and start of field line comment (this line has @cFieldComment = 2@)
+    , cDeriving         :: !Int
+      -- ^ Indent before @deriving@ lines (measured from column 0)
+    } deriving (Show)
+
 datas :: H.Module l -> [H.Decl l]
 datas (H.Module _ _ _ _ decls) = decls
 datas _                        = []
 
 type ChangeLine = Change String
 
-step :: Int -> Step
-step indentSize = makeStep "Data" (step' indentSize)
+step :: Config -> Step
+step cfg = makeStep "Data" (step' cfg)
 
-step' :: Int -> Lines -> Module -> Lines
-step' indentSize ls (module', allComments) = applyChanges changes ls
+step' :: Config -> Lines -> Module -> Lines
+step' cfg ls (module', allComments) = applyChanges changes ls
   where
     datas' = datas $ fmap linesFromSrcSpan module'
-    changes = datas' >>= maybeToList . changeDecl allComments indentSize
+    changes = datas' >>= maybeToList . changeDecl allComments cfg
 
 findCommentOnLine :: LineBlock -> [Comment] -> Maybe Comment
 findCommentOnLine lb = find commentOnLine
@@ -43,9 +61,9 @@ commentsWithin lb = filter within
     within (Comment _ (H.SrcSpan _ start _ end _) _) =
       start >= blockStart lb && end <= blockEnd lb
 
-changeDecl :: [Comment] -> Int -> H.Decl LineBlock -> Maybe ChangeLine
+changeDecl :: [Comment] -> Config -> H.Decl LineBlock -> Maybe ChangeLine
 changeDecl _ _ (H.DataDecl _ (H.DataType _) Nothing _ [] _) = Nothing
-changeDecl allComments indentSize (H.DataDecl block (H.DataType _) Nothing dhead decls derivings)
+changeDecl allComments cfg@Config{..} (H.DataDecl block (H.DataType _) Nothing dhead decls derivings)
   | hasRecordFields = Just $ change block (const $ concat newLines)
   | otherwise       = Nothing
   where
@@ -54,27 +72,55 @@ changeDecl allComments indentSize (H.DataDecl block (H.DataType _) Nothing dhead
                   (H.QualConDecl _ _ _ (H.RecDecl {})) -> True
                   _ -> False)
       decls
-    newLines = fmap constructors zipped ++ [fmap (indented . H.prettyPrint) derivings]
+
+    typeConstructor = "data " <> H.prettyPrint dhead
+
+    -- In any case set @pipeIndent@ such that @|@ is aligned with @=@.
+    (firstLine, firstLineInit, pipeIndent) =
+      case cEquals of
+        SameLine -> (Nothing, typeConstructor <> " = ", length typeConstructor + 1)
+        Indent n -> (Just [[typeConstructor]], indent n "= ", n)
+
+    newLines = fromMaybe [] firstLine ++ fmap constructors zipped <> [fmap (indent cDeriving . H.prettyPrint) derivings]
     zipped = zip decls ([1..] ::[Int])
-    constructors (decl, 1) = processConstructor allComments typeConstructor indentSize decl
-    constructors (decl, _) = processConstructor allComments (indented "| ") indentSize decl
-    typeConstructor = "data " <> H.prettyPrint dhead <> " = "
-    indented = indent indentSize
+
+    constructors (decl, 1) = processConstructor allComments firstLineInit cfg decl
+    constructors (decl, _) = processConstructor allComments (indent pipeIndent "| ") cfg decl
 changeDecl _ _ _ = Nothing
 
-processConstructor :: [Comment] -> String -> Int -> H.QualConDecl LineBlock -> [String]
-processConstructor allComments init indentSize (H.QualConDecl _ _ _ (H.RecDecl _ dname fields)) = do
-  init <> H.prettyPrint dname : n1 ++ ns ++ [indented "}"]
+processConstructor :: [Comment] -> String -> Config -> H.QualConDecl LineBlock -> [String]
+processConstructor allComments init Config{..} (H.QualConDecl _ _ _ (H.RecDecl _ dname (f:fs))) = do
+  fromMaybe [] firstLine <> n1 <> ns <> [indent fieldIndent "}"]
   where
-    n1 = processName "{ " ( extractField $ head fields)
-    ns = tail fields >>= (processName ", " . extractField)
+    n1 = processName firstLinePrefix (extractField f)
+    ns = fs >>= processName (indent fieldIndent ", ") . extractField
+
+    -- Set @fieldIndent@ such that @,@ is aligned with @{@.
+    (firstLine, firstLinePrefix, fieldIndent) =
+      case cFirstField of
+        SameLine ->
+          ( Nothing
+          , init <> H.prettyPrint dname <> " { "
+          , length init + length (H.prettyPrint dname) + 1
+          )
+        Indent n ->
+          ( Just [init <> H.prettyPrint dname]
+          , indent (length init + n) "{ "
+          , length init + n
+          )
+
     processName prefix (fnames, _type, lineComment, commentBelowLine) =
-      [indented prefix <> intercalate ", " (fmap H.prettyPrint fnames) <> " :: " <> H.prettyPrint _type <> addLineComment lineComment] ++ addCommentBelow commentBelowLine
+      [prefix <> intercalate ", " (fmap H.prettyPrint fnames) <> " :: " <> H.prettyPrint _type <> addLineComment lineComment
+      ] ++ addCommentBelow commentBelowLine
+
     addLineComment (Just (Comment _ _ c)) = " --" <> c
     addLineComment Nothing                = ""
+
+    -- Field comment indent is measured from the column with @{@, hence adding of @fieldIndent@ here.
     addCommentBelow Nothing                = []
-    addCommentBelow (Just (Comment _ _ c)) = [indented "--" <> c]
+    addCommentBelow (Just (Comment _ _ c)) = [indent (fieldIndent + cFieldComment) "--" <> c]
+
     extractField (H.FieldDecl lb names _type) =
       (names, _type, findCommentOnLine lb allComments, findCommentBelowLine lb allComments)
-    indented = indent indentSize
+
 processConstructor _ init _ decl = [init <> trimLeft (H.prettyPrint decl)]