Implement experimental semicolon-into-newlines feature

src-literatetests/Main.hs

@@ -179,6 +179,7 @@ defaultTestConfig = Config
     , _lconfig_reformatModulePreamble    = coerce True
     , _lconfig_allowSingleLineExportList = coerce True
     , _lconfig_allowHangingQuasiQuotes   = coerce True
+    , _lconfig_experimentalSemicolonNewlines = coerce False
     }
   , _conf_errorHandling             = (_conf_errorHandling staticDefaultConfig)
     { _econf_omit_output_valid_check = coerce True

src-unittests/TestUtils.hs

@@ -60,6 +60,7 @@ defaultTestConfig = Config
     , _lconfig_reformatModulePreamble    = coerce True
     , _lconfig_allowSingleLineExportList = coerce True
     , _lconfig_allowHangingQuasiQuotes   = coerce True
+    , _lconfig_experimentalSemicolonNewlines = coerce False
     }
   , _conf_errorHandling             = (_conf_errorHandling staticDefaultConfig)
     { _econf_ExactPrintFallback = coerce ExactPrintFallbackModeNever

src/Language/Haskell/Brittany/Internal/Backend.hs

@@ -225,11 +225,18 @@ layoutBriDocM = \case
       -- mModify $ \s -> s { _lstate_curYOrAddNewline = Right 0 }
   BDAnnotationRest annKey bd -> do
     layoutBriDocM bd
-    mComments <- do
+    annMay <- do
       state <- mGet
       let m = _lstate_comments state
-      let mComments = nonEmpty =<< extractAllComments <$> Map.lookup annKey m
-      mSet $ state
+      pure $ Map.lookup annKey m
+    let mComments = nonEmpty =<< extractAllComments <$> annMay
+    let semiCount = length [ ()
+                | Just ann <- [ annMay ]
+                , (ExactPrint.Types.AnnSemiSep, _) <- ExactPrint.Types.annsDP ann
+                ]
+    shouldAddSemicolonNewlines <- mAsk <&>
+      _conf_layout .> _lconfig_experimentalSemicolonNewlines .> confUnpack
+    mModify $ \state -> state
       { _lstate_comments = Map.adjust
         ( \ann -> ann { ExactPrint.annFollowingComments = []
                       , ExactPrint.annPriorComments     = []
@@ -240,11 +247,12 @@ layoutBriDocM = \case
                       }
         )
         annKey
-          m
+        (_lstate_comments state)
       }
-      return mComments
     case mComments of
-      Nothing -> pure ()
+      Nothing -> do
+        when shouldAddSemicolonNewlines $ do
+          [1..semiCount] `forM_` \_ -> layoutWriteNewline
       Just comments -> do
         comments `forM_` \(ExactPrint.Types.Comment comment _ _, ExactPrint.Types.DP (y, x)) ->
           when (not $ comment == "(" || comment == ")") $ do

src/Language/Haskell/Brittany/Internal/Config.hs

@@ -76,6 +76,7 @@ staticDefaultConfig = Config
     , _lconfig_reformatModulePreamble    = coerce True
     , _lconfig_allowSingleLineExportList = coerce False
     , _lconfig_allowHangingQuasiQuotes   = coerce True
+    , _lconfig_experimentalSemicolonNewlines = coerce False
     }
   , _conf_errorHandling = ErrorHandlingConfig
     { _econf_produceOutputOnErrors   = coerce False
@@ -179,6 +180,7 @@ cmdlineConfigParser = do
       , _lconfig_reformatModulePreamble    = mempty
       , _lconfig_allowSingleLineExportList = mempty
       , _lconfig_allowHangingQuasiQuotes   = mempty
+      , _lconfig_experimentalSemicolonNewlines = mempty
       }
     , _conf_errorHandling = ErrorHandlingConfig
       { _econf_produceOutputOnErrors   = wrapLast $ falseToNothing outputOnErrors

src/Language/Haskell/Brittany/Internal/Config/Types.hs

@@ -127,6 +127,21 @@ data CLayoutConfig f = LayoutConfig
     -- > let body = [json|
     -- >     hello
     -- >     |]
+  , _lconfig_experimentalSemicolonNewlines :: f (Last Bool)
+    -- enables an experimental feature to turn semicolons in brace notation
+    -- into newlines when using layout:
+    --
+    -- > do { a ;; b }
+    --
+    -- turns into
+    -- > do
+    -- >   a
+    -- >
+    -- >   b
+    --
+    -- The implementation for this is a bit hacky and not tested; it might
+    -- break output syntax or not work properly for every kind of brace. So
+    -- far I have considered `do` and `case-of`.
   }
   deriving (Generic)