ghc-exactprint-0.6: src/Language/Haskell/GHC/ExactPrint/Transform.hs

{-# LANGUAGE CPP #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE ViewPatterns #-}
-----------------------------------------------------------------------------
-- |
-- Module      :  Language.Haskell.GHC.ExactPrint.Transform
--
-- This module is currently under heavy development, and no promises are made
-- about API stability. Use with care.
--
-- We welcome any feedback / contributions on this, as it is the main point of
-- the library.
--
-----------------------------------------------------------------------------
module Language.Haskell.GHC.ExactPrint.Transform
        (
        -- * The Transform Monad
          Transform
        , TransformT(..)
        , hoistTransform
        , runTransform
        , runTransformT
        , runTransformFrom
        , runTransformFromT

        -- * Transform monad operations
        , logTr
        , logDataWithAnnsTr
        , getAnnsT, putAnnsT, modifyAnnsT
        , uniqueSrcSpanT

        , cloneT
        , graftT

        , getEntryDPT
        , setEntryDPT
        , transferEntryDPT
        , setPrecedingLinesDeclT
        , setPrecedingLinesT
        , addSimpleAnnT
        , addTrailingCommaT
        , removeTrailingCommaT

        -- ** Managing declarations, in Transform monad
        , HasTransform (..)
        , HasDecls (..)
        , hasDeclsSybTransform
        , hsDeclsGeneric
        , hsDeclsPatBind, hsDeclsPatBindD
        , replaceDeclsPatBind, replaceDeclsPatBindD
        , modifyDeclsT
        , modifyValD
        -- *** Utility, does not manage layout
        , hsDeclsValBinds, replaceDeclsValbinds

        -- ** Managing lists, Transform monad
        , insertAtStart
        , insertAtEnd
        , insertAfter
        , insertBefore

        -- *** Low level operations used in 'HasDecls'
        , balanceComments
        , balanceTrailingComments
        , moveTrailingComments

        -- ** Managing lists, pure functions
        , captureOrder
        , captureOrderAnnKey

        -- * Operations
        , isUniqueSrcSpan

        -- * Pure functions
        , mergeAnns
        , mergeAnnList
        , setPrecedingLinesDecl
        , setPrecedingLines
        , getEntryDP
        , setEntryDP
        , transferEntryDP
        , addTrailingComma
        , wrapSig, wrapDecl
        , decl2Sig, decl2Bind

        ) where

import Language.Haskell.GHC.ExactPrint.Types
import Language.Haskell.GHC.ExactPrint.Utils

import Control.Monad.RWS
import qualified Control.Monad.Fail as Fail

import qualified Bag           as GHC
import qualified FastString    as GHC
import qualified GHC           as GHC hiding (parseModule)

import qualified Data.Generics as SYB

import Data.Data
import Data.List
import Data.Maybe

import qualified Data.Map as Map

import Data.Functor.Identity
import Control.Monad.State
import Control.Monad.Writer

-- import Debug.Trace

------------------------------------------------------------------------------
-- Transformation of source elements

-- | Monad type for updating the AST and managing the annotations at the same
-- time. The W state is used to generate logging information if required.
type Transform = TransformT Identity

-- |Monad transformer version of 'Transform' monad
newtype TransformT m a = TransformT { unTransformT :: RWST () [String] (Anns,Int) m a }
                deriving (Monad,Applicative,Functor
                         ,MonadReader ()
                         ,MonadWriter [String]
                         ,MonadState (Anns,Int)
                         ,MonadTrans
                         )

instance Fail.MonadFail m => Fail.MonadFail (TransformT m) where
    fail msg = TransformT $ RWST $ \_ _ -> Fail.fail msg

-- | Run a transformation in the 'Transform' monad, returning the updated
-- annotations and any logging generated via 'logTr'
runTransform :: Anns -> Transform a -> (a,(Anns,Int),[String])
runTransform ans f = runTransformFrom 0 ans f

runTransformT :: Anns -> TransformT m a -> m (a,(Anns,Int),[String])
runTransformT ans f = runTransformFromT 0 ans f

-- | Run a transformation in the 'Transform' monad, returning the updated
-- annotations and any logging generated via 'logTr', allocating any new
-- SrcSpans from the provided initial value.
runTransformFrom :: Int -> Anns -> Transform a -> (a,(Anns,Int),[String])
runTransformFrom seed ans f = runRWS (unTransformT f) () (ans,seed)

-- |Run a monad transformer stack for the 'TransformT' monad transformer
runTransformFromT :: Int -> Anns -> TransformT m a -> m (a,(Anns,Int),[String])
runTransformFromT seed ans f = runRWST (unTransformT f) () (ans,seed)

-- | Change inner monad of 'TransformT'.
hoistTransform :: (forall x. m x -> n x) -> TransformT m a -> TransformT n a
hoistTransform nt (TransformT m) = TransformT (mapRWST nt m)

-- |Log a string to the output of the Monad
logTr :: (Monad m) => String -> TransformT m ()
logTr str = tell [str]

-- |Log a representation of the given AST with annotations to the output of the
-- Monad
logDataWithAnnsTr :: (Monad m) => (SYB.Data a) => String -> a -> TransformT m ()
logDataWithAnnsTr str ast = do
  anns <- getAnnsT
  logTr $ str ++ showAnnData anns 0 ast

-- |Access the 'Anns' being modified in this transformation
getAnnsT :: (Monad m) => TransformT m Anns
getAnnsT = gets fst

-- |Replace the 'Anns' after any changes
putAnnsT :: (Monad m) => Anns -> TransformT m ()
putAnnsT ans = do
  (_,col) <- get
  put (ans,col)

-- |Change the stored 'Anns'
modifyAnnsT :: (Monad m) => (Anns -> Anns) -> TransformT m ()
modifyAnnsT f = do
  ans <- getAnnsT
  putAnnsT (f ans)

-- ---------------------------------------------------------------------

-- |Once we have 'Anns', a 'GHC.SrcSpan' is used purely as part of an 'AnnKey'
-- to index into the 'Anns'. If we need to add new elements to the AST, they
-- need their own 'GHC.SrcSpan' for this.
uniqueSrcSpanT :: (Monad m) => TransformT m GHC.SrcSpan
uniqueSrcSpanT = do
  (an,col) <- get
  put (an,col + 1 )
  let pos = GHC.mkSrcLoc (GHC.mkFastString "ghc-exactprint") (-1) col
  return $ GHC.mkSrcSpan pos pos

-- |Test whether a given 'GHC.SrcSpan' was generated by 'uniqueSrcSpanT'
isUniqueSrcSpan :: GHC.SrcSpan -> Bool
isUniqueSrcSpan ss = srcSpanStartLine ss == -1

-- ---------------------------------------------------------------------
-- |Make a copy of an AST element, replacing the existing SrcSpans with new
-- ones, and duplicating the matching annotations.
cloneT :: (Data a,Monad m) => a -> TransformT m (a, [(GHC.SrcSpan, GHC.SrcSpan)])
cloneT ast = do
  runWriterT $ SYB.everywhereM (return `SYB.ext2M` replaceLocated) ast
  where
    replaceLocated :: forall loc a m. (Typeable loc,Data a,Monad m)
                    => (GHC.GenLocated loc a) -> WriterT [(GHC.SrcSpan, GHC.SrcSpan)] (TransformT m) (GHC.GenLocated loc a)
    replaceLocated (GHC.L l t) = do
      case cast l :: Maybe GHC.SrcSpan of
        Just ss -> do
          newSpan <- lift uniqueSrcSpanT
          lift $ modifyAnnsT (\anns -> case Map.lookup (mkAnnKey (GHC.L ss t)) anns of
                                  Nothing -> anns
                                  Just an -> Map.insert (mkAnnKey (GHC.L newSpan t)) an anns)
          tell [(ss, newSpan)]
          return $ fromJust . cast  $ GHC.L newSpan t
        Nothing -> return (GHC.L l t)

-- ---------------------------------------------------------------------
-- |Slightly more general form of cloneT
graftT :: (Data a,Monad m) => Anns -> a -> TransformT m a
graftT origAnns = SYB.everywhereM (return `SYB.ext2M` replaceLocated)
  where
    replaceLocated :: forall loc a m. (Typeable loc, Data a, Monad m)
                    => GHC.GenLocated loc a -> TransformT m (GHC.GenLocated loc a)
    replaceLocated (GHC.L l t) = do
      case cast l :: Maybe GHC.SrcSpan of
        Just ss -> do
          newSpan <- uniqueSrcSpanT
          modifyAnnsT (\anns -> case Map.lookup (mkAnnKey (GHC.L ss t)) origAnns of
                                  Nothing -> anns
                                  Just an -> Map.insert (mkAnnKey (GHC.L newSpan t)) an anns)
          return $ fromJust $ cast $ GHC.L newSpan t
        Nothing -> return (GHC.L l t)

-- ---------------------------------------------------------------------

-- |If a list has been re-ordered or had items added, capture the new order in
-- the appropriate 'annSortKey' attached to the 'Annotation' for the first
-- parameter.
captureOrder :: (Data a) => GHC.Located a -> [GHC.Located b] -> Anns -> Anns
captureOrder parent ls ans = captureOrderAnnKey (mkAnnKey parent) ls ans

-- |If a list has been re-ordered or had items added, capture the new order in
-- the appropriate 'annSortKey' item of the supplied 'AnnKey'
captureOrderAnnKey :: AnnKey -> [GHC.Located b] -> Anns -> Anns
captureOrderAnnKey parentKey ls ans = ans'
  where
    newList = map GHC.getLoc ls
    reList = Map.adjust (\an -> an {annSortKey = Just newList }) parentKey
    ans' = reList ans

-- ---------------------------------------------------------------------

-- |Pure function to convert a 'GHC.LHsDecl' to a 'GHC.LHsBind'. This does
-- nothing to any annotations that may be attached to either of the elements.
-- It is used as a utility function in 'replaceDecls'
decl2Bind :: GHC.LHsDecl name -> [GHC.LHsBind name]
#if __GLASGOW_HASKELL__ > 804
decl2Bind (GHC.L l (GHC.ValD _ s)) = [GHC.L l s]
#else
decl2Bind (GHC.L l (GHC.ValD s)) = [GHC.L l s]
#endif
decl2Bind _                      = []

-- |Pure function to convert a 'GHC.LSig' to a 'GHC.LHsBind'. This does
-- nothing to any annotations that may be attached to either of the elements.
-- It is used as a utility function in 'replaceDecls'
decl2Sig :: GHC.LHsDecl name -> [GHC.LSig name]
#if __GLASGOW_HASKELL__ > 804
decl2Sig (GHC.L l (GHC.SigD _ s)) = [GHC.L l s]
#else
decl2Sig (GHC.L l (GHC.SigD s)) = [GHC.L l s]
#endif
decl2Sig _                      = []

-- ---------------------------------------------------------------------

-- |Convert a 'GHC.LSig' into a 'GHC.LHsDecl'
wrapSig :: GHC.LSig GhcPs -> GHC.LHsDecl GhcPs
#if __GLASGOW_HASKELL__ > 804
wrapSig (GHC.L l s) = GHC.L l (GHC.SigD GHC.noExt s)
#else
wrapSig (GHC.L l s) = GHC.L l (GHC.SigD s)
#endif

-- ---------------------------------------------------------------------

-- |Convert a 'GHC.LHsBind' into a 'GHC.LHsDecl'
wrapDecl :: GHC.LHsBind GhcPs -> GHC.LHsDecl GhcPs
#if __GLASGOW_HASKELL__ > 804
wrapDecl (GHC.L l s) = GHC.L l (GHC.ValD GHC.noExt s)
#else
wrapDecl (GHC.L l s) = GHC.L l (GHC.ValD s)
#endif

-- ---------------------------------------------------------------------

-- |Create a simple 'Annotation' without comments, and attach it to the first
-- parameter.
addSimpleAnnT :: (Data a,Monad m) => GHC.Located a -> DeltaPos -> [(KeywordId, DeltaPos)] -> TransformT m ()
addSimpleAnnT ast dp kds = do
  let ann = annNone { annEntryDelta = dp
                    , annsDP = kds
                    }
  modifyAnnsT (Map.insert (mkAnnKey ast) ann)

-- ---------------------------------------------------------------------

-- |Add a trailing comma annotation, unless there is already one
addTrailingCommaT :: (Data a,Monad m) => GHC.Located a -> TransformT m ()
addTrailingCommaT ast = do
  modifyAnnsT (addTrailingComma ast (DP (0,0)))

-- ---------------------------------------------------------------------

-- |Remove a trailing comma annotation, if there is one one
removeTrailingCommaT :: (Data a,Monad m) => GHC.Located a -> TransformT m ()
removeTrailingCommaT ast = do
  modifyAnnsT (removeTrailingComma ast)

-- ---------------------------------------------------------------------

-- |'Transform' monad version of 'getEntryDP'
getEntryDPT :: (Data a,Monad m) => GHC.Located a -> TransformT m DeltaPos
getEntryDPT ast = do
  anns <- getAnnsT
  return (getEntryDP anns ast)

-- ---------------------------------------------------------------------

-- |'Transform' monad version of 'getEntryDP'
setEntryDPT :: (Data a,Monad m) => GHC.Located a -> DeltaPos -> TransformT m ()
setEntryDPT ast dp = do
  modifyAnnsT (setEntryDP ast dp)

-- ---------------------------------------------------------------------

-- |'Transform' monad version of 'transferEntryDP'
transferEntryDPT :: (Data a,Data b,Monad m) => GHC.Located a -> GHC.Located b -> TransformT m ()
transferEntryDPT a b =
  modifyAnnsT (transferEntryDP a b)

-- ---------------------------------------------------------------------

-- |'Transform' monad version of 'setPrecedingLinesDecl'
setPrecedingLinesDeclT :: (Monad m) => GHC.LHsDecl GhcPs -> Int -> Int -> TransformT m ()
setPrecedingLinesDeclT ld n c =
  modifyAnnsT (setPrecedingLinesDecl ld n c)

-- ---------------------------------------------------------------------

-- |'Transform' monad version of 'setPrecedingLines'
setPrecedingLinesT ::  (SYB.Data a,Monad m) => GHC.Located a -> Int -> Int -> TransformT m ()
setPrecedingLinesT ld n c =
  modifyAnnsT (setPrecedingLines ld n c)

-- ---------------------------------------------------------------------

-- | Left bias pair union
mergeAnns :: Anns -> Anns -> Anns
mergeAnns
  = Map.union

-- |Combine a list of annotations
mergeAnnList :: [Anns] -> Anns
mergeAnnList [] = error "mergeAnnList must have at lease one entry"
mergeAnnList (x:xs) = foldr mergeAnns x xs

-- ---------------------------------------------------------------------

-- |Unwrap a HsDecl and call setPrecedingLines on it
-- ++AZ++ TODO: get rid of this, it is a synonym only
setPrecedingLinesDecl :: GHC.LHsDecl GhcPs -> Int -> Int -> Anns -> Anns
setPrecedingLinesDecl ld n c ans = setPrecedingLines ld n c ans

-- ---------------------------------------------------------------------

-- | Adjust the entry annotations to provide an `n` line preceding gap
setPrecedingLines :: (SYB.Data a) => GHC.Located a -> Int -> Int -> Anns -> Anns
setPrecedingLines ast n c anne = setEntryDP ast (DP (n,c)) anne

-- ---------------------------------------------------------------------

-- |Return the true entry 'DeltaPos' from the annotation for a given AST
-- element. This is the 'DeltaPos' ignoring any comments.
getEntryDP :: (Data a) => Anns -> GHC.Located a -> DeltaPos
getEntryDP anns ast =
  case Map.lookup (mkAnnKey ast) anns of
    Nothing  -> DP (0,0)
    Just ann -> annTrueEntryDelta ann

-- ---------------------------------------------------------------------

-- |Set the true entry 'DeltaPos' from the annotation for a given AST
-- element. This is the 'DeltaPos' ignoring any comments.
setEntryDP :: (Data a) => GHC.Located a -> DeltaPos -> Anns -> Anns
setEntryDP ast dp anns =
  case Map.lookup (mkAnnKey ast) anns of
    Nothing  -> Map.insert (mkAnnKey ast) (annNone { annEntryDelta = dp}) anns
    Just ann -> Map.insert (mkAnnKey ast) (ann'    { annEntryDelta = annCommentEntryDelta ann' dp}) anns
      where
        ann' = setCommentEntryDP ann dp

-- ---------------------------------------------------------------------

-- |When setting an entryDP, the leading comment needs to be adjusted too
setCommentEntryDP :: Annotation -> DeltaPos -> Annotation
-- setCommentEntryDP ann dp = error $ "setCommentEntryDP:ann'=" ++ show ann'
setCommentEntryDP ann dp = ann'
  where
    ann' = case (annPriorComments ann) of
      [] -> ann
      [(pc,_)]     -> ann { annPriorComments = [(pc,dp)] }
      ((pc,_):pcs) -> ann { annPriorComments = ((pc,dp):pcs) }

-- ---------------------------------------------------------------------

-- |Take the annEntryDelta associated with the first item and associate it with the second.
-- Also transfer any comments occuring before it.
transferEntryDP :: (SYB.Data a, SYB.Data b) => GHC.Located a -> GHC.Located b -> Anns -> Anns
transferEntryDP a b anns = (const anns2) anns
  where
    maybeAnns = do -- Maybe monad
      anA <- Map.lookup (mkAnnKey a) anns
      anB <- Map.lookup (mkAnnKey b) anns
      let anB'  = Ann
            { annEntryDelta        = DP (0,0) -- Need to adjust for comments after
            , annPriorComments     = annPriorComments     anB
            , annFollowingComments = annFollowingComments anB
            , annsDP               = annsDP          anB
            , annSortKey           = annSortKey      anB
            , annCapturedSpan      = annCapturedSpan anB
            }
      return ((Map.insert (mkAnnKey b) anB' anns),annLeadingCommentEntryDelta anA)
    (anns',dp) = fromMaybe
                  (error $ "transferEntryDP: lookup failed (a,b)=" ++ show (mkAnnKey a,mkAnnKey b))
                  maybeAnns
    anns2 = setEntryDP b dp anns'

-- ---------------------------------------------------------------------

addTrailingComma :: (SYB.Data a) => GHC.Located a -> DeltaPos -> Anns -> Anns
addTrailingComma a dp anns =
  case Map.lookup (mkAnnKey a) anns of
    Nothing -> anns
    Just an ->
      case find isAnnComma (annsDP an) of
        Nothing -> Map.insert (mkAnnKey a) (an { annsDP = annsDP an ++ [(G GHC.AnnComma,dp)]}) anns
        Just _  -> anns
      where
        isAnnComma (G GHC.AnnComma,_) = True
        isAnnComma _                  = False

-- ---------------------------------------------------------------------

removeTrailingComma :: (SYB.Data a) => GHC.Located a -> Anns -> Anns
removeTrailingComma a anns =
  case Map.lookup (mkAnnKey a) anns of
    Nothing -> anns
    Just an ->
      case find isAnnComma (annsDP an) of
        Nothing -> anns
        Just _  -> Map.insert (mkAnnKey a) (an { annsDP = filter (not.isAnnComma) (annsDP an) }) anns
      where
        isAnnComma (G GHC.AnnComma,_) = True
        isAnnComma _                  = False

-- ---------------------------------------------------------------------

-- |The relatavise phase puts all comments appearing between the end of one AST
-- item and the beginning of the next as 'annPriorComments' for the second one.
-- This function takes two adjacent AST items and moves any 'annPriorComments'
-- from the second one to the 'annFollowingComments' of the first if they belong
-- to it instead. This is typically required before deleting or duplicating
-- either of the AST elements.
balanceComments :: (Data a,Data b,Monad m) => GHC.Located a -> GHC.Located b -> TransformT m ()
balanceComments first second = do
  -- ++AZ++ : replace the nested casts with appropriate SYB.gmapM
  -- logTr $ "balanceComments entered"
  -- logDataWithAnnsTr "first" first
  case cast first :: Maybe (GHC.LHsDecl GhcPs) of
#if __GLASGOW_HASKELL__ > 804
    Just (GHC.L l (GHC.ValD _ fb@(GHC.FunBind{}))) -> do
#else
    Just (GHC.L l (GHC.ValD   fb@(GHC.FunBind{}))) -> do
#endif
      balanceCommentsFB (GHC.L l fb) second
    _ -> case cast first :: Maybe (GHC.LHsBind GhcPs) of
      Just fb'@(GHC.L _ (GHC.FunBind{})) -> do
        balanceCommentsFB fb' second
      _ -> balanceComments' first second

-- |Prior to moving an AST element, make sure any trailing comments belonging to
-- it are attached to it, and not the following element. Of necessity this is a
-- heuristic process, to be tuned later. Possibly a variant should be provided
-- with a passed-in decision function.
balanceComments' :: (Data a,Data b,Monad m) => GHC.Located a -> GHC.Located b -> TransformT m ()
balanceComments' first second = do
  let
    k1 = mkAnnKey first
    k2 = mkAnnKey second
    moveComments p ans = ans'
      where
        an1 = gfromJust "balanceComments' k1" $ Map.lookup k1 ans
        an2 = gfromJust "balanceComments' k2" $ Map.lookup k2 ans
        cs1f = annFollowingComments an1
        cs2b = annPriorComments an2
        (move,stay) = break p cs2b
        an1' = an1 { annFollowingComments = cs1f ++ move}
        an2' = an2 { annPriorComments = stay}
        ans' = Map.insert k1 an1' $ Map.insert k2 an2' ans

    simpleBreak (_,DP (r,_c)) = r > 0

  modifyAnnsT (moveComments simpleBreak)

-- |Once 'balanceComments' has been called to move trailing comments to a
-- 'GHC.FunBind', these need to be pushed down from the top level to the last
-- 'GHC.Match' if that 'GHC.Match' needs to be manipulated.
balanceCommentsFB :: (Data b,Monad m) => GHC.LHsBind GhcPs -> GHC.Located b -> TransformT m ()
#if __GLASGOW_HASKELL__ > 804
balanceCommentsFB (GHC.L _ (GHC.FunBind _ _ (GHC.MG _ (GHC.L _ matches) _) _ _)) second = do
#elif __GLASGOW_HASKELL__ > 710
balanceCommentsFB (GHC.L _ (GHC.FunBind _ (GHC.MG (GHC.L _ matches) _ _ _) _ _ _)) second = do
#else
balanceCommentsFB (GHC.L _ (GHC.FunBind _ _ (GHC.MG matches _ _ _) _ _ _)) second = do
#endif
  -- logTr $ "balanceCommentsFB entered"
  balanceComments' (last matches) second
balanceCommentsFB f s = balanceComments' f s

-- ---------------------------------------------------------------------


-- |After moving an AST element, make sure any comments that may belong
-- with the following element in fact do. Of necessity this is a heuristic
-- process, to be tuned later. Possibly a variant should be provided with a
-- passed-in decision function.
balanceTrailingComments :: (Monad m) => (Data a,Data b) => GHC.Located a -> GHC.Located b
                        -> TransformT m [(Comment, DeltaPos)]
balanceTrailingComments first second = do
  let
    k1 = mkAnnKey first
    k2 = mkAnnKey second
    moveComments p ans = (ans',move)
      where
        an1 = gfromJust "balanceTrailingComments k1" $ Map.lookup k1 ans
        an2 = gfromJust "balanceTrailingComments k2" $ Map.lookup k2 ans
        cs1f = annFollowingComments an1
        (move,stay) = break p cs1f
        an1' = an1 { annFollowingComments = stay }
        ans' = Map.insert k1 an1' $ Map.insert k2 an2 ans

    simpleBreak (_,DP (r,_c)) = r > 0

  ans <- getAnnsT
  let (ans',mov) = moveComments simpleBreak ans
  putAnnsT ans'
  return mov

-- ---------------------------------------------------------------------

-- ++AZ++ TODO: This needs to be renamed/reworked, based on what it actually gets used for
-- |Move any 'annFollowingComments' values from the 'Annotation' associated to
-- the first parameter to that of the second.
moveTrailingComments :: (Data a,Data b)
                     => GHC.Located a -> GHC.Located b -> Transform ()
moveTrailingComments first second = do
  let
    k1 = mkAnnKey first
    k2 = mkAnnKey second
    moveComments ans = ans'
      where
        an1 = gfromJust "moveTrailingComments k1" $ Map.lookup k1 ans
        an2 = gfromJust "moveTrailingComments k2" $ Map.lookup k2 ans
        cs1f = annFollowingComments an1
        cs2f = annFollowingComments an2
        an1' = an1 { annFollowingComments = [] }
        an2' = an2 { annFollowingComments = cs1f ++ cs2f }
        ans' = Map.insert k1 an1' $ Map.insert k2 an2' ans

  modifyAnnsT moveComments

-- ---------------------------------------------------------------------

-- |Insert a declaration into an AST element having sub-declarations
-- (@HasDecls@) according to the given location function.
insertAt :: (HasDecls (GHC.Located ast))
              => (GHC.LHsDecl GhcPs
                  -> [GHC.LHsDecl GhcPs]
                  -> [GHC.LHsDecl GhcPs])
              -> GHC.Located ast
              -> GHC.LHsDecl GhcPs
              -> Transform (GHC.Located ast)
insertAt f t decl = do
  oldDecls <- hsDecls t
  replaceDecls t (f decl oldDecls)

-- |Insert a declaration at the beginning or end of the subdecls of the given
-- AST item
insertAtStart, insertAtEnd :: (HasDecls (GHC.Located ast))
              => GHC.Located ast
              -> GHC.LHsDecl GhcPs
              -> Transform (GHC.Located ast)

insertAtStart = insertAt (:)
insertAtEnd   = insertAt (\x xs -> xs ++ [x])

-- |Insert a declaration at a specific location in the subdecls of the given
-- AST item
insertAfter, insertBefore :: (HasDecls (GHC.Located ast))
                          => GHC.Located old
                          -> GHC.Located ast
                          -> GHC.LHsDecl GhcPs
                          -> Transform (GHC.Located ast)
insertAfter (GHC.getLoc -> k) = insertAt findAfter
  where
    findAfter x xs =
      let (fs, b:bs) = span (\(GHC.L l _) -> l /= k) xs
      in fs ++ (b : x : bs)
insertBefore (GHC.getLoc -> k) = insertAt findBefore
  where
    findBefore x xs =
      let (fs, bs) = span (\(GHC.L l _) -> l /= k) xs
      in fs ++ (x : bs)

-- =====================================================================
-- start of HasDecls instances
-- =====================================================================

-- |Provide a means to get and process the immediate child declartions of a
-- given AST element.
class (Data t) => HasDecls t where
-- ++AZ++: TODO: add tests to confirm that hsDecls followed by replaceDecls is idempotent

    -- | Return the 'GHC.HsDecl's that are directly enclosed in the
    -- given syntax phrase. They are always returned in the wrapped 'GHC.HsDecl'
    -- form, even if orginating in local decls. This is safe, as annotations
    -- never attach to the wrapper, only to the wrapped item.
    hsDecls :: (Monad m) => t -> TransformT m [GHC.LHsDecl GhcPs]

    -- | Replace the directly enclosed decl list by the given
    --  decl list. Runs in the 'Transform' monad to be able to update list order
    --  annotations, and rebalance comments and other layout changes as needed.
    --
    -- For example, a call on replaceDecls for a wrapped 'GHC.FunBind' having no
    -- where clause will convert
    --
    -- @
    -- -- |This is a function
    -- foo = x -- comment1
    -- @
    -- in to
    --
    -- @
    -- -- |This is a function
    -- foo = x -- comment1
    --   where
    --     nn = 2
    -- @
    replaceDecls :: (Monad m) => t -> [GHC.LHsDecl GhcPs] -> TransformT m t

-- ---------------------------------------------------------------------

instance HasDecls GHC.ParsedSource where
  hsDecls (GHC.L _ (GHC.HsModule _mn _exps _imps decls _ _)) = return decls
  replaceDecls m@(GHC.L l (GHC.HsModule mn exps imps _decls deps haddocks)) decls
    = do
        logTr "replaceDecls LHsModule"
        modifyAnnsT (captureOrder m decls)
        return (GHC.L l (GHC.HsModule mn exps imps decls deps haddocks))

-- ---------------------------------------------------------------------

instance HasDecls (GHC.LMatch GhcPs (GHC.LHsExpr GhcPs)) where
#if __GLASGOW_HASKELL__ > 804
  hsDecls d@(GHC.L _ (GHC.Match _ _ _ (GHC.GRHSs _ _ (GHC.L _ lb)))) = do
#elif __GLASGOW_HASKELL__ >= 804
  hsDecls d@(GHC.L _ (GHC.Match _ _ (GHC.GRHSs _ (GHC.L _ lb)))) = do
#elif __GLASGOW_HASKELL__ >= 800
  hsDecls d@(GHC.L _ (GHC.Match _ _ _ (GHC.GRHSs _ (GHC.L _ lb)))) = do
#elif __GLASGOW_HASKELL__ >= 710
  hsDecls d@(GHC.L _ (GHC.Match _ _ _ (GHC.GRHSs _ lb))) = do
#else
  hsDecls d@(GHC.L _ (GHC.Match _ _ _ (GHC.GRHSs _ lb))) = do
#endif
    decls <- hsDeclsValBinds lb
    orderedDecls d decls
#if __GLASGOW_HASKELL__ > 804
  hsDecls (GHC.L _ (GHC.Match _ _ _ (GHC.XGRHSs _))) = return []
  hsDecls (GHC.L _ (GHC.XMatch _))                   = return []
#endif


#if __GLASGOW_HASKELL__ > 804
  replaceDecls m@(GHC.L l (GHC.Match xm c p (GHC.GRHSs xr rhs binds))) []
#elif __GLASGOW_HASKELL__ >= 804
  replaceDecls m@(GHC.L l (GHC.Match c p (GHC.GRHSs rhs binds))) []
#else
  replaceDecls m@(GHC.L l (GHC.Match mf p t (GHC.GRHSs rhs binds))) []
#endif
    = do
        logTr "replaceDecls LMatch"
        let
          noWhere (G GHC.AnnWhere,_) = False
          noWhere _                  = True

          removeWhere mkds =
            case Map.lookup (mkAnnKey m) mkds of
              Nothing -> error "wtf"
              Just ann -> Map.insert (mkAnnKey m) ann1 mkds
                where
                  ann1 = ann { annsDP = filter noWhere (annsDP ann)
                                 }
        modifyAnnsT removeWhere

#if __GLASGOW_HASKELL__ <= 710
        binds' <- replaceDeclsValbinds binds []
#else
        binds'' <- replaceDeclsValbinds (GHC.unLoc binds) []
        let binds' = GHC.L (GHC.getLoc binds) binds''
#endif
#if __GLASGOW_HASKELL__ > 804
        return (GHC.L l (GHC.Match xm c p (GHC.GRHSs xr rhs binds')))
#elif __GLASGOW_HASKELL__ >= 804
        return (GHC.L l (GHC.Match c p (GHC.GRHSs rhs binds')))
#else
        return (GHC.L l (GHC.Match mf p t (GHC.GRHSs rhs binds')))
#endif

#if __GLASGOW_HASKELL__ > 804
  replaceDecls m@(GHC.L l (GHC.Match xm c p (GHC.GRHSs xr rhs binds))) newBinds
#elif __GLASGOW_HASKELL__ >= 804
  replaceDecls m@(GHC.L l (GHC.Match c p (GHC.GRHSs rhs binds))) newBinds
#else
  replaceDecls m@(GHC.L l (GHC.Match mf p t (GHC.GRHSs rhs binds))) newBinds
#endif
    = do
        logTr "replaceDecls LMatch"
        -- Need to throw in a fresh where clause if the binds were empty,
        -- in the annotations.
#if __GLASGOW_HASKELL__ <= 710
        case binds of
#else
        case GHC.unLoc binds of
#endif
#if __GLASGOW_HASKELL__ > 804
          GHC.EmptyLocalBinds{} -> do
#else
          GHC.EmptyLocalBinds -> do
#endif
            let
              addWhere mkds =
                case Map.lookup (mkAnnKey m) mkds of
                  Nothing -> error "wtf"
                  Just ann -> Map.insert (mkAnnKey m) ann1 mkds
                    where
                      ann1 = ann { annsDP = annsDP ann ++ [(G GHC.AnnWhere,DP (1,2))]
                                 }
            modifyAnnsT addWhere
            modifyAnnsT (setPrecedingLines (ghead "LMatch.replaceDecls" newBinds) 1 4)

            -- only move the comment if the original where clause was empty.
            toMove <- balanceTrailingComments m m
            insertCommentBefore (mkAnnKey m) toMove (matchApiAnn GHC.AnnWhere)
          _ -> return ()

        modifyAnnsT (captureOrderAnnKey (mkAnnKey m) newBinds)
#if __GLASGOW_HASKELL__ <= 710
        binds' <- replaceDeclsValbinds binds newBinds
#else
        binds'' <- replaceDeclsValbinds (GHC.unLoc binds) newBinds
        let binds' = GHC.L (GHC.getLoc binds) binds''
#endif
        -- logDataWithAnnsTr "Match.replaceDecls:binds'" binds'
#if __GLASGOW_HASKELL__ > 804
        return (GHC.L l (GHC.Match xm c p (GHC.GRHSs xr rhs binds')))
#elif __GLASGOW_HASKELL__ >= 804
        return (GHC.L l (GHC.Match c p (GHC.GRHSs rhs binds')))
#else
        return (GHC.L l (GHC.Match mf p t (GHC.GRHSs rhs binds')))
#endif
#if __GLASGOW_HASKELL__ > 804
  replaceDecls (GHC.L _ (GHC.Match _ _ _ (GHC.XGRHSs _))) _ = error "replaceDecls"
  replaceDecls (GHC.L _ (GHC.XMatch _)) _                   = error "replaceDecls"
#endif

-- ---------------------------------------------------------------------

instance HasDecls (GHC.LHsExpr GhcPs) where
#if __GLASGOW_HASKELL__ > 804
  hsDecls ls@(GHC.L _ (GHC.HsLet _ (GHC.L _ decls) _ex)) = do
#elif __GLASGOW_HASKELL__ > 710
  hsDecls ls@(GHC.L _ (GHC.HsLet (GHC.L _ decls) _ex)) = do
#else
  hsDecls ls@(GHC.L _ (GHC.HsLet decls _ex)) = do
#endif
    ds <- hsDeclsValBinds decls
    orderedDecls ls ds
  hsDecls _                               = return []

#if __GLASGOW_HASKELL__ > 804
  replaceDecls e@(GHC.L l (GHC.HsLet x decls ex)) newDecls
#else
  replaceDecls e@(GHC.L l (GHC.HsLet decls ex)) newDecls
#endif
    = do
        logTr "replaceDecls HsLet"
        modifyAnnsT (captureOrder e newDecls)
#if __GLASGOW_HASKELL__ <= 710
        decls' <- replaceDeclsValbinds decls newDecls
#else
        decls'' <- replaceDeclsValbinds (GHC.unLoc decls) newDecls
        let decls' = GHC.L (GHC.getLoc decls) decls''
#endif
#if __GLASGOW_HASKELL__ > 804
        return (GHC.L l (GHC.HsLet x decls' ex))
#else
        return (GHC.L l (GHC.HsLet decls' ex))
#endif

#if __GLASGOW_HASKELL__ > 804
  replaceDecls (GHC.L l (GHC.HsPar x e)) newDecls
#else
  replaceDecls (GHC.L l (GHC.HsPar e)) newDecls
#endif
    = do
        logTr "replaceDecls HsPar"
        e' <- replaceDecls e newDecls
#if __GLASGOW_HASKELL__ > 804
        return (GHC.L l (GHC.HsPar x e'))
#else
        return (GHC.L l (GHC.HsPar e'))
#endif
  replaceDecls old _new = error $ "replaceDecls (GHC.LHsExpr GhcPs) undefined for:" ++ showGhc old

-- ---------------------------------------------------------------------

-- | Extract the immediate declarations for a 'GHC.PatBind' wrapped in a 'GHC.ValD'. This
-- cannot be a member of 'HasDecls' because a 'GHC.FunBind' is not idempotent
-- for 'hsDecls' \/ 'replaceDecls'. 'hsDeclsPatBindD' \/ 'replaceDeclsPatBindD' is
-- idempotent.
hsDeclsPatBindD :: (Monad m) => GHC.LHsDecl GhcPs -> TransformT m [GHC.LHsDecl GhcPs]
#if __GLASGOW_HASKELL__ > 804
hsDeclsPatBindD (GHC.L l (GHC.ValD _ d)) = hsDeclsPatBind (GHC.L l d)
#else
hsDeclsPatBindD (GHC.L l (GHC.ValD d)) = hsDeclsPatBind (GHC.L l d)
#endif
hsDeclsPatBindD x = error $ "hsDeclsPatBindD called for:" ++ showGhc x

-- | Extract the immediate declarations for a 'GHC.PatBind'. This
-- cannot be a member of 'HasDecls' because a 'GHC.FunBind' is not idempotent
-- for 'hsDecls' \/ 'replaceDecls'. 'hsDeclsPatBind' \/ 'replaceDeclsPatBind' is
-- idempotent.
hsDeclsPatBind :: (Monad m) => GHC.LHsBind GhcPs -> TransformT m [GHC.LHsDecl GhcPs]
#if __GLASGOW_HASKELL__ > 804
hsDeclsPatBind d@(GHC.L _ (GHC.PatBind _ _ (GHC.GRHSs _ _grhs (GHC.L _ lb)) _)) = do
#elif __GLASGOW_HASKELL__ > 710
hsDeclsPatBind d@(GHC.L _ (GHC.PatBind _ (GHC.GRHSs _grhs (GHC.L _ lb)) _ _ _)) = do
#else
hsDeclsPatBind d@(GHC.L _ (GHC.PatBind _ (GHC.GRHSs _grhs lb) _ _ _)) = do
#endif
  decls <- hsDeclsValBinds lb
  orderedDecls d decls
hsDeclsPatBind x = error $ "hsDeclsPatBind called for:" ++ showGhc x

-- -------------------------------------

-- | Replace the immediate declarations for a 'GHC.PatBind' wrapped in a 'GHC.ValD'. This
-- cannot be a member of 'HasDecls' because a 'GHC.FunBind' is not idempotent
-- for 'hsDecls' \/ 'replaceDecls'. 'hsDeclsPatBindD' \/ 'replaceDeclsPatBindD' is
-- idempotent.
replaceDeclsPatBindD :: (Monad m) => GHC.LHsDecl GhcPs -> [GHC.LHsDecl GhcPs]
                     -> TransformT m (GHC.LHsDecl GhcPs)
#if __GLASGOW_HASKELL__ > 804
replaceDeclsPatBindD (GHC.L l (GHC.ValD x d)) newDecls = do
  (GHC.L _ d') <- replaceDeclsPatBind (GHC.L l d) newDecls
  return (GHC.L l (GHC.ValD x d'))
#else
replaceDeclsPatBindD (GHC.L l (GHC.ValD d)) newDecls = do
  (GHC.L _ d') <- replaceDeclsPatBind (GHC.L l d) newDecls
  return (GHC.L l (GHC.ValD d'))
#endif
replaceDeclsPatBindD x _ = error $ "replaceDeclsPatBindD called for:" ++ showGhc x

-- | Replace the immediate declarations for a 'GHC.PatBind'. This
-- cannot be a member of 'HasDecls' because a 'GHC.FunBind' is not idempotent
-- for 'hsDecls' \/ 'replaceDecls'. 'hsDeclsPatBind' \/ 'replaceDeclsPatBind' is
-- idempotent.
replaceDeclsPatBind :: (Monad m) => GHC.LHsBind GhcPs -> [GHC.LHsDecl GhcPs]
                    -> TransformT m (GHC.LHsBind GhcPs)
#if __GLASGOW_HASKELL__ > 804
replaceDeclsPatBind p@(GHC.L l (GHC.PatBind x a (GHC.GRHSs xr rhss binds) b)) newDecls
#else
replaceDeclsPatBind p@(GHC.L l (GHC.PatBind a (GHC.GRHSs rhss binds) b c d)) newDecls
#endif
    = do
        logTr "replaceDecls PatBind"
        -- Need to throw in a fresh where clause if the binds were empty,
        -- in the annotations.
#if __GLASGOW_HASKELL__ <= 710
        case binds of
#else
        case GHC.unLoc binds of
#endif
#if __GLASGOW_HASKELL__ > 804
          GHC.EmptyLocalBinds{} -> do
#else
          GHC.EmptyLocalBinds -> do
#endif
            let
              addWhere mkds =
                case Map.lookup (mkAnnKey p) mkds of
                  Nothing -> error "wtf"
                  Just ann -> Map.insert (mkAnnKey p) ann1 mkds
                    where
                      ann1 = ann { annsDP = annsDP ann ++ [(G GHC.AnnWhere,DP (1,2))]
                                 }
            modifyAnnsT addWhere
            modifyAnnsT (setPrecedingLines (ghead "LMatch.replaceDecls" newDecls) 1 4)

          _ -> return ()

        modifyAnnsT (captureOrderAnnKey (mkAnnKey p) newDecls)
#if __GLASGOW_HASKELL__ <= 710
        binds' <- replaceDeclsValbinds binds newDecls
#else
        binds'' <- replaceDeclsValbinds (GHC.unLoc binds) newDecls
        let binds' = GHC.L (GHC.getLoc binds) binds''
#endif
#if __GLASGOW_HASKELL__ > 804
        return (GHC.L l (GHC.PatBind x a (GHC.GRHSs xr rhss binds') b))
#else
        return (GHC.L l (GHC.PatBind a (GHC.GRHSs rhss binds') b c d))
#endif
replaceDeclsPatBind x _ = error $ "replaceDeclsPatBind called for:" ++ showGhc x

-- ---------------------------------------------------------------------

instance HasDecls (GHC.LStmt GhcPs (GHC.LHsExpr GhcPs)) where
#if __GLASGOW_HASKELL__ > 804
  hsDecls ls@(GHC.L _ (GHC.LetStmt _ (GHC.L _ lb))) = do
#elif __GLASGOW_HASKELL__ > 710
  hsDecls ls@(GHC.L _ (GHC.LetStmt (GHC.L _ lb))) = do
#else
  hsDecls ls@(GHC.L _ (GHC.LetStmt lb))       = do
#endif
    decls <- hsDeclsValBinds lb
    orderedDecls ls decls
#if __GLASGOW_HASKELL__ > 804
  hsDecls (GHC.L _ (GHC.LastStmt _ e _ _))    = hsDecls e
#elif __GLASGOW_HASKELL__ >= 804
  hsDecls (GHC.L _ (GHC.LastStmt e _ _))      = hsDecls e
#elif __GLASGOW_HASKELL__ > 800
  hsDecls (GHC.L _ (GHC.LastStmt e _ _))      = hsDecls e
#elif __GLASGOW_HASKELL__ > 710
  hsDecls (GHC.L _ (GHC.LastStmt e _ _))      = hsDecls e
#else
  hsDecls (GHC.L _ (GHC.LastStmt e _))        = hsDecls e
#endif
#if __GLASGOW_HASKELL__ > 804
  hsDecls (GHC.L _ (GHC.BindStmt _ _pat e _ _)) = hsDecls e
#elif __GLASGOW_HASKELL__ > 710
  hsDecls (GHC.L _ (GHC.BindStmt _pat e _ _ _)) = hsDecls e
#else
  hsDecls (GHC.L _ (GHC.BindStmt _pat e _ _)) = hsDecls e
#endif
#if __GLASGOW_HASKELL__ > 804
  hsDecls (GHC.L _ (GHC.BodyStmt _ e _ _))    = hsDecls e
#else
  hsDecls (GHC.L _ (GHC.BodyStmt e _ _ _))    = hsDecls e
#endif
  hsDecls _                                   = return []

#if __GLASGOW_HASKELL__ > 804
  replaceDecls s@(GHC.L l (GHC.LetStmt x lb)) newDecls
#else
  replaceDecls s@(GHC.L l (GHC.LetStmt lb)) newDecls
#endif
    = do
        modifyAnnsT (captureOrder s newDecls)
#if __GLASGOW_HASKELL__ <= 710
        lb' <- replaceDeclsValbinds lb newDecls
#else
        lb'' <- replaceDeclsValbinds (GHC.unLoc lb) newDecls
        let lb' = GHC.L (GHC.getLoc lb) lb''
#endif
#if __GLASGOW_HASKELL__ > 804
        return (GHC.L l (GHC.LetStmt x lb'))
#else
        return (GHC.L l (GHC.LetStmt   lb'))
#endif
#if __GLASGOW_HASKELL__ > 804
  replaceDecls (GHC.L l (GHC.LastStmt x e d se)) newDecls
    = do
        e' <- replaceDecls e newDecls
        return (GHC.L l (GHC.LastStmt x e' d se))
#elif __GLASGOW_HASKELL__ > 710
  replaceDecls (GHC.L l (GHC.LastStmt e d se)) newDecls
    = do
        e' <- replaceDecls e newDecls
        return (GHC.L l (GHC.LastStmt e' d se))
#else
  replaceDecls (GHC.L l (GHC.LastStmt e se)) newDecls
    = do
        e' <- replaceDecls e newDecls
        return (GHC.L l (GHC.LastStmt e' se))
#endif
#if __GLASGOW_HASKELL__ > 804
  replaceDecls (GHC.L l (GHC.BindStmt x pat e a b)) newDecls
    = do
      e' <- replaceDecls e newDecls
      return (GHC.L l (GHC.BindStmt x pat e' a b))
#elif __GLASGOW_HASKELL__ > 710
  replaceDecls (GHC.L l (GHC.BindStmt pat e a b c)) newDecls
    = do
      e' <- replaceDecls e newDecls
      return (GHC.L l (GHC.BindStmt pat e' a b c))
#else
  replaceDecls (GHC.L l (GHC.BindStmt pat e a b)) newDecls
    = do
      e' <- replaceDecls e newDecls
      return (GHC.L l (GHC.BindStmt pat e' a b))
#endif

#if __GLASGOW_HASKELL__ > 804
  replaceDecls (GHC.L l (GHC.BodyStmt x e a b)) newDecls
    = do
      e' <- replaceDecls e newDecls
      return (GHC.L l (GHC.BodyStmt x e' a b))
#else
  replaceDecls (GHC.L l (GHC.BodyStmt e a b c)) newDecls
    = do
      e' <- replaceDecls e newDecls
      return (GHC.L l (GHC.BodyStmt e' a b c))
#endif
  replaceDecls x _newDecls = return x

-- =====================================================================
-- end of HasDecls instances
-- =====================================================================

-- ---------------------------------------------------------------------

-- |Do a transformation on an AST fragment by providing a function to process
-- the general case and one specific for a 'GHC.LHsBind'. This is required
-- because a 'GHC.FunBind' may have multiple 'GHC.Match' items, so we cannot
-- gurantee that 'replaceDecls' after 'hsDecls' is idempotent.
hasDeclsSybTransform :: (SYB.Data t2,Monad m)
       => (forall t. HasDecls t => t -> m t)
             -- ^Worker function for the general case
       -> (GHC.LHsBind GhcPs -> m (GHC.LHsBind GhcPs))
             -- ^Worker function for FunBind/PatBind
       -> t2 -- ^Item to be updated
       -> m t2
hasDeclsSybTransform workerHasDecls workerBind t = trf t
  where
    trf = SYB.mkM   parsedSource
         `SYB.extM` lmatch
         `SYB.extM` lexpr
         `SYB.extM` lstmt
         `SYB.extM` lhsbind
         `SYB.extM` lvald

    parsedSource (p::GHC.ParsedSource) = workerHasDecls p

    lmatch (lm::GHC.LMatch GhcPs (GHC.LHsExpr GhcPs))
      = workerHasDecls lm

    lexpr (le::GHC.LHsExpr GhcPs)
      = workerHasDecls le

    lstmt (d::GHC.LStmt GhcPs (GHC.LHsExpr GhcPs))
      = workerHasDecls d

    lhsbind (b@(GHC.L _ GHC.FunBind{}):: GHC.LHsBind GhcPs)
      = workerBind b
    lhsbind b@(GHC.L _ GHC.PatBind{})
      = workerBind b
    lhsbind x = return x

#if __GLASGOW_HASKELL__ > 804
    lvald (GHC.L l (GHC.ValD x d)) = do
      (GHC.L _ d') <- lhsbind (GHC.L l d)
      return (GHC.L l (GHC.ValD x d'))
#else
    lvald (GHC.L l (GHC.ValD d)) = do
      (GHC.L _ d') <- lhsbind (GHC.L l d)
      return (GHC.L l (GHC.ValD d'))
#endif
    lvald x = return x

-- ---------------------------------------------------------------------

-- |A 'GHC.FunBind' wraps up one or more 'GHC.Match' items. 'hsDecls' cannot
-- return anything for these as there is not meaningful 'replaceDecls' for it.
-- This function provides a version of 'hsDecls' that returns the 'GHC.FunBind'
-- decls too, where they are needed for analysis only.
hsDeclsGeneric :: (SYB.Data t,Monad m) => t -> TransformT m [GHC.LHsDecl GhcPs]
hsDeclsGeneric t = q t
  where
    q = return []
        `SYB.mkQ`  parsedSource
        `SYB.extQ` lmatch
        `SYB.extQ` lexpr
        `SYB.extQ` lstmt
        `SYB.extQ` lhsbind
        `SYB.extQ` lhsbindd
        `SYB.extQ` llocalbinds
        `SYB.extQ` localbinds

    parsedSource (p::GHC.ParsedSource) = hsDecls p

    lmatch (lm::GHC.LMatch GhcPs (GHC.LHsExpr GhcPs)) = hsDecls lm

    lexpr (le::GHC.LHsExpr GhcPs) = hsDecls le

    lstmt (d::GHC.LStmt GhcPs (GHC.LHsExpr GhcPs)) = hsDecls d

    -- ---------------------------------

    lhsbind :: (Monad m) => GHC.LHsBind GhcPs -> TransformT m [GHC.LHsDecl GhcPs]
#if __GLASGOW_HASKELL__ > 804
    lhsbind (GHC.L _ (GHC.FunBind _ _ (GHC.MG _ (GHC.L _ matches) _) _ _)) = do
#elif __GLASGOW_HASKELL__ > 710
    lhsbind (GHC.L _ (GHC.FunBind _ (GHC.MG (GHC.L _ matches) _ _ _) _ _ _)) = do
#else
    lhsbind (GHC.L _ (GHC.FunBind _ _ (GHC.MG matches _ _ _) _ _ _)) = do
#endif
        dss <- mapM hsDecls matches
        return (concat dss)
    lhsbind p@(GHC.L _ (GHC.PatBind{})) = do
      hsDeclsPatBind p
    lhsbind _ = return []

    -- ---------------------------------

#if __GLASGOW_HASKELL__ > 804
    lhsbindd (GHC.L l (GHC.ValD _ d)) = lhsbind (GHC.L l d)
#else
    lhsbindd (GHC.L l (GHC.ValD d)) = lhsbind (GHC.L l d)
#endif
    lhsbindd _ = return []

    -- ---------------------------------

    llocalbinds :: (Monad m) => GHC.Located (GHC.HsLocalBinds GhcPs) -> TransformT m [GHC.LHsDecl GhcPs]
    llocalbinds (GHC.L _ ds) = localbinds ds

    -- ---------------------------------

    localbinds :: (Monad m) => GHC.HsLocalBinds GhcPs -> TransformT m [GHC.LHsDecl GhcPs]
    localbinds d = hsDeclsValBinds d

-- ---------------------------------------------------------------------

-- |Look up the annotated order and sort the decls accordingly
orderedDecls :: (Data a,Monad m) => GHC.Located a -> [GHC.LHsDecl GhcPs] -> TransformT m [GHC.LHsDecl GhcPs]
orderedDecls parent decls = do
  ans <- getAnnsT
  case getAnnotationEP parent ans of
    Nothing -> error $ "orderedDecls:no annotation for:" ++ showAnnData emptyAnns 0 parent
    Just ann -> case annSortKey ann of
      Nothing -> do
        return decls
      Just keys -> do
        let ds = map (\s -> (GHC.getLoc s,s)) decls
            ordered = map snd $ orderByKey ds keys
        return ordered

-- ---------------------------------------------------------------------

-- | Utility function for extracting decls from 'GHC.HsLocalBinds'. Use with
-- care, as this does not necessarily return the declarations in order, the
-- ordering should be done by the calling function from the 'GHC.HsLocalBinds'
-- context in the AST.
hsDeclsValBinds :: (Monad m) => GHC.HsLocalBinds GhcPs -> TransformT m [GHC.LHsDecl GhcPs]
hsDeclsValBinds lb = case lb of
#if __GLASGOW_HASKELL__ > 804
    GHC.HsValBinds _ (GHC.ValBinds _ bs sigs) -> do
      let
        bds = map wrapDecl (GHC.bagToList bs)
        sds = map wrapSig sigs
      return (bds ++ sds)
    GHC.HsValBinds _ (GHC.XValBindsLR _) -> error $ "hsDecls.XValBindsLR not valid"
    GHC.HsIPBinds {}       -> return []
    GHC.EmptyLocalBinds {} -> return []
    GHC.XHsLocalBindsLR {} -> return []
#else
    GHC.HsValBinds (GHC.ValBindsIn bs sigs) -> do
      let
        bds = map wrapDecl (GHC.bagToList bs)
        sds = map wrapSig sigs
      return (bds ++ sds)
    GHC.HsValBinds (GHC.ValBindsOut _ _) -> error $ "hsDecls.ValbindsOut not valid"
    GHC.HsIPBinds _     -> return []
    GHC.EmptyLocalBinds -> return []
#endif

-- | Utility function for returning decls to 'GHC.HsLocalBinds'. Use with
-- care, as this does not manage the declaration order, the
-- ordering should be done by the calling function from the 'GHC.HsLocalBinds'
-- context in the AST.
replaceDeclsValbinds :: (Monad m)
                     => GHC.HsLocalBinds GhcPs -> [GHC.LHsDecl GhcPs]
                     -> TransformT m (GHC.HsLocalBinds GhcPs)
replaceDeclsValbinds _ [] = do
#if __GLASGOW_HASKELL__ > 804
  return (GHC.EmptyLocalBinds GHC.noExt)
#else
  return (GHC.EmptyLocalBinds)
#endif
#if __GLASGOW_HASKELL__ > 804
replaceDeclsValbinds (GHC.HsValBinds _ _b) new
#else
replaceDeclsValbinds (GHC.HsValBinds _b) new
#endif
    = do
        logTr "replaceDecls HsLocalBinds"
        let decs = GHC.listToBag $ concatMap decl2Bind new
        let sigs = concatMap decl2Sig new
#if __GLASGOW_HASKELL__ > 804
        return (GHC.HsValBinds GHC.noExt (GHC.ValBinds GHC.noExt decs sigs))
#else
        return (GHC.HsValBinds (GHC.ValBindsIn decs sigs))
#endif
replaceDeclsValbinds (GHC.HsIPBinds {}) _new    = error "undefined replaceDecls HsIPBinds"
#if __GLASGOW_HASKELL__ > 804
replaceDeclsValbinds (GHC.EmptyLocalBinds _) new
#else
replaceDeclsValbinds (GHC.EmptyLocalBinds) new
#endif
    = do
        logTr "replaceDecls HsLocalBinds"
        let newBinds = map decl2Bind new
            newSigs  = map decl2Sig  new
        let decs = GHC.listToBag $ concat newBinds
        let sigs = concat newSigs
#if __GLASGOW_HASKELL__ > 804
        return (GHC.HsValBinds GHC.noExt (GHC.ValBinds GHC.noExt decs sigs))
#else
        return (GHC.HsValBinds (GHC.ValBindsIn decs sigs))
#endif
#if __GLASGOW_HASKELL__ > 804
replaceDeclsValbinds (GHC.XHsLocalBindsLR _) _ = error "replaceDeclsValbinds. XHsLocalBindsLR"
#endif

-- ---------------------------------------------------------------------

type Decl  = GHC.LHsDecl GhcPs
type Match = GHC.LMatch GhcPs (GHC.LHsExpr GhcPs)

-- |Modify a 'GHC.LHsBind' wrapped in a 'GHC.ValD'. For a 'GHC.PatBind' the
-- declarations are extracted and returned after modification. For a
-- 'GHC.FunBind' the supplied 'GHC.SrcSpan' is used to identify the specific
-- 'GHC.Match' to be transformed, for when there are multiple of them.
modifyValD :: forall m t. (HasTransform m)
                => GHC.SrcSpan
                -> Decl
                -> (Match -> [Decl] -> m ([Decl], Maybe t))
                -> m (Decl,Maybe t)
#if __GLASGOW_HASKELL__ > 804
modifyValD p pb@(GHC.L ss (GHC.ValD _ (GHC.PatBind {} ))) f =
#else
modifyValD p pb@(GHC.L ss (GHC.ValD (GHC.PatBind {} ))) f =
#endif
  if ss == p
     then do
       ds <- liftT $ hsDeclsPatBindD pb
       (ds',r) <- f (error "modifyValD.PatBind should not touch Match") ds
       pb' <- liftT $ replaceDeclsPatBindD pb ds'
       return (pb',r)
     else return (pb,Nothing)
modifyValD p ast f = do
  (ast',r) <- runStateT (SYB.everywhereM (SYB.mkM doModLocal) ast) Nothing
  return (ast',r)
  where
    doModLocal :: Match -> StateT (Maybe t) m Match
    doModLocal  (match@(GHC.L ss _) :: Match) = do
         let
         if ss == p
           then do
             ds <- lift $ liftT $ hsDecls match
             (ds',r) <- lift $ f match ds
             put r
             match' <- lift $ liftT $ replaceDecls match ds'
             return match'
           else return match

-- ---------------------------------------------------------------------

-- |Used to integrate a @Transform@ into other Monad stacks
class (Monad m) => (HasTransform m) where
  liftT :: Transform a -> m a

instance Monad m => HasTransform (TransformT m) where
  liftT = hoistTransform (return . runIdentity)

-- ---------------------------------------------------------------------

-- | Apply a transformation to the decls contained in @t@
modifyDeclsT :: (HasDecls t,HasTransform m)
             => ([GHC.LHsDecl GhcPs] -> m [GHC.LHsDecl GhcPs])
             -> t -> m t
modifyDeclsT action t = do
  decls <- liftT $ hsDecls t
  decls' <- action decls
  liftT $ replaceDecls t decls'

-- ---------------------------------------------------------------------

matchApiAnn :: GHC.AnnKeywordId -> (KeywordId,DeltaPos) -> Bool
matchApiAnn mkw (kw,_)
  = case kw of
     (G akw) -> mkw == akw
     _       -> False


-- We comments extracted from annPriorComments or annFollowingComments, which
-- need to move to just before the item identified by the predicate, if it
-- fires, else at the end of the annotations.
insertCommentBefore :: (Monad m) => AnnKey -> [(Comment, DeltaPos)]
                    -> ((KeywordId, DeltaPos) -> Bool) -> TransformT m ()
insertCommentBefore key toMove p = do
  let
    doInsert ans =
      case Map.lookup key ans of
        Nothing -> error $ "insertCommentBefore:no AnnKey for:" ++ showGhc key
        Just ann -> Map.insert key ann' ans
          where
            (before,after) = break p (annsDP ann)
            ann' = ann { annsDP = before ++ (map comment2dp toMove) ++ after}

  modifyAnnsT doInsert