path: root/compiler/rename/RnPat.hs

{-
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998

\section[RnPat]{Renaming of patterns}

Basically dependency analysis.

Handles @Match@, @GRHSs@, @HsExpr@, and @Qualifier@ datatypes.  In
general, all of these functions return a renamed thing, and a set of
free variables.
-}

{-# LANGUAGE CPP, RankNTypes, ScopedTypeVariables #-}

module RnPat (-- main entry points
              rnPat, rnPats, rnBindPat, rnPatAndThen,

              NameMaker, applyNameMaker,     -- a utility for making names:
              localRecNameMaker, topRecNameMaker,  --   sometimes we want to make local names,
                                             --   sometimes we want to make top (qualified) names.
              isTopRecNameMaker,

              rnHsRecFields, HsRecFieldContext(..),
              rnHsRecUpdFields,

              -- CpsRn monad
              CpsRn, liftCps,

              -- Literals
              rnLit, rnOverLit,

             -- Pattern Error messages that are also used elsewhere
             checkTupSize, patSigErr
             ) where

-- ENH: thin imports to only what is necessary for patterns

import {-# SOURCE #-} RnExpr ( rnLExpr )
import {-# SOURCE #-} RnSplice ( rnSplicePat )

#include "HsVersions.h"

import HsSyn
import TcRnMonad
import TcHsSyn             ( hsOverLitName )
import RnEnv
import RnTypes
import PrelNames
import TyCon               ( tyConName )
import ConLike
import Type                ( TyThing(..) )
import Name
import NameSet
import RdrName
import BasicTypes
import Util
import ListSetOps          ( removeDups )
import Outputable
import SrcLoc
import Literal             ( inCharRange )
import TysWiredIn          ( nilDataCon )
import DataCon
import qualified GHC.LanguageExtensions as LangExt

import Control.Monad       ( when, liftM, ap )
import Data.Ratio

{-
*********************************************************
*                                                      *
        The CpsRn Monad
*                                                      *
*********************************************************

Note [CpsRn monad]
~~~~~~~~~~~~~~~~~~
The CpsRn monad uses continuation-passing style to support this
style of programming:

        do { ...
           ; ns <- bindNames rs
           ; ...blah... }

   where rs::[RdrName], ns::[Name]

The idea is that '...blah...'
  a) sees the bindings of ns
  b) returns the free variables it mentions
     so that bindNames can report unused ones

In particular,
    mapM rnPatAndThen [p1, p2, p3]
has a *left-to-right* scoping: it makes the binders in
p1 scope over p2,p3.
-}

newtype CpsRn b = CpsRn { unCpsRn :: forall r. (b -> RnM (r, FreeVars))
                                            -> RnM (r, FreeVars) }
        -- See Note [CpsRn monad]

instance Functor CpsRn where
    fmap = liftM

instance Applicative CpsRn where
    pure x = CpsRn (\k -> k x)
    (<*>) = ap

instance Monad CpsRn where
  (CpsRn m) >>= mk = CpsRn (\k -> m (\v -> unCpsRn (mk v) k))

runCps :: CpsRn a -> RnM (a, FreeVars)
runCps (CpsRn m) = m (\r -> return (r, emptyFVs))

liftCps :: RnM a -> CpsRn a
liftCps rn_thing = CpsRn (\k -> rn_thing >>= k)

liftCpsFV :: RnM (a, FreeVars) -> CpsRn a
liftCpsFV rn_thing = CpsRn (\k -> do { (v,fvs1) <- rn_thing
                                     ; (r,fvs2) <- k v
                                     ; return (r, fvs1 `plusFV` fvs2) })

wrapSrcSpanCps :: (a -> CpsRn b) -> Located a -> CpsRn (Located b)
-- Set the location, and also wrap it around the value returned
wrapSrcSpanCps fn (L loc a)
  = CpsRn (\k -> setSrcSpan loc $
                 unCpsRn (fn a) $ \v ->
                 k (L loc v))

lookupConCps :: Located RdrName -> CpsRn (Located Name)
lookupConCps con_rdr
  = CpsRn (\k -> do { con_name <- lookupLocatedOccRn con_rdr
                    ; (r, fvs) <- k con_name
                    ; return (r, addOneFV fvs (unLoc con_name)) })
    -- We add the constructor name to the free vars
    -- See Note [Patterns are uses]

{-
Note [Patterns are uses]
~~~~~~~~~~~~~~~~~~~~~~~~
Consider
  module Foo( f, g ) where
  data T = T1 | T2

  f T1 = True
  f T2 = False

  g _ = T1

Arguably we should report T2 as unused, even though it appears in a
pattern, because it never occurs in a constructed position.  See
Trac #7336.
However, implementing this in the face of pattern synonyms would be
less straightforward, since given two pattern synonyms

  pattern P1 <- P2
  pattern P2 <- ()

we need to observe the dependency between P1 and P2 so that type
checking can be done in the correct order (just like for value
bindings). Dependencies between bindings is analyzed in the renamer,
where we don't know yet whether P2 is a constructor or a pattern
synonym. So for now, we do report conid occurrences in patterns as
uses.

*********************************************************
*                                                      *
        Name makers
*                                                      *
*********************************************************

Externally abstract type of name makers,
which is how you go from a RdrName to a Name
-}

data NameMaker
  = LamMk       -- Lambdas
      Bool      -- True <=> report unused bindings
                --   (even if True, the warning only comes out
                --    if -Wunused-matches is on)

  | LetMk       -- Let bindings, incl top level
                -- Do *not* check for unused bindings
      TopLevelFlag
      MiniFixityEnv

topRecNameMaker :: MiniFixityEnv -> NameMaker
topRecNameMaker fix_env = LetMk TopLevel fix_env

isTopRecNameMaker :: NameMaker -> Bool
isTopRecNameMaker (LetMk TopLevel _) = True
isTopRecNameMaker _ = False

localRecNameMaker :: MiniFixityEnv -> NameMaker
localRecNameMaker fix_env = LetMk NotTopLevel fix_env

matchNameMaker :: HsMatchContext a -> NameMaker
matchNameMaker ctxt = LamMk report_unused
  where
    -- Do not report unused names in interactive contexts
    -- i.e. when you type 'x <- e' at the GHCi prompt
    report_unused = case ctxt of
                      StmtCtxt GhciStmtCtxt -> False
                      -- also, don't warn in pattern quotes, as there
                      -- is no RHS where the variables can be used!
                      ThPatQuote            -> False
                      _                     -> True

rnHsSigCps :: LHsSigWcType RdrName -> CpsRn (LHsSigWcType Name)
rnHsSigCps sig = CpsRn (rnHsSigWcTypeScoped PatCtx sig)

newPatLName :: NameMaker -> Located RdrName -> CpsRn (Located Name)
newPatLName name_maker rdr_name@(L loc _)
  = do { name <- newPatName name_maker rdr_name
       ; return (L loc name) }

newPatName :: NameMaker -> Located RdrName -> CpsRn Name
newPatName (LamMk report_unused) rdr_name
  = CpsRn (\ thing_inside ->
        do { name <- newLocalBndrRn rdr_name
           ; (res, fvs) <- bindLocalNames [name] (thing_inside name)
           ; when report_unused $ warnUnusedMatches [name] fvs
           ; return (res, name `delFV` fvs) })

newPatName (LetMk is_top fix_env) rdr_name
  = CpsRn (\ thing_inside ->
        do { name <- case is_top of
                       NotTopLevel -> newLocalBndrRn rdr_name
                       TopLevel    -> newTopSrcBinder rdr_name
           ; bindLocalNames [name] $       -- Do *not* use bindLocalNameFV here
                                        -- See Note [View pattern usage]
             addLocalFixities fix_env [name] $
             thing_inside name })

    -- Note: the bindLocalNames is somewhat suspicious
    --       because it binds a top-level name as a local name.
    --       however, this binding seems to work, and it only exists for
    --       the duration of the patterns and the continuation;
    --       then the top-level name is added to the global env
    --       before going on to the RHSes (see RnSource.hs).

{-
Note [View pattern usage]
~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
  let (r, (r -> x)) = x in ...
Here the pattern binds 'r', and then uses it *only* in the view pattern.
We want to "see" this use, and in let-bindings we collect all uses and
report unused variables at the binding level. So we must use bindLocalNames
here, *not* bindLocalNameFV.  Trac #3943.

*********************************************************
*                                                      *
        External entry points
*                                                      *
*********************************************************

There are various entry points to renaming patterns, depending on
 (1) whether the names created should be top-level names or local names
 (2) whether the scope of the names is entirely given in a continuation
     (e.g., in a case or lambda, but not in a let or at the top-level,
      because of the way mutually recursive bindings are handled)
 (3) whether the a type signature in the pattern can bind
        lexically-scoped type variables (for unpacking existential
        type vars in data constructors)
 (4) whether we do duplicate and unused variable checking
 (5) whether there are fixity declarations associated with the names
     bound by the patterns that need to be brought into scope with them.

 Rather than burdening the clients of this module with all of these choices,
 we export the three points in this design space that we actually need:
-}

-- ----------- Entry point 1: rnPats -------------------
-- Binds local names; the scope of the bindings is entirely in the thing_inside
--   * allows type sigs to bind type vars
--   * local namemaker
--   * unused and duplicate checking
--   * no fixities
rnPats :: HsMatchContext Name -- for error messages
       -> [LPat RdrName]
       -> ([LPat Name] -> RnM (a, FreeVars))
       -> RnM (a, FreeVars)
rnPats ctxt pats thing_inside
  = do  { envs_before <- getRdrEnvs

          -- (1) rename the patterns, bringing into scope all of the term variables
          -- (2) then do the thing inside.
        ; unCpsRn (rnLPatsAndThen (matchNameMaker ctxt) pats) $ \ pats' -> do
        { -- Check for duplicated and shadowed names
          -- Must do this *after* renaming the patterns
          -- See Note [Collect binders only after renaming] in HsUtils
          -- Because we don't bind the vars all at once, we can't
          --    check incrementally for duplicates;
          -- Nor can we check incrementally for shadowing, else we'll
          --    complain *twice* about duplicates e.g. f (x,x) = ...
        ; addErrCtxt doc_pat $
          checkDupAndShadowedNames envs_before $
          collectPatsBinders pats'
        ; thing_inside pats' } }
  where
    doc_pat = text "In" <+> pprMatchContext ctxt

rnPat :: HsMatchContext Name -- for error messages
      -> LPat RdrName
      -> (LPat Name -> RnM (a, FreeVars))
      -> RnM (a, FreeVars)     -- Variables bound by pattern do not
                               -- appear in the result FreeVars
rnPat ctxt pat thing_inside
  = rnPats ctxt [pat] (\pats' -> let [pat'] = pats' in thing_inside pat')

applyNameMaker :: NameMaker -> Located RdrName -> RnM (Located Name)
applyNameMaker mk rdr = do { (n, _fvs) <- runCps (newPatLName mk rdr)
                           ; return n }

-- ----------- Entry point 2: rnBindPat -------------------
-- Binds local names; in a recursive scope that involves other bound vars
--      e.g let { (x, Just y) = e1; ... } in ...
--   * does NOT allows type sig to bind type vars
--   * local namemaker
--   * no unused and duplicate checking
--   * fixities might be coming in
rnBindPat :: NameMaker
          -> LPat RdrName
          -> RnM (LPat Name, FreeVars)
   -- Returned FreeVars are the free variables of the pattern,
   -- of course excluding variables bound by this pattern

rnBindPat name_maker pat = runCps (rnLPatAndThen name_maker pat)

{-
*********************************************************
*                                                      *
        The main event
*                                                      *
*********************************************************
-}

-- ----------- Entry point 3: rnLPatAndThen -------------------
-- General version: parametrized by how you make new names

rnLPatsAndThen :: NameMaker -> [LPat RdrName] -> CpsRn [LPat Name]
rnLPatsAndThen mk = mapM (rnLPatAndThen mk)
  -- Despite the map, the monad ensures that each pattern binds
  -- variables that may be mentioned in subsequent patterns in the list

--------------------
-- The workhorse
rnLPatAndThen :: NameMaker -> LPat RdrName -> CpsRn (LPat Name)
rnLPatAndThen nm lpat = wrapSrcSpanCps (rnPatAndThen nm) lpat

rnPatAndThen :: NameMaker -> Pat RdrName -> CpsRn (Pat Name)
rnPatAndThen _  (WildPat _)   = return (WildPat placeHolderType)
rnPatAndThen mk (ParPat pat)  = do { pat' <- rnLPatAndThen mk pat; return (ParPat pat') }
rnPatAndThen mk (LazyPat pat) = do { pat' <- rnLPatAndThen mk pat; return (LazyPat pat') }
rnPatAndThen mk (BangPat pat) = do { pat' <- rnLPatAndThen mk pat; return (BangPat pat') }
rnPatAndThen mk (VarPat (L l rdr)) = do { loc <- liftCps getSrcSpanM
                                        ; name <- newPatName mk (L loc rdr)
                                        ; return (VarPat (L l name)) }
     -- we need to bind pattern variables for view pattern expressions
     -- (e.g. in the pattern (x, x -> y) x needs to be bound in the rhs of the tuple)

rnPatAndThen mk (SigPatIn pat sig)
  -- When renaming a pattern type signature (e.g. f (a :: T) = ...), it is
  -- important to rename its type signature _before_ renaming the rest of the
  -- pattern, so that type variables are first bound by the _outermost_ pattern
  -- type signature they occur in. This keeps the type checker happy when
  -- pattern type signatures happen to be nested (#7827)
  --
  -- f ((Just (x :: a) :: Maybe a)
  -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~^       `a' is first bound here
  -- ~~~~~~~~~~~~~~~^                   the same `a' then used here
  = do { sig' <- rnHsSigCps sig
       ; pat' <- rnLPatAndThen mk pat
       ; return (SigPatIn pat' sig') }

rnPatAndThen mk (LitPat lit)
  | HsString src s <- lit
  = do { ovlStr <- liftCps (xoptM LangExt.OverloadedStrings)
       ; if ovlStr
         then rnPatAndThen mk
                           (mkNPat (noLoc (mkHsIsString src s placeHolderType))
                                      Nothing)
         else normal_lit }
  | otherwise = normal_lit
  where
    normal_lit = do { liftCps (rnLit lit); return (LitPat lit) }

rnPatAndThen _ (NPat (L l lit) mb_neg _eq _)
  = do { lit'    <- liftCpsFV $ rnOverLit lit
       ; mb_neg' <- liftCpsFV $ case mb_neg of
                      Nothing -> return (Nothing, emptyFVs)
                      Just _  -> do { (neg, fvs) <- lookupSyntaxName negateName
                                    ; return (Just neg, fvs) }
       ; eq' <- liftCpsFV $ lookupSyntaxName eqName
       ; return (NPat (L l lit') mb_neg' eq' placeHolderType) }

rnPatAndThen mk (NPlusKPat rdr (L l lit) _ _ _ _)
  = do { new_name <- newPatName mk rdr
       ; lit'  <- liftCpsFV $ rnOverLit lit
       ; minus <- liftCpsFV $ lookupSyntaxName minusName
       ; ge    <- liftCpsFV $ lookupSyntaxName geName
       ; return (NPlusKPat (L (nameSrcSpan new_name) new_name)
                           (L l lit') lit' ge minus placeHolderType) }
                -- The Report says that n+k patterns must be in Integral

rnPatAndThen mk (AsPat rdr pat)
  = do { new_name <- newPatLName mk rdr
       ; pat' <- rnLPatAndThen mk pat
       ; return (AsPat new_name pat') }

rnPatAndThen mk p@(ViewPat expr pat _ty)
  = do { liftCps $ do { vp_flag <- xoptM LangExt.ViewPatterns
                      ; checkErr vp_flag (badViewPat p) }
         -- Because of the way we're arranging the recursive calls,
         -- this will be in the right context
       ; expr' <- liftCpsFV $ rnLExpr expr
       ; pat' <- rnLPatAndThen mk pat
       -- Note: at this point the PreTcType in ty can only be a placeHolder
       -- ; return (ViewPat expr' pat' ty) }
       ; return (ViewPat expr' pat' placeHolderType) }

rnPatAndThen mk (ConPatIn con stuff)
   -- rnConPatAndThen takes care of reconstructing the pattern
   -- The pattern for the empty list needs to be replaced by an empty explicit list pattern when overloaded lists is turned on.
  = case unLoc con == nameRdrName (dataConName nilDataCon) of
      True    -> do { ol_flag <- liftCps $ xoptM LangExt.OverloadedLists
                    ; if ol_flag then rnPatAndThen mk (ListPat [] placeHolderType Nothing)
                                 else rnConPatAndThen mk con stuff}
      False   -> rnConPatAndThen mk con stuff

rnPatAndThen mk (ListPat pats _ _)
  = do { opt_OverloadedLists <- liftCps $ xoptM LangExt.OverloadedLists
       ; pats' <- rnLPatsAndThen mk pats
       ; case opt_OverloadedLists of
          True -> do { (to_list_name,_) <- liftCps $ lookupSyntaxName toListName
                     ; return (ListPat pats' placeHolderType
                                       (Just (placeHolderType, to_list_name)))}
          False -> return (ListPat pats' placeHolderType Nothing) }

rnPatAndThen mk (PArrPat pats _)
  = do { pats' <- rnLPatsAndThen mk pats
       ; return (PArrPat pats' placeHolderType) }

rnPatAndThen mk (TuplePat pats boxed _)
  = do { liftCps $ checkTupSize (length pats)
       ; pats' <- rnLPatsAndThen mk pats
       ; return (TuplePat pats' boxed []) }

rnPatAndThen mk (SumPat pat alt arity _)
  = do { pat <- rnLPatAndThen mk pat
       ; return (SumPat pat alt arity PlaceHolder)
       }

-- If a splice has been run already, just rename the result.
rnPatAndThen mk (SplicePat (HsSpliced mfs (HsSplicedPat pat)))
  = SplicePat . HsSpliced mfs . HsSplicedPat <$> rnPatAndThen mk pat

rnPatAndThen mk (SplicePat splice)
  = do { eith <- liftCpsFV $ rnSplicePat splice
       ; case eith of   -- See Note [rnSplicePat] in RnSplice
           Left  not_yet_renamed -> rnPatAndThen mk not_yet_renamed
           Right already_renamed -> return already_renamed }

rnPatAndThen _ pat = pprPanic "rnLPatAndThen" (ppr pat)


--------------------
rnConPatAndThen :: NameMaker
                -> Located RdrName          -- the constructor
                -> HsConPatDetails RdrName
                -> CpsRn (Pat Name)

rnConPatAndThen mk con (PrefixCon pats)
  = do  { con' <- lookupConCps con
        ; pats' <- rnLPatsAndThen mk pats
        ; return (ConPatIn con' (PrefixCon pats')) }

rnConPatAndThen mk con (InfixCon pat1 pat2)
  = do  { con' <- lookupConCps con
        ; pat1' <- rnLPatAndThen mk pat1
        ; pat2' <- rnLPatAndThen mk pat2
        ; fixity <- liftCps $ lookupFixityRn (unLoc con')
        ; liftCps $ mkConOpPatRn con' fixity pat1' pat2' }

rnConPatAndThen mk con (RecCon rpats)
  = do  { con' <- lookupConCps con
        ; rpats' <- rnHsRecPatsAndThen mk con' rpats
        ; return (ConPatIn con' (RecCon rpats')) }

--------------------
rnHsRecPatsAndThen :: NameMaker
                   -> Located Name      -- Constructor
                   -> HsRecFields RdrName (LPat RdrName)
                   -> CpsRn (HsRecFields Name (LPat Name))
rnHsRecPatsAndThen mk (L _ con) hs_rec_fields@(HsRecFields { rec_dotdot = dd })
  = do { flds <- liftCpsFV $ rnHsRecFields (HsRecFieldPat con) mkVarPat
                                            hs_rec_fields
       ; flds' <- mapM rn_field (flds `zip` [1..])
       ; return (HsRecFields { rec_flds = flds', rec_dotdot = dd }) }
  where
    mkVarPat l n = VarPat (L l n)
    rn_field (L l fld, n') = do { arg' <- rnLPatAndThen (nested_mk dd mk n')
                                                        (hsRecFieldArg fld)
                                ; return (L l (fld { hsRecFieldArg = arg' })) }

        -- Suppress unused-match reporting for fields introduced by ".."
    nested_mk Nothing  mk                    _  = mk
    nested_mk (Just _) mk@(LetMk {})         _  = mk
    nested_mk (Just n) (LamMk report_unused) n' = LamMk (report_unused && (n' <= n))

{-
************************************************************************
*                                                                      *
        Record fields
*                                                                      *
************************************************************************
-}

data HsRecFieldContext
  = HsRecFieldCon Name
  | HsRecFieldPat Name
  | HsRecFieldUpd

rnHsRecFields
    :: forall arg.
       HsRecFieldContext
    -> (SrcSpan -> RdrName -> arg)
         -- When punning, use this to build a new field
    -> HsRecFields RdrName (Located arg)
    -> RnM ([LHsRecField Name (Located arg)], FreeVars)

-- This surprisingly complicated pass
--   a) looks up the field name (possibly using disambiguation)
--   b) fills in puns and dot-dot stuff
-- When we we've finished, we've renamed the LHS, but not the RHS,
-- of each x=e binding
--
-- This is used for record construction and pattern-matching, but not updates.

rnHsRecFields ctxt mk_arg (HsRecFields { rec_flds = flds, rec_dotdot = dotdot })
  = do { pun_ok      <- xoptM LangExt.RecordPuns
       ; disambig_ok <- xoptM LangExt.DisambiguateRecordFields
       ; parent <- check_disambiguation disambig_ok mb_con
       ; flds1  <- mapM (rn_fld pun_ok parent) flds
       ; mapM_ (addErr . dupFieldErr ctxt) dup_flds
       ; dotdot_flds <- rn_dotdot dotdot mb_con flds1
       ; let all_flds | null dotdot_flds = flds1
                      | otherwise        = flds1 ++ dotdot_flds
       ; return (all_flds, mkFVs (getFieldIds all_flds)) }
  where
    mb_con = case ctxt of
                HsRecFieldCon con | not (isUnboundName con) -> Just con
                HsRecFieldPat con | not (isUnboundName con) -> Just con
                _ {- update or isUnboundName con -}         -> Nothing
           -- The unbound name test is because if the constructor
           -- isn't in scope the constructor lookup will add an error
           -- add an error, but still return an unbound name.
           -- We don't want that to screw up the dot-dot fill-in stuff.

    doc = case mb_con of
            Nothing  -> text "constructor field name"
            Just con -> text "field of constructor" <+> quotes (ppr con)

    rn_fld :: Bool -> Maybe Name -> LHsRecField RdrName (Located arg)
           -> RnM (LHsRecField Name (Located arg))
    rn_fld pun_ok parent (L l (HsRecField { hsRecFieldLbl
                                              = L loc (FieldOcc (L ll lbl) _)
                                          , hsRecFieldArg = arg
                                          , hsRecPun      = pun }))
      = do { sel <- setSrcSpan loc $ lookupRecFieldOcc parent doc lbl
           ; arg' <- if pun
                     then do { checkErr pun_ok (badPun (L loc lbl))
                               -- Discard any module qualifier (#11662)
                             ; let arg_rdr = mkRdrUnqual (rdrNameOcc lbl)
                             ; return (L loc (mk_arg loc arg_rdr)) }
                     else return arg
           ; return (L l (HsRecField { hsRecFieldLbl
                                         = L loc (FieldOcc (L ll lbl) sel)
                                     , hsRecFieldArg = arg'
                                     , hsRecPun      = pun })) }

    rn_dotdot :: Maybe Int      -- See Note [DotDot fields] in HsPat
              -> Maybe Name     -- The constructor (Nothing for an
                                --    out of scope constructor)
              -> [LHsRecField Name (Located arg)] -- Explicit fields
              -> RnM [LHsRecField Name (Located arg)]   -- Filled in .. fields
    rn_dotdot Nothing _mb_con _flds     -- No ".." at all
      = return []
    rn_dotdot (Just {}) Nothing _flds   -- Constructor out of scope
      = return []
    rn_dotdot (Just n) (Just con) flds -- ".." on record construction / pat match
      = ASSERT( n == length flds )
        do { loc <- getSrcSpanM -- Rather approximate
           ; dd_flag <- xoptM LangExt.RecordWildCards
           ; checkErr dd_flag (needFlagDotDot ctxt)
           ; (rdr_env, lcl_env) <- getRdrEnvs
           ; con_fields <- lookupConstructorFields con
           ; when (null con_fields) (addErr (badDotDotCon con))
           ; let present_flds = map (occNameFS . rdrNameOcc) $ getFieldLbls flds

                   -- For constructor uses (but not patterns)
                   -- the arg should be in scope locally;
                   -- i.e. not top level or imported
                   -- Eg.  data R = R { x,y :: Int }
                   --      f x = R { .. }   -- Should expand to R {x=x}, not R{x=x,y=y}
                 arg_in_scope lbl = mkVarUnqual lbl `elemLocalRdrEnv` lcl_env

                 dot_dot_gres = [ (lbl, sel, head gres)
                                | fl <- con_fields
                                , let lbl = flLabel fl
                                , let sel = flSelector fl
                                , not (lbl `elem` present_flds)
                                , let gres = lookupGRE_Field_Name rdr_env sel lbl
                                , not (null gres)  -- Check selector is in scope
                                , case ctxt of
                                    HsRecFieldCon {} -> arg_in_scope lbl
                                    _other           -> True ]

           ; addUsedGREs (map thdOf3 dot_dot_gres)
           ; return [ L loc (HsRecField
                        { hsRecFieldLbl = L loc (FieldOcc (L loc arg_rdr) sel)
                        , hsRecFieldArg = L loc (mk_arg loc arg_rdr)
                        , hsRecPun      = False })
                    | (lbl, sel, _) <- dot_dot_gres
                    , let arg_rdr = mkVarUnqual lbl ] }

    check_disambiguation :: Bool -> Maybe Name -> RnM (Maybe Name)
    -- When disambiguation is on, return name of parent tycon.
    check_disambiguation disambig_ok mb_con
      | disambig_ok, Just con <- mb_con
      = do { env <- getGlobalRdrEnv; return (find_tycon env con) }
      | otherwise = return Nothing

    find_tycon :: GlobalRdrEnv -> Name {- DataCon -} -> Maybe Name {- TyCon -}
    -- Return the parent *type constructor* of the data constructor
    -- (that is, the parent of the data constructor),
    -- or 'Nothing' if it is a pattern synonym or not in scope.
    -- That's the parent to use for looking up record fields.
    find_tycon env con_name
      | Just (AConLike (RealDataCon dc)) <- wiredInNameTyThing_maybe con_name
      = Just (tyConName (dataConTyCon dc))
        -- Special case for [], which is built-in syntax
        -- and not in the GlobalRdrEnv (Trac #8448)

      | Just gre <- lookupGRE_Name env con_name
      = case gre_par gre of
          ParentIs p -> Just p
          _          -> Nothing   -- Can happen if the con_name
                                  -- is for a pattern synonym

      | otherwise = Nothing
        -- Data constructor not lexically in scope at all
        -- See Note [Disambiguation and Template Haskell]

    dup_flds :: [[RdrName]]
        -- Each list represents a RdrName that occurred more than once
        -- (the list contains all occurrences)
        -- Each list in dup_fields is non-empty
    (_, dup_flds) = removeDups compare (getFieldLbls flds)


{- Note [Disambiguation and Template Haskell]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider (Trac #12130)
   module Foo where
     import M
     b = $(funny)

   module M(funny) where
     data T = MkT { x :: Int }
     funny :: Q Exp
     funny = [| MkT { x = 3 } |]

When we splice, neither T nor MkT are lexically in scope, so find_tycon will
fail.  But there is no need for diambiguation anyway, so we just return Nothing
-}

rnHsRecUpdFields
    :: [LHsRecUpdField RdrName]
    -> RnM ([LHsRecUpdField Name], FreeVars)
rnHsRecUpdFields flds
  = do { pun_ok        <- xoptM LangExt.RecordPuns
       ; overload_ok   <- xoptM LangExt.DuplicateRecordFields
       ; (flds1, fvss) <- mapAndUnzipM (rn_fld pun_ok overload_ok) flds
       ; mapM_ (addErr . dupFieldErr HsRecFieldUpd) dup_flds

       -- Check for an empty record update  e {}
       -- NB: don't complain about e { .. }, because rn_dotdot has done that already
       ; when (null flds) $ addErr emptyUpdateErr

       ; return (flds1, plusFVs fvss) }
  where
    doc = text "constructor field name"

    rn_fld :: Bool -> Bool -> LHsRecUpdField RdrName -> RnM (LHsRecUpdField Name, FreeVars)
    rn_fld pun_ok overload_ok (L l (HsRecField { hsRecFieldLbl = L loc f
                                               , hsRecFieldArg = arg
                                               , hsRecPun      = pun }))
      = do { let lbl = rdrNameAmbiguousFieldOcc f
           ; sel <- setSrcSpan loc $
                      -- Defer renaming of overloaded fields to the typechecker
                      -- See Note [Disambiguating record fields] in TcExpr
                      if overload_ok
                          then do { mb <- lookupGlobalOccRn_overloaded overload_ok lbl
                                  ; case mb of
                                      Nothing -> do { addErr (unknownSubordinateErr doc lbl)
                                                    ; return (Right []) }
                                      Just r  -> return r }
                          else fmap Left $ lookupGlobalOccRn lbl
           ; arg' <- if pun
                     then do { checkErr pun_ok (badPun (L loc lbl))
                               -- Discard any module qualifier (#11662)
                             ; let arg_rdr = mkRdrUnqual (rdrNameOcc lbl)
                             ; return (L loc (HsVar (L loc arg_rdr))) }
                     else return arg
           ; (arg'', fvs) <- rnLExpr arg'

           ; let fvs' = case sel of
                          Left sel_name -> fvs `addOneFV` sel_name
                          Right [FieldOcc _ sel_name] -> fvs `addOneFV` sel_name
                          Right _       -> fvs
                 lbl' = case sel of
                          Left sel_name ->
                                     L loc (Unambiguous (L loc lbl) sel_name)
                          Right [FieldOcc lbl sel_name] ->
                                     L loc (Unambiguous lbl sel_name)
                          Right _ -> L loc (Ambiguous   (L loc lbl) PlaceHolder)

           ; return (L l (HsRecField { hsRecFieldLbl = lbl'
                                     , hsRecFieldArg = arg''
                                     , hsRecPun      = pun }), fvs') }

    dup_flds :: [[RdrName]]
        -- Each list represents a RdrName that occurred more than once
        -- (the list contains all occurrences)
        -- Each list in dup_fields is non-empty
    (_, dup_flds) = removeDups compare (getFieldUpdLbls flds)



getFieldIds :: [LHsRecField Name arg] -> [Name]
getFieldIds flds = map (unLoc . hsRecFieldSel . unLoc) flds

getFieldLbls :: [LHsRecField id arg] -> [RdrName]
getFieldLbls flds
  = map (unLoc . rdrNameFieldOcc . unLoc . hsRecFieldLbl . unLoc) flds

getFieldUpdLbls :: [LHsRecUpdField id] -> [RdrName]
getFieldUpdLbls flds = map (rdrNameAmbiguousFieldOcc . unLoc . hsRecFieldLbl . unLoc) flds

needFlagDotDot :: HsRecFieldContext -> SDoc
needFlagDotDot ctxt = vcat [text "Illegal `..' in record" <+> pprRFC ctxt,
                            text "Use RecordWildCards to permit this"]

badDotDotCon :: Name -> SDoc
badDotDotCon con
  = vcat [ text "Illegal `..' notation for constructor" <+> quotes (ppr con)
         , nest 2 (text "The constructor has no labelled fields") ]

emptyUpdateErr :: SDoc
emptyUpdateErr = text "Empty record update"

badPun :: Located RdrName -> SDoc
badPun fld = vcat [text "Illegal use of punning for field" <+> quotes (ppr fld),
                   text "Use NamedFieldPuns to permit this"]

dupFieldErr :: HsRecFieldContext -> [RdrName] -> SDoc
dupFieldErr ctxt dups
  = hsep [text "duplicate field name",
          quotes (ppr (head dups)),
          text "in record", pprRFC ctxt]

pprRFC :: HsRecFieldContext -> SDoc
pprRFC (HsRecFieldCon {}) = text "construction"
pprRFC (HsRecFieldPat {}) = text "pattern"
pprRFC (HsRecFieldUpd {}) = text "update"

{-
************************************************************************
*                                                                      *
\subsubsection{Literals}
*                                                                      *
************************************************************************

When literals occur we have to make sure
that the types and classes they involve
are made available.
-}

rnLit :: HsLit -> RnM ()
rnLit (HsChar _ c) = checkErr (inCharRange c) (bogusCharError c)
rnLit _ = return ()

-- Turn a Fractional-looking literal which happens to be an integer into an
-- Integer-looking literal.
generalizeOverLitVal :: OverLitVal -> OverLitVal
generalizeOverLitVal (HsFractional (FL {fl_text=src,fl_value=val}))
    | denominator val == 1 = HsIntegral src (numerator val)
generalizeOverLitVal lit = lit

rnOverLit :: HsOverLit t -> RnM (HsOverLit Name, FreeVars)
rnOverLit origLit
  = do  { opt_NumDecimals <- xoptM LangExt.NumDecimals
        ; let { lit@(OverLit {ol_val=val})
            | opt_NumDecimals = origLit {ol_val = generalizeOverLitVal (ol_val origLit)}
            | otherwise       = origLit
          }
        ; let std_name = hsOverLitName val
        ; (SyntaxExpr { syn_expr = from_thing_name }, fvs)
            <- lookupSyntaxName std_name
        ; let rebindable = case from_thing_name of
                                HsVar (L _ v) -> v /= std_name
                                _             -> panic "rnOverLit"
        ; return (lit { ol_witness = from_thing_name
                      , ol_rebindable = rebindable
                      , ol_type = placeHolderType }, fvs) }

{-
************************************************************************
*                                                                      *
\subsubsection{Errors}
*                                                                      *
************************************************************************
-}

patSigErr :: Outputable a => a -> SDoc
patSigErr ty
  =  (text "Illegal signature in pattern:" <+> ppr ty)
        $$ nest 4 (text "Use ScopedTypeVariables to permit it")

bogusCharError :: Char -> SDoc
bogusCharError c
  = text "character literal out of range: '\\" <> char c  <> char '\''

badViewPat :: Pat RdrName -> SDoc
badViewPat pat = vcat [text "Illegal view pattern: " <+> ppr pat,
                       text "Use ViewPatterns to enable view patterns"]