content: {-
  
  This module contains code which maintains and manipulates the
  fixity environment during renaming.
  
  -}
  module Eta.Rename.RnFixity ( MiniFixityEnv,
                    addLocalFixities,
    lookupFixityRn, lookupFixityRn_help,
    lookupFieldFixityRn, lookupTyFixityRn ) where
  
  import Eta.Iface.LoadIface
  import Eta.HsSyn.HsSyn
  import Eta.BasicTypes.RdrName
  import Eta.Main.HscTypes
  import Eta.TypeCheck.TcRnMonad
  import Eta.BasicTypes.Name
  import Eta.BasicTypes.NameEnv
  import Eta.BasicTypes.Module
  import Eta.BasicTypes.BasicTypes       ( Fixity(..), FixityDirection(..), minPrecedence,
                            defaultFixity, SourceText(..) )
  import Eta.BasicTypes.SrcLoc
  import Eta.Utils.Outputable
  import Eta.Utils.Maybes
  import Data.List
  import Data.Function    ( on )
  import Eta.Rename.RnUnbound
  
  {-
  *********************************************************
  *                                                      *
                  Fixities
  *                                                      *
  *********************************************************
  
  Note [Fixity signature lookup]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  A fixity declaration like
  
      infixr 2 ?
  
  can refer to a value-level operator, e.g.:
  
      (?) :: String -> String -> String
  
  or a type-level operator, like:
  
      data (?) a b = A a | B b
  
  so we extend the lookup of the reader name '?' to the TcClsName namespace, as
  well as the original namespace.
  
  The extended lookup is also used in other places, like resolution of
  deprecation declarations, and lookup of names in GHCi.
  -}
  
  --------------------------------
  type MiniFixityEnv = FastStringEnv (Located Fixity)
          -- Mini fixity env for the names we're about
          -- to bind, in a single binding group
          --
          -- It is keyed by the *FastString*, not the *OccName*, because
          -- the single fixity decl       infix 3 T
          -- affects both the data constructor T and the type constrctor T
          --
          -- We keep the location so that if we find
          -- a duplicate, we can report it sensibly
  
  --------------------------------
  -- Used for nested fixity decls to bind names along with their fixities.
  -- the fixities are given as a UFM from an OccName's FastString to a fixity decl
  
  addLocalFixities :: MiniFixityEnv -> [Name] -> RnM a -> RnM a
  addLocalFixities mini_fix_env names thing_inside
    = extendFixityEnv (mapMaybe find_fixity names) thing_inside
    where
      find_fixity name
        = case lookupFsEnv mini_fix_env (occNameFS occ) of
            Just (L _ fix) -> Just (name, FixItem occ fix)
            Nothing        -> Nothing
        where
          occ = nameOccName name
  
  {-
  --------------------------------
  lookupFixity is a bit strange.
  
  * Nested local fixity decls are put in the local fixity env, which we
    find with getFixtyEnv
  
  * Imported fixities are found in the PIT
  
  * Top-level fixity decls in this module may be for Names that are
      either  Global         (constructors, class operations)
      or      Local/Exported (everything else)
    (See notes with RnNames.getLocalDeclBinders for why we have this split.)
    We put them all in the local fixity environment
  -}
  
  lookupFixityRn :: Name -> RnM Fixity
  lookupFixityRn name = lookupFixityRn' name (nameOccName name)
  
  lookupFixityRn' :: Name -> OccName -> RnM Fixity
  lookupFixityRn' name = fmap snd . lookupFixityRn_help' name
  
  -- | 'lookupFixityRn_help' returns @(True, fixity)@ if it finds a 'Fixity'
  -- in a local environment or from an interface file. Otherwise, it returns
  -- @(False, fixity)@ (e.g., for unbound 'Name's or 'Name's without
  -- user-supplied fixity declarations).
  lookupFixityRn_help :: Name
                      -> RnM (Bool, Fixity)
  lookupFixityRn_help name =
      lookupFixityRn_help' name (nameOccName name)
  
  lookupFixityRn_help' :: Name
                       -> OccName
                       -> RnM (Bool, Fixity)
  lookupFixityRn_help' name occ
    | isUnboundName name
    = return (False, Fixity NoSourceText minPrecedence InfixL)
      -- Minimise errors from ubound names; eg
      --    a>0 `foo` b>0
      -- where 'foo' is not in scope, should not give an error (Trac #7937)
  
    | otherwise
    = do { local_fix_env <- getFixityEnv
         ; case lookupNameEnv local_fix_env name of {
             Just (FixItem _ fix) -> return (True, fix) ;
             Nothing ->
  
      do { this_mod <- getModule
         ; if nameIsLocalOrFrom this_mod name
                 -- Local (and interactive) names are all in the
                 -- fixity env, and don't have entries in the HPT
           then return (False, defaultFixity)
           else lookup_imported } } }
    where
      lookup_imported
        -- For imported names, we have to get their fixities by doing a
        -- loadInterfaceForName, and consulting the Ifaces that comes back
        -- from that, because the interface file for the Name might not
        -- have been loaded yet.  Why not?  Suppose you import module A,
        -- which exports a function 'f', thus;
        --        module CurrentModule where
        --          import A( f )
        --        module A( f ) where
        --          import B( f )
        -- Then B isn't loaded right away (after all, it's possible that
        -- nothing from B will be used).  When we come across a use of
        -- 'f', we need to know its fixity, and it's then, and only
        -- then, that we load B.hi.  That is what's happening here.
        --
        -- loadInterfaceForName will find B.hi even if B is a hidden module,
        -- and that's what we want.
        = do { iface <- loadInterfaceForName doc name
             ; let mb_fix = mi_fix_fn iface occ
             ; let msg = case mb_fix of
                              Nothing ->
                                    text "looking up name" <+> ppr name
                                <+> text "in iface, but found no fixity for it."
                                <+> text "Using default fixity instead."
                              Just f ->
                                    text "looking up name in iface and found:"
                                <+> vcat [ppr name, ppr f]
             ; traceRn "lookupFixityRn_either:" msg
             ; return (maybe (False, defaultFixity) (\f -> (True, f)) mb_fix)  }
  
      doc = text "Checking fixity for" <+> ppr name
  
  ---------------
  lookupTyFixityRn :: Located Name -> RnM Fixity
  lookupTyFixityRn (L _ n) = lookupFixityRn n
  
  -- | Look up the fixity of a (possibly ambiguous) occurrence of a record field
  -- selector.  We use 'lookupFixityRn'' so that we can specifiy the 'OccName' as
  -- the field label, which might be different to the 'OccName' of the selector
  -- 'Name' if @DuplicateRecordFields@ is in use (Trac #1173). If there are
  -- multiple possible selectors with different fixities, generate an error.
  lookupFieldFixityRn :: AmbiguousFieldOcc GhcRn -> RnM Fixity
  lookupFieldFixityRn (Unambiguous n (L _ rdr))
    = lookupFixityRn' n (rdrNameOcc rdr)
  lookupFieldFixityRn (Ambiguous _ (L _ rdr)) = get_ambiguous_fixity rdr
    where
      get_ambiguous_fixity :: RdrName -> RnM Fixity
      get_ambiguous_fixity rdr_name = do
        traceRn "get_ambiguous_fixity" (ppr rdr_name)
        rdr_env <- getGlobalRdrEnv
        let elts =  lookupGRE_RdrName rdr_name rdr_env
  
        fixities <- groupBy ((==) `on` snd) . zip elts
                    <$> mapM lookup_gre_fixity elts
  
        case fixities of
          -- There should always be at least one fixity.
          -- Something's very wrong if there are no fixity candidates, so panic
          [] -> panic "get_ambiguous_fixity: no candidates for a given RdrName"
          [ (_, fix):_ ] -> return fix
          ambigs -> addErr (ambiguous_fixity_err rdr_name ambigs)
                    >> return (Fixity NoSourceText minPrecedence InfixL)
  
      lookup_gre_fixity gre = lookupFixityRn' (gre_name gre) (greOccName gre)
  
      ambiguous_fixity_err rn ambigs
        = vcat [ text "Ambiguous fixity for record field" <+> quotes (ppr rn)
               , hang (text "Conflicts: ") 2 . vcat .
                 map format_ambig $ concat ambigs ]
  
      format_ambig (elt, fix) = hang (ppr fix)
                                   2 (pprNameProvenance elt)
  lookupFieldFixityRn (XAmbiguousFieldOcc{}) = panic "lookupFieldFixityRn"
  