content: {-
  (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
  
  \section[StgLint]{A ``lint'' pass to check for Stg correctness}
  -}
  
  {-# LANGUAGE CPP #-}
  
  module Eta.StgSyn.StgLint ( lintStgBindings ) where
  
  import Eta.StgSyn.StgSyn
  
  import Eta.Utils.Bag              ( Bag, emptyBag, isEmptyBag, snocBag, bagToList )
  import Eta.BasicTypes.Id               ( Id, idType, isLocalId )
  import Eta.BasicTypes.VarSet
  import Eta.BasicTypes.DataCon
  import Eta.Core.CoreSyn          ( AltCon(..) )
  import Eta.Prelude.PrimOp           ( primOpType )
  import Eta.BasicTypes.Literal          ( literalType )
  import Eta.Utils.Maybes
  import Eta.BasicTypes.Name             ( getSrcLoc )
  import Eta.Main.ErrUtils         ( MsgDoc, Severity(..), mkLocMessage )
  import Eta.Types.TypeRep
  import Eta.Types.Type
  import Eta.Types.TyCon
  import Eta.Utils.Util
  import Eta.BasicTypes.SrcLoc
  import Eta.Utils.Outputable
  import qualified Eta.Utils.Outputable as Outputable
  import Eta.Utils.FastString
  import Control.Monad
  import Data.Function
  
  #include "HsVersions.h"
  
  {-
  Checks for
          (a) *some* type errors
          (b) locally-defined variables used but not defined
  
  
  Note: unless -dverbose-stg is on, display of lint errors will result
  in "panic: bOGUS_LVs".
  
  WARNING:
  ~~~~~~~~
  
  This module has suffered bit-rot; it is likely to yield lint errors
  for Stg code that is currently perfectly acceptable for code
  generation.  Solution: don't use it!  (KSW 2000-05).
  
  
  ************************************************************************
  *                                                                      *
  \subsection{``lint'' for various constructs}
  *                                                                      *
  ************************************************************************
  
  @lintStgBindings@ is the top-level interface function.
  -}
  
  lintStgBindings :: String -> [StgBinding] -> [StgBinding]
  
  lintStgBindings whodunnit binds
    = {-# SCC "StgLint" #-}
      case (initL (lint_binds binds)) of
        Nothing  -> binds
        Just msg -> pprPanic "" (vcat [
                          ptext (sLit "*** Stg Lint ErrMsgs: in") <+>
                                text whodunnit <+> ptext (sLit "***"),
                          msg,
                          ptext (sLit "*** Offending Program ***"),
                          pprStgBindings binds,
                          ptext (sLit "*** End of Offense ***")])
    where
      lint_binds :: [StgBinding] -> LintM ()
  
      lint_binds [] = return ()
      lint_binds (bind:binds) = do
          binders <- lintStgBinds bind
          addInScopeVars binders $
              lint_binds binds
  
  lintStgArg :: StgArg -> LintM (Maybe Type)
  lintStgArg (StgLitArg lit) = return (Just (literalType lit))
  lintStgArg (StgVarArg v)   = lintStgVar v
  
  lintStgVar :: Id -> LintM (Maybe Kind)
  lintStgVar v = do checkInScope v
                    return (Just (idType v))
  
  lintStgBinds :: StgBinding -> LintM [Id] -- Returns the binders
  lintStgBinds (StgNonRec binder rhs) = do
      lint_binds_help (binder,rhs)
      return [binder]
  
  lintStgBinds (StgRec pairs)
    = addInScopeVars binders $ do
          mapM_ lint_binds_help pairs
          return binders
    where
      binders = [b | (b,_) <- pairs]
  
  lint_binds_help :: (Id, StgRhs) -> LintM ()
  lint_binds_help (binder, rhs)
    = addLoc (RhsOf binder) $ do
          -- Check the rhs
          _maybe_rhs_ty <- lintStgRhs rhs
  
          -- Check binder doesn't have unlifted type
          checkL (not (isUnLiftedType binder_ty))
                 (mkUnLiftedTyMsg binder rhs)
  
          -- Check match to RHS type
          -- Actually we *can't* check the RHS type, because
          -- unsafeCoerce means it really might not match at all
          -- notably;  eg x::Int = (error @Bool "urk") |> unsafeCoerce...
          -- case maybe_rhs_ty of
          --  Nothing     -> return ()
          --    Just rhs_ty -> checkTys binder_ty
          --                          rhs_ty
          ---                         (mkRhsMsg binder rhs_ty)
  
          return ()
    where
      binder_ty = idType binder
  
  lintStgRhs :: StgRhs -> LintM (Maybe Type)   -- Just ty => type is exact
  
  lintStgRhs (StgRhsClosure _ _ _ _ _ [] expr)
    = lintStgExpr expr
  
  lintStgRhs (StgRhsClosure _ _ _ _ _ binders expr)
    = addLoc (LambdaBodyOf binders) $
        addInScopeVars binders $ runMaybeT $ do
          body_ty <- MaybeT $ lintStgExpr expr
          return (mkFunTys (map idType binders) body_ty)
  
  lintStgRhs (StgRhsCon _ con args) = runMaybeT $ do
      arg_tys <- mapM (MaybeT . lintStgArg) args
      MaybeT $ checkFunApp con_ty arg_tys (mkRhsConMsg con_ty arg_tys)
    where
      con_ty = dataConRepType con
  
  lintStgExpr :: StgExpr -> LintM (Maybe Type) -- Just ty => type is exact
  
  lintStgExpr (StgLit l) = return (Just (literalType l))
  
  lintStgExpr e@(StgApp fun args) = runMaybeT $ do
      fun_ty <- MaybeT $ lintStgVar fun
      arg_tys <- mapM (MaybeT . lintStgArg) args
      MaybeT $ checkFunApp fun_ty arg_tys (mkFunAppMsg fun_ty arg_tys e)
  
  lintStgExpr e@(StgConApp con args) = runMaybeT $ do
      arg_tys <- mapM (MaybeT . lintStgArg) args
      MaybeT $ checkFunApp con_ty arg_tys (mkFunAppMsg con_ty arg_tys e)
    where
      con_ty = dataConRepType con
  
  lintStgExpr e@(StgOpApp (StgPrimOp op) args _) = runMaybeT $ do
      arg_tys <- mapM (MaybeT . lintStgArg) args
      MaybeT $ checkFunApp op_ty arg_tys (mkFunAppMsg op_ty arg_tys e)
    where
      op_ty = primOpType op
  
  lintStgExpr (StgOpApp _ args res_ty) = runMaybeT $ do
          -- We don't have enough type information to check
          -- the application for StgFCallOp and StgPrimCallOp; ToDo
      _maybe_arg_tys <- mapM (MaybeT . lintStgArg) args
      return res_ty
  
  lintStgExpr (StgLam bndrs _) = do
      addErrL (ptext (sLit "Unexpected StgLam") <+> ppr bndrs)
      return Nothing
  
  lintStgExpr (StgLet binds body) = do
      binders <- lintStgBinds binds
      addLoc (BodyOfLetRec binders) $
        addInScopeVars binders $
          lintStgExpr body
  
  lintStgExpr (StgLetNoEscape _ _ binds body) = do
      binders <- lintStgBinds binds
      addLoc (BodyOfLetRec binders) $
        addInScopeVars binders $
          lintStgExpr body
  
  lintStgExpr (StgTick _ expr) = lintStgExpr expr
  
  lintStgExpr (StgCase scrut _ _ bndr _ alts_type alts) = runMaybeT $ do
      _ <- MaybeT $ lintStgExpr scrut
  
      in_scope <- MaybeT $ liftM Just $
       case alts_type of
          AlgAlt tc    -> check_bndr tc >> return True
          PrimAlt tc   -> check_bndr tc >> return True
          UbxTupAlt _  -> return False -- Binder is always dead in this case
          PolyAlt      -> return True
  
      MaybeT $ addInScopeVars [bndr | in_scope] $
               lintStgAlts alts scrut_ty
    where
      scrut_ty          = idType bndr
      UnaryRep scrut_rep = repType scrut_ty -- Not used if scrutinee is unboxed tuple
      check_bndr tc = case tyConAppTyCon_maybe scrut_rep of
                          Just bndr_tc -> checkL (tc == bndr_tc) bad_bndr
                          Nothing      -> addErrL bad_bndr
                    where
                       bad_bndr = mkDefltMsg bndr tc
  
  lintStgAlts :: [StgAlt]
              -> Type               -- Type of scrutinee
              -> LintM (Maybe Type) -- Just ty => type is accurage
  
  lintStgAlts alts scrut_ty = do
      maybe_result_tys <- mapM (lintAlt scrut_ty) alts
  
      -- Check the result types
      case catMaybes (maybe_result_tys) of
        []             -> return Nothing
  
        (first_ty:_tys) -> do -- mapM_ check tys
                             return (Just first_ty)
          where
            -- check ty = checkTys first_ty ty (mkCaseAltMsg alts)
            -- We can't check that the alternatives have the
            -- same type, because they don't, with unsafeCoerce#
  
  lintAlt :: Type -> (AltCon, [Id], [Bool], StgExpr) -> LintM (Maybe Type)
  lintAlt _ (DEFAULT, _, _, rhs)
   = lintStgExpr rhs
  
  lintAlt scrut_ty (LitAlt lit, _, _, rhs) = do
     checkTys (literalType lit) scrut_ty (mkAltMsg1 scrut_ty)
     lintStgExpr rhs
  
  lintAlt scrut_ty (DataAlt con, args, _, rhs) = do
      case splitTyConApp_maybe scrut_ty of
        Just (tycon, tys_applied) | isAlgTyCon tycon &&
                                    not (isNewTyCon tycon) -> do
           let
             cons    = tyConDataCons tycon
             arg_tys = dataConInstArgTys con tys_applied
                  -- This does not work for existential constructors
  
           checkL (con `elem` cons) (mkAlgAltMsg2 scrut_ty con)
           checkL (length args == dataConRepArity con) (mkAlgAltMsg3 con args)
           when (isVanillaDataCon con) $
             mapM_ check (zipEqual "lintAlgAlt:stg" arg_tys args)
           return ()
        _ ->
           addErrL (mkAltMsg1 scrut_ty)
  
      addInScopeVars args $
           lintStgExpr rhs
    where
      check (ty, arg) = checkTys ty (idType arg) (mkAlgAltMsg4 ty arg)
  
      -- elem: yes, the elem-list here can sometimes be long-ish,
      -- but as it's use-once, probably not worth doing anything different
      -- We give it its own copy, so it isn't overloaded.
      elem _ []       = False
      elem x (y:ys)   = x==y || elem x ys
  
  {-
  ************************************************************************
  *                                                                      *
  \subsection[lint-monad]{The Lint monad}
  *                                                                      *
  ************************************************************************
  -}
  
  newtype LintM a = LintM
      { unLintM :: [LintLocInfo]      -- Locations
                -> IdSet              -- Local vars in scope
                -> Bag MsgDoc        -- Error messages so far
                -> (a, Bag MsgDoc)   -- Result and error messages (if any)
      }
  
  data LintLocInfo
    = RhsOf Id            -- The variable bound
    | LambdaBodyOf [Id]   -- The lambda-binder
    | BodyOfLetRec [Id]   -- One of the binders
  
  dumpLoc :: LintLocInfo -> (SrcSpan, SDoc)
  dumpLoc (RhsOf v) =
    (srcLocSpan (getSrcLoc v), ptext (sLit " [RHS of ") <> pp_binders [v] <> char ']' )
  dumpLoc (LambdaBodyOf bs) =
    (srcLocSpan (getSrcLoc (head bs)), ptext (sLit " [in body of lambda with binders ") <> pp_binders bs <> char ']' )
  
  dumpLoc (BodyOfLetRec bs) =
    (srcLocSpan (getSrcLoc (head bs)), ptext (sLit " [in body of letrec with binders ") <> pp_binders bs <> char ']' )
  
  
  pp_binders :: [Id] -> SDoc
  pp_binders bs
    = sep (punctuate comma (map pp_binder bs))
    where
      pp_binder b
        = hsep [ppr b, dcolon, ppr (idType b)]
  
  initL :: LintM a -> Maybe MsgDoc
  initL (LintM m)
    = case (m [] emptyVarSet emptyBag) of { (_, errs) ->
      if isEmptyBag errs then
          Nothing
      else
          Just (vcat (punctuate blankLine (bagToList errs)))
      }
  
  instance Functor LintM where
        fmap = liftM
  
  instance Applicative LintM where
        pure = return
        (<*>) = ap
  
  instance Monad LintM where
      return a = LintM $ \_loc _scope errs -> (a, errs)
      (>>=) = thenL
      (>>)  = thenL_
  
  thenL :: LintM a -> (a -> LintM b) -> LintM b
  thenL m k = LintM $ \loc scope errs
    -> case unLintM m loc scope errs of
        (r, errs') -> unLintM (k r) loc scope errs'
  
  thenL_ :: LintM a -> LintM b -> LintM b
  thenL_ m k = LintM $ \loc scope errs
    -> case unLintM m loc scope errs of
        (_, errs') -> unLintM k loc scope errs'
  
  checkL :: Bool -> MsgDoc -> LintM ()
  checkL True  _   = return ()
  checkL False msg = addErrL msg
  
  addErrL :: MsgDoc -> LintM ()
  addErrL msg = LintM $ \loc _scope errs -> ((), addErr errs msg loc)
  
  addErr :: Bag MsgDoc -> MsgDoc -> [LintLocInfo] -> Bag MsgDoc
  addErr errs_so_far msg locs
    = errs_so_far `snocBag` mk_msg locs
    where
      mk_msg (loc:_) = let (l,hdr) = dumpLoc loc
                       in  mkLocMessage SevWarning l (hdr $$ msg)
      mk_msg []      = msg
  
  addLoc :: LintLocInfo -> LintM a -> LintM a
  addLoc extra_loc m = LintM $ \loc scope errs
     -> unLintM m (extra_loc:loc) scope errs
  
  addInScopeVars :: [Id] -> LintM a -> LintM a
  addInScopeVars ids m = LintM $ \loc scope errs
   -> -- We check if these "new" ids are already
      -- in scope, i.e., we have *shadowing* going on.
      -- For now, it's just a "trace"; we may make
      -- a real error out of it...
      let
          new_set = mkVarSet ids
      in
  --  After adding -fliberate-case, Simon decided he likes shadowed
  --  names after all.  WDP 94/07
  --  (if isEmptyVarSet shadowed
  --  then id
  --  else pprTrace "Shadowed vars:" (ppr (varSetElems shadowed))) $
      unLintM m loc (scope `unionVarSet` new_set) errs
  
  {-
  Checking function applications: we only check that the type has the
  right *number* of arrows, we don't actually compare the types.  This
  is because we can't expect the types to be equal - the type
  applications and type lambdas that we use to calculate accurate types
  have long since disappeared.
  -}
  
  checkFunApp :: Type                 -- The function type
              -> [Type]               -- The arg type(s)
              -> MsgDoc              -- Error message
              -> LintM (Maybe Type)   -- Just ty => result type is accurate
  
  checkFunApp fun_ty arg_tys msg
   = do { case mb_msg of
            Just msg -> addErrL msg
            Nothing  -> return ()
        ; return mb_ty }
   where
    (mb_ty, mb_msg) = cfa True fun_ty arg_tys
  
    cfa :: Bool -> Type -> [Type] -> (Maybe Type          -- Accurate result?
                                     , Maybe MsgDoc)      -- Errors?
  
    cfa accurate fun_ty []      -- Args have run out; that's fine
        = (if accurate then Just fun_ty else Nothing, Nothing)
  
    cfa accurate fun_ty arg_tys@(arg_ty':arg_tys')
        | Just (arg_ty, res_ty) <- splitFunTy_maybe fun_ty
        = if accurate && not (arg_ty `stgEqType` arg_ty')
          then (Nothing, Just msg)       -- Arg type mismatch
          else cfa accurate res_ty arg_tys'
  
        | Just (_, fun_ty') <- splitForAllTy_maybe fun_ty
        = cfa False fun_ty' arg_tys
  
        | Just (tc,tc_args) <- splitTyConApp_maybe fun_ty
        , isNewTyCon tc
        = if length tc_args < tyConArity tc
          then WARN( True, text "cfa: unsaturated newtype" <+> ppr fun_ty $$ msg )
               (Nothing, Nothing)   -- This is odd, but I've seen it
          else cfa False (newTyConInstRhs tc tc_args) arg_tys
  
        | Just tc <- tyConAppTyCon_maybe fun_ty
        , not (isTypeFamilyTyCon tc)      -- Definite error
        = (Nothing, Just msg)             -- Too many args
  
        | otherwise
        = (Nothing, Nothing)
  
  stgEqType :: Type -> Type -> Bool
  -- Compare types, but crudely because we have discarded
  -- both casts and type applications, so types might look
  -- different but be the same.  So reply "True" if in doubt.
  -- "False" means that the types are definitely different.
  --
  -- Fundamentally this is a losing battle because of unsafeCoerce
  
  stgEqType orig_ty1 orig_ty2
    = gos (repType orig_ty1) (repType orig_ty2)
    where
      gos :: RepType -> RepType -> Bool
      gos (UbxTupleRep tys1) (UbxTupleRep tys2)
        = equalLength tys1 tys2 && and (zipWith go tys1 tys2)
      gos (UnaryRep ty1) (UnaryRep ty2) = go ty1 ty2
      gos _ _ = False
  
      go :: UnaryType -> UnaryType -> Bool
      go ty1 ty2
        | Just (tc1, tc_args1) <- splitTyConApp_maybe ty1
        , Just (tc2, tc_args2) <- splitTyConApp_maybe ty2
        , let res = if tc1 == tc2
                    then equalLength tc_args1 tc_args2 && and (zipWith (gos `on` repType) tc_args1 tc_args2)
                    else  -- TyCons don't match; but don't bleat if either is a
                          -- family TyCon because a coercion might have made it
                          -- equal to something else
                      (isFamilyTyCon tc1 || isFamilyTyCon tc2)
        = if res then True
          else
          pprTrace "stgEqType: unequal" (vcat [ppr ty1, ppr ty2])
          False
  
        | otherwise = True  -- Conservatively say "fine".
                            -- Type variables in particular
  
  checkInScope :: Id -> LintM ()
  checkInScope id = LintM $ \loc scope errs
   -> if isLocalId id && not (id `elemVarSet` scope) then
          ((), addErr errs (hsep [ppr id, ptext (sLit "is out of scope")]) loc)
      else
          ((), errs)
  
  checkTys :: Type -> Type -> MsgDoc -> LintM ()
  checkTys ty1 ty2 msg = LintM $ \loc _scope errs
    -> if (ty1 `stgEqType` ty2)
       then ((), errs)
       else ((), addErr errs msg loc)
  
  _mkCaseAltMsg :: [StgAlt] -> MsgDoc
  _mkCaseAltMsg _alts
    = ($$) (text "In some case alternatives, type of alternatives not all same:")
              (Outputable.empty) -- LATER: ppr alts
  
  mkDefltMsg :: Id -> TyCon -> MsgDoc
  mkDefltMsg bndr tc
    = ($$) (ptext (sLit "Binder of a case expression doesn't match type of scrutinee:"))
           (ppr bndr $$ ppr (idType bndr) $$ ppr tc)
  
  mkFunAppMsg :: Type -> [Type] -> StgExpr -> MsgDoc
  mkFunAppMsg fun_ty arg_tys expr
    = vcat [text "In a function application, function type doesn't match arg types:",
                hang (ptext (sLit "Function type:")) 4 (ppr fun_ty),
                hang (ptext (sLit "Arg types:")) 4 (vcat (map (ppr) arg_tys)),
                hang (ptext (sLit "Expression:")) 4 (ppr expr)]
  
  mkRhsConMsg :: Type -> [Type] -> MsgDoc
  mkRhsConMsg fun_ty arg_tys
    = vcat [text "In a RHS constructor application, con type doesn't match arg types:",
                hang (ptext (sLit "Constructor type:")) 4 (ppr fun_ty),
                hang (ptext (sLit "Arg types:")) 4 (vcat (map (ppr) arg_tys))]
  
  mkAltMsg1 :: Type -> MsgDoc
  mkAltMsg1 ty
    = ($$) (text "In a case expression, type of scrutinee does not match patterns")
           (ppr ty)
  
  mkAlgAltMsg2 :: Type -> DataCon -> MsgDoc
  mkAlgAltMsg2 ty con
    = vcat [
          text "In some algebraic case alternative, constructor is not a constructor of scrutinee type:",
          ppr ty,
          ppr con
      ]
  
  mkAlgAltMsg3 :: DataCon -> [Id] -> MsgDoc
  mkAlgAltMsg3 con alts
    = vcat [
          text "In some algebraic case alternative, number of arguments doesn't match constructor:",
          ppr con,
          ppr alts
      ]
  
  mkAlgAltMsg4 :: Type -> Id -> MsgDoc
  mkAlgAltMsg4 ty arg
    = vcat [
          text "In some algebraic case alternative, type of argument doesn't match data constructor:",
          ppr ty,
          ppr arg
      ]
  
  _mkRhsMsg :: Id -> Type -> MsgDoc
  _mkRhsMsg binder ty
    = vcat [hsep [ptext (sLit "The type of this binder doesn't match the type of its RHS:"),
                       ppr binder],
                hsep [ptext (sLit "Binder's type:"), ppr (idType binder)],
                hsep [ptext (sLit "Rhs type:"), ppr ty]
               ]
  
  mkUnLiftedTyMsg :: Id -> StgRhs -> SDoc
  mkUnLiftedTyMsg binder rhs
    = (ptext (sLit "Let(rec) binder") <+> quotes (ppr binder) <+>
       ptext (sLit "has unlifted type") <+> quotes (ppr (idType binder)))
      $$
      (ptext (sLit "RHS:") <+> ppr rhs)
  