    {-
    (c) The University of Glasgow 2006
    (c) The GRASP/AQUA Project, Glasgow University, 1992-1998

    Type checking of type signatures in interface files
    -}

    {-# LANGUAGE CPP #-}

    module TcIface (
            tcLookupImported_maybe,
            importDecl, checkWiredInTyCon, tcHiBootIface, typecheckIface,
            tcIfaceDecl, tcIfaceInst, tcIfaceFamInst, tcIfaceRules,
            tcIfaceVectInfo, tcIfaceAnnotations,
            tcIfaceExpr,    -- Desired by HERMIT (Trac #7683)
            tcIfaceGlobal
     ) where

    #include "HsVersions.h"

    import TcTypeNats(typeNatCoAxiomRules)
    import IfaceSyn
    import LoadIface
    import IfaceEnv
    import BuildTyCl
    import TcRnMonad
    import TcType
    import Type
    import Coercion hiding (substTy)
    import TypeRep
    import HscTypes
    import Annotations
    import InstEnv
    import FamInstEnv
    import CoreSyn
    import CoreUtils
    import CoreUnfold
    import CoreLint
    import MkCore
    import Id
    import MkId
    import IdInfo
    import Class
    import TyCon
    import CoAxiom
    import ConLike
    import DataCon
    import PrelNames
    import TysWiredIn
    import TysPrim          ( superKindTyConName )
    import BasicTypes       ( strongLoopBreaker )
    import Literal
    import qualified Var
    import VarEnv
    import VarSet
    import Name
    import NameEnv
    import NameSet
    import OccurAnal        ( occurAnalyseExpr )
    import Demand
    import Module
    import UniqFM
    import UniqSupply
    import Outputable
    import Maybes
    import SrcLoc
    import DynFlags
    import Util
    import FastString

    import Control.Monad
    import qualified Data.Map as Map
    #if __GLASGOW_HASKELL__ < 709
    import Data.Traversable ( traverse )
    #endif

    {-
    This module takes

            IfaceDecl -> TyThing
            IfaceType -> Type
            etc

    An IfaceDecl is populated with RdrNames, and these are not renamed to
    Names before typechecking, because there should be no scope errors etc.

            -- For (b) consider: f = \$(...h....)
            -- where h is imported, and calls f via an hi-boot file.
            -- This is bad!  But it is not seen as a staging error, because h
            -- is indeed imported.  We don't want the type-checker to black-hole
            -- when simplifying and compiling the splice!
            --
            -- Simple solution: discard any unfolding that mentions a variable
            -- bound in this module (and hence not yet processed).
            -- The discarding happens when forkM finds a type error.

    ************************************************************************
    *                                                                      *
                    Type-checking a complete interface
    *                                                                      *
    ************************************************************************

    Suppose we discover we don't need to recompile.  Then we must type
    check the old interface file.  This is a bit different to the
    incremental type checking we do as we suck in interface files.  Instead
    we do things similarly as when we are typechecking source decls: we
    bring into scope the type envt for the interface all at once, using a
    knot.  Remember, the decls aren't necessarily in dependency order --
    and even if they were, the type decls might be mutually recursive.
    -}

    typecheckIface :: ModIface      -- Get the decls from here
                   -> TcRnIf gbl lcl ModDetails
    typecheckIface iface
      = initIfaceTc iface $ \ tc_env_var -> do
            -- The tc_env_var is freshly allocated, private to
            -- type-checking this particular interface
            {       -- Get the right set of decls and rules.  If we are compiling without -O
                    -- we discard pragmas before typechecking, so that we don't "see"
                    -- information that we shouldn't.  From a versioning point of view
                    -- It's not actually *wrong* to do so, but in fact GHCi is unable
                    -- to handle unboxed tuples, so it must not see unfoldings.
              ignore_prags <- goptM Opt_IgnoreInterfacePragmas

                    -- Typecheck the decls.  This is done lazily, so that the knot-tying
                    -- within this single module work out right.  In the If monad there is
                    -- no global envt for the current interface; instead, the knot is tied
                    -- through the if_rec_types field of IfGblEnv
            ; names_w_things <- loadDecls ignore_prags (mi_decls iface)
            ; let type_env = mkNameEnv names_w_things
            ; writeMutVar tc_env_var type_env

                    -- Now do those rules, instances and annotations
            ; insts     <- mapM tcIfaceInst (mi_insts iface)
            ; fam_insts <- mapM tcIfaceFamInst (mi_fam_insts iface)
            ; rules     <- tcIfaceRules ignore_prags (mi_rules iface)
            ; anns      <- tcIfaceAnnotations (mi_anns iface)

                    -- Vectorisation information
            ; vect_info <- tcIfaceVectInfo (mi_module iface) type_env (mi_vect_info iface)

                    -- Exports
            ; exports <- ifaceExportNames (mi_exports iface)

                    -- Finished
            ; traceIf (vcat [text "Finished typechecking interface for" <+> ppr (mi_module iface),
                             text "Type envt:" <+> ppr type_env])
            ; return $ ModDetails { md_types     = type_env
                                  , md_insts     = insts
                                  , md_fam_insts = fam_insts
                                  , md_rules     = rules
                                  , md_anns      = anns
                                  , md_vect_info = vect_info
                                  , md_exports   = exports
                                  }
        }

    {-
    ************************************************************************
    *                                                                      *
                    Type and class declarations
    *                                                                      *
    ************************************************************************
    -}

    tcHiBootIface :: HscSource -> Module -> TcRn ModDetails
    -- Load the hi-boot iface for the module being compiled,
    -- if it indeed exists in the transitive closure of imports
    -- Return the ModDetails, empty if no hi-boot iface
    tcHiBootIface hsc_src mod
      | HsBootFile <- hsc_src            -- Already compiling a hs-boot file
      = return emptyModDetails
      | otherwise
      = do  { traceIf (text "loadHiBootInterface" <+> ppr mod)

            ; mode <- getGhcMode
            ; if not (isOneShot mode)
                    -- In --make and interactive mode, if this module has an hs-boot file
                    -- we'll have compiled it already, and it'll be in the HPT
                    --
                    -- We check wheher the interface is a *boot* interface.
                    -- It can happen (when using GHC from Visual Studio) that we
                    -- compile a module in TypecheckOnly mode, with a stable,
                    -- fully-populated HPT.  In that case the boot interface isn't there
                    -- (it's been replaced by the mother module) so we can't check it.
                    -- And that's fine, because if M's ModInfo is in the HPT, then
                    -- it's been compiled once, and we don't need to check the boot iface
              then do { hpt <- getHpt
                      ; case lookupUFM hpt (moduleName mod) of
                          Just info | mi_boot (hm_iface info)
                                    -> return (hm_details info)
                          _ -> return emptyModDetails }
              else do

            -- OK, so we're in one-shot mode.
            -- Re #9245, we always check if there is an hi-boot interface
            -- to check consistency against, rather than just when we notice
            -- that an hi-boot is necessary due to a circular import.
            { read_result <- findAndReadIface
                                    need mod
                                    True    -- Hi-boot file

            ; case read_result of {
                    Succeeded (iface, _path) -> typecheckIface iface ;
                    Failed err               ->

            -- There was no hi-boot file. But if there is circularity in
            -- the module graph, there really should have been one.
            -- Since we've read all the direct imports by now,
            -- eps_is_boot will record if any of our imports mention the
            -- current module, which either means a module loop (not
            -- a SOURCE import) or that our hi-boot file has mysteriously
            -- disappeared.
        do  { eps <- getEps
            ; case lookupUFM (eps_is_boot eps) (moduleName mod) of
                Nothing -> return emptyModDetails -- The typical case

                Just (_, False) -> failWithTc moduleLoop
                    -- Someone below us imported us!
                    -- This is a loop with no hi-boot in the way

                Just (_mod, True) -> failWithTc (elaborate err)
                    -- The hi-boot file has mysteriously disappeared.
        }}}}
      where
        need = ptext (sLit "Need the hi-boot interface for") <+> ppr mod
                     <+> ptext (sLit "to compare against the Real Thing")

        moduleLoop = ptext (sLit "Circular imports: module") <+> quotes (ppr mod)
                         <+> ptext (sLit "depends on itself")

        elaborate err = hang (ptext (sLit "Could not find hi-boot interface for") <+>
                              quotes (ppr mod) <> colon) 4 err

    {-
    ************************************************************************
    *                                                                      *
                    Type and class declarations
    *                                                                      *
    ************************************************************************

    When typechecking a data type decl, we *lazily* (via forkM) typecheck
    the constructor argument types.  This is in the hope that we may never
    poke on those argument types, and hence may never need to load the
    interface files for types mentioned in the arg types.

    E.g.
            data Foo.S = MkS Baz.T
    Mabye we can get away without even loading the interface for Baz!

    This is not just a performance thing.  Suppose we have
            data Foo.S = MkS Baz.T
            data Baz.T = MkT Foo.S
    (in different interface files, of course).
    Now, first we load and typecheck Foo.S, and add it to the type envt.
    If we do explore MkS's argument, we'll load and typecheck Baz.T.
    If we explore MkT's argument we'll find Foo.S already in the envt.

    If we typechecked constructor args eagerly, when loading Foo.S we'd try to
    typecheck the type Baz.T.  So we'd fault in Baz.T... and then need Foo.S...
    which isn't done yet.

    All very cunning. However, there is a rather subtle gotcha which bit
    me when developing this stuff.  When we typecheck the decl for S, we
    extend the type envt with S, MkS, and all its implicit Ids.  Suppose
    (a bug, but it happened) that the list of implicit Ids depended in
    turn on the constructor arg types.  Then the following sequence of
    events takes place:
            * we build a thunk <t> for the constructor arg tys
            * we build a thunk for the extended type environment (depends on <t>)
            * we write the extended type envt into the global EPS mutvar

    Now we look something up in the type envt
            * that pulls on <t>
            * which reads the global type envt out of the global EPS mutvar
            * but that depends in turn on <t>

    It's subtle, because, it'd work fine if we typechecked the constructor args
    eagerly -- they don't need the extended type envt.  They just get the extended
    type envt by accident, because they look at it later.

    What this means is that the implicitTyThings MUST NOT DEPEND on any of
    the forkM stuff.
    -}

    tcIfaceDecl :: Bool     -- True <=> discard IdInfo on IfaceId bindings
                -> IfaceDecl
                -> IfL TyThing
    tcIfaceDecl = tc_iface_decl NoParentTyCon

    tc_iface_decl :: TyConParent    -- For nested declarations
                  -> Bool   -- True <=> discard IdInfo on IfaceId bindings
                  -> IfaceDecl
                  -> IfL TyThing
    tc_iface_decl _ ignore_prags (IfaceId {ifName = occ_name, ifType = iface_type,
                                           ifIdDetails = details, ifIdInfo = info})
      = do  { name <- lookupIfaceTop occ_name
            ; ty <- tcIfaceType iface_type
            ; details <- tcIdDetails ty details
            ; info <- tcIdInfo ignore_prags name ty info
            ; return (AnId (mkGlobalId details name ty info)) }

    tc_iface_decl parent _ (IfaceData {ifName = occ_name,
                              ifCType = cType,
                              ifTyVars = tv_bndrs,
                              ifRoles = roles,
                              ifCtxt = ctxt, ifGadtSyntax = gadt_syn,
                              ifCons = rdr_cons,
                              ifRec = is_rec, ifPromotable = is_prom,
                              ifParent = mb_parent })
      = bindIfaceTyVars_AT tv_bndrs $ \ tyvars -> do
        { tc_name <- lookupIfaceTop occ_name
        ; tycon <- fixM $ \ tycon -> do
                { stupid_theta <- tcIfaceCtxt ctxt
                ; parent' <- tc_parent mb_parent
                ; cons <- tcIfaceDataCons tc_name tycon tyvars rdr_cons
                ; return (buildAlgTyCon tc_name tyvars roles cType stupid_theta
                                        cons is_rec is_prom gadt_syn parent') }
        ; traceIf (text "tcIfaceDecl4" <+> ppr tycon)
        ; return (ATyCon tycon) }
      where
        tc_parent :: IfaceTyConParent -> IfL TyConParent
        tc_parent IfNoParent = return parent
        tc_parent (IfDataInstance ax_name _ arg_tys)
          = ASSERT( isNoParent parent )
            do { ax <- tcIfaceCoAxiom ax_name
               ; let fam_tc  = coAxiomTyCon ax
                     ax_unbr = toUnbranchedAxiom ax
               ; lhs_tys <- tcIfaceTcArgs arg_tys
               ; return (FamInstTyCon ax_unbr fam_tc lhs_tys) }

    tc_iface_decl _ _ (IfaceSynonym {ifName = occ_name, ifTyVars = tv_bndrs,
                                          ifRoles = roles,
                                          ifSynRhs = rhs_ty,
                                          ifSynKind = kind })
       = bindIfaceTyVars_AT tv_bndrs $ \ tyvars -> do
         { tc_name  <- lookupIfaceTop occ_name
         ; rhs_kind <- tcIfaceKind kind     -- Note [Synonym kind loop]
         ; rhs      <- forkM (mk_doc tc_name) $
                       tcIfaceType rhs_ty
         ; tycon    <- buildSynonymTyCon tc_name tyvars roles rhs rhs_kind
         ; return (ATyCon tycon) }
       where
         mk_doc n = ptext (sLit "Type synonym") <+> ppr n

    tc_iface_decl parent _ (IfaceFamily {ifName = occ_name, ifTyVars = tv_bndrs,
                                         ifFamFlav = fam_flav,
                                         ifFamKind = kind })
       = bindIfaceTyVars_AT tv_bndrs $ \ tyvars -> do
         { tc_name  <- lookupIfaceTop occ_name
         ; rhs_kind <- tcIfaceKind kind     -- Note [Synonym kind loop]
         ; rhs      <- forkM (mk_doc tc_name) $
                       tc_fam_flav fam_flav
         ; tycon    <- buildFamilyTyCon tc_name tyvars rhs rhs_kind parent
         ; return (ATyCon tycon) }
       where
         mk_doc n = ptext (sLit "Type synonym") <+> ppr n
         tc_fam_flav IfaceOpenSynFamilyTyCon   = return OpenSynFamilyTyCon
         tc_fam_flav (IfaceClosedSynFamilyTyCon ax_name _)
           = do { ax <- tcIfaceCoAxiom ax_name
                ; return (ClosedSynFamilyTyCon ax) }
         tc_fam_flav IfaceAbstractClosedSynFamilyTyCon
             = return AbstractClosedSynFamilyTyCon
         tc_fam_flav IfaceBuiltInSynFamTyCon
             = pprPanic "tc_iface_decl"
                        (text "IfaceBuiltInSynFamTyCon in interface file")

    tc_iface_decl _parent ignore_prags
                (IfaceClass {ifCtxt = rdr_ctxt, ifName = tc_occ,
                             ifTyVars = tv_bndrs, ifRoles = roles, ifFDs = rdr_fds,
                             ifATs = rdr_ats, ifSigs = rdr_sigs,
                             ifMinDef = mindef_occ, ifRec = tc_isrec })
    -- ToDo: in hs-boot files we should really treat abstract classes specially,
    --       as we do abstract tycons
      = bindIfaceTyVars tv_bndrs $ \ tyvars -> do
        { tc_name <- lookupIfaceTop tc_occ
        ; traceIf (text "tc-iface-class1" <+> ppr tc_occ)
        ; ctxt <- mapM tc_sc rdr_ctxt
        ; traceIf (text "tc-iface-class2" <+> ppr tc_occ)
        ; sigs <- mapM tc_sig rdr_sigs
        ; fds  <- mapM tc_fd rdr_fds
        ; traceIf (text "tc-iface-class3" <+> ppr tc_occ)
        ; mindef <- traverse (lookupIfaceTop . mkVarOccFS) mindef_occ
        ; cls  <- fixM $ \ cls -> do
                  { ats  <- mapM (tc_at cls) rdr_ats
                  ; traceIf (text "tc-iface-class4" <+> ppr tc_occ)
                  ; buildClass tc_name tyvars roles ctxt fds ats sigs mindef tc_isrec }
        ; return (ATyCon (classTyCon cls)) }
      where
       tc_sc pred = forkM (mk_sc_doc pred) (tcIfaceType pred)
            -- The *length* of the superclasses is used by buildClass, and hence must
            -- not be inside the thunk.  But the *content* maybe recursive and hence
            -- must be lazy (via forkM).  Example:
            --     class C (T a) => D a where
            --       data T a
            -- Here the associated type T is knot-tied with the class, and
            -- so we must not pull on T too eagerly.  See Trac #5970

       tc_sig (IfaceClassOp occ dm rdr_ty)
         = do { op_name <- lookupIfaceTop occ
              ; op_ty   <- forkM (mk_op_doc op_name rdr_ty) (tcIfaceType rdr_ty)
                    -- Must be done lazily for just the same reason as the
                    -- type of a data con; to avoid sucking in types that
                    -- it mentions unless it's necessary to do so
              ; return (op_name, dm, op_ty) }

       tc_at cls (IfaceAT tc_decl if_def)
         = do ATyCon tc <- tc_iface_decl (AssocFamilyTyCon cls) ignore_prags tc_decl
              mb_def <- case if_def of
                          Nothing  -> return Nothing
                          Just def -> forkM (mk_at_doc tc)                 $
                                      extendIfaceTyVarEnv (tyConTyVars tc) $
                                      do { tc_def <- tcIfaceType def
                                         ; return (Just tc_def) }
                      -- Must be done lazily in case the RHS of the defaults mention
                      -- the type constructor being defined here
                      -- e.g.   type AT a; type AT b = AT [b]   Trac #8002
              return (ATI tc mb_def)

       mk_sc_doc pred = ptext (sLit "Superclass") <+> ppr pred
       mk_at_doc tc = ptext (sLit "Associated type") <+> ppr tc
       mk_op_doc op_name op_ty = ptext (sLit "Class op") <+> sep [ppr op_name, ppr op_ty]

       tc_fd (tvs1, tvs2) = do { tvs1' <- mapM tcIfaceTyVar tvs1
                               ; tvs2' <- mapM tcIfaceTyVar tvs2
                               ; return (tvs1', tvs2') }

    tc_iface_decl _ _ (IfaceAxiom { ifName = ax_occ, ifTyCon = tc
                                  , ifAxBranches = branches, ifRole = role })
      = do { tc_name     <- lookupIfaceTop ax_occ
           ; tc_tycon    <- tcIfaceTyCon tc
           ; tc_branches <- tc_ax_branches branches
           ; let axiom = CoAxiom { co_ax_unique   = nameUnique tc_name
                                 , co_ax_name     = tc_name
                                 , co_ax_tc       = tc_tycon
                                 , co_ax_role     = role
                                 , co_ax_branches = toBranchList tc_branches
                                 , co_ax_implicit = False }
           ; return (ACoAxiom axiom) }

    tc_iface_decl _ _ (IfacePatSyn{ ifName = occ_name
                                  , ifPatMatcher = if_matcher
                                  , ifPatBuilder = if_builder
                                  , ifPatIsInfix = is_infix
                                  , ifPatUnivTvs = univ_tvs
                                  , ifPatExTvs = ex_tvs
                                  , ifPatProvCtxt = prov_ctxt
                                  , ifPatReqCtxt = req_ctxt
                                  , ifPatArgs = args
                                  , ifPatTy = pat_ty })
      = do { name <- lookupIfaceTop occ_name
           ; traceIf (ptext (sLit "tc_iface_decl") <+> ppr name)
           ; matcher <- tc_pr if_matcher
           ; builder <- fmapMaybeM tc_pr if_builder
           ; bindIfaceTyVars univ_tvs $ \univ_tvs -> do
           { bindIfaceTyVars ex_tvs $ \ex_tvs -> do
           { patsyn <- forkM (mk_doc name) $
                 do { prov_theta <- tcIfaceCtxt prov_ctxt
                    ; req_theta  <- tcIfaceCtxt req_ctxt
                    ; pat_ty     <- tcIfaceType pat_ty
                    ; arg_tys    <- mapM tcIfaceType args
                    ; return $ buildPatSyn name is_infix matcher builder
                                           (univ_tvs, req_theta) (ex_tvs, prov_theta)
                                           arg_tys pat_ty }
           ; return $ AConLike . PatSynCon $ patsyn }}}
      where
         mk_doc n = ptext (sLit "Pattern synonym") <+> ppr n
         tc_pr :: (IfExtName, Bool) -> IfL (Id, Bool)
         tc_pr (nm, b) = do { id <- forkM (ppr nm) (tcIfaceExtId nm)
                            ; return (id, b) }

    tc_ax_branches :: [IfaceAxBranch] -> IfL [CoAxBranch]
    tc_ax_branches if_branches = foldlM tc_ax_branch [] if_branches

    tc_ax_branch :: [CoAxBranch] -> IfaceAxBranch -> IfL [CoAxBranch]
    tc_ax_branch prev_branches
                 (IfaceAxBranch { ifaxbTyVars = tv_bndrs, ifaxbLHS = lhs, ifaxbRHS = rhs
                                , ifaxbRoles = roles, ifaxbIncomps = incomps })
      = bindIfaceTyVars_AT tv_bndrs $ \ tvs -> do
             -- The _AT variant is needed here; see Note [CoAxBranch type variables] in CoAxiom
        { tc_lhs <- tcIfaceTcArgs lhs   -- See Note [Checking IfaceTypes vs IfaceKinds]
        ; tc_rhs <- tcIfaceType rhs
        ; let br = CoAxBranch { cab_loc     = noSrcSpan
                              , cab_tvs     = tvs
                              , cab_lhs     = tc_lhs
                              , cab_roles   = roles
                              , cab_rhs     = tc_rhs
                              , cab_incomps = map (prev_branches !!) incomps }
        ; return (prev_branches ++ [br]) }

    tcIfaceDataCons :: Name -> TyCon -> [TyVar] -> IfaceConDecls -> IfL AlgTyConRhs
    tcIfaceDataCons tycon_name tycon tc_tyvars if_cons
      = case if_cons of
            IfAbstractTyCon dis -> return (AbstractTyCon dis)
            IfDataFamTyCon  -> return DataFamilyTyCon
            IfDataTyCon cons -> do  { data_cons <- mapM tc_con_decl cons
                                    ; return (mkDataTyConRhs data_cons) }
            IfNewTyCon con   -> do  { data_con <- tc_con_decl con
                                    ; mkNewTyConRhs tycon_name tycon data_con }
      where
        tc_con_decl (IfCon { ifConInfix = is_infix,
                             ifConExTvs = ex_tvs,
                             ifConOcc = occ, ifConCtxt = ctxt, ifConEqSpec = spec,
                             ifConArgTys = args, ifConFields = field_lbls,
                             ifConStricts = if_stricts})
         = -- Universally-quantified tyvars are shared with
           -- parent TyCon, and are alrady in scope
           bindIfaceTyVars ex_tvs    $ \ ex_tyvars -> do
            { traceIf (text "Start interface-file tc_con_decl" <+> ppr occ)
            ; name  <- lookupIfaceTop occ

            -- Read the context and argument types, but lazily for two reasons
            -- (a) to avoid looking tugging on a recursive use of
            --     the type itself, which is knot-tied
            -- (b) to avoid faulting in the component types unless
            --     they are really needed
            ; ~(eq_spec, theta, arg_tys, stricts) <- forkM (mk_doc name) $
                 do { eq_spec <- tcIfaceEqSpec spec
                    ; theta   <- tcIfaceCtxt ctxt
                    ; arg_tys <- mapM tcIfaceType args
                    ; stricts <- mapM tc_strict if_stricts
                            -- The IfBang field can mention
                            -- the type itself; hence inside forkM
                    ; return (eq_spec, theta, arg_tys, stricts) }
            ; lbl_names <- mapM lookupIfaceTop field_lbls

            -- Remember, tycon is the representation tycon
            ; let orig_res_ty = mkFamilyTyConApp tycon
                                    (substTyVars (mkTopTvSubst eq_spec) tc_tyvars)

            ; con <- buildDataCon (pprPanic "tcIfaceDataCons: FamInstEnvs" (ppr name))
                           name is_infix
                           stricts     -- Pass the HsImplBangs (i.e. final decisions
                                       -- to buildDataCon; it'll use these to guide
                                       -- the construction of a worker
                           lbl_names
                           tc_tyvars ex_tyvars
                           eq_spec theta
                           arg_tys orig_res_ty tycon
            ; traceIf (text "Done interface-file tc_con_decl" <+> ppr name)
            ; return con }
        mk_doc con_name = ptext (sLit "Constructor") <+> ppr con_name

        tc_strict :: IfaceBang -> IfL HsImplBang
        tc_strict IfNoBang = return HsNoBang
        tc_strict IfStrict = return HsStrict
        tc_strict IfUnpack = return (HsUnpack Nothing)
        tc_strict (IfUnpackCo if_co) = do { co <- tcIfaceCo if_co
                                          ; return (HsUnpack (Just co)) }

    tcIfaceEqSpec :: IfaceEqSpec -> IfL [(TyVar, Type)]
    tcIfaceEqSpec spec
      = mapM do_item spec
      where
        do_item (occ, if_ty) = do { tv <- tcIfaceTyVar occ
                                  ; ty <- tcIfaceType if_ty
                                  ; return (tv,ty) }

    {-
    Note [Synonym kind loop]
    ~~~~~~~~~~~~~~~~~~~~~~~~
    Notice that we eagerly grab the *kind* from the interface file, but
    build a forkM thunk for the *rhs* (and family stuff).  To see why,
    consider this (Trac #2412)

    M.hs:       module M where { import X; data T = MkT S }
    X.hs:       module X where { import {-# SOURCE #-} M; type S = T }
    M.hs-boot:  module M where { data T }

    When kind-checking M.hs we need S's kind.  But we do not want to
    find S's kind from (typeKind S-rhs), because we don't want to look at
    S-rhs yet!  Since S is imported from X.hi, S gets just one chance to
    be defined, and we must not do that until we've finished with M.T.

    Solution: record S's kind in the interface file; now we can safely
    look at it.

    ************************************************************************
    *                                                                      *
                    Instances
    *                                                                      *
    ************************************************************************
    -}

    tcIfaceInst :: IfaceClsInst -> IfL ClsInst
    tcIfaceInst (IfaceClsInst { ifDFun = dfun_occ, ifOFlag = oflag
                              , ifInstCls = cls, ifInstTys = mb_tcs
                              , ifInstOrph = orph })
      = do { dfun <- forkM (ptext (sLit "Dict fun") <+> ppr dfun_occ) $
                     tcIfaceExtId dfun_occ
           ; let mb_tcs' = map (fmap ifaceTyConName) mb_tcs
           ; return (mkImportedInstance cls mb_tcs' dfun oflag orph) }

    tcIfaceFamInst :: IfaceFamInst -> IfL FamInst
    tcIfaceFamInst (IfaceFamInst { ifFamInstFam = fam, ifFamInstTys = mb_tcs
                                 , ifFamInstAxiom = axiom_name } )
        = do { axiom' <- forkM (ptext (sLit "Axiom") <+> ppr axiom_name) $
                         tcIfaceCoAxiom axiom_name
                 -- will panic if branched, but that's OK
             ; let axiom'' = toUnbranchedAxiom axiom'
                   mb_tcs' = map (fmap ifaceTyConName) mb_tcs
             ; return (mkImportedFamInst fam mb_tcs' axiom'') }

    {-
    ************************************************************************
    *                                                                      *
                    Rules
    *                                                                      *
    ************************************************************************

    We move a IfaceRule from eps_rules to eps_rule_base when all its LHS free vars
    are in the type environment.  However, remember that typechecking a Rule may
    (as a side effect) augment the type envt, and so we may need to iterate the process.
    -}

    tcIfaceRules :: Bool            -- True <=> ignore rules
                 -> [IfaceRule]
                 -> IfL [CoreRule]
    tcIfaceRules ignore_prags if_rules
      | ignore_prags = return []
      | otherwise    = mapM tcIfaceRule if_rules

    tcIfaceRule :: IfaceRule -> IfL CoreRule
    tcIfaceRule (IfaceRule {ifRuleName = name, ifActivation = act, ifRuleBndrs = bndrs,
                            ifRuleHead = fn, ifRuleArgs = args, ifRuleRhs = rhs,
                            ifRuleAuto = auto })
      = do  { ~(bndrs', args', rhs') <-
                    -- Typecheck the payload lazily, in the hope it'll never be looked at
                    forkM (ptext (sLit "Rule") <+> ftext name) $
                    bindIfaceBndrs bndrs                      $ \ bndrs' ->
                    do { args' <- mapM tcIfaceExpr args
                       ; rhs'  <- tcIfaceExpr rhs
                       ; return (bndrs', args', rhs') }
            ; let mb_tcs = map ifTopFreeName args
            ; return (Rule { ru_name = name, ru_fn = fn, ru_act = act,
                              ru_bndrs = bndrs', ru_args = args',
                              ru_rhs = occurAnalyseExpr rhs',
                              ru_rough = mb_tcs,
                              ru_auto = auto,
                              ru_local = False }) } -- An imported RULE is never for a local Id
                                                    -- or, even if it is (module loop, perhaps)
                                                    -- we'll just leave it in the non-local set
      where
            -- This function *must* mirror exactly what Rules.topFreeName does
            -- We could have stored the ru_rough field in the iface file
            -- but that would be redundant, I think.
            -- The only wrinkle is that we must not be deceived by
            -- type syononyms at the top of a type arg.  Since
            -- we can't tell at this point, we are careful not
            -- to write them out in coreRuleToIfaceRule
        ifTopFreeName :: IfaceExpr -> Maybe Name
        ifTopFreeName (IfaceType (IfaceTyConApp tc _ )) = Just (ifaceTyConName tc)
        ifTopFreeName (IfaceApp f _)                    = ifTopFreeName f
        ifTopFreeName (IfaceExt n)                      = Just n
        ifTopFreeName _                                 = Nothing

    {-
    ************************************************************************
    *                                                                      *
                    Annotations
    *                                                                      *
    ************************************************************************
    -}

    tcIfaceAnnotations :: [IfaceAnnotation] -> IfL [Annotation]
    tcIfaceAnnotations = mapM tcIfaceAnnotation

    tcIfaceAnnotation :: IfaceAnnotation -> IfL Annotation
    tcIfaceAnnotation (IfaceAnnotation target serialized) = do
        target' <- tcIfaceAnnTarget target
        return $ Annotation {
            ann_target = target',
            ann_value = serialized
        }

    tcIfaceAnnTarget :: IfaceAnnTarget -> IfL (AnnTarget Name)
    tcIfaceAnnTarget (NamedTarget occ) = do
        name <- lookupIfaceTop occ
        return $ NamedTarget name
    tcIfaceAnnTarget (ModuleTarget mod) = do
        return $ ModuleTarget mod

    {-
    ************************************************************************
    *                                                                      *
                    Vectorisation information
    *                                                                      *
    ************************************************************************
    -}

    -- We need access to the type environment as we need to look up information about type constructors
    -- (i.e., their data constructors and whether they are class type constructors).  If a vectorised
    -- type constructor or class is defined in the same module as where it is vectorised, we cannot
    -- look that information up from the type constructor that we obtained via a 'forkM'ed
    -- 'tcIfaceTyCon' without recursively loading the interface that we are already type checking again
    -- and again and again...
    --
    tcIfaceVectInfo :: Module -> TypeEnv -> IfaceVectInfo -> IfL VectInfo
    tcIfaceVectInfo mod typeEnv (IfaceVectInfo
                                 { ifaceVectInfoVar            = vars
                                 , ifaceVectInfoTyCon          = tycons
                                 , ifaceVectInfoTyConReuse     = tyconsReuse
                                 , ifaceVectInfoParallelVars   = parallelVars
                                 , ifaceVectInfoParallelTyCons = parallelTyCons
                                 })
      = do { let parallelTyConsSet = mkNameSet parallelTyCons
           ; vVars         <- mapM vectVarMapping                  vars
           ; let varsSet = mkVarSet (map fst vVars)
           ; tyConRes1     <- mapM (vectTyConVectMapping varsSet)  tycons
           ; tyConRes2     <- mapM (vectTyConReuseMapping varsSet) tyconsReuse
           ; vParallelVars <- mapM vectVar                         parallelVars
           ; let (vTyCons, vDataCons, vScSels) = unzip3 (tyConRes1 ++ tyConRes2)
           ; return $ VectInfo
                      { vectInfoVar            = mkVarEnv  vVars `extendVarEnvList` concat vScSels
                      , vectInfoTyCon          = mkNameEnv vTyCons
                      , vectInfoDataCon        = mkNameEnv (concat vDataCons)
                      , vectInfoParallelVars   = mkVarSet  vParallelVars
                      , vectInfoParallelTyCons = parallelTyConsSet
                      }
           }
      where
        vectVarMapping name
          = do { vName <- lookupOrig mod (mkLocalisedOccName mod mkVectOcc name)
               ; var   <- forkM (ptext (sLit "vect var")  <+> ppr name)  $
                            tcIfaceExtId name
               ; vVar  <- forkM (ptext (sLit "vect vVar [mod =") <+>
                                 ppr mod <> ptext (sLit "; nameModule =") <+>
                                 ppr (nameModule name) <> ptext (sLit "]") <+> ppr vName) $
                           tcIfaceExtId vName
               ; return (var, (var, vVar))
               }
          -- where
          --   lookupLocalOrExternalId name
          --     = do { let mb_id = lookupTypeEnv typeEnv name
          --          ; case mb_id of
          --                -- id is local
          --              Just (AnId id) -> return id
          --                -- name is not an Id => internal inconsistency
          --              Just _         -> notAnIdErr
          --                -- Id is external
          --              Nothing        -> tcIfaceExtId name
          --          }
          --
          --   notAnIdErr = pprPanic "TcIface.tcIfaceVectInfo: not an id" (ppr name)

        vectVar name
          = forkM (ptext (sLit "vect scalar var")  <+> ppr name)  $
              tcIfaceExtId name

        vectTyConVectMapping vars name
          = do { vName  <- lookupOrig mod (mkLocalisedOccName mod mkVectTyConOcc name)
               ; vectTyConMapping vars name vName
               }

        vectTyConReuseMapping vars name
          = vectTyConMapping vars name name

        vectTyConMapping vars name vName
          = do { tycon  <- lookupLocalOrExternalTyCon name
               ; vTycon <- forkM (ptext (sLit "vTycon of") <+> ppr vName) $
                             lookupLocalOrExternalTyCon vName

                   -- Map the data constructors of the original type constructor to those of the
                   -- vectorised type constructor /unless/ the type constructor was vectorised
                   -- abstractly; if it was vectorised abstractly, the workers of its data constructors
                   -- do not appear in the set of vectorised variables.
                   --
                   -- NB: This is lazy!  We don't pull at the type constructors before we actually use
                   --     the data constructor mapping.
               ; let isAbstract | isClassTyCon tycon = False
                                | datacon:_ <- tyConDataCons tycon
                                                     = not $ dataConWrapId datacon `elemVarSet` vars
                                | otherwise          = True
                     vDataCons  | isAbstract = []
                                | otherwise  = [ (dataConName datacon, (datacon, vDatacon))
                                               | (datacon, vDatacon) <- zip (tyConDataCons tycon)
                                                                            (tyConDataCons vTycon)
                                               ]

                       -- Map the (implicit) superclass and methods selectors as they don't occur in
                       -- the var map.
                     vScSels    | Just cls  <- tyConClass_maybe tycon
                                , Just vCls <- tyConClass_maybe vTycon
                                = [ (sel, (sel, vSel))
                                  | (sel, vSel) <- zip (classAllSelIds cls) (classAllSelIds vCls)
                                  ]
                                | otherwise
                                = []

               ; return ( (name, (tycon, vTycon))          -- (T, T_v)
                        , vDataCons                        -- list of (Ci, Ci_v)
                        , vScSels                          -- list of (seli, seli_v)
                        )
               }
          where
              -- we need a fully defined version of the type constructor to be able to extract
              -- its data constructors etc.
            lookupLocalOrExternalTyCon name
              = do { let mb_tycon = lookupTypeEnv typeEnv name
                   ; case mb_tycon of
                         -- tycon is local
                       Just (ATyCon tycon) -> return tycon
                         -- name is not a tycon => internal inconsistency
                       Just _              -> notATyConErr
                         -- tycon is external
                       Nothing             -> tcIfaceTyCon (IfaceTc name)
                   }

            notATyConErr = pprPanic "TcIface.tcIfaceVectInfo: not a tycon" (ppr name)

    {-
    ************************************************************************
    *                                                                      *
                            Types
    *                                                                      *
    ************************************************************************
    -}

    tcIfaceType :: IfaceType -> IfL Type
    tcIfaceType (IfaceTyVar n)         = do { tv <- tcIfaceTyVar n; return (TyVarTy tv) }
    tcIfaceType (IfaceAppTy t1 t2)     = do { t1' <- tcIfaceType t1; t2' <- tcIfaceType t2; return (AppTy t1' t2') }
    tcIfaceType (IfaceLitTy l)         = do { l1 <- tcIfaceTyLit l; return (LitTy l1) }
    tcIfaceType (IfaceFunTy t1 t2)     = tcIfaceTypeFun t1 t2
    tcIfaceType (IfaceDFunTy t1 t2)    = tcIfaceTypeFun t1 t2
    tcIfaceType (IfaceTyConApp tc tks) = do { tc' <- tcIfaceTyCon tc
                                            ; tks' <- tcIfaceTcArgs tks
                                            ; return (mkTyConApp tc' tks') }
    tcIfaceType (IfaceForAllTy tv t)  = bindIfaceTyVar tv $ \ tv' -> do { t' <- tcIfaceType t; return (ForAllTy tv' t') }

    tcIfaceTypeFun :: IfaceType -> IfaceType -> IfL Type
    tcIfaceTypeFun t1 t2 = do { t1' <- tcIfaceType t1; t2' <- tcIfaceType t2; return (FunTy t1' t2') }

    tcIfaceKind :: IfaceKind -> IfL Type
    tcIfaceKind (IfaceAppTy t1 t2)  = do { t1' <- tcIfaceKind t1; t2' <- tcIfaceKind t2; return (AppTy t1' t2') }
    tcIfaceKind (IfaceFunTy t1 t2)  = tcIfaceKindFun t1 t2
    tcIfaceKind (IfaceDFunTy t1 t2) = tcIfaceKindFun t1 t2
    tcIfaceKind (IfaceLitTy l)      = pprPanic "tcIfaceKind" (ppr l)
    tcIfaceKind k                   = tcIfaceType k

    tcIfaceKindFun :: IfaceKind -> IfaceKind -> IfL Type
    tcIfaceKindFun t1 t2 = do { t1' <- tcIfaceKind t1; t2' <- tcIfaceKind t2; return (FunTy t1' t2') }

    tcIfaceTcArgs :: IfaceTcArgs -> IfL [Type]
    tcIfaceTcArgs args
      = case args of
          ITC_Type t ts ->
            do { t'  <- tcIfaceType t
               ; ts' <- tcIfaceTcArgs ts
               ; return (t':ts') }
          ITC_Kind k ks ->
            do { k'  <- tcIfaceKind k
               ; ks' <- tcIfaceTcArgs ks
               ; return (k':ks') }
          ITC_Nil -> return []
    -----------------------------------------
    tcIfaceCtxt :: IfaceContext -> IfL ThetaType
    tcIfaceCtxt sts = mapM tcIfaceType sts

    -----------------------------------------
    tcIfaceTyLit :: IfaceTyLit -> IfL TyLit
    tcIfaceTyLit (IfaceNumTyLit n) = return (NumTyLit n)
    tcIfaceTyLit (IfaceStrTyLit n) = return (StrTyLit n)

    {-
    ************************************************************************
    *                                                                      *
                            Coercions
    *                                                                      *
    ************************************************************************
    -}

    tcIfaceCo :: IfaceCoercion -> IfL Coercion
    tcIfaceCo (IfaceReflCo r t)         = mkReflCo r <$> tcIfaceType t
    tcIfaceCo (IfaceFunCo r c1 c2)      = mkFunCo r <$> tcIfaceCo c1 <*> tcIfaceCo c2
    tcIfaceCo (IfaceTyConAppCo r tc cs) = mkTyConAppCo r <$> tcIfaceTyCon tc
                                                         <*> mapM tcIfaceCo cs
    tcIfaceCo (IfaceAppCo c1 c2)        = mkAppCo <$> tcIfaceCo c1
                                                  <*> tcIfaceCo c2
    tcIfaceCo (IfaceForAllCo tv c)      = bindIfaceTyVar tv $ \ tv' ->
                                          mkForAllCo tv' <$> tcIfaceCo c
    tcIfaceCo (IfaceCoVarCo n)          = mkCoVarCo <$> tcIfaceCoVar n
    tcIfaceCo (IfaceAxiomInstCo n i cs) = AxiomInstCo <$> tcIfaceCoAxiom n
                                                      <*> pure i
                                                      <*> mapM tcIfaceCo cs
    tcIfaceCo (IfaceUnivCo s r t1 t2)   = UnivCo s r <$> tcIfaceType t1
                                                   <*> tcIfaceType t2
    tcIfaceCo (IfaceSymCo c)            = SymCo    <$> tcIfaceCo c
    tcIfaceCo (IfaceTransCo c1 c2)      = TransCo  <$> tcIfaceCo c1
                                                   <*> tcIfaceCo c2
    tcIfaceCo (IfaceInstCo c1 t2)       = InstCo   <$> tcIfaceCo c1
                                                   <*> tcIfaceType t2
    tcIfaceCo (IfaceNthCo d c)          = NthCo d  <$> tcIfaceCo c
    tcIfaceCo (IfaceLRCo lr c)          = LRCo lr  <$> tcIfaceCo c
    tcIfaceCo (IfaceSubCo c)            = SubCo    <$> tcIfaceCo c
    tcIfaceCo (IfaceAxiomRuleCo ax tys cos) = AxiomRuleCo
                                                <$> tcIfaceCoAxiomRule ax
                                                <*> mapM tcIfaceType tys
                                                <*> mapM tcIfaceCo cos

    tcIfaceCoVar :: FastString -> IfL CoVar
    tcIfaceCoVar = tcIfaceLclId

    tcIfaceCoAxiomRule :: FastString -> IfL CoAxiomRule
    tcIfaceCoAxiomRule n =
      case Map.lookup n typeNatCoAxiomRules of
        Just ax -> return ax
        _  -> pprPanic "tcIfaceCoAxiomRule" (ppr n)

    {-
    ************************************************************************
    *                                                                      *
                            Core
    *                                                                      *
    ************************************************************************
    -}

    tcIfaceExpr :: IfaceExpr -> IfL CoreExpr
    tcIfaceExpr (IfaceType ty)
      = Type <$> tcIfaceType ty

    tcIfaceExpr (IfaceCo co)
      = Coercion <$> tcIfaceCo co

    tcIfaceExpr (IfaceCast expr co)
      = Cast <$> tcIfaceExpr expr <*> tcIfaceCo co

    tcIfaceExpr (IfaceLcl name)
      = Var <$> tcIfaceLclId name

    tcIfaceExpr (IfaceExt gbl)
      = Var <$> tcIfaceExtId gbl

    tcIfaceExpr (IfaceLit lit)
      = do lit' <- tcIfaceLit lit
           return (Lit lit')

    tcIfaceExpr (IfaceFCall cc ty) = do
        ty' <- tcIfaceType ty
        u <- newUnique
        dflags <- getDynFlags
        return (Var (mkFCallId dflags u cc ty'))

    tcIfaceExpr (IfaceTuple boxity args)  = do
        args' <- mapM tcIfaceExpr args
        -- Put the missing type arguments back in
        let con_args = map (Type . exprType) args' ++ args'
        return (mkApps (Var con_id) con_args)
      where
        arity = length args
        con_id = dataConWorkId (tupleCon boxity arity)

    tcIfaceExpr (IfaceLam (bndr, os) body)
      = bindIfaceBndr bndr $ \bndr' ->
        Lam (tcIfaceOneShot os bndr') <$> tcIfaceExpr body
      where
        tcIfaceOneShot IfaceOneShot b = setOneShotLambda b
        tcIfaceOneShot _            b = b

    tcIfaceExpr (IfaceApp fun arg)
      = tcIfaceApps fun arg

    tcIfaceExpr (IfaceECase scrut ty)
      = do { scrut' <- tcIfaceExpr scrut
           ; ty' <- tcIfaceType ty
           ; return (castBottomExpr scrut' ty') }

    tcIfaceExpr (IfaceCase scrut case_bndr alts)  = do
        scrut' <- tcIfaceExpr scrut
        case_bndr_name <- newIfaceName (mkVarOccFS case_bndr)
        let
            scrut_ty   = exprType scrut'
            case_bndr' = mkLocalId case_bndr_name scrut_ty
            tc_app     = splitTyConApp scrut_ty
                    -- NB: Won't always succeed (polymorphic case)
                    --     but won't be demanded in those cases
                    -- NB: not tcSplitTyConApp; we are looking at Core here
                    --     look through non-rec newtypes to find the tycon that
                    --     corresponds to the datacon in this case alternative

        extendIfaceIdEnv [case_bndr'] $ do
         alts' <- mapM (tcIfaceAlt scrut' tc_app) alts
         return (Case scrut' case_bndr' (coreAltsType alts') alts')

    tcIfaceExpr (IfaceLet (IfaceNonRec (IfLetBndr fs ty info) rhs) body)
      = do  { name    <- newIfaceName (mkVarOccFS fs)
            ; ty'     <- tcIfaceType ty
            ; id_info <- tcIdInfo False {- Don't ignore prags; we are inside one! -}
                                  name ty' info
            ; let id = mkLocalIdWithInfo name ty' id_info
            ; rhs' <- tcIfaceExpr rhs
            ; body' <- extendIfaceIdEnv [id] (tcIfaceExpr body)
            ; return (Let (NonRec id rhs') body') }

    tcIfaceExpr (IfaceLet (IfaceRec pairs) body)
      = do { ids <- mapM tc_rec_bndr (map fst pairs)
           ; extendIfaceIdEnv ids $ do
           { pairs' <- zipWithM tc_pair pairs ids
           ; body' <- tcIfaceExpr body
           ; return (Let (Rec pairs') body') } }
     where
       tc_rec_bndr (IfLetBndr fs ty _)
         = do { name <- newIfaceName (mkVarOccFS fs)
              ; ty'  <- tcIfaceType ty
              ; return (mkLocalId name ty') }
       tc_pair (IfLetBndr _ _ info, rhs) id
         = do { rhs' <- tcIfaceExpr rhs
              ; id_info <- tcIdInfo False {- Don't ignore prags; we are inside one! -}
                                    (idName id) (idType id) info
              ; return (setIdInfo id id_info, rhs') }

    tcIfaceExpr (IfaceTick tickish expr) = do
        expr' <- tcIfaceExpr expr
        -- If debug flag is not set: Ignore source notes
        dbgFlag <- fmap (gopt Opt_Debug) getDynFlags
        case tickish of
          IfaceSource{} | not dbgFlag
                        -> return expr'
          _otherwise    -> do
            tickish' <- tcIfaceTickish tickish
            return (Tick tickish' expr')

    -------------------------
    tcIfaceApps :: IfaceExpr -> IfaceExpr -> IfL CoreExpr
    -- See Note [Checking IfaceTypes vs IfaceKinds]
    tcIfaceApps fun arg
      = go_down fun [arg]
      where
        go_down (IfaceApp fun arg) args = go_down fun (arg:args)
        go_down fun args = do { fun' <- tcIfaceExpr fun
                              ; go_up fun' (exprType fun') args }

        go_up :: CoreExpr -> Type -> [IfaceExpr] -> IfL CoreExpr
        go_up fun _ [] = return fun
        go_up fun fun_ty (IfaceType t : args)
           | Just (tv,body_ty) <- splitForAllTy_maybe fun_ty
           = do { t' <- if isKindVar tv
                        then tcIfaceKind t
                        else tcIfaceType t
                ; let fun_ty' = substTyWith [tv] [t'] body_ty
                ; go_up (App fun (Type t')) fun_ty' args }
        go_up fun fun_ty (arg : args)
           | Just (_, fun_ty') <- splitFunTy_maybe fun_ty
           = do { arg' <- tcIfaceExpr arg
                ; go_up (App fun arg') fun_ty' args }
        go_up fun fun_ty args = pprPanic "tcIfaceApps" (ppr fun $$ ppr fun_ty $$ ppr args)

    -------------------------
    tcIfaceTickish :: IfaceTickish -> IfM lcl (Tickish Id)
    tcIfaceTickish (IfaceHpcTick modl ix)   = return (HpcTick modl ix)
    tcIfaceTickish (IfaceSCC  cc tick push) = return (ProfNote cc tick push)
    tcIfaceTickish (IfaceSource src name)   = return (SourceNote src name)

    -------------------------
    tcIfaceLit :: Literal -> IfL Literal
    -- Integer literals deserialise to (LitInteger i <error thunk>)
    -- so tcIfaceLit just fills in the type.
    -- See Note [Integer literals] in Literal
    tcIfaceLit (LitInteger i _)
      = do t <- tcIfaceTyCon (IfaceTc integerTyConName)
           return (mkLitInteger i (mkTyConTy t))
    tcIfaceLit lit = return lit

    -------------------------
    tcIfaceAlt :: CoreExpr -> (TyCon, [Type])
               -> (IfaceConAlt, [FastString], IfaceExpr)
               -> IfL (AltCon, [TyVar], CoreExpr)
    tcIfaceAlt _ _ (IfaceDefault, names, rhs)
      = ASSERT( null names ) do
        rhs' <- tcIfaceExpr rhs
        return (DEFAULT, [], rhs')

    tcIfaceAlt _ _ (IfaceLitAlt lit, names, rhs)
      = ASSERT( null names ) do
        lit' <- tcIfaceLit lit
        rhs' <- tcIfaceExpr rhs
        return (LitAlt lit', [], rhs')

    -- A case alternative is made quite a bit more complicated
    -- by the fact that we omit type annotations because we can
    -- work them out.  True enough, but its not that easy!
    tcIfaceAlt scrut (tycon, inst_tys) (IfaceDataAlt data_occ, arg_strs, rhs)
      = do  { con <- tcIfaceDataCon data_occ
            ; when (debugIsOn && not (con `elem` tyConDataCons tycon))
                   (failIfM (ppr scrut $$ ppr con $$ ppr tycon $$ ppr (tyConDataCons tycon)))
            ; tcIfaceDataAlt con inst_tys arg_strs rhs }

    tcIfaceDataAlt :: DataCon -> [Type] -> [FastString] -> IfaceExpr
                   -> IfL (AltCon, [TyVar], CoreExpr)
    tcIfaceDataAlt con inst_tys arg_strs rhs
      = do  { us <- newUniqueSupply
            ; let uniqs = uniqsFromSupply us
            ; let (ex_tvs, arg_ids)
                          = dataConRepFSInstPat arg_strs uniqs con inst_tys

            ; rhs' <- extendIfaceTyVarEnv ex_tvs    $
                      extendIfaceIdEnv arg_ids      $
                      tcIfaceExpr rhs
            ; return (DataAlt con, ex_tvs ++ arg_ids, rhs') }

    {-
    ************************************************************************
    *                                                                      *
                    IdInfo
    *                                                                      *
    ************************************************************************
    -}

    tcIdDetails :: Type -> IfaceIdDetails -> IfL IdDetails
    tcIdDetails _  IfVanillaId = return VanillaId
    tcIdDetails ty (IfDFunId ns)
      = return (DFunId ns (isNewTyCon (classTyCon cls)))
      where
        (_, _, cls, _) = tcSplitDFunTy ty

    tcIdDetails _ (IfRecSelId tc naughty)
      = do { tc' <- tcIfaceTyCon tc
           ; return (RecSelId { sel_tycon = tc', sel_naughty = naughty }) }

    tcIdInfo :: Bool -> Name -> Type -> IfaceIdInfo -> IfL IdInfo
    tcIdInfo ignore_prags name ty info
      | ignore_prags = return vanillaIdInfo
      | otherwise    = case info of
                            NoInfo       -> return vanillaIdInfo
                            HasInfo info -> foldlM tcPrag init_info info
      where
        -- Set the CgInfo to something sensible but uninformative before
        -- we start; default assumption is that it has CAFs
        init_info = vanillaIdInfo

        tcPrag :: IdInfo -> IfaceInfoItem -> IfL IdInfo
        tcPrag info HsNoCafRefs        = return (info `setCafInfo`   NoCafRefs)
        tcPrag info (HsArity arity)    = return (info `setArityInfo` arity)
        tcPrag info (HsStrictness str) = return (info `setStrictnessInfo` str)
        tcPrag info (HsInline prag)    = return (info `setInlinePragInfo` prag)

            -- The next two are lazy, so they don't transitively suck stuff in
        tcPrag info (HsUnfold lb if_unf)
          = do { unf <- tcUnfolding name ty info if_unf
               ; let info1 | lb        = info `setOccInfo` strongLoopBreaker
                           | otherwise = info
               ; return (info1 `setUnfoldingInfoLazily` unf) }

    tcUnfolding :: Name -> Type -> IdInfo -> IfaceUnfolding -> IfL Unfolding
    tcUnfolding name _ info (IfCoreUnfold stable if_expr)
      = do  { dflags <- getDynFlags
            ; mb_expr <- tcPragExpr name if_expr
            ; let unf_src | stable    = InlineStable
                          | otherwise = InlineRhs
            ; return $ case mb_expr of
                Nothing -> NoUnfolding
                Just expr -> mkUnfolding dflags unf_src
                               True {- Top level -}
                               (isBottomingSig strict_sig)
                               expr
            }
      where
         -- Strictness should occur before unfolding!
        strict_sig = strictnessInfo info
    tcUnfolding name _ _ (IfCompulsory if_expr)
      = do  { mb_expr <- tcPragExpr name if_expr
            ; return (case mb_expr of
                        Nothing   -> NoUnfolding
                        Just expr -> mkCompulsoryUnfolding expr) }

    tcUnfolding name _ _ (IfInlineRule arity unsat_ok boring_ok if_expr)
      = do  { mb_expr <- tcPragExpr name if_expr
            ; return (case mb_expr of
                        Nothing   -> NoUnfolding
                        Just expr -> mkCoreUnfolding InlineStable True expr guidance )}
      where
        guidance = UnfWhen { ug_arity = arity, ug_unsat_ok = unsat_ok, ug_boring_ok = boring_ok }

    tcUnfolding name dfun_ty _ (IfDFunUnfold bs ops)
      = bindIfaceBndrs bs $ \ bs' ->
        do { mb_ops1 <- forkM_maybe doc $ mapM tcIfaceExpr ops
           ; return (case mb_ops1 of
                        Nothing   -> noUnfolding
                        Just ops1 -> mkDFunUnfolding bs' (classDataCon cls) ops1) }
      where
        doc = text "Class ops for dfun" <+> ppr name
        (_, _, cls, _) = tcSplitDFunTy dfun_ty

    {-
    For unfoldings we try to do the job lazily, so that we never type check
    an unfolding that isn't going to be looked at.
    -}

    tcPragExpr :: Name -> IfaceExpr -> IfL (Maybe CoreExpr)
    tcPragExpr name expr
      = forkM_maybe doc $ do
        core_expr' <- tcIfaceExpr expr

                    -- Check for type consistency in the unfolding
        whenGOptM Opt_DoCoreLinting $ do
            in_scope <- get_in_scope
            case lintUnfolding noSrcLoc in_scope core_expr' of
              Nothing       -> return ()
              Just fail_msg -> do { mod <- getIfModule
                                  ; pprPanic "Iface Lint failure"
                                      (vcat [ ptext (sLit "In interface for") <+> ppr mod
                                            , hang doc 2 fail_msg
                                            , ppr name <+> equals <+> ppr core_expr'
                                            , ptext (sLit "Iface expr =") <+> ppr expr ]) }
        return core_expr'
      where
        doc = text "Unfolding of" <+> ppr name

        get_in_scope :: IfL [Var] -- Totally disgusting; but just for linting
        get_in_scope
            = do { (gbl_env, lcl_env) <- getEnvs
                 ; rec_ids <- case if_rec_types gbl_env of
                                Nothing -> return []
                                Just (_, get_env) -> do
                                   { type_env <- setLclEnv () get_env
                                   ; return (typeEnvIds type_env) }
                 ; return (varEnvElts (if_tv_env lcl_env) ++
                           varEnvElts (if_id_env lcl_env) ++
                           rec_ids) }

    {-
    ************************************************************************
    *                                                                      *
                    Getting from Names to TyThings
    *                                                                      *
    ************************************************************************
    -}

    tcIfaceGlobal :: Name -> IfL TyThing
    tcIfaceGlobal name
      | Just thing <- wiredInNameTyThing_maybe name
            -- Wired-in things include TyCons, DataCons, and Ids
            -- Even though we are in an interface file, we want to make
            -- sure the instances and RULES of this thing (particularly TyCon) are loaded
            -- Imagine: f :: Double -> Double
      = do { ifCheckWiredInThing thing; return thing }
      | otherwise
      = do  { env <- getGblEnv
            ; case if_rec_types env of {    -- Note [Tying the knot]
                Just (mod, get_type_env)
                    | nameIsLocalOrFrom mod name
                    -> do           -- It's defined in the module being compiled
                    { type_env <- setLclEnv () get_type_env         -- yuk
                    ; case lookupNameEnv type_env name of
                            Just thing -> return thing
                            Nothing   -> pprPanic "tcIfaceGlobal (local): not found:"
                                                    (ppr name $$ ppr type_env) }

              ; _ -> do

            { hsc_env <- getTopEnv
            ; mb_thing <- liftIO (lookupTypeHscEnv hsc_env name)
            ; case mb_thing of {
                Just thing -> return thing ;
                Nothing    -> do

            { mb_thing <- importDecl name   -- It's imported; go get it
            ; case mb_thing of
                Failed err      -> failIfM err
                Succeeded thing -> return thing
        }}}}}

    -- Note [Tying the knot]
    -- ~~~~~~~~~~~~~~~~~~~~~
    -- The if_rec_types field is used in two situations:
    --
    -- a) Compiling M.hs, which indiretly imports Foo.hi, which mentions M.T
    --    Then we look up M.T in M's type environment, which is splatted into if_rec_types
    --    after we've built M's type envt.
    --
    -- b) In ghc --make, during the upsweep, we encounter M.hs, whose interface M.hi
    --    is up to date.  So we call typecheckIface on M.hi.  This splats M.T into
    --    if_rec_types so that the (lazily typechecked) decls see all the other decls
    --
    -- In case (b) it's important to do the if_rec_types check *before* looking in the HPT
    -- Because if M.hs also has M.hs-boot, M.T will *already be* in the HPT, but in its
    -- emasculated form (e.g. lacking data constructors).

    tcIfaceTyCon :: IfaceTyCon -> IfL TyCon
    tcIfaceTyCon itc
      = do {
        ; thing <- tcIfaceGlobal (ifaceTyConName itc)
        ; case itc of
            IfaceTc _ -> return $ tyThingTyCon thing
            IfacePromotedDataCon _ -> return $ promoteDataCon $ tyThingDataCon thing
            IfacePromotedTyCon name ->
              let ktycon tc
                    | isSuperKind (tyConKind tc) = return tc
                    | Just prom_tc <- promotableTyCon_maybe tc = return prom_tc
                    | otherwise = pprPanic "tcIfaceTyCon" (ppr name $$ ppr thing)
              in ktycon (tyThingTyCon thing)
        }

    tcIfaceCoAxiom :: Name -> IfL (CoAxiom Branched)
    tcIfaceCoAxiom name = do { thing <- tcIfaceGlobal name
                             ; return (tyThingCoAxiom thing) }

    tcIfaceDataCon :: Name -> IfL DataCon
    tcIfaceDataCon name = do { thing <- tcIfaceGlobal name
                             ; case thing of
                                    AConLike (RealDataCon dc) -> return dc
                                    _       -> pprPanic "tcIfaceExtDC" (ppr name$$ ppr thing) }

    tcIfaceExtId :: Name -> IfL Id
    tcIfaceExtId name = do { thing <- tcIfaceGlobal name
                           ; case thing of
                              AnId id -> return id
                              _       -> pprPanic "tcIfaceExtId" (ppr name$$ ppr thing) }

    {-
    ************************************************************************
    *                                                                      *
                    Bindings
    *                                                                      *
    ************************************************************************
    -}

    bindIfaceBndr :: IfaceBndr -> (CoreBndr -> IfL a) -> IfL a
    bindIfaceBndr (IfaceIdBndr (fs, ty)) thing_inside
      = do  { name <- newIfaceName (mkVarOccFS fs)
            ; ty' <- tcIfaceType ty
            ; let id = mkLocalId name ty'
            ; extendIfaceIdEnv [id] (thing_inside id) }
    bindIfaceBndr (IfaceTvBndr bndr) thing_inside
      = bindIfaceTyVar bndr thing_inside

    bindIfaceBndrs :: [IfaceBndr] -> ([CoreBndr] -> IfL a) -> IfL a
    bindIfaceBndrs []     thing_inside = thing_inside []
    bindIfaceBndrs (b:bs) thing_inside
      = bindIfaceBndr b     $ \ b' ->
        bindIfaceBndrs bs   $ \ bs' ->
        thing_inside (b':bs')

    -----------------------
    bindIfaceTyVar :: IfaceTvBndr -> (TyVar -> IfL a) -> IfL a
    bindIfaceTyVar (occ,kind) thing_inside
      = do  { name <- newIfaceName (mkTyVarOccFS occ)
            ; tyvar <- mk_iface_tyvar name kind
            ; extendIfaceTyVarEnv [tyvar] (thing_inside tyvar) }

    bindIfaceTyVars :: [IfaceTvBndr] -> ([TyVar] -> IfL a) -> IfL a
    bindIfaceTyVars bndrs thing_inside
      = do { names <- newIfaceNames (map mkTyVarOccFS occs)
            ; let (kis_kind, tys_kind) = span isSuperIfaceKind kinds
                  (kis_name, tys_name) = splitAt (length kis_kind) names
              -- We need to bring the kind variables in scope since type
              -- variables may mention them.
            ; kvs <- zipWithM mk_iface_tyvar kis_name kis_kind
            ; extendIfaceTyVarEnv kvs $ do
            { tvs <- zipWithM mk_iface_tyvar tys_name tys_kind
            ; extendIfaceTyVarEnv tvs (thing_inside (kvs ++ tvs)) } }
      where
        (occs,kinds) = unzip bndrs

    isSuperIfaceKind :: IfaceKind -> Bool
    isSuperIfaceKind (IfaceTyConApp tc ITC_Nil) = ifaceTyConName tc == superKindTyConName
    isSuperIfaceKind _ = False

    mk_iface_tyvar :: Name -> IfaceKind -> IfL TyVar
    mk_iface_tyvar name ifKind
       = do { kind <- tcIfaceKind ifKind
            ; return (Var.mkTyVar name kind) }

    bindIfaceTyVars_AT :: [IfaceTvBndr] -> ([TyVar] -> IfL a) -> IfL a
    -- Used for type variable in nested associated data/type declarations
    -- where some of the type variables are already in scope
    --    class C a where { data T a b }
    -- Here 'a' is in scope when we look at the 'data T'
    bindIfaceTyVars_AT [] thing_inside
      = thing_inside []
    bindIfaceTyVars_AT (b@(tv_occ,_) : bs) thing_inside
      = do { mb_tv <- lookupIfaceTyVar tv_occ
           ; let bind_b :: (TyVar -> IfL a) -> IfL a
                 bind_b = case mb_tv of
                            Just b' -> \k -> k b'
                            Nothing -> bindIfaceTyVar b
           ; bind_b $ \b' ->
             bindIfaceTyVars_AT bs $ \bs' ->
             thing_inside (b':bs') }