content: {-# LANGUAGE CPP #-}
  {-# LANGUAGE LambdaCase #-}
  {-# LANGUAGE NondecreasingIndentation #-}
  {-# LANGUAGE TypeFamilies #-}
  {-# LANGUAGE MultiWayIf #-}
  
  {-# OPTIONS_GHC -Wno-incomplete-record-updates #-}
  
  {-
  (c) The University of Glasgow 2006
  (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
  
  -}
  
  -- | Typechecking a whole module
  --
  -- https://gitlab.haskell.org/ghc/ghc/wikis/commentary/compiler/type-checker
  module GHC.Tc.Module (
          tcRnStmt, tcRnExpr, TcRnExprMode(..),
          tcRnType, tcRnTypeSkolemising,
          tcRnImportDecls,
          tcRnLookupRdrName,
          getModuleInterface,
          tcRnDeclsi,
          isGHCiMonad,
          runTcInteractive,    -- Used by GHC API clients (#8878)
          withTcPlugins,       -- Used by GHC API clients (#20499)
          withHoleFitPlugins,  -- Used by GHC API clients (#20499)
          withDefaultingPlugins,
          tcRnLookupName,
          tcRnGetInfo,
          tcRnModule, tcRnModuleTcRnM,
          tcTopSrcDecls,
          rnTopSrcDecls,
          checkBootDecl, checkHiBootIface',
          findExtraSigImports,
          implicitRequirements,
          checkUnit,
          mergeSignatures,
          tcRnMergeSignatures,
          instantiateSignature,
          tcRnInstantiateSignature,
          loadUnqualIfaces,
          -- More private...
          checkBootDeclM,
          getRenamedStuff, RenamedStuff
      ) where
  
  import GHC.Prelude
  
  import GHC.Driver.Env
  import GHC.Driver.Plugins
  import GHC.Driver.DynFlags
  import GHC.Driver.Config.Diagnostic
  import GHC.IO.Unsafe ( unsafeInterleaveIO )
  
  import GHC.Tc.Errors.Types
  import {-# SOURCE #-} GHC.Tc.Gen.Splice ( finishTH, runRemoteModFinalizers )
  import GHC.Tc.Gen.HsType
  import GHC.Tc.Validity( checkValidType )
  import GHC.Tc.Gen.Match
  import GHC.Tc.Utils.Unify( checkConstraints, tcSubTypeSigma )
  import GHC.Tc.Zonk.Type
  import GHC.Tc.Gen.Expr
  import GHC.Tc.Utils.Monad
  import GHC.Tc.Gen.Export
  import GHC.Tc.Types.Evidence
  import GHC.Tc.Types.Constraint
  import GHC.Tc.Types.Origin
  import GHC.Tc.Instance.Family
  import GHC.Tc.Gen.Annotation
  import GHC.Tc.Gen.Bind
  import GHC.Tc.Gen.Default
  import GHC.Tc.Utils.Env
  import GHC.Tc.Gen.Sig( tcRules )
  import GHC.Tc.Gen.Foreign
  import GHC.Tc.TyCl.Instance
  import GHC.Tc.Utils.TcMType
  import GHC.Tc.Utils.TcType
  import GHC.Tc.Solver
  import GHC.Tc.TyCl
  import GHC.Tc.Instance.Typeable ( mkTypeableBinds )
  import GHC.Tc.Utils.Backpack
  import GHC.Tc.Zonk.TcType
  
  import GHC.Rename.Bind ( rejectBootDecls )
  import GHC.Rename.Splice ( rnTopSpliceDecls, traceSplice, SpliceInfo(..) )
  import GHC.Rename.HsType
  import GHC.Rename.Expr
  import GHC.Rename.Fixity ( lookupFixityRn )
  import GHC.Rename.Names
  import GHC.Rename.Env
  import GHC.Rename.Module
  import GHC.Rename.Doc
  import GHC.Rename.Utils ( mkNameClashErr, mkRnSyntaxExpr )
  
  import GHC.Iface.Decl    ( coAxiomToIfaceDecl )
  import GHC.Iface.Env     ( externaliseName )
  import GHC.Iface.Load
  
  import GHC.Builtin.Types ( mkListTy, anyTypeOfKind )
  import GHC.Builtin.Names
  import GHC.Builtin.Utils
  
  import GHC.Hs hiding ( FunDep(..) )
  import GHC.Hs.Dump
  
  import GHC.Core.PatSyn
  import GHC.Core.Predicate ( classMethodTy )
  import GHC.Core.InstEnv
  import GHC.Core.TyCon
  import GHC.Core.DataCon
  import GHC.Core.TyCo.Rep
  import GHC.Core.Type
  import GHC.Core.Class
  import GHC.Core.Coercion.Axiom
  import GHC.Core.Reduction ( Reduction(..) )
  import GHC.Core.TyCo.Ppr( debugPprType )
  import GHC.Core.TyCo.Tidy( tidyTopType )
  import GHC.Core.FamInstEnv
     ( FamInst, pprFamInst, famInstsRepTyCons, orphNamesOfFamInst
     , famInstEnvElts, extendFamInstEnvList, normaliseType )
  
  import GHC.Parser.Header       ( mkPrelImports )
  
  import GHC.IfaceToCore
  
  import GHC.Runtime.Context
  
  import GHC.Utils.Error
  import GHC.Utils.Outputable as Outputable
  import GHC.Utils.Panic
  import GHC.Utils.Misc
  import GHC.Utils.Logger
  
  import GHC.Types.Error
  import GHC.Types.Name.Reader
  import GHC.Types.DefaultEnv
  import GHC.Types.Fixity.Env
  import GHC.Types.Id as Id
  import GHC.Types.Id.Info( IdDetails(..) )
  import GHC.Types.Var.Env
  import GHC.Types.TypeEnv
  import GHC.Types.Name
  import GHC.Types.Name.Env
  import GHC.Types.Name.Set
  import GHC.Types.Avail
  import GHC.Types.Basic hiding( SuccessFlag(..) )
  import GHC.Types.Annotations
  import GHC.Types.SrcLoc
  import GHC.Types.SourceFile
  import qualified GHC.LanguageExtensions as LangExt
  
  import GHC.Unit.Env as UnitEnv
  import GHC.Unit.External
  import GHC.Unit.Types
  import GHC.Unit.State
  import GHC.Unit.Home
  import GHC.Unit.Module
  import GHC.Unit.Module.Warnings
  import GHC.Unit.Module.ModSummary
  import GHC.Unit.Module.ModIface
  import GHC.Unit.Module.ModDetails
  import GHC.Unit.Module.Deps
  import GHC.Driver.Downsweep
  
  import GHC.Data.FastString
  import GHC.Data.Maybe
  import GHC.Data.List.SetOps
  import GHC.Data.Bag
  import qualified GHC.Data.BooleanFormula as BF
  
  import Control.Arrow ( second )
  import Control.DeepSeq
  import Control.Monad
  import Control.Monad.Trans.Writer.CPS
  import Data.Data ( Data )
  import Data.Function (on)
  import Data.Functor.Classes ( liftEq )
  import Data.List ( sort, sortBy )
  import Data.List.NonEmpty ( NonEmpty (..) )
  import qualified Data.List.NonEmpty as NE
  import Data.Ord
  import qualified Data.Set as S
  import qualified Data.Map as M
  import Data.Foldable ( for_ )
  import Data.Traversable ( for )
  import Data.IORef( newIORef )
  
  
  
  {-
  ************************************************************************
  *                                                                      *
          Typecheck and rename a module
  *                                                                      *
  ************************************************************************
  -}
  
  -- | Top level entry point for typechecker and renamer
  tcRnModule :: HscEnv
             -> ModSummary
             -> Bool              -- True <=> save renamed syntax
             -> HsParsedModule
             -> IO (Messages TcRnMessage, Maybe TcGblEnv)
  
  tcRnModule hsc_env mod_sum save_rn_syntax
     parsedModule@HsParsedModule {hpm_module= L loc this_module}
   | RealSrcSpan real_loc _ <- loc
   = withTiming logger
                (text "Renamer/typechecker"<+>brackets (ppr this_mod))
                (const ()) $
     initTc hsc_env hsc_src save_rn_syntax this_mod real_loc $
            tcRnModuleTcRnM hsc_env mod_sum parsedModule this_mod
  
    | otherwise
    = return (err_msg `addMessage` emptyMessages, Nothing)
  
    where
      hsc_src = ms_hsc_src mod_sum
      logger  = hsc_logger hsc_env
      home_unit = hsc_home_unit hsc_env
      err_msg = mkPlainErrorMsgEnvelope loc $
                TcRnModMissingRealSrcSpan this_mod
  
      this_mod
        | Just (L _ mod) <- hsmodName this_module
        = mkHomeModule home_unit mod
  
        | otherwise   -- 'module M where' is omitted
        = mkHomeModule home_unit mAIN_NAME
  
  
  
  
  tcRnModuleTcRnM :: HscEnv
                  -> ModSummary
                  -> HsParsedModule
                  -> Module
                  -> TcRn TcGblEnv
  -- Factored out separately from tcRnModule so that a Core plugin can
  -- call the type checker directly
  tcRnModuleTcRnM hsc_env mod_sum
                  (HsParsedModule {
                     hpm_module =
                        (L loc (HsModule (XModulePs _ _ mod_deprec maybe_doc_hdr)
                                         maybe_mod export_ies import_decls local_decls)),
                     hpm_src_files = src_files
                  })
                  this_mod
   = setSrcSpan loc $
     do { let { explicit_mod_hdr = isJust maybe_mod
              ; hsc_src          = ms_hsc_src mod_sum }
        ; -- Load the hi-boot interface for this module, if any
          -- We do this now so that the boot_names can be passed
          -- to tcTyAndClassDecls, because the boot_names are
          -- automatically considered to be loop breakers
          tcg_env <- getGblEnv
        ; boot_info <- tcHiBootIface hsc_src this_mod
        ; setGblEnv (tcg_env { tcg_self_boot = boot_info })
          $ do
          { -- Deal with imports; first add implicit prelude
            implicit_prelude <- xoptM LangExt.ImplicitPrelude
          ; let { prel_imports = mkPrelImports (moduleName this_mod) implicit_prelude import_decls }
  
          ; when (notNull prel_imports) $ do
              addDiagnostic TcRnImplicitImportOfPrelude
  
          ; -- TODO This is a little skeevy; maybe handle a bit more directly
            let { simplifyImport (L _ idecl) =
                    ( renameRawPkgQual (hsc_unit_env hsc_env) (unLoc $ ideclName idecl) (ideclPkgQual idecl)
                    , reLoc $ ideclName idecl)
                }
          ; raw_sig_imports <- liftIO
                               $ findExtraSigImports hsc_env hsc_src
                                   (moduleName this_mod)
          ; raw_req_imports <- liftIO
                               $ implicitRequirements hsc_env
                                  (map simplifyImport (prel_imports
                                                       ++ import_decls))
          ; let { mkImport mod_name = noLocA
                  $ (simpleImportDecl mod_name)
                    { ideclImportList = Just (Exactly, noLocA [])}}
          ; let { withReason t imps = map (,text t) imps }
          ; let { all_imports = withReason "is implicitly imported" prel_imports
                    ++ withReason "is directly imported" import_decls
                    ++ withReason "is an extra sig import" (map mkImport raw_sig_imports)
                    ++ withReason "is an implicit req import" (map mkImport raw_req_imports) }
          ; -- OK now finally rename the imports
            (defaultImportsByClass, tcg_env) <-
              {-# SCC "tcRnImports" #-} tcRnImports hsc_env all_imports
  
          -- Put a version of the header without identifier info into the tcg_env
          -- Make sure to do this before 'tcRnSrcDecls', because we need the
          -- module header when we're splicing TH, since it can be accessed via
          -- 'getDoc'.
          -- We will rename it properly after renaming everything else so that
          -- haddock can link the identifiers
          ; tcg_env <- return (tcg_env
                                { tcg_hdr_info = (fmap (\(WithHsDocIdentifiers str _) -> WithHsDocIdentifiers str [])
                                                  <$> maybe_doc_hdr , maybe_mod ) })
          ; -- If the whole module is warned about or deprecated
            -- (via mod_deprec) record that in tcg_warns. If we do thereby add
            -- a WarnAll, it will override any subsequent deprecations added to tcg_warns
          ; tcg_env1 <- case mod_deprec of
                               Just (L _ txt) -> do { txt' <- rnWarningTxt txt
                                                    ; pure $ tcg_env {tcg_warns = WarnAll txt'}
                                                    }
                               Nothing            -> pure tcg_env
          ; setGblEnv tcg_env1
            $ do { -- Rename and type check the declarations
                   traceRn "rn1a" empty
                 ; tcg_env <-
                     case hsc_src of
                      -- See Note [Don't typecheck GHC.Internal.Prim]
                      _ | tcg_mod tcg_env1 == gHC_PRIM -> pure tcg_env1
  
                      HsBootOrSig boot_or_sig ->
                        do { tcg_env <- tcRnHsBootDecls boot_or_sig local_decls
                           ; traceRn "rn4a: before exports" empty
                           ; tcg_env <- setGblEnv tcg_env $
                                        rnExports explicit_mod_hdr export_ies
                           ; traceRn "rn4b: after exports" empty
                           ; return tcg_env
                           }
                      HsSrcFile ->
                        {-# SCC "tcRnSrcDecls" #-}
                          tcRnSrcDecls explicit_mod_hdr export_ies local_decls
  
                 ; whenM (goptM Opt_DoCoreLinting) $
                   lintGblEnv (hsc_logger hsc_env) (hsc_dflags hsc_env) tcg_env
  
                 ; setGblEnv tcg_env
                   $ do { -- Compare hi-boot iface (if any) with the real thing
                          -- Must be done after processing the exports
                          tcg_env <- checkHiBootIface tcg_env boot_info
                        ; -- The new type env is already available to stuff
                          -- slurped from interface files, via
                          -- GHC.Tc.Utils.Env.setGlobalTypeEnv. It's important that this
                          -- includes the stuff in checkHiBootIface,
                          -- because the latter might add new bindings for
                          -- boot_dfuns, which may be mentioned in imported
                          -- unfoldings.
                        ; -- Report unused names
                          -- Do this /after/ type inference, so that when reporting
                          -- a function with no type signature we can give the
                          -- inferred type
                        ; reportUnusedNames tcg_env hsc_src
                        ; reportClashingDefaultImports defaultImportsByClass (tcg_default tcg_env)
  
                        -- Rename the module header properly after we have renamed everything else
                        ; maybe_doc_hdr <- traverse rnLHsDoc maybe_doc_hdr;
                        ; tcg_env <- return (tcg_env
                                              { tcg_hdr_info = (maybe_doc_hdr, maybe_mod) })
  
                        ; -- add extra source files to tcg_dependent_files
                          addDependentFiles src_files
                          -- Ensure plugins run with the same tcg_env that we pass in
                        ; setGblEnv tcg_env
                          $ do { tcg_env <- runTypecheckerPlugin mod_sum tcg_env
                               ; -- Dump output and return
                                 tcDump tcg_env
                               ; return tcg_env
                               }
                        }
                 }
          }
        }
  
  {- Note [Don't typecheck GHC.Internal.Prim]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  GHC (currently) can't type-check GHC.Internal.Prim, as that module
  contains primitive functions that can't be defined in source Haskell.
  The GHC.Internal.Prim source file is only used to generate Haddock documentation;
  the actual contents of the module are wired in to GHC.
  -}
  
  {- Note [Disambiguation of multiple default declarations]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
  See Note [Named default declarations] in GHC.Tc.Gen.Default
  
  Only a single default declaration can be in effect in any single module for
  any particular class.
  
  * Two declarations for the same class explicitly declared in the same module
    are considered a static error.
  
  * Definition: given two default declarations for the same class
  
    default C (Type_1a , … , Type_ma)
    default C (Type_1b , … , Type_nb)
  
    if the first type sequence Type_1a , … , Type_ma is a sub-sequence of the
    second sequence Type_1b , … , Type_nb (i.e., the former can be obtained by
    removing a number of Type_ib items from the latter), we say that the second
    declaration *subsumes* the first one.
  
  * A default declaration in a module takes precedence over any imported default
    declarations for the same class. However the compiler warns the user if an
    imported declaration is not subsumed by the local declaration.
  
  * For any two imported default declarations for the same class where one
    subsumes the other, we ignore the subsumed declaration.
  
  * If a class has neither a local default declaration nor an imported default
    declaration that subsumes all other imported default declarations for the
    class, the conflict between the imports is unresolvable. The effect is to
    ignore all default declarations for the class, so that no declaration is in
    effect in the module. The compiler emits a warning in this case, but no
    error.
  -}
  
  -- See Note [Disambiguation of multiple default declarations]
  -- | Warn about any imported default declaration that is not subsumed by either
  -- a local or an imported default declaration.
  reportClashingDefaultImports :: [NonEmpty ClassDefaults] -> DefaultEnv -> TcM ()
  reportClashingDefaultImports importsByClass local = mapM_ check importsByClass
    where
      check cds@(ClassDefaults{cd_class = cls} :| _) = do
        let cdLocal  = lookupDefaultEnv local (className cls)
        case cdLocal of
          Just ClassDefaults{cd_types = localTypes}
            | all ((`isTypeSubsequenceOf` localTypes) . cd_types) cds -> pure ()
          Nothing
            | not (isEmptyDefaultEnv $ subsume cds) -> pure ()
          _ -> do
            warn_default <- woptM Opt_WarnTypeDefaults
            diagnosticTc warn_default $
              TcRnWarnClashingDefaultImports cls (cd_types <$> cdLocal) cds
  
  -- | Collapse a non-empty list of @default@ declarations for the same class to
  -- the single declaration among them that subsumes all others, or to no
  -- declaration otherwise.
  subsume :: NonEmpty ClassDefaults -> DefaultEnv
  subsume (deft :| []) = unitDefaultEnv deft
  subsume (deft :| deft' : defts)
    | cd_types deft  `isTypeSubsequenceOf` cd_types deft' = subsume (deft' :| defts)
    | cd_types deft' `isTypeSubsequenceOf` cd_types deft  = subsume (deft  :| defts)
    | otherwise = emptyDefaultEnv
  
  isTypeSubsequenceOf :: [Type] -> [Type] -> Bool
  isTypeSubsequenceOf [] _ = True
  isTypeSubsequenceOf _ [] = False
  isTypeSubsequenceOf (t1:t1s) (t2:t2s)
    | tcEqType t1 t2 = isTypeSubsequenceOf t1s t2s
    | otherwise = isTypeSubsequenceOf (t1:t1s) t2s
  
  {-
  ************************************************************************
  *                                                                      *
                  Import declarations
  *                                                                      *
  ************************************************************************
  -}
  
  tcRnImports :: HscEnv -> [(LImportDecl GhcPs, SDoc)] -> TcM ([NonEmpty ClassDefaults], TcGblEnv)
  tcRnImports hsc_env import_decls
    = do  { (rn_imports, imp_user_spec, rdr_env, imports) <- rnImports import_decls
          -- Get the default declarations for the classes imported by this module
          -- and group them by class.
          ; tc_defaults <-(NE.groupBy ((==) `on` cd_class) . (concatMap defaultList))
                          <$> tcGetClsDefaults (M.keys $ imp_mods imports)
          ; this_mod <- getModule
          ; gbl_env <- getGblEnv
          ; let unitId = homeUnitId $ hsc_home_unit hsc_env
                mnwib = GWIB (moduleName this_mod)(hscSourceToIsBoot (tcg_src gbl_env))
          ;       -- We want instance declarations from all home-package
                  -- modules below this one, including boot modules, except
                  -- ourselves.  The 'except ourselves' is so that we don't
                  -- get the instances from this module's hs-boot file.  This
                  -- filtering also ensures that we don't see instances from
                  -- modules batch (@--make@) compiled before this one, but
                  -- which are not below this one.
                ; (home_insts, home_fam_insts) <- liftIO $
                      hugInstancesBelow hsc_env unitId mnwib
  
                  -- We use 'unsafeInterleaveIO' to avoid redundant memory allocations
                  -- See Note [Lazily loading COMPLETE pragmas] from GHC.HsToCore.Monad
                  -- and see https://gitlab.haskell.org/ghc/ghc/-/merge_requests/14274#note_620545
                ; completeSigsBelow <- liftIO $ unsafeInterleaveIO $
                      hugCompleteSigsBelow hsc_env unitId mnwib
  
                  -- Record boot-file info in the EPS, so that it's
                  -- visible to loadHiBootInterface in tcRnSrcDecls,
                  -- and any other incrementally-performed imports
                ; when (isOneShot (ghcMode (hsc_dflags hsc_env))) $ do {
                    updateEps_ $ \eps  -> eps { eps_is_boot = imp_boot_mods imports }
                 }
  
                  -- Update the gbl env
          ; updGblEnv ( \ gbl ->
              gbl {
                tcg_rdr_env      = tcg_rdr_env gbl `plusGlobalRdrEnv` rdr_env,
                tcg_imports      = tcg_imports gbl `plusImportAvails` imports,
                tcg_complete_match_env = tcg_complete_match_env gbl ++
                                         completeSigsBelow,
                tcg_import_decls = imp_user_spec,
                tcg_rn_imports   = rn_imports,
                tcg_default      = foldMap subsume tc_defaults,
                tcg_inst_env     = tcg_inst_env gbl `unionInstEnv` home_insts,
                tcg_fam_inst_env = extendFamInstEnvList (tcg_fam_inst_env gbl)
                                                        home_fam_insts
              }) $ do {
  
          ; traceRn "rn1" (ppr (imp_direct_dep_mods imports))
                  -- Fail if there are any errors so far
                  -- The error printing (if needed) takes advantage
                  -- of the tcg_env we have now set
  --      ; traceIf (text "rdr_env: " <+> ppr rdr_env)
          ; failIfErrsM
  
                  -- Load any orphan-module (including orphan family
                  -- instance-module) interfaces, so that their rules and
                  -- instance decls will be found.  But filter out a
                  -- self hs-boot: these instances will be checked when
                  -- we define them locally.
                  -- (We don't need to load non-orphan family instance
                  -- modules until we either try to use the instances they
                  -- define, or define our own family instances, at which
                  -- point we need to check them for consistency.)
          ; loadModuleInterfaces (text "Loading orphan modules")
                                 (filter (/= this_mod) (imp_orphs imports))
  
                  -- Check type-family consistency between imports.
                  -- See Note [The type family instance consistency story]
          ; traceRn "rn1: checking family instance consistency {" empty
          ; let { dir_imp_mods = M.keys
                               . imp_mods
                               $ imports }
          ; logger <- getLogger
          ; withTiming logger (text "ConsistencyCheck"<+>brackets (ppr this_mod)) (const ())
              $ checkFamInstConsistency dir_imp_mods
          ; traceRn "rn1: } checking family instance consistency" empty
  
          ; gbl_env <- getGblEnv
          ; return (tc_defaults, gbl_env) } }
  
  {-
  ************************************************************************
  *                                                                      *
          Type-checking the top level of a module
  *                                                                      *
  ************************************************************************
  -}
  
  tcRnSrcDecls :: Bool  -- False => no 'module M(..) where' header at all
               -> Maybe (LocatedLI [LIE GhcPs])
               -> [LHsDecl GhcPs]               -- Declarations
               -> TcM TcGblEnv
  tcRnSrcDecls explicit_mod_hdr export_ies decls
   = do { -- Do all the declarations
        ; (tcg_env, tcl_env, lie) <- tc_rn_src_decls decls
  
        ------ Simplify constraints ---------
        --
        -- We do this after checkMainType, so that we use the type
        -- info that checkMainType adds
        --
        -- We do it with both global and local env in scope:
        --  * the global env exposes the instances to simplifyTop,
        --    and affects how names are rendered in error messages
        --  * the local env exposes the local Ids to simplifyTop,
        --    so that we get better error messages (monomorphism restriction)
        ; new_ev_binds <- {-# SCC "simplifyTop" #-}
                          restoreEnvs (tcg_env, tcl_env) $
                          do { lie_main <- checkMainType tcg_env
                             ; simplifyTop (lie `andWC` lie_main) }
  
          -- Emit Typeable bindings
        ; tcg_env <- setGblEnv tcg_env $
                     mkTypeableBinds
  
        ; traceTc "Tc9" empty
        ; failIfErrsM    -- Stop now if if there have been errors
                         -- Continuing is a waste of time; and we may get debug
                         -- warnings when zonking about strangely-typed TyCons!
  
          -- Zonk the final code.  This must be done last.
          -- Even simplifyTop may do some unification.
          -- This pass also warns about missing type signatures
        ; (id_env, ev_binds', binds', fords', imp_specs', rules')
              <- zonkTcGblEnv new_ev_binds tcg_env
  
        --------- Run finalizers --------------
        -- Finalizers must run after constraints are simplified, lest types
        --    might not be complete when using reify (see #12777).
        -- and also after we zonk the first time because we run typed splices
        --    in the zonker which gives rise to the finalisers.
        ; let -- init_tcg_env:
              --   * Remove accumulated bindings, rules and so on from
              --     TcGblEnv.  They are now in ev_binds', binds', etc.
              --   * Add the zonked Ids from the value bindings to tcg_type_env
              --     Up to now these Ids are only in tcl_env's type-envt
              init_tcg_env = tcg_env { tcg_binds     = []
                                     , tcg_ev_binds  = emptyBag
                                     , tcg_imp_specs = []
                                     , tcg_rules     = []
                                     , tcg_fords     = []
                                     , tcg_type_env  = tcg_type_env tcg_env
                                                       `plusTypeEnv` id_env }
        ; (tcg_env, tcl_env) <- setGblEnv init_tcg_env
                                run_th_modfinalizers
        ; finishTH
        ; traceTc "Tc11" empty
  
        --------- Deal with the exports ----------
        -- Can't be done earlier, because the export list must "see"
        -- the declarations created by the finalizers
        ; tcg_env <- restoreEnvs (tcg_env, tcl_env) $
                     rnExports explicit_mod_hdr export_ies
  
        --------- Emit the ':Main.main = runMainIO main' declaration ----------
        -- Do this /after/ rnExports, so that it can consult
        -- the tcg_exports created by rnExports
        ; (tcg_env, main_ev_binds)
             <- restoreEnvs (tcg_env, tcl_env) $
                do { (tcg_env, lie) <- captureTopConstraints $
                                       checkMain explicit_mod_hdr export_ies
                   ; ev_binds <- simplifyTop lie
                   ; return (tcg_env, ev_binds) }
  
        ; failIfErrsM    -- Stop now if if there have been errors
                         -- Continuing is a waste of time; and we may get debug
                         -- warnings when zonking about strangely-typed TyCons!
  
        ---------- Final zonking ---------------
        -- Zonk the new bindings arising from running the finalisers,
        -- and main. This won't give rise to any more finalisers as you
        -- can't nest finalisers inside finalisers.
        ; (id_env_mf, ev_binds_mf, binds_mf, fords_mf, imp_specs_mf, rules_mf)
              <- zonkTcGblEnv main_ev_binds tcg_env
  
        ; let { !final_type_env = tcg_type_env tcg_env
                                  `plusTypeEnv` id_env_mf
                -- Add the zonked Ids from the value bindings (they were in tcl_env)
                -- Force !final_type_env, lest we retain an old reference
                -- to the previous tcg_env
  
              ; tcg_env' = tcg_env
                            { tcg_binds     = binds'     ++ binds_mf
                            , tcg_ev_binds  = ev_binds' `unionBags` ev_binds_mf
                            , tcg_imp_specs = imp_specs' ++ imp_specs_mf
                            , tcg_rules     = rules'     ++ rules_mf
                            , tcg_fords     = fords'     ++ fords_mf } } ;
  
        ; setGlobalTypeEnv tcg_env' final_type_env
     }
  
  zonkTcGblEnv :: Bag EvBind -> TcGblEnv
               -> TcM (TypeEnv, Bag EvBind, LHsBinds GhcTc,
                         [LForeignDecl GhcTc], [LTcSpecPrag], [LRuleDecl GhcTc])
  zonkTcGblEnv ev_binds tcg_env@(TcGblEnv { tcg_binds     = binds
                                          , tcg_ev_binds  = cur_ev_binds
                                          , tcg_imp_specs = imp_specs
                                          , tcg_rules     = rules
                                          , tcg_fords     = fords })
    = {-# SCC "zonkTopDecls" #-}
      setGblEnv tcg_env $ -- This sets the GlobalRdrEnv which is used when rendering
                          --   error messages during zonking (notably levity errors)
      do { let all_ev_binds = cur_ev_binds `unionBags` ev_binds
         ; zonkTopDecls all_ev_binds binds rules imp_specs fords }
  
  -- | Runs TH finalizers and renames and typechecks the top-level declarations
  -- that they could introduce.
  run_th_modfinalizers :: TcM (TcGblEnv, TcLclEnv)
  run_th_modfinalizers = do
    th_modfinalizers_var <- fmap tcg_th_modfinalizers getGblEnv
    th_modfinalizers <- readTcRef th_modfinalizers_var
    if null th_modfinalizers
    then getEnvs
    else do
      writeTcRef th_modfinalizers_var []
      let run_finalizer (lcl_env, f) =
              restoreLclEnv lcl_env (runRemoteModFinalizers f)
  
      (_, lie_th) <- captureTopConstraints $
                     mapM_ run_finalizer th_modfinalizers
  
        -- Finalizers can add top-level declarations with addTopDecls, so
        -- we have to run tc_rn_src_decls to get them
      (tcg_env, tcl_env, lie_top_decls) <- tc_rn_src_decls []
  
      restoreEnvs (tcg_env, tcl_env) $ do
        -- Subsequent rounds of finalizers run after any new constraints are
        -- simplified, or some types might not be complete when using reify
        -- (see #12777).
        new_ev_binds <- {-# SCC "simplifyTop2" #-}
                        simplifyTop (lie_th `andWC` lie_top_decls)
        addTopEvBinds new_ev_binds run_th_modfinalizers
          -- addTopDecls can add declarations which add new finalizers.
  
  tc_rn_src_decls :: [LHsDecl GhcPs]
                  -> TcM (TcGblEnv, TcLclEnv, WantedConstraints)
  -- Loops around dealing with each top level inter-splice group
  -- in turn, until it's dealt with the entire module
  -- Never emits constraints; calls captureTopConstraints internally
  tc_rn_src_decls ds
   = {-# SCC "tc_rn_src_decls" #-}
     do { (first_group, group_tail) <- findSplice ds
                  -- If ds is [] we get ([], Nothing)
  
          -- Deal with decls up to, but not including, the first splice
        ; (tcg_env, rn_decls) <- rnTopSrcDecls first_group
                  -- rnTopSrcDecls fails if there are any errors
  
          -- Get TH-generated top-level declarations and make sure they don't
          -- contain any splices since we don't handle that at the moment
          --
          -- The plumbing here is a bit odd: see #10853
        ; th_topdecls_var <- fmap tcg_th_topdecls getGblEnv
        ; th_ds <- readTcRef th_topdecls_var
        ; writeTcRef th_topdecls_var []
  
        ; (tcg_env, rn_decls) <-
              if null th_ds
              then return (tcg_env, rn_decls)
              else do { (th_group, th_group_tail) <- findSplice th_ds
                      ; case th_group_tail of
                          { Nothing -> return ()
                          ; Just (SpliceDecl _ (L loc _) _, _) ->
                              setSrcSpanA loc $ addErr $
                              TcRnTHError $ AddTopDeclsError
                                AddTopDeclsUnexpectedDeclarationSplice
                          }
                        -- Rename TH-generated top-level declarations
                      ; (tcg_env, th_rn_decls) <- setGblEnv tcg_env
                          $ rnTopSrcDecls th_group
  
                        -- Dump generated top-level declarations
                      ; let msg = "top-level declarations added with 'addTopDecls'"
                      ; traceSplice
                          $ SpliceInfo { spliceDescription = msg
                                       , spliceIsDecl    = True
                                       , spliceSource    = Nothing
                                       , spliceGenerated = ppr th_rn_decls }
                      ; return (tcg_env, appendGroups rn_decls th_rn_decls)
                      }
  
        -- Type check all declarations
        -- NB: set the env **before** captureTopConstraints so that error messages
        -- get reported w.r.t. the right GlobalRdrEnv. It is for this reason that
        -- the captureTopConstraints must go here, not in tcRnSrcDecls.
        ; ((tcg_env, tcl_env), lie1) <- setGblEnv tcg_env $
                                        captureTopConstraints $
                                        tcTopSrcDecls rn_decls
  
          -- If there is no splice, we're nearly done
        ; restoreEnvs (tcg_env, tcl_env) $
          case group_tail of
            { Nothing -> return (tcg_env, tcl_env, lie1)
  
              -- If there's a splice, we must carry on
            ; Just (SpliceDecl _ (L _ splice) _, rest_ds) ->
              do {
                   -- We need to simplify any constraints from the previous declaration
                   -- group, or else we might reify metavariables, as in #16980.
                 ; ev_binds1 <- simplifyTop lie1
  
                   -- Rename the splice expression, and get its supporting decls
                 ; (spliced_decls, splice_fvs) <- rnTopSpliceDecls splice
  
                   -- Glue them on the front of the remaining decls and loop
                 ; setGblEnv (tcg_env `addTcgDUs` usesOnly splice_fvs) $
                   addTopEvBinds ev_binds1                             $
                   tc_rn_src_decls (spliced_decls ++ rest_ds)
                 }
            }
        }
  
  {-
  ************************************************************************
  *                                                                      *
          Compiling hs-boot source files, and
          comparing the hi-boot interface with the real thing
  *                                                                      *
  ************************************************************************
  -}
  
  tcRnHsBootDecls :: HsBootOrSig -> [LHsDecl GhcPs] -> TcM TcGblEnv
  tcRnHsBootDecls boot_or_sig decls
     = do { (first_group, group_tail) <- findSplice decls
  
                  -- Rename the declarations
          ; (tcg_env, HsGroup { hs_tyclds = tycl_decls
                              , hs_derivds = deriv_decls
                              , hs_fords  = for_decls
                              , hs_defds  = def_decls
                              , hs_ruleds = rule_decls
                              , hs_annds  = _
                              , hs_valds  = XValBindsLR (NValBinds val_binds val_sigs) })
                <- rnTopSrcDecls first_group
  
          ; (gbl_env, lie) <- setGblEnv tcg_env $ captureTopConstraints $ do {
                -- NB: setGblEnv **before** captureTopConstraints so that
                -- if the latter reports errors, it knows what's in scope
  
                  -- Check for illegal declarations
          ; case group_tail of
               Just (SpliceDecl _ d _, _) -> rejectBootDecls boot_or_sig BootSpliceDecls [d]
               Nothing                    -> return ()
          ; rejectBootDecls boot_or_sig BootForeignDecls for_decls
          ; rejectBootDecls boot_or_sig BootDefaultDecls def_decls
          ; rejectBootDecls boot_or_sig BootRuleDecls    rule_decls
  
                  -- Typecheck type/class/instance decls
          ; traceTc "Tc2 (boot)" empty
          ; (tcg_env, inst_infos, _deriv_binds, _th_bndrs)
               <- tcTyClsInstDecls tycl_decls deriv_decls def_decls val_binds
          ; setGblEnv tcg_env     $ do {
  
          -- Emit Typeable bindings
          ; tcg_env <- mkTypeableBinds
          ; setGblEnv tcg_env $ do {
  
                  -- Typecheck value declarations
          ; traceTc "Tc5" empty
          ; val_ids <- tcHsBootSigs val_binds val_sigs
  
                  -- Wrap up
                  -- No simplification or zonking to do
          ; traceTc "Tc7a" empty
          ; gbl_env <- getGblEnv
  
                  -- Make the final type-env
                  -- Include the dfun_ids so that their type sigs
                  -- are written into the interface file.
          ; let { type_env0 = tcg_type_env gbl_env
                ; type_env1 = extendTypeEnvWithIds type_env0 val_ids
                ; type_env2 = extendTypeEnvWithIds type_env1 dfun_ids
                ; dfun_ids = map iDFunId inst_infos
                }
  
          ; setGlobalTypeEnv gbl_env type_env2
     }}}
     ; traceTc "boot" (ppr lie); return gbl_env }
  
  {-
  Once we've typechecked the body of the module, we want to compare what
  we've found (gathered in a TypeEnv) with the hi-boot details (if any).
  -}
  
  checkHiBootIface :: TcGblEnv -> SelfBootInfo -> TcM TcGblEnv
  -- Compare the hi-boot file for this module (if there is one)
  -- with the type environment we've just come up with
  -- In the common case where there is no hi-boot file, the list
  -- of boot_names is empty.
  
  checkHiBootIface tcg_env boot_info
    | NoSelfBoot <- boot_info  -- Common case
    = return tcg_env
  
    | HsBootFile <- tcg_src tcg_env   -- Current module is already a hs-boot file!
    = return tcg_env
  
    | SelfBoot { sb_mds = boot_details } <- boot_info
    , TcGblEnv { tcg_binds    = binds
               , tcg_insts    = local_insts
               , tcg_type_env = local_type_env
               , tcg_exports  = local_exports } <- tcg_env
    = do  { -- This code is tricky, see Note [DFun knot-tying]
          ; imp_prs <- checkHiBootIface' local_insts local_type_env
                                         local_exports boot_details
  
          -- Now add the impedance-matching boot bindings:
          --
          --  - dfun bindings  $fxblah = $fblah
          --  - record bindings fld{var} = fld{rec field of ..}
          --
          -- to (a) the type envt, and (b) the top-level bindings
          ; let boot_impedance_bds = map fst imp_prs
                type_env'          = extendTypeEnvWithIds local_type_env boot_impedance_bds
                impedance_binds    =  [ mkVarBind boot_id (nlHsVar id)
                                      | (boot_id, id) <- imp_prs ]
                tcg_env_w_binds
                  = tcg_env { tcg_binds = binds ++ impedance_binds }
  
          ; type_env' `seq`
               -- Why the seq?  Without, we will put a TypeEnv thunk in
               -- tcg_type_env_var.  That thunk will eventually get
               -- forced if we are typechecking interfaces, but that
               -- is no good if we are trying to typecheck the very
               -- DFun we were going to put in.
               -- TODO: Maybe setGlobalTypeEnv should be strict.
            setGlobalTypeEnv tcg_env_w_binds type_env' }
  
  {- Note [DFun impedance matching]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  We return a list of "impedance-matching" bindings for the dfuns
  defined in the hs-boot file, such as
            $fxEqT = $fEqT
  We need these because the module and hi-boot file might differ in
  the name it chose for the dfun: the name of a dfun is not
  uniquely determined by its type; there might be multiple dfuns
  which, individually, would map to the same name (in which case
  we have to disambiguate them.)  There's no way for the hi file
  to know exactly what disambiguation to use... without looking
  at the hi-boot file itself.
  
  In fact, the names will always differ because we always pick names
  prefixed with "$fx" for boot dfuns, and "$f" for real dfuns
  (so that this impedance matching is always possible).
  
  Note [Record field impedance matching]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  When a hs-boot file defines a function whose implementation in the hs file
  is a record selector, we have to do something similar to Note [DFun impedance matching].
  
  Example:
  
    -- M.hs-boot
    module M where
      data A
      fld :: A -> ()
  
    -- M.hs
    module M where
      data A = MkA { fld :: () }
  
  Recall from Note [Record field namespacing] in GHC.Types.Name.Occurrence that
  record fields have their own namespaces. This means that M.hs exports the Id
  fld{record selector of MkA} :: A -> (), while M.hs-boot exports the Id
  fld{variable} :: A -> ().
  
  To remedy this, we add an impedance-matching binding in M.hs:
  
    fld{variable} :: A -> ()
    fld{variable} = fld{record selector of MkA}
  
  Note that we imperatively need to add a binding for fld{variable} in M.hs, as we
  might have an exact Name reference to it (e.g. in a module that imports M.hs-boot).
  Not doing so would cause Core Lint errors, at the very least.
  
  These bindings are returned by the check_export in checkHiBootIface', and
  added to the DFun impedance-matching bindings.
  
  [Wrinkle: exports]
  
    We MUST NOT add fld{variable} to the export list of M.hs, as this
    would mean that M.hs exports both a record field and variable with the same
    occNameFS, which would cause ambiguity errors at use-sites.
    It's OK to only export the field name even though the boot-file exported
    the variable: name resolution will take care of that.
  
  Another situation is that we are re-exporting, e.g. (with M as above):
  
    -- N.hs-boot
    module N ( module M ) where
      import {-# SOURCE #-} M
  
    -- N.hs
    module N ( module M where )
      import M
  
  In this case, N.hs-boot re-exports the variable fld, and N re-exports the
  record field fld, but not the variable fld. We don't need to do anything in
  this situation; in particular, don't re-export the variable name from N.hs,
  as per [Wrinkle: exports] above.
  
  Note [DFun knot-tying]
  ~~~~~~~~~~~~~~~~~~~~~~
  The 'SelfBootInfo' that is fed into 'checkHiBootIface' comes from
  typechecking the hi-boot file that we are presently implementing.
  Suppose we are typechecking the module A: when we typecheck the
  hi-boot file, whenever we see an identifier A.T, we knot-tie this
  identifier to the *local* type environment (via if_rec_types.)  The
  contract then is that we don't *look* at 'SelfBootInfo' until we've
  finished typechecking the module and updated the type environment with
  the new tycons and ids.
  
  This most works well, but there is one problem: DFuns!  We do not want
  to look at the mb_insts of the ModDetails in SelfBootInfo, because a
  dfun in one of those ClsInsts is gotten (in GHC.IfaceToCore.tcIfaceInst) by a
  (lazily evaluated) lookup in the if_rec_types.  We could extend the
  type env, do a setGloblaTypeEnv etc; but that all seems very indirect.
  It is much more directly simply to extract the DFunIds from the
  md_types of the SelfBootInfo.
  
  See #4003, #16038 for why we need to take care here.
  -}
  
  checkHiBootIface' :: [ClsInst] -> TypeEnv -> [AvailInfo]
                    -> ModDetails -> TcM [(Id, Id)]
  -- Variant which doesn't require a full TcGblEnv; you could get the
  -- local components from another ModDetails.
  checkHiBootIface'
          local_insts local_type_env local_exports
          (ModDetails { md_types = boot_type_env
                      , md_fam_insts = boot_fam_insts
                      , md_exports = boot_exports })
    = do  { traceTc "checkHiBootIface" $ vcat
               [ ppr boot_type_env, ppr boot_exports ]
  
          ; mod <- tcg_mod <$> getGblEnv
  
          -- See Note [Don't typecheck GHC.Internal.Prim]
          ; if mod == gHC_PRIM then pure [] else do {
  
          ; gre_env <- getGlobalRdrEnv
  
                  -- Check the exports of the boot module, one by one
          ; fld_prs <- mapMaybeM (check_export gre_env) boot_exports
  
                  -- Check for no family instances
          ; unless (null boot_fam_insts) $
              panic ("GHC.Tc.Module.checkHiBootIface: Cannot handle family " ++
                     "instances in boot files yet...")
              -- FIXME: Why?  The actual comparison is not hard, but what would
              --        be the equivalent to the dfun bindings returned for class
              --        instances?  We can't easily equate tycons...
  
                  -- Check instance declarations
                  -- and generate an impedance-matching binding
          ; dfun_prs <- mapMaybeM check_cls_inst boot_dfuns
  
          ; failIfErrsM
  
          ; return (fld_prs ++ dfun_prs) }}
  
    where
      boot_dfun_names = map idName boot_dfuns
      boot_dfuns      = filter isDFunId $ typeEnvIds boot_type_env
         -- NB: boot_dfuns is /not/ defined thus: map instanceDFunId md_insts
         --     We don't want to look at md_insts!
         --     Why not?  See Note [DFun knot-tying]
  
      check_export gre_env boot_avail     -- boot_avail is exported by the boot iface
        | name `elem` boot_dfun_names
        = return Nothing
  
          -- Check that the actual module exports the same thing
        | missing_name:_ <- missing_names
        = -- Lookup might have failed because the hs-boot file defines a variable
          -- that is implemented in the hs file as a record selector, which
          -- lives in a different namespace.
          --
          -- See Note [Record field impedance matching].
          let missing_occ = nameOccName missing_name
              mb_ok :: GlobalRdrElt -> Maybe (GlobalRdrElt, Maybe Id)
              mb_ok gre
                -- Ensure that this GRE refers to an Id that is exported.
                | isNothing $ lookupNameEnv local_export_env (greName gre)
                = Nothing
                -- We locally define the field: create an impedance-matching
                -- binding for the variable.
                | Just (AnId id) <- lookupTypeEnv local_type_env (greName gre)
                = Just (gre, Just id)
                -- We are re-exporting the field but not the variable: not a problem,
                -- as per [Wrinkle: exports] in Note [Record field impedance matching].
                | otherwise
                = Just (gre, Nothing)
              matching_flds
                | isVarOcc missing_occ -- (This only applies to variables.)
                = lookupGRE gre_env $
                  LookupOccName missing_occ (RelevantGREsFOS WantField)
                | otherwise
                = [] -- BootFldReexport T18999_NoDisambiguateRecordFields T16745A
  
          in case mapMaybe mb_ok $ matching_flds of
  
            -- At least 2 matches: report an ambiguity error.
            (gre1,_):(gre2,_):gres_ids -> do
             addErrAt (nameSrcSpan missing_name) $
               mkNameClashErr gre_env (nameRdrName missing_name)
                 (gre1 NE.:| gre2 : map fst gres_ids)
             return Nothing
  
            -- Single match: resolve the issue.
            [(_,mb_fld_id)] ->
              -- See Note [Record field impedance matching].
              for mb_fld_id $ \ fld_id -> do
                let local_boot_var =
                      Id.mkExportedVanillaId missing_name (idType fld_id)
                return (local_boot_var, fld_id)
  
            -- Otherwise: report that the hs file does not export something
            -- that the hs-boot file exports.
            [] -> do
             addErrAt (nameSrcSpan missing_name)
               (missingBootThing HsBoot missing_name MissingBootExport)
             return Nothing
  
          -- If the boot module does not *define* the thing, we are done
          -- (it simply re-exports it, and names match, so nothing further to do)
        | isNothing mb_boot_thing
        = return Nothing
  
          -- Check that the actual module also defines the thing, and
          -- then compare the definitions
        | Just real_thing <- lookupTypeEnv local_type_env name,
          Just boot_thing <- mb_boot_thing
        = do checkBootDeclM HsBoot boot_thing real_thing
             return Nothing
  
        | otherwise
        = do addErrTc (missingBootThing HsBoot name MissingBootDefinition)
             return Nothing
        where
          name          = availName boot_avail
          mb_boot_thing = lookupTypeEnv boot_type_env name
          missing_names = case lookupNameEnv local_export_env name of
                            Nothing    -> [name]
                            Just avail -> availNames boot_avail
                              `minusList` availNames avail
  
      local_export_env :: NameEnv AvailInfo
      local_export_env = availsToNameEnv local_exports
  
      check_cls_inst :: DFunId -> TcM (Maybe (Id,Id))
          -- Returns a pair of the boot dfun in terms of the equivalent
          -- real dfun. Delicate (like checkBootDecl) because it depends
          -- on the types lining up precisely even to the ordering of
          -- the type variables in the foralls.
      check_cls_inst boot_dfun
        | (real_dfun : _) <- find_real_dfun boot_dfun
        , let dfun_name = idName boot_dfun
              local_boot_dfun = Id.mkExportedVanillaId dfun_name (idType real_dfun)
        = return $ Just (local_boot_dfun, real_dfun)
            -- Two tricky points here:
            --
            --  * The local_boot_fun should have a Name from the /boot-file/,
            --    but type from the dfun defined in /this module/.
            --    That ensures that the TyCon etc inside the type are
            --    the ones defined in this module, not the ones gotten
            --    from the hi-boot file, which may have a lot less info
            --    (#8743, comment:10).
            --
            --  * The DFunIds from boot_details are /GlobalIds/, because
            --    they come from typechecking M.hi-boot.
            --    But all bindings in this module should be for /LocalIds/,
            --    otherwise dependency analysis fails (#16038). This
            --    is another reason for using mkExportedVanillaId, rather
            --    that modifying boot_dfun, to make local_boot_fun.
            --
            -- See Note [DFun impedance matching].
  
        | otherwise
        = setSrcSpan (nameSrcSpan (getName boot_dfun)) $
          do { traceTc "check_cls_inst" $ vcat
                  [ text "local_insts"  <+>
                       vcat (map (ppr . idType . instanceDFunId) local_insts)
                  , text "boot_dfun_ty" <+> ppr (idType boot_dfun) ]
  
             ; addErrTc $ TcRnBootMismatch HsBoot
                        $ MissingBootInstance boot_dfun
             ; return Nothing }
  
      find_real_dfun :: DFunId -> [DFunId]
      find_real_dfun boot_dfun
         = [dfun | inst <- local_insts
                 , let dfun = instanceDFunId inst
                 , idType dfun `eqType` boot_dfun_ty ]
         where
            boot_dfun_ty   = idType boot_dfun
  
  
  -- In general, to perform these checks we have to
  -- compare the TyThing from the .hi-boot file to the TyThing
  -- in the current source file.  We must be careful to allow alpha-renaming
  -- where appropriate, and also the boot declaration is allowed to omit
  -- constructors and class methods.
  --
  -- See rnfail055 for a good test of this stuff.
  
  -- | Compares two things for equivalence between boot-file and normal code,
  -- reporting an error if they don't match up.
  checkBootDeclM :: HsBootOrSig
                 -> TyThing -- ^ boot thing
                 -> TyThing -- ^ real thing
                 -> TcM ()
  checkBootDeclM boot_or_sig boot_thing real_thing
    = for_ boot_errs $ \ boot_err ->
        addErrAt span $
          TcRnBootMismatch boot_or_sig $
          BootMismatch boot_thing real_thing boot_err
    where
      boot_errs = execWriter $ checkBootDecl boot_or_sig boot_thing real_thing
  
      -- Here we use the span of the boot thing or, if it doesn't have a sensible
      -- span, that of the real thing,
      span
        | let span = nameSrcSpan (getName boot_thing)
        , isGoodSrcSpan span
        = span
        | otherwise
        = nameSrcSpan (getName real_thing)
  
  -- | Writer monad for accumulating errors when comparing an hs-boot or
  -- signature file with its implementing module.
  type BootErrsM err = Writer [err] ()
  
  -- | If the test in the first parameter is True, succeed.
  -- Otherwise, record the given error.
  check :: Bool -> err -> BootErrsM err
  check True  _   = checkSuccess
  check False err = bootErr err
  
  -- | Record an error.
  bootErr :: err -> BootErrsM err
  bootErr err = tell [err]
  
  -- | A convenience synonym for a lack of errors, for @checkBootDecl@ and friends.
  checkSuccess :: BootErrsM err
  checkSuccess = return ()
  
  -- | Map over the error types in an error-accumulating computation.
  embedErrs :: (err1 -> err2) -> BootErrsM err1 -> BootErrsM err2
  embedErrs f = mapWriter (second (fmap f))
  
  -- | Wrap up a list of errors into a single message.
  wrapErrs :: (NE.NonEmpty err1 -> err2) -> BootErrsM err1 -> BootErrsM err2
  wrapErrs f w =
    case execWriter w of
      []         -> checkSuccess
      err : errs -> bootErr (f $ err :| errs)
  
  -- | Compares the two things for equivalence between boot-file and normal
  -- code. Returns @Nothing@ on success or @Just "some helpful info for user"@
  -- failure. If the difference will be apparent to the user, @Just empty@ is
  -- perfectly suitable.
  checkBootDecl :: HsBootOrSig -> TyThing -> TyThing -> BootErrsM BootMismatchWhat
  
  checkBootDecl _ (AnId id1) (AnId id2)
    = assert (id1 == id2) $
      check (idType id1 `eqType` idType id2)
            (BootMismatchedIdTypes id1 id2)
  
  checkBootDecl boot_or_sig (ATyCon tc1) (ATyCon tc2)
    = wrapErrs (BootMismatchedTyCons tc1 tc2) $
      checkBootTyCon boot_or_sig tc1 tc2
  
  checkBootDecl _ t1 t2
    = pprPanic "checkBootDecl" (ppr t1 $$ ppr t2)
  
  -- | Run the check provided for every pair of elements in the lists.
  --
  -- Records an error:
  --
  --  - when any two items at the same position in the two lists don't match
  --    according to the given function,
  --  - when the lists are of different lengths.
  checkListBy :: (a -> a -> BootErrsM err) -> [a] -> [a]
              -> (BootListMismatches a err -> err2)
              -> BootErrsM err2
  checkListBy check_fun as bs mk_err = wrapErrs mk_err $ go 1 as bs
    where
      go _  [] [] = checkSuccess
      go !i (x:xs) (y:ys) =
        do { embedErrs (MismatchedThing i x y) $ check_fun x y
           ; go (i+1) xs ys }
      go _  _  _ = bootErr MismatchedLength
  
  ----------------
  checkBootTyCon :: HsBootOrSig -> TyCon -> TyCon -> BootErrsM BootTyConMismatch
  checkBootTyCon boot_or_sig tc1 tc2
    | not (eqType (tyConKind tc1) (tyConKind tc2))
    -- First off, check the kind
    = bootErr TyConKindMismatch
  
    | Just c1 <- tyConClass_maybe tc1
    , Just c2 <- tyConClass_maybe tc2
    , let (clas_tvs1, clas_fds1, sc_theta1, _, ats1, op_stuff1)
            = classExtraBigSig c1
          (clas_tvs2, clas_fds2, sc_theta2, _, ats2, op_stuff2)
            = classExtraBigSig c2
    , Just env <- eqVarBndrs emptyRnEnv2 clas_tvs1 clas_tvs2
    = do { check_roles
         ; embedErrs (TyConMismatchedClasses c1 c2) $
      do { -- Checks kind of class
         ; check (liftEq (eqFD env) clas_fds1 clas_fds2)
             MismatchedFunDeps
         ; unless (isAbstractTyCon tc1) $
      do { check (liftEq (eqTypeX env) sc_theta1 sc_theta2)
             MismatchedSuperclasses
         ; checkListBy (compatClassOp env boot_or_sig) op_stuff1 op_stuff2
             MismatchedMethods
         ; checkListBy (compatAT env boot_or_sig) ats1 ats2
             MismatchedATs
         ; check (classMinimalDef c1 `BF.implies` classMinimalDef c2)
             MismatchedMinimalPragmas
         } } }
  
    | Just syn_rhs1 <- synTyConRhs_maybe tc1
    , Just syn_rhs2 <- synTyConRhs_maybe tc2
    , Just env <- eqVarBndrs emptyRnEnv2 (tyConTyVars tc1) (tyConTyVars tc2)
    = assert (tc1 == tc2) $
    do { check_roles
       ; check (eqTypeX env syn_rhs1 syn_rhs2) $
          TyConSynonymMismatch syn_rhs1 syn_rhs2 }
  
    -- This allows abstract 'data T a' to be implemented using 'type T = ...'
    -- and abstract 'class K a' to be implement using 'type K = ...'
    -- See Note [Synonyms implement abstract data]
    | Hsig <- boot_or_sig -- don't support for hs-boot yet
    , isAbstractTyCon tc1
    , Just (tvs, ty) <- synTyConDefn_maybe tc2
    = checkSynAbsData tc1 tc2 tvs ty
  
    | Just fam_flav1 <- famTyConFlav_maybe tc1
    , Just fam_flav2 <- famTyConFlav_maybe tc2
    = assert (tc1 == tc2) $
      do { let injInfo1 = tyConInjectivityInfo tc1
               injInfo2 = tyConInjectivityInfo tc2
         ; -- check equality of roles, family flavours and injectivity annotations
           -- (NB: Type family roles are always nominal. But the check is
           -- harmless enough.)
         ; check_roles
         ; compatFamFlav fam_flav1 fam_flav2
         ; check (injInfo1 == injInfo2) TyConInjectivityMismatch }
  
    | isAlgTyCon tc1 && isAlgTyCon tc2
    , Just env <- eqVarBndrs emptyRnEnv2 (tyConTyVars tc1) (tyConTyVars tc2)
    = assert (tc1 == tc2) $
    do { check_roles
       ; let rhs1 = algTyConRhs tc1
             rhs2 = algTyConRhs tc2
       ; embedErrs (TyConMismatchedData rhs1 rhs2) $
    do { check (liftEq (eqTypeX env)
                       (tyConStupidTheta tc1) (tyConStupidTheta tc2))
                        MismatchedDatatypeContexts
       ; compatAlgRhs rhs1 rhs2 } }
  
    | otherwise = bootErr TyConsVeryDifferent
                  -- two very different types;
                  -- should be obvious to the user what the problem is
    where
      check_roles = checkRoles boot_or_sig tc1 (tyConRoles tc2)
  
  
  emptyRnEnv2 :: RnEnv2
  emptyRnEnv2 = mkRnEnv2 emptyInScopeSet
  
  -- | Check that two class methods have compatible type signatures.
  compatClassOp :: RnEnv2 -> HsBootOrSig -> ClassOpItem -> ClassOpItem -> BootErrsM BootMethodMismatch
  compatClassOp env boot_or_sig (id1, def_meth1) (id2, def_meth2)
    = do { check (name1 == name2) $
             MismatchedMethodNames
         ; check (eqTypeX env op_ty1 op_ty2) $
             MismatchedMethodTypes op_ty1 op_ty2
         ; case boot_or_sig of
             HsBoot ->
               check (liftEq eqDM def_meth1 def_meth2) $
                 MismatchedDefaultMethods False
             Hsig ->
               check (subDM op_ty1 def_meth1 def_meth2) $
                 MismatchedDefaultMethods True }
    where
      name1 = idName id1
      name2 = idName id2
      op_ty1 = classMethodTy id1
      op_ty2 = classMethodTy id2
  
      eqDM (_, VanillaDM)    (_, VanillaDM)    = True
      eqDM (_, GenericDM t1) (_, GenericDM t2) = eqTypeX env t1 t2
      eqDM _ _ = False
  
      -- NB: first argument is from hsig, second is from real impl.
      -- Order of pattern matching matters.
      subDM _ Nothing _ = True
      subDM _ _ Nothing = False
  
      -- If the hsig wrote:
      --
      --   f :: a -> a
      --   default f :: a -> a
      --
      -- this should be validly implementable using an old-fashioned
      -- vanilla default method.
      subDM t1 (Just (_, GenericDM gdm_t1)) (Just (_, VanillaDM))
       = eqType t1 gdm_t1   -- Take care (#22476).  Both t1 and gdm_t1 come
                               -- from tc1, so use eqType, and /not/ eqTypeX
  
      -- This case can occur when merging signatures
      subDM t1 (Just (_, VanillaDM)) (Just (_, GenericDM t2))
       = eqTypeX env t1 t2
  
      subDM _ (Just (_, VanillaDM)) (Just (_, VanillaDM)) = True
      subDM _ (Just (_, GenericDM t1)) (Just (_, GenericDM t2))
       = eqTypeX env t1 t2
  
  -- | Check that two associated types are compatible.
  compatAT :: RnEnv2 -> HsBootOrSig -> ClassATItem -> ClassATItem
           -> BootErrsM BootATMismatch
  compatAT env boot_or_sig (ATI tc1 def_ats1) (ATI tc2 def_ats2)
    = do { embedErrs MismatchedTyConAT $
             checkBootTyCon boot_or_sig tc1 tc2
         ; check (compatATDef def_ats1 def_ats2)
             MismatchedATDefaultType }
  
    where
      -- Ignore the location of the defaults
      compatATDef Nothing             Nothing             = True
      compatATDef (Just (ty1, _loc1)) (Just (ty2, _loc2)) = eqTypeX env ty1 ty2
      compatATDef _ _ = False
  
  -- | Check that two functional dependencies are the same.
  eqFD :: RnEnv2 -> FunDep TyVar -> FunDep TyVar -> Bool
  eqFD env (as1,bs1) (as2,bs2) =
    liftEq (eqTypeX env) (mkTyVarTys as1) (mkTyVarTys as2) &&
    liftEq (eqTypeX env) (mkTyVarTys bs1) (mkTyVarTys bs2)
  
  -- | Check compatibility of two type family flavours.
  compatFamFlav :: FamTyConFlav -> FamTyConFlav -> BootErrsM BootTyConMismatch
  compatFamFlav OpenSynFamilyTyCon   OpenSynFamilyTyCon
    = checkSuccess
  compatFamFlav (DataFamilyTyCon {}) (DataFamilyTyCon {})
    = checkSuccess
  compatFamFlav AbstractClosedSynFamilyTyCon AbstractClosedSynFamilyTyCon
    = checkSuccess -- This case only happens for hsig merging.
  compatFamFlav AbstractClosedSynFamilyTyCon (ClosedSynFamilyTyCon {})
    = checkSuccess
  compatFamFlav (ClosedSynFamilyTyCon {}) AbstractClosedSynFamilyTyCon
    = checkSuccess
  compatFamFlav (ClosedSynFamilyTyCon ax1) (ClosedSynFamilyTyCon ax2)
    = eqClosedFamilyAx ax1 ax2
  compatFamFlav (BuiltInSynFamTyCon {}) (BuiltInSynFamTyCon {})
    = checkSuccess
  compatFamFlav flav1 flav2
    = bootErr $ TyConFlavourMismatch flav1 flav2
  
  -- | Check that two 'AlgTyConRhs's are compatible.
  compatAlgRhs :: AlgTyConRhs -> AlgTyConRhs -> BootErrsM BootDataMismatch
  compatAlgRhs (AbstractTyCon {}) _rhs2 =
    checkSuccess -- rhs2 is guaranteed to be injective, since it's an AlgTyCon
  compatAlgRhs  tc1@DataTyCon{} tc2@DataTyCon{} =
    checkListBy compatCon (data_cons tc1) (data_cons tc2) MismatchedConstructors
  compatAlgRhs  tc1@NewTyCon{ data_con = dc1 } tc2@NewTyCon{ data_con = dc2 } =
    embedErrs (MismatchedConstructors . NE.singleton . MismatchedThing 1 dc1 dc2) $
      compatCon (data_con tc1) (data_con tc2)
  compatAlgRhs _ _ = bootErr MismatchedNewtypeVsData
  
  -- | Check that two 'DataCon's are compatible.
  compatCon :: DataCon -> DataCon -> BootErrsM BootDataConMismatch
  compatCon c1 c2
    = do { check (dataConName c1 == dataConName c2)
             MismatchedDataConNames
         ; check (dataConIsInfix c1 == dataConIsInfix c2)
             MismatchedDataConFixities
         ; check (liftEq eqHsBang (dataConImplBangs c1) (dataConImplBangs c2))
             MismatchedDataConBangs
         ; check (map flSelector (dataConFieldLabels c1) == map flSelector (dataConFieldLabels c2))
             MismatchedDataConFieldLabels
         ; check (eqType (dataConWrapperType c1) (dataConWrapperType c2))
             MismatchedDataConTypes }
  
  eqClosedFamilyAx :: Maybe (CoAxiom br) -> Maybe (CoAxiom br1)
                   -> BootErrsM BootTyConMismatch
  eqClosedFamilyAx Nothing Nothing  = checkSuccess
  eqClosedFamilyAx Nothing (Just _) = bootErr $ TyConAxiomMismatch $ NE.singleton MismatchedLength
  eqClosedFamilyAx (Just _) Nothing = bootErr $ TyConAxiomMismatch $ NE.singleton MismatchedLength
  eqClosedFamilyAx (Just (CoAxiom { co_ax_branches = branches1 }))
                   (Just (CoAxiom { co_ax_branches = branches2 }))
    = checkListBy eqClosedFamilyBranch branch_list1 branch_list2
        TyConAxiomMismatch
    where
      branch_list1 = fromBranches branches1
      branch_list2 = fromBranches branches2
  
  eqClosedFamilyBranch :: CoAxBranch -> CoAxBranch -> BootErrsM BootAxiomBranchMismatch
  eqClosedFamilyBranch (CoAxBranch { cab_tvs = tvs1, cab_cvs = cvs1
                                   , cab_lhs = lhs1, cab_rhs = rhs1 })
                       (CoAxBranch { cab_tvs = tvs2, cab_cvs = cvs2
                                   , cab_lhs = lhs2, cab_rhs = rhs2 })
    | Just env1 <- eqVarBndrs emptyRnEnv2 tvs1 tvs2
    , Just env  <- eqVarBndrs env1        cvs1 cvs2
    = do { check (liftEq (eqTypeX env) lhs1 lhs2) MismatchedAxiomLHS
         ; check (eqTypeX env rhs1 rhs2)          MismatchedAxiomRHS }
    | otherwise
    = bootErr MismatchedAxiomBinders
  
  {- Note [Role subtyping]
  ~~~~~~~~~~~~~~~~~~~~~~~~
  In the current formulation of roles, role subtyping is only OK if the
  "abstract" TyCon was not representationally injective.  Among the most
  notable examples of non representationally injective TyCons are abstract
  data, which can be implemented via newtypes (which are not
  representationally injective).  The key example is
  in this example from #13140:
  
       -- In an hsig file
       data T a -- abstract!
       type role T nominal
  
       -- Elsewhere
       foo :: Coercible (T a) (T b) => a -> b
       foo x = x
  
  We must NOT allow foo to typecheck, because if we instantiate
  T with a concrete data type with a phantom role would cause
  Coercible (T a) (T b) to be provable.  Fortunately, if T is not
  representationally injective, we cannot make the inference that a ~N b if
  T a ~R T b.
  
  Unconditional role subtyping would be possible if we setup
  an extra set of roles saying when we can project out coercions
  (we call these proj-roles); then it would NOT be valid to instantiate T
  with a data type at phantom since the proj-role subtyping check
  would fail.  See #13140 for more details.
  
  One consequence of this is we get no role subtyping for non-abstract
  data types in signatures. Suppose you have:
  
       signature A where
           type role T nominal
           data T a = MkT
  
  If you write this, we'll treat T as injective, and make inferences
  like T a ~R T b ==> a ~N b (mkSelCo).  But if we can
  subsequently replace T with one at phantom role, we would then be able to
  infer things like T Int ~R T Bool which is bad news.
  
  We could allow role subtyping here if we didn't treat *any* data types
  defined in signatures as injective.  But this would be a bit surprising,
  replacing a data type in a module with one in a signature could cause
  your code to stop typechecking (whereas if you made the type abstract,
  it is more understandable that the type checker knows less).
  
  It would have been best if this was purely a question of defaults
  (i.e., a user could explicitly ask for one behavior or another) but
  the current role system isn't expressive enough to do this.
  Having explicit proj-roles would solve this problem.
  -}
  
  checkRoles :: HsBootOrSig -> TyCon -> [Role] -> BootErrsM BootTyConMismatch
  checkRoles boot_or_sig tc1 r2
    |  boot_or_sig == HsBoot
    || isInjectiveTyCon tc1 Representational -- See Note [Role subtyping]
    = check (r1 == r2) (TyConRoleMismatch False)
    | otherwise
    = check (r2 `rolesSubtypeOf` r1) (TyConRoleMismatch True)
    where
  
      r1 = tyConRoles tc1
  
      rolesSubtypeOf [] [] = True
      -- NB: this relation is the OPPOSITE of the subroling relation
      rolesSubtypeOf (x:xs) (y:ys) = x >= y && rolesSubtypeOf xs ys
      rolesSubtypeOf _ _ = False
  
  {- Note [Synonyms implement abstract data]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  An abstract data type or class can be implemented using a type synonym,
  but ONLY if:
  
    1. T, as a standalone occurrence, is a valid type
       (T is "curryable"), and
  
    2. T is valid in an instance head.
  
  This gives rise to the following conditions under which we can implement
  an abstract data declaration @data T@ using a type synonym @type T tvs = rhs@:
  
    1. The type synonym T is nullary (tvs is null).
  
    2. The rhs must not contain any foralls, quantified types, or type family
       applications.
       See 'invalidAbsDataSubTypes' which computes a collection of
       invalid subtypes.
  
  See also 'HowAbstract' and Note [Skolem abstract data].
  -}
  
  -- | We are implementing an abstract data declaration of the form @data T@
  -- in a signature file, with a type synonym @type T tvs = rhs@ in the
  -- implementing module.
  --
  -- This function checks that the implementation is valid:
  --
  --  1. the type synonym T is nullary, i.e. tvs is null,
  --  2. rhs doesn't contain any type families, foralls, or qualified types.
  --
  -- See Note [Synonyms implement abstract data]
  checkSynAbsData :: TyCon   -- ^ @tc1@, the abstract data 'TyCon' we are implementing
                  -> TyCon   -- ^ @tc2@, a type synonym @type T tvs = ty@
                             --   we are using to implement @tc1@
                  -> [TyVar] -- ^ @tvs@
                  -> Type    -- ^ @ty@
                  -> BootErrsM BootTyConMismatch
  checkSynAbsData tc1 tc2 syn_tvs syn_rhs
    -- We are implementing @data T@ with @type T tvs = rhs@.
    -- Check the conditions of Note [Synonyms implement abstract data].
    = do { -- (1): T is nullary.
         ; check (null syn_tvs) $
             SynAbstractData SynAbsDataTySynNotNullary
           -- (2): the RHS of the type synonym is valid.
         ; case invalidAbsDataSubTypes syn_rhs of
            []       -> checkSuccess
            err:errs -> bootErr $ SynAbstractData $
                        SynAbstractDataInvalidRHS (err :| errs)
           -- NB: this allows implementing e.g. @data T :: Nat@ with @type T = 3@.
           -- See #15138.
  
    -- TODO: When it's a synonym implementing a class, we really
    -- should check that the fundeps are satisfied, but
    -- there is not an obvious way to do this for a constraint synonym.
    -- So for now, let it all through (it won't cause segfaults, anyway).
    -- Tracked at #12704.
  
           -- ... we also need to check roles.
         ; if | Just (tc2', args) <- tcSplitTyConApp_maybe syn_rhs
              , null syn_tvs -- Don't report role errors unless the type synonym is nullary
              -> assert (null (tyConRoles tc2)) $
                 -- If we have something like:
                 --
                 --  signature H where
                 --      data T a
                 --  module H where
                 --      data K a b = ...
                 --      type T = K Int
                 --
                 -- we need to drop the first role of K when comparing!
                 checkRoles Hsig tc1 (drop (length args) (tyConRoles tc2'))
              | otherwise
              -> checkSuccess
         }
  
  {-
      -- Hypothetically, if we were allow to non-nullary type synonyms, here
      -- is how you would check the roles
      if length tvs == length roles1
      then checkRoles roles1 roles2
      else case tcSplitTyConApp_maybe ty of
              Just (tc2', args) ->
                  checkRoles Hsig tc1 (drop (length args) (tyConRoles tc2') ++ roles2)
              Nothing -> Just roles_msg
  -}
  
  -- | Is this type a valid implementation of abstract data?
  --
  -- Returns a list of invalid sub-types encountered.
  invalidAbsDataSubTypes :: Type -> [Type]
  invalidAbsDataSubTypes = execWriter . go
    where
      go :: Type -> Writer [Type] ()
      go ty
        | Just ty' <- coreView ty
        = go ty'
      go TyVarTy{}
        = ok -- We report an error at the binding site of type variables,
             -- e.g. in the TySyn LHS or in the forall.
             -- It's not useful to report a second error for their occurrences
      go (AppTy t1 t2)
        = do { go t1; go t2 }
      go ty@(TyConApp tc tys)
        | isTypeFamilyTyCon tc
        = invalid ty
        | otherwise
        = mapM_ go tys
      go ty@(ForAllTy{})
        = invalid ty
      go ty@(FunTy af w t1 t2)
        | af == FTF_T_T
        = do { go w
             ; go (typeKind t1) ; go t1
             ; go (typeKind t2) ; go t2
             }
        | otherwise
        = invalid ty
      go LitTy{}
        = ok
      go ty@(CastTy{})
        = invalid ty
      go ty@(CoercionTy{})
        = invalid ty
  
      ok         = pure ()
      invalid ty = tell [ty]
  
  {-
  ************************************************************************
  *                                                                      *
          Type-checking the top level of a module (continued)
  *                                                                      *
  ************************************************************************
  -}
  
  rnTopSrcDecls :: HsGroup GhcPs -> TcM (TcGblEnv, HsGroup GhcRn)
  -- Fails if there are any errors
  rnTopSrcDecls group
   = do { -- Rename the source decls
          traceRn "rn12" empty ;
          (tcg_env, rn_decls) <- checkNoErrs $ rnSrcDecls group ;
          traceRn "rn13" empty ;
          (tcg_env, rn_decls) <- runRenamerPlugin tcg_env rn_decls ;
          traceRn "rn13-plugin" empty ;
  
          -- save the renamed syntax, if we want it
          let { tcg_env'
                  | Just grp <- tcg_rn_decls tcg_env
                    = tcg_env{ tcg_rn_decls = Just (appendGroups grp rn_decls) }
                  | otherwise
                     = tcg_env };
  
                  -- Dump trace of renaming part
          rnDump rn_decls ;
          return (tcg_env', rn_decls)
     }
  
  tcTopSrcDecls :: HsGroup GhcRn -> TcM (TcGblEnv, TcLclEnv)
  tcTopSrcDecls (HsGroup { hs_tyclds = tycl_decls,
                           hs_derivds = deriv_decls,
                           hs_fords  = foreign_decls,
                           hs_defds  = default_decls,
                           hs_annds  = annotation_decls,
                           hs_ruleds = rule_decls,
                           hs_valds  = hs_val_binds@(XValBindsLR
                                                (NValBinds val_binds val_sigs)) })
   = do {         -- Type-check the type and class decls, and all imported decls
                  -- The latter come in via tycl_decls
          traceTc "Tc2 (src)" empty ;
  
                  -- Source-language instances, including derivings,
                  -- and import the supporting declarations
          traceTc "Tc3" empty ;
          (tcg_env, inst_infos, th_bndrs,
           XValBindsLR (NValBinds deriv_binds deriv_sigs))
              <- tcTyClsInstDecls tycl_decls deriv_decls default_decls val_binds ;
  
          updLclCtxt (\tcl_env -> tcl_env { tcl_th_bndrs = th_bndrs `plusNameEnv` tcl_th_bndrs tcl_env }) $
          setGblEnv tcg_env       $ do {
  
                  -- Foreign import declarations next.
          traceTc "Tc4" empty ;
          (fi_ids, fi_decls, fi_gres) <- tcForeignImports foreign_decls ;
          tcExtendGlobalValEnv fi_ids     $ do {
  
                  -- Value declarations next.
                  -- It is important that we check the top-level value bindings
                  -- before the GHC-generated derived bindings, since the latter
                  -- may be defined in terms of the former. (For instance,
                  -- the bindings produced in a Data instance.)
          traceTc "Tc5" empty ;
          tc_envs <- tcTopBinds val_binds val_sigs;
          restoreEnvs tc_envs $ do {
  
                  -- Now GHC-generated derived bindings, generics, and selectors
                  -- Do not generate warnings from compiler-generated code;
                  -- hence the use of discardWarnings
          tc_envs@(tcg_env, tcl_env)
              <- discardWarnings (tcTopBinds deriv_binds deriv_sigs) ;
          restoreEnvs tc_envs $ do {  -- Environment doesn't change now
  
                  -- Second pass over class and instance declarations,
                  -- now using the kind-checked decls
          traceTc "Tc6" empty ;
          inst_binds <- tcInstDecls2 (tyClGroupTyClDecls tycl_decls) inst_infos ;
  
                  -- Foreign exports
          traceTc "Tc7" empty ;
          (foe_binds, foe_decls, foe_gres) <- tcForeignExports foreign_decls ;
  
                  -- Annotations
          annotations <- tcAnnotations annotation_decls ;
  
                  -- Rules
          rules <- tcRules rule_decls ;
  
                  -- Wrap up
          traceTc "Tc7a" empty ;
          let { all_binds = inst_binds ++ foe_binds
  
              ; fo_gres = fi_gres `unionBags` foe_gres
              ; fo_fvs = foldr (\gre fvs -> fvs `addOneFV` (greName gre))
                                  emptyFVs fo_gres
  
              ; sig_names = mkNameSet (collectHsValBinders CollNoDictBinders hs_val_binds)
                            `minusNameSet` getTypeSigNames val_sigs
  
                  -- Extend the GblEnv with the (as yet un-zonked)
                  -- bindings, rules, foreign decls
              ; tcg_env' = tcg_env { tcg_binds   = tcg_binds tcg_env ++ all_binds
                                   , tcg_sigs    = tcg_sigs tcg_env `unionNameSet` sig_names
                                   , tcg_rules   = tcg_rules tcg_env
                                                        ++ flattenRuleDecls rules
                                   , tcg_anns    = tcg_anns tcg_env ++ annotations
                                   , tcg_ann_env = extendAnnEnvList (tcg_ann_env tcg_env) annotations
                                   , tcg_fords   = tcg_fords tcg_env ++ foe_decls ++ fi_decls
                                   , tcg_dus     = tcg_dus tcg_env `plusDU` usesOnly fo_fvs } } ;
                                   -- tcg_dus: see Note [Newtype constructor usage in foreign declarations]
  
          -- See Note [Newtype constructor usage in foreign declarations]
          addUsedGREs NoDeprecationWarnings (bagToList fo_gres) ;
  
          return (tcg_env', tcl_env)
      }}}}}
  
  tcTopSrcDecls _ = panic "tcTopSrcDecls: ValBindsIn"
  
  ---------------------------
  tcTyClsInstDecls :: [TyClGroup GhcRn]
                   -> [LDerivDecl GhcRn]
                   -> [LDefaultDecl GhcRn]
                   -> [(RecFlag, LHsBinds GhcRn)]
                   -> TcM (TcGblEnv,            -- The full inst env
                           [InstInfo GhcRn],    -- Source-code instance decls to
                                                -- process; contains all dfuns for
                                                -- this module
                            ThBindEnv,          -- TH binding levels
                            HsValBinds GhcRn)   -- Supporting bindings for derived
                                                -- instances
  
  tcTyClsInstDecls tycl_decls deriv_decls default_decls binds
   = tcAddDataFamConPlaceholders (tycl_decls >>= group_instds) $
     tcAddPatSynPlaceholders (getPatSynBinds binds) $
     do { (tcg_env, inst_info, deriv_info, th_bndrs)
            <- tcTyAndClassDecls tycl_decls ;
  
        ; setGblEnv tcg_env $ do {
  
            -- With the @TyClDecl@s and @InstDecl@s checked we're ready to
            -- process the deriving clauses, including data family deriving
            -- clauses discovered in @tcTyAndClassDecls@.
            --
            -- But only after we've typechecked 'default' declarations.
            -- See Note [Typechecking default declarations]
            defaults <- tcDefaultDecls default_decls
            ; extendDefaultEnvWithLocalDefaults defaults $ do {
  
            -- Careful to quit now in case there were instance errors, so that
            -- the deriving errors don't pile up as well.
            ; failIfErrsM
            ; (tcg_env', inst_info', val_binds)
                <- tcInstDeclsDeriv deriv_info deriv_decls
            ; setGblEnv tcg_env' $ do {
                  failIfErrsM
                ; pure ( tcg_env', inst_info' ++ inst_info, th_bndrs, val_binds )
        }}}}
  
  {- *********************************************************************
  *                                                                      *
          Checking for 'main'
  *                                                                      *
  ************************************************************************
  -}
  
  checkMainType :: TcGblEnv -> TcRn WantedConstraints
  -- If this is the Main module, and it defines a function main,
  --   check that its type is of form IO tau.
  -- If not, do nothing
  -- See Note [Dealing with main]
  checkMainType tcg_env
    = do { hsc_env <- getTopEnv
         ; if tcg_mod tcg_env /= mainModIs (hsc_HUE hsc_env)
           then return emptyWC else
  
      do { rdr_env <- getGlobalRdrEnv
         ; let dflags    = hsc_dflags hsc_env
               main_occ  = getMainOcc dflags
               main_gres = lookupGRE rdr_env (LookupOccName main_occ SameNameSpace)
         ; case filter isLocalGRE main_gres of {
              []         -> return emptyWC ;
              (_:_:_)    -> return emptyWC ;
              [main_gre] ->
  
      do { let main_name = greName main_gre
               ctxt      = FunSigCtxt main_name NoRRC
         ; main_id   <- tcLookupId main_name
         ; (io_ty,_) <- getIOType
         ; let main_ty   = idType main_id
               eq_orig   = TypeEqOrigin { uo_actual    = main_ty
                                        , uo_expected  = io_ty
                                        , uo_thing     = Nothing
                                        , uo_invisible = Nothing }
         ; (_, lie)  <- captureTopConstraints       $
                        setMainCtxt main_name io_ty $
                        tcSubTypeSigma eq_orig ctxt main_ty io_ty
         ; return lie } } } }
  
  checkMain :: Bool  -- False => no 'module M(..) where' header at all
            -> Maybe (LocatedLI [LIE GhcPs])  -- Export specs of Main module
            -> TcM TcGblEnv
  -- If we are in module Main, check that 'main' is exported,
  -- and generate the runMainIO binding that calls it
  -- See Note [Dealing with main]
  checkMain explicit_mod_hdr export_ies
   = do { hsc_env  <- getTopEnv
        ; tcg_env <- getGblEnv
  
        ; let dflags      = hsc_dflags hsc_env
              main_mod    = mainModIs (hsc_HUE hsc_env)
              main_occ    = getMainOcc dflags
  
              exported_mains :: [Name]
              -- Exported things that are called 'main'
              exported_mains  = [ name | avail <- tcg_exports tcg_env
                                       , name  <- availNames avail
                                       , nameOccName name == main_occ ]
  
        ; if | tcg_mod tcg_env /= main_mod
             -> -- Not the main module
                return tcg_env
  
             | [main_name] <- exported_mains
             -> -- The module indeed exports a function called 'main'
                generateMainBinding tcg_env main_name
  
             | otherwise
             -> assert (null exported_mains) $
                -- A fully-checked export list can't contain more
                -- than one function with the same OccName
                do { complain_no_main dflags main_mod main_occ
                   ; return tcg_env } }
    where
      complain_no_main dflags main_mod main_occ
        = unless (interactive && not explicit_mod_hdr) $
          addErrTc (noMainMsg main_mod main_occ)          -- #12906
        where
          interactive = ghcLink dflags == LinkInMemory
          -- Without an explicit module header...
          -- in interactive mode, don't worry about the absence of 'main'.
          -- in other modes, add error message and go on with typechecking.
  
      noMainMsg main_mod main_occ
        = TcRnMissingMain explicit_export_list main_mod main_occ
      explicit_export_list = explicit_mod_hdr && isJust export_ies
  
  -- | Get the unqualified name of the function to use as the \"main\" for the main module.
  -- Either returns the default name or the one configured on the command line with -main-is
  getMainOcc :: DynFlags -> OccName
  getMainOcc dflags = case mainFunIs dflags of
                        Just fn -> mkVarOccFS (mkFastString fn)
                        Nothing -> mkVarOccFS (fsLit "main")
  
  generateMainBinding :: TcGblEnv -> Name -> TcM TcGblEnv
  -- There is a single exported 'main' function, called 'foo' (say),
  -- which may be locally defined or imported
  -- Define and typecheck the binding
  --     :Main.main :: IO res_ty = runMainIO res_ty foo
  -- This wraps the user's main function in the top-level stuff
  -- defined in runMainIO (eg catching otherwise un-caught exceptions)
  -- See Note [Dealing with main]
  generateMainBinding tcg_env main_name = do
      { traceTc "checkMain found" (ppr main_name)
      ; (io_ty, res_ty) <- getIOType
      ; let loc = getSrcSpan main_name
            main_expr_rn = L (noAnnSrcSpan loc) (mkHsVar (L (noAnnSrcSpan loc) main_name))
      ; (ev_binds, main_expr) <- setMainCtxt main_name io_ty $
                                 tcCheckMonoExpr main_expr_rn io_ty
  
              -- See Note [Root-main Id]
              -- Construct the binding
              --      :Main.main :: IO res_ty = runMainIO res_ty main
      ; run_main_id <- tcLookupId runMainIOName
      ; let { root_main_name =  mkExternalName rootMainKey rOOT_MAIN
                                 (mkVarOccFS (fsLit "main"))
                                 (getSrcSpan main_name)
            ; root_main_id = Id.mkExportedVanillaId root_main_name io_ty
            ; co  = mkWpTyApps [res_ty]
            -- The ev_binds of the `main` function may contain deferred
            -- type errors when type of `main` is not `IO a`. The `ev_binds`
            -- must be put inside `runMainIO` to ensure the deferred type
            -- error can be emitted correctly. See #13838.
            ; rhs = nlHsApp (mkLHsWrap co (nlHsVar run_main_id)) $
                      mkHsDictLet ev_binds main_expr
            ; main_bind = mkVarBind root_main_id rhs }
  
      ; return (tcg_env { tcg_main  = Just main_name
                        , tcg_binds = tcg_binds tcg_env
                                      ++ [main_bind]
                        , tcg_dus   = tcg_dus tcg_env
                                      `plusDU` usesOnly (unitFV main_name) })
                      -- Record the use of 'main', so that we don't
                      -- complain about it being defined but not used
      }
  
  getIOType :: TcM (TcType, TcType)
  -- Return (IO alpha, alpha) for fresh alpha
  getIOType = do { ioTyCon <- tcLookupTyCon ioTyConName
                 ; res_ty <- newFlexiTyVarTy liftedTypeKind
                 ; return (mkTyConApp ioTyCon [res_ty], res_ty) }
  
  setMainCtxt :: Name -> TcType -> TcM a -> TcM (TcEvBinds, a)
  setMainCtxt main_name io_ty thing_inside
    = setSrcSpan (getSrcSpan main_name) $
      addErrCtxt (MainCtxt main_name)   $
      checkConstraints skol_info [] []  $  -- Builds an implication if necessary
      thing_inside                         -- e.g. with -fdefer-type-errors
    where
      skol_info = SigSkol (FunSigCtxt main_name NoRRC) io_ty []
  
  {- Note [Dealing with main]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Dealing with the 'main' declaration is surprisingly tricky. Here are
  the moving parts:
  
  * The flag -main-is=M.foo allows you to set the main module to 'M',
    and the main function to 'foo'.  We access them through
        mainModIs  :: HscEnv -> Module     -- returns M
        getMainOcc :: DynFlags -> OccName  -- returns foo
    Of course usually M = Main, and foo = main.
  
  * checkMainType: when typechecking module M, we add an extra check that
      foo :: IO tau, for some type tau.
    This avoids getting ambiguous-type errors from the monomorphism restriction
    applying to things like
        main = return ()
    Note that checkMainType does not consult the export list because
    we have not yet done rnExports (and can't do it until later).
  
  * rnExports: checks the export list.  Very annoyingly, we can only do
    this after running any finalisers, which may add new declarations.
    That's why checkMainType and checkMain have to be separate.
  
  * checkMain: does two things:
    - check that the export list does indeed export something called 'foo'
    - generateMainBinding: generate the root-main binding
         :Main.main = runMainIO M.foo
    See Note [Root-main Id]
  
  An annoying consequence of having both checkMainType and checkMain is
  that, when (but only when) -fdefer-type-errors is on, we may report an
  ill-typed 'main' twice (as warnings): once in checkMainType and once
  in checkMain. See test typecheck/should_fail/T13292.
  
  We have the following tests to check this processing:
  ----------------+----------------------------------------------------------------------------------+
                  |                                  Module Header:                                  |
                  +-------------+-------------+-------------+-------------+-------------+------------+
                  | module      | module Main | <No Header> | module Main |module       |module Main |
                  |  Main(main) |             |             |   (module X)|   Main ()   |  (Sub.main)|
  ----------------+==================================================================================+
  `main` function | ERROR:      | Main.main   | ERROR:      | Main.main   | ERROR:      | Sub.main   |
  in Main module  |  Ambiguous  |             |  Ambiguous  |             |  `main` not |            |
  and in imported |             |             |             |             |  exported   |            |
  module Sub.     | T19397E1    | T16453M0    | T19397E2    | T16453M3    |             | T16453M1   |
                  |             |             |             | X = Main    | Remark 2)   |            |
  ----------------+-------------+-------------+-------------+-------------+-------------+------------+
  `main`function  | Sub.main    | ERROR:      | Sub.main    | Sub.main    | ERROR:      | Sub.main   |
  only in imported|             | No `main` in|             |             |  `main` not |            |
  submodule Sub.  |             |   `Main`    |             |             |  exported   |            |
                  | T19397M0    | T16453E1    | T19397M1    | T16453M4    |             | T16453M5   |
                  |             |             |             | X = Sub     | Remark 2)   |            |
  ----------------+-------------+-------------+-------------+-------------+-------------+------------+
  `foo` function  | Sub.foo     | ERROR:      | Sub.foo     | Sub.foo     | ERROR:      | Sub.foo    |
  in submodule    |             | No `foo` in |             |             |  `foo` not  |            |
  Sub.            |             |   `Main`    |             |             |  exported   |            |
  GHC option:     |             |             |             |             |             |            |
    -main-is foo  | T19397M2    | T19397E3    | T19397M3    | T19397M4    | T19397E4    | T16453M6   |
                  | Remark 1)   |             |             | X = Sub     |             | Remark 3)  |
  ----------------+-------------+-------------+-------------+-------------+-------------+------------+
  
  Remarks:
  * The first line shows the exported `main` function or the error.
  * The second line shows the coresponding test case.
  * The module `Sub` contains the following functions:
       main :: IO ()
       foo :: IO ()
  * Remark 1) Here the header is `Main (foo)`.
  * Remark 2) Here we have no extra test case. It would exercise the same code path as `T19397E4`.
  * Remark 3) Here the header is `Main (Sub.foo)`.
  
  
  Note [Root-main Id]
  ~~~~~~~~~~~~~~~~~~~
  The function that the RTS invokes is always :Main.main, which we call
  root_main_id.  (Because GHC allows the user to have a module not
  called Main as the main module, we can't rely on the main function
  being called "Main.main".  That's why root_main_id has a fixed module
  ":Main".)
  
  This is unusual: it's a LocalId whose Name has a Module from another
  module. Tiresomely, we must filter it out again in GHC.Iface.Make, less we
  get two defns for 'main' in the interface file!
  
  When using `-fwrite-if-simplified-core` the root_main_id can end up in an interface file.
  When the interface is read back in we have to add a special case when creating the
  Id because otherwise we would go looking for the :Main module which obviously doesn't
  exist. For this logic see GHC.IfaceToCore.mk_top_id.
  
  There is also some similar (probably dead) logic in GHC.Rename.Env which says it
  was added for External Core which faced a similar issue.
  
  Note [runTcInteractive module graph]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
  The `withInteractiveModuleNode` function sets up the module graph which contains
  the interactive module used by `runTcInteractive`.
  
  The module graph is essentially the ambient module graph which is set up when
  ghci loads a module using `load`, with the addition of the interactive module (Ghci<N>),
  which imports the parts specified by the `InteractiveImports`.
  
  Therefore `downsweepInteractiveImports` presumes that any import which is
  determined to be from the home module is already present in the module graph.
  This saves resummarising and performing the whole downsweep again if it's already been
  done.
  
  On the other hand, when GHCi starts up, and no modules have been loaded yet, the
  module graph will be empty. Therefore `downsweepInteractiveImports` will perform
  for the unit portion of the graph, if it's not already been performed.
  
  
  *********************************************************
  *                                                       *
                  GHCi stuff
  *                                                       *
  *********************************************************
  -}
  
  -- See Note [runTcInteractive module graph]
  withInteractiveModuleNode :: HscEnv -> TcM a -> TcM a
  withInteractiveModuleNode hsc_env thing_inside = do
    mg <- liftIO $ downsweepInteractiveImports hsc_env (hsc_IC hsc_env)
    updTopEnv (setModuleGraph mg) thing_inside
  
  
  runTcInteractive :: HscEnv -> TcRn a -> IO (Messages TcRnMessage, Maybe a)
  -- Initialise the tcg_inst_env with instances from all home modules.
  -- This mimics the more selective call to hptInstances in tcRnImports
  runTcInteractive hsc_env thing_inside
    = initTcInteractive hsc_env $ withTcPlugins hsc_env $
      withDefaultingPlugins hsc_env $ withHoleFitPlugins hsc_env $
      withInteractiveModuleNode hsc_env $
      do { traceTc "setInteractiveContext" $
              vcat [ text "ic_tythings:" <+> vcat (map ppr (ic_tythings icxt))
                   , text "ic_insts:" <+> vcat (map (pprBndr LetBind . instanceDFunId) (instEnvElts ic_insts))
                   , text "icReaderEnv (LocalDef)" <+>
                        vcat (map ppr [ local_gres | gres <- nonDetOccEnvElts (icReaderEnv icxt)
                                                   , let local_gres = filter isLocalGRE gres
                                                   , not (null local_gres) ]) ]
  
         ; let getOrphansForModuleName m mb_pkg = do
                iface <- loadSrcInterface (text "runTcInteractive") m NotBoot mb_pkg
                pure $ mi_module iface : dep_orphs (mi_deps iface)
  
               getOrphansForModule m = do
                iface <- loadModuleInterface (text "runTcInteractive") m
                pure $ mi_module iface : dep_orphs (mi_deps iface)
  
         ; !orphs <- fmap (force . concat) . forM (ic_imports icxt) $ \i ->
              case i of                   -- force above: see #15111
                  IIModule n -> getOrphansForModule n
                  IIDecl i   -> getOrphansForModuleName (unLoc (ideclName i))
                                           (renameRawPkgQual (hsc_unit_env hsc_env) (unLoc $ ideclName i) (ideclPkgQual i))
  
  
         ; (home_insts, home_fam_insts) <- liftIO $ UnitEnv.hugAllInstances (hsc_unit_env hsc_env)
  
         ; let imports = emptyImportAvails { imp_orphs = orphs }
  
               upd_envs (gbl_env, lcl_env) = (gbl_env', lcl_env')
  
                 where
                   gbl_env' = gbl_env
                     { tcg_rdr_env      = icReaderEnv icxt
                     , tcg_type_env     = type_env
                     , tcg_inst_env     = tcg_inst_env gbl_env `unionInstEnv` ic_insts `unionInstEnv` home_insts
                     , tcg_fam_inst_env = extendFamInstEnvList
                                (extendFamInstEnvList (tcg_fam_inst_env gbl_env)
                                                      ic_finsts)
                                home_fam_insts
                     , tcg_fix_env      = ic_fix_env icxt
                     , tcg_default      = ic_default icxt
                          -- must calculate imp_orphs of the ImportAvails
                          -- so that instance visibility is done correctly
                     , tcg_imports      = imports }
  
                   lcl_env' = modifyLclCtxt (tcExtendLocalTypeEnv lcl_ids) lcl_env
  
         ; updEnvs upd_envs thing_inside }
    where
      icxt                     = hsc_IC hsc_env
      (ic_insts, ic_finsts)    = ic_instances icxt
      (lcl_ids, top_ty_things) = partitionWith is_closed (ic_tythings icxt)
  
      is_closed :: TyThing -> Either (Name, TcTyThing) TyThing
      -- Put Ids with free type variables (always RuntimeUnks)
      -- in the *local* type environment
      -- See Note [Initialising the type environment for GHCi]
      is_closed thing
        | AnId id <- thing
        , not (isTypeClosedLetBndr id)
        = Left (idName id, ATcId { tct_id = id
                                 , tct_info = NotLetBound })
        | otherwise
        = Right thing
  
      type_env1 = mkTypeEnvWithImplicits top_ty_things
      type_env  = extendTypeEnvWithIds type_env1
                $ map instanceDFunId (instEnvElts ic_insts)
                  -- Putting the dfuns in the type_env
                  -- is just to keep Core Lint happy
  
  {- Note [Initialising the type environment for GHCi]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Most of the Ids in ic_things, defined by the user in 'let' stmts,
  have closed types. E.g.
     ghci> let foo x y = x && not y
  
  However the GHCi debugger creates top-level bindings for Ids whose
  types have free RuntimeUnk skolem variables, standing for unknown
  types.  If we don't register these free TyVars as global TyVars then
  the typechecker will try to quantify over them and fall over in
  skolemiseQuantifiedTyVar. so we must add any free TyVars to the
  typechecker's global TyVar set.  That is done by using
  tcExtendLocalTypeEnv.
  
  We do this by splitting out the Ids with open types, using 'is_closed'
  to do the partition.  The top-level things go in the global TypeEnv;
  the open, NotTopLevel, Ids, with free RuntimeUnk tyvars, go in the
  local TypeEnv.
  
  Note that we don't extend the local RdrEnv (tcl_rdr); all the in-scope
  things are already in the interactive context's GlobalRdrEnv.
  Extending the local RdrEnv isn't terrible, but it means there is an
  entry for the same Name in both global and local RdrEnvs, and that
  lead to duplicate "perhaps you meant..." suggestions (e.g. T5564).
  
  We don't bother with the tcl_th_bndrs environment either.
  -}
  
  -- | The returned [Id] is the list of new Ids bound by this statement. It can
  -- be used to extend the InteractiveContext via extendInteractiveContext.
  --
  -- The returned TypecheckedHsExpr is of type IO [ Any ], a list of the bound
  -- values, coerced to Any.
  tcRnStmt :: HscEnv -> GhciLStmt GhcPs
           -> IO (Messages TcRnMessage, Maybe ([Id], LHsExpr GhcTc, FixityEnv))
  tcRnStmt hsc_env rdr_stmt
    = runTcInteractive hsc_env $ do {
  
      -- The real work is done here
      ((bound_ids, tc_expr), fix_env) <- tcUserStmt rdr_stmt ;
      zonked_expr <- zonkTopLExpr tc_expr ;
      zonked_ids  <- zonkTopBndrs bound_ids ;
  
      failIfErrsM ;  -- we can't do the next step if there are
                     -- representation polymorphism errors
                     -- test case: ghci/scripts/T13202{,a}
  
          -- None of the Ids should be of unboxed type, because we
          -- cast them all to HValues in the end!
      mapM_ (addErr . TcRnGhciUnliftedBind) $
        filter (mightBeUnliftedType . idType) zonked_ids ;
  
      traceTc "tcs 1" empty ;
      this_mod <- getModule ;
      global_ids <- mapM (externaliseAndTidyId this_mod) zonked_ids ;
          -- Note [Interactively-bound Ids in GHCi] in GHC.Driver.Env
  
      traceOptTcRn Opt_D_dump_tc
          (vcat [text "Bound Ids" <+> pprWithCommas ppr global_ids,
                 text "Typechecked expr" <+> ppr zonked_expr]) ;
  
      return (global_ids, zonked_expr, fix_env)
      }
  
  {-
  --------------------------------------------------------------------------
                  Typechecking Stmts in GHCi
  
  Here is the grand plan, implemented in tcUserStmt
  
          What you type                   The IO [HValue] that hscStmt returns
          -------------                   ------------------------------------
          let pat = expr          ==>     let pat = expr in return [coerce HVal x, coerce HVal y, ...]
                                          bindings: [x,y,...]
  
          pat <- expr             ==>     expr >>= \ pat -> return [coerce HVal x, coerce HVal y, ...]
                                          bindings: [x,y,...]
  
          expr (of IO type)       ==>     expr >>= \ it -> return [coerce HVal it]
            [NB: result not printed]      bindings: [it]
  
          expr (of non-IO type,   ==>     let it = expr in print it >> return [coerce HVal it]
            result showable)              bindings: [it]
  
          expr (of non-IO type,
            result not showable)  ==>     error
  -}
  
  -- | A plan is an attempt to lift some code into the IO monad.
  type PlanResult = ([Id], LHsExpr GhcTc)
  type Plan = TcM PlanResult
  
  -- | Try the plans in order. If one fails (by raising an exn), try the next.
  -- If one succeeds, take it.
  runPlans :: NonEmpty Plan -> Plan
  runPlans = foldr1 (flip tryTcDiscardingErrs)
  
  -- | Typecheck (and 'lift') a stmt entered by the user in GHCi into the
  -- GHCi 'environment'.
  --
  -- By 'lift' and 'environment we mean that the code is changed to
  -- execute properly in an IO monad. See Note [Interactively-bound Ids
  -- in GHCi] in GHC.Driver.Env for more details. We do this lifting by trying
  -- different ways ('plans') of lifting the code into the IO monad and
  -- type checking each plan until one succeeds.
  tcUserStmt :: GhciLStmt GhcPs -> TcM (PlanResult, FixityEnv)
  
  -- An expression typed at the prompt is treated very specially
  tcUserStmt (L loc (BodyStmt _ expr _ _))
    = do  { (rn_expr, fvs) <- checkNoErrs (rnLExpr expr)
  
          ; dumpOptTcRn Opt_D_dump_rn_ast "Renamer" FormatHaskell
              (showAstData NoBlankSrcSpan NoBlankEpAnnotations rn_expr)
                 -- Don't try to typecheck if the renamer fails!
          ; ghciStep <- getGhciStepIO
          ; uniq <- newUnique
          ; let loc' = noAnnSrcSpan $ locA loc
          ; interPrintName <- getInteractivePrintName
          ; let fresh_it  = itName uniq (locA loc)
                matches   = [mkMatch (mkPrefixFunRhs (L loc' fresh_it) noAnn) (noLocA []) rn_expr
                                     emptyLocalBinds]
                -- [it = expr]
                the_bind  = L loc $ (mkTopFunBind FromSource
                                       (L loc' fresh_it) matches)
                                           { fun_ext = fvs }
                -- Care here!  In GHCi the expression might have
                -- free variables, and they in turn may have free type variables
                -- (if we are at a breakpoint, say).  We must put those free vars
  
                -- [let it = expr]
                let_stmt  = L loc $ LetStmt noAnn $ HsValBinds noAnn
                             $ XValBindsLR
                                 (NValBinds [(NonRecursive,[the_bind])] [])
  
                -- [it <- e]
                bind_stmt = L loc $ BindStmt
                                         (XBindStmtRn
                                            { xbsrn_bindOp = mkRnSyntaxExpr bindIOName
                                            , xbsrn_failOp = Nothing
                                            })
                                         (L loc (VarPat noExtField (L loc' fresh_it)))
                                         (nlHsApp ghciStep rn_expr)
  
                -- [; print it]
                print_it  = L loc $ BodyStmt noExtField
                                             (nlHsApp (nlHsVar interPrintName)
                                             (nlHsVar fresh_it))
                                             (mkRnSyntaxExpr thenIOName)
                                                    noSyntaxExpr
  
                -- NewA
                no_it_a = L loc $ BodyStmt noExtField (nlHsApps bindIOName
                                         [rn_expr , nlHsVar interPrintName])
                                         (mkRnSyntaxExpr thenIOName)
                                         noSyntaxExpr
  
                no_it_b = L loc $ BodyStmt noExtField (rn_expr)
                                         (mkRnSyntaxExpr thenIOName)
                                         noSyntaxExpr
  
                no_it_c = L loc $ BodyStmt noExtField
                                        (nlHsApp (nlHsVar interPrintName) rn_expr)
                                        (mkRnSyntaxExpr thenIOName)
                                        noSyntaxExpr
  
                -- See Note [GHCi Plans]
  
                it_plans =
                      -- Plan A
                      do { stuff@([it_id], _) <- tcGhciStmts [bind_stmt, print_it]
                         ; it_ty <- liftZonkM $ zonkTcType (idType it_id)
                         ; when (isUnitTy it_ty) failM
                         ; return stuff } :|
  
                          -- Plan B; a naked bind statement
                    [ tcGhciStmts [bind_stmt]
  
                          -- Plan C; check that the let-binding is typeable all by itself.
                          -- If not, fail; if so, try to print it.
                          -- The two-step process avoids getting two errors: one from
                          -- the expression itself, and one from the 'print it' part
                          -- This two-step story is very clunky, alas
                    , do { _ <- checkNoErrs (tcGhciStmts [let_stmt])
                                  --- checkNoErrs defeats the error recovery of let-bindings
                         ; tcGhciStmts [let_stmt, print_it] } ]
  
                -- Plans where we don't bind "it"
                no_it_plans =
                  tcGhciStmts [no_it_a] :|
                  tcGhciStmts [no_it_b] :
                  tcGhciStmts [no_it_c] :
                  []
  
          ; generate_it <- goptM Opt_NoIt
  
          -- We disable `-fdefer-type-errors` in GHCi for naked expressions.
          -- See Note [Deferred type errors in GHCi]
  
          -- NB: The flag `-fdefer-type-errors` implies `-fdefer-type-holes`
          -- and `-fdefer-out-of-scope-variables`. However the flag
          -- `-fno-defer-type-errors` doesn't imply `-fdefer-type-holes` and
          -- `-fno-defer-out-of-scope-variables`. Thus the later two flags
          -- also need to be unset here.
          ; plan <- unsetGOptM Opt_DeferTypeErrors $
                    unsetGOptM Opt_DeferTypedHoles $
                    unsetGOptM Opt_DeferOutOfScopeVariables $
                      runPlans $ if generate_it
                                   then no_it_plans
                                   else it_plans
  
          ; dumpOptTcRn Opt_D_dump_tc_ast "Typechecker AST" FormatHaskell
                (showAstData NoBlankSrcSpan NoBlankEpAnnotations plan)
  
          ; fix_env <- getFixityEnv
          ; return (plan, fix_env) }
  
  {- Note [Deferred type errors in GHCi]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  In GHCi, we ensure that type errors don't get deferred when type checking the
  naked expressions. Deferring type errors here is unhelpful because the
  expression gets evaluated right away anyway. It also would potentially emit
  two redundant type-error warnings, one from each plan.
  
  #14963 reveals another bug that when deferred type errors is enabled
  in GHCi, any reference of imported/loaded variables (directly or indirectly)
  in interactively issued naked expressions will cause ghc panic. See more
  detailed discussion in #14963.
  
  The interactively issued declarations, statements, as well as the modules
  loaded into GHCi, are not affected. That means, for declaration, you could
  have
  
      Prelude> :set -fdefer-type-errors
      Prelude> x :: IO (); x = putStrLn True
      <interactive>:14:26: warning: [-Wdeferred-type-errors]
          ? Couldn't match type ‘Bool’ with ‘[Char]’
            Expected type: String
              Actual type: Bool
          ? In the first argument of ‘putStrLn’, namely ‘True’
            In the expression: putStrLn True
            In an equation for ‘x’: x = putStrLn True
  
  But for naked expressions, you will have
  
      Prelude> :set -fdefer-type-errors
      Prelude> putStrLn True
      <interactive>:2:10: error:
          ? Couldn't match type ‘Bool’ with ‘[Char]’
            Expected type: String
              Actual type: Bool
          ? In the first argument of ‘putStrLn’, namely ‘True’
            In the expression: putStrLn True
            In an equation for ‘it’: it = putStrLn True
  
      Prelude> let x = putStrLn True
      <interactive>:2:18: warning: [-Wdeferred-type-errors]
          ? Couldn't match type ‘Bool’ with ‘[Char]’
            Expected type: String
              Actual type: Bool
          ? In the first argument of ‘putStrLn’, namely ‘True’
            In the expression: putStrLn True
            In an equation for ‘x’: x = putStrLn True
  -}
  
  tcUserStmt rdr_stmt@(L loc _)
    = do { (([rn_stmt], fix_env), fvs) <- checkNoErrs $
             rnStmts (HsDoStmt GhciStmtCtxt) rnExpr [rdr_stmt] $ \_ -> do
               fix_env <- getFixityEnv
               return (fix_env, emptyFVs)
              -- Don't try to typecheck if the renamer fails!
         ; traceRn "tcRnStmt" (vcat [ppr rdr_stmt, ppr rn_stmt, ppr fvs])
         ; rnDump rn_stmt ;
  
         ; ghciStep <- getGhciStepIO
         ; let gi_stmt
                 | (L loc (BindStmt x pat expr)) <- rn_stmt
                       = L loc $ BindStmt x pat (nlHsApp ghciStep expr)
                 | otherwise = rn_stmt
  
         ; opt_pr_flag <- goptM Opt_PrintBindResult
         ; let print_result_plan
                 | opt_pr_flag                         -- The flag says "print result"
                 , [v] <- collectLStmtBinders CollNoDictBinders gi_stmt  -- One binder
                 = Just $ mk_print_result_plan gi_stmt v
                 | otherwise = Nothing
  
          -- The plans are:
          --      [stmt; print v]         if one binder and not v::()
          --      [stmt]                  otherwise
         ; plan <- runPlans $ maybe id (NE.<|) print_result_plan $ NE.singleton $ tcGhciStmts [gi_stmt]
         ; return (plan, fix_env) }
    where
      mk_print_result_plan stmt v
        = do { stuff@([v_id], _) <- tcGhciStmts [stmt, print_v]
             ; v_ty <- liftZonkM $ zonkTcType (idType v_id)
             ; when (isUnitTy v_ty || not (isTauTy v_ty)) failM
             ; return stuff }
        where
          print_v  = L loc $ BodyStmt noExtField (nlHsApp (nlHsVar printName)
                                      (nlHsVar v))
                                      (mkRnSyntaxExpr thenIOName) noSyntaxExpr
  
  {-
  Note [GHCi Plans]
  ~~~~~~~~~~~~~~~~~
  When a user types an expression in the repl we try to print it in three different
  ways. Also, depending on whether -fno-it is set, we bind a variable called `it`
  which can be used to refer to the result of the expression subsequently in the repl.
  
  The normal plans are :
    A. [it <- e; print e]     but not if it::()
    B. [it <- e]
    C. [let it = e; print it]
  
  When -fno-it is set, the plans are:
    A. [e >>= print]
    B. [e]
    C. [let it = e in print it]
  
  The reason for -fno-it is explained in #14336. `it` can lead to the repl
  leaking memory as it is repeatedly queried.
  -}
  
  any_lifted :: Type
  any_lifted = anyTypeOfKind liftedTypeKind
  
  -- | Typecheck the statements given and then return the results of the
  -- statement in the form 'IO [Any]'.
  tcGhciStmts :: [GhciLStmt GhcRn] -> TcM PlanResult
  tcGhciStmts stmts
   = do { ioTyCon <- tcLookupTyCon ioTyConName
        ; ret_id  <- tcLookupId returnIOName             -- return @ IO
        ; let ret_ty      = mkListTy any_lifted
              io_ret_ty   = mkTyConApp ioTyCon [ret_ty]
              tc_io_stmts = tcStmtsAndThen (HsDoStmt GhciStmtCtxt) tcDoStmt stmts
                                           (mkCheckExpType io_ret_ty)
              names = collectLStmtsBinders CollNoDictBinders stmts
  
          -- OK, we're ready to typecheck the stmts
        ; traceTc "GHC.Tc.Module.tcGhciStmts: tc stmts" empty
        ; ((tc_stmts, ids), lie) <- captureTopConstraints $
                                    tc_io_stmts $ \ _ ->
                                    mapM tcLookupId names
                          -- Look up the names right in the middle,
                          -- where they will all be in scope
  
          -- Simplify the context
        ; traceTc "GHC.Tc.Module.tcGhciStmts: simplify ctxt" empty
        ; const_binds <- checkNoErrs (simplifyInteractive lie)
                  -- checkNoErrs ensures that the plan fails if context redn fails
  
  
        ; traceTc "GHC.Tc.Module.tcGhciStmts: done" empty
  
        -- ret_expr is the expression
        --      returnIO @[Any] [unsafeCoerce# @Any x, ..,  unsafeCoerce# @Any z]
        --
        -- Despite the inconvenience of building the type applications etc,
        -- this *has* to be done in type-annotated post-typecheck form
        -- because we are going to return a list of *polymorphic* values
        -- coerced to type Any. If we built a *source* stmt
        --      return [coerce x, ..., coerce z]
        -- then the type checker would instantiate x..z, and we wouldn't
        -- get their *polymorphic* values.  (And we'd get ambiguity errs
        -- if they were overloaded, since they aren't applied to anything.)
        --
        -- We use Any rather than a dummy type such as () because of
        -- the rules of unsafeCoerce#; see Unsafe/Coerce.hs for the details.
  
        ; AnId unsafe_coerce_id <- tcLookupGlobal unsafeCoercePrimName
             -- We use unsafeCoerce# here because of (U11) in
             -- Note [Implementing unsafeCoerce] in base:Unsafe.Coerce
  
        ; let ret_expr = nlHsApp (nlHsTyApp ret_id [ret_ty]) $
                         noLocA $ ExplicitList any_lifted $
                         map mk_item ids
  
              mk_item id = unsafe_coerce_id `nlHsTyApp` [ getRuntimeRep (idType id)
                                                        , getRuntimeRep any_lifted
                                                        , idType id, any_lifted]
                                            `nlHsApp` nlHsVar id
              stmts = tc_stmts ++ [noLocA (mkLastStmt ret_expr)]
  
        ; return (ids, mkHsDictLet (EvBinds const_binds) $
                       noLocA (HsDo io_ret_ty GhciStmtCtxt (noLocA stmts)))
      }
  
  -- | Generate a typed ghciStepIO expression (ghciStep :: Ty a -> IO a)
  getGhciStepIO :: TcM (LHsExpr GhcRn)
  getGhciStepIO = do
      ghciTy <- getGHCiMonad
      a_tv <- newName (mkTyVarOccFS (fsLit "a"))
      let ghciM   = nlHsAppTy (nlHsTyVar NotPromoted ghciTy) (nlHsTyVar NotPromoted a_tv)
          ioM     = nlHsAppTy (nlHsTyVar NotPromoted ioTyConName) (nlHsTyVar NotPromoted a_tv)
  
          step_ty :: LHsSigType GhcRn
          step_ty = noLocA $ HsSig
                       { sig_bndrs = HsOuterImplicit{hso_ximplicit = [a_tv]}
                       , sig_ext = noExtField
                       , sig_body = nlHsFunTy ghciM ioM }
  
          stepTy :: LHsSigWcType GhcRn
          stepTy = mkEmptyWildCardBndrs step_ty
  
      return (noLocA $ ExprWithTySig noExtField (nlHsVar ghciStepIoMName) stepTy)
  
  isGHCiMonad :: HscEnv -> String -> IO (Messages TcRnMessage, Maybe Name)
  isGHCiMonad hsc_env ty
    = runTcInteractive hsc_env $ do
          rdrEnv <- getGlobalRdrEnv
          let occIO = lookupOccEnv rdrEnv (mkOccName tcName ty)
          case occIO of
              Just [n] -> do
                  let name = greName n
                  ghciClass <- tcLookupClass ghciIoClassName
                  userTyCon <- tcLookupTyCon name
                  let userTy = mkTyConApp userTyCon []
                  _ <- tcLookupInstance ghciClass [userTy]
                  return name
              _ -> failWithTc $ TcRnGhciMonadLookupFail ty occIO
  
  -- | How should we infer a type? See Note [TcRnExprMode]
  data TcRnExprMode = TM_Inst     -- ^ Instantiate inferred quantifiers only (:type)
                    | TM_Default  -- ^ Instantiate all quantifiers,
                                  --   and do eager defaulting (:type +d)
  
  -- | tcRnExpr just finds the type of an expression
  --   for :type
  tcRnExpr :: HscEnv
           -> TcRnExprMode
           -> LHsExpr GhcPs
           -> IO (Messages TcRnMessage, Maybe Type)
  tcRnExpr hsc_env mode rdr_expr
    = runTcInteractive hsc_env $
      do {
  
      (rn_expr, _fvs) <- rnLExpr rdr_expr ;
      failIfErrsM ;
  
      -- Typecheck the expression
      ((tclvl, (_tc_expr, res_ty)), lie)
            <- captureTopConstraints $
               pushTcLevelM          $
               (if inst then tcInferRho rn_expr
                        else tcInferSigma rn_expr);
  
      -- Generalise
      uniq <- newUnique ;
      let { fresh_it = itName uniq (getLocA rdr_expr) } ;
      ((qtvs, dicts, _, _), residual)
           <- captureConstraints $
              simplifyInfer TopLevel tclvl infer_mode
                            []    {- No sig vars -}
                            [(fresh_it, res_ty)]
                            lie ;
  
      -- Ignore the dictionary bindings
      _ <- perhaps_disable_default_warnings $
           simplifyInteractive residual ;
  
      let { all_expr_ty = mkInfForAllTys qtvs $
                          mkPhiTy (map idType dicts) res_ty } ;
      ty <- liftZonkM $ zonkTcType all_expr_ty ;
  
      -- See Note [Normalising the type in :type]
      fam_envs <- tcGetFamInstEnvs ;
      let { normalised_type = reductionReducedType $ normaliseType fam_envs Nominal ty
            -- normaliseType returns a coercion which we discard, so the Role is irrelevant.
          ; final_type = if isSigmaTy res_ty then ty else normalised_type } ;
      return final_type }
    where
      -- Optionally instantiate the type of the expression
      -- See Note [TcRnExprMode]
      (inst, infer_mode, perhaps_disable_default_warnings) = case mode of
        TM_Inst    -> (False, NoRestrictions,  id)
        TM_Default -> (True,  EagerDefaulting, unsetWOptM Opt_WarnTypeDefaults)
  
  {- Note [Implementing :type]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Consider   :type const
  
  We want    forall a b. a -> b -> a
  and not    forall {a}{b}. a -> b -> a
  
  The latter is what we'd get if we eagerly instantiated and then
  re-generalised with Inferred binders.  It makes a difference, because
  it tells us we where we can use Visible Type Application (VTA).
  
  And also for   :type const @Int
  we want        forall b. Int -> b -> Int
  and not        forall {b}. Int -> b -> Int
  
  Solution: use tcInferSigma, which in turn uses tcInferApp, which
  has a special case for application chains.
  
  Note [Normalising the type in :type]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  In :t <expr> we usually normalise the type (to simplify type functions)
  before displaying the result.  Reason (see #10321): otherwise we may show
  types like
      <expr> :: Vec (1+2) Int
  rather than the simpler
      <expr> :: Vec 3 Int
  In GHC.Tc.Gen.Bind.mkInferredPolyId we normalise for a very similar reason.
  
  However this normalisation is less helpful when <expr> is just
  an identifier, whose user-written type happens to contain type-function
  applications.  E.g. (#20974)
      test :: F [Monad, A, B] m => m ()
  where F is a type family.  If we say `:t test`, we'd prefer to see
  the type family un-expanded.
  
  We adopt the following ad-hoc solution: if the type inferred for <expr>
  (before generalisation, namely res_ty) is a SigmaType (i.e. is not
  fully instantiated) then do not normalise; otherwise normalise.
  This is not ideal; for example, suppose  x :: F Int.  Then
    :t x
  would be normalised because `F Int` is not a SigmaType.  But
  anything here is ad-hoc, and it's a user-sought improvement.
  -}
  
  --------------------------
  tcRnImportDecls :: HscEnv
                  -> [LImportDecl GhcPs]
                  -> IO (Messages TcRnMessage, Maybe GlobalRdrEnv)
  -- Find the new chunk of GlobalRdrEnv created by this list of import
  -- decls.  In contract tcRnImports *extends* the TcGblEnv.
  tcRnImportDecls hsc_env import_decls
   =  runTcInteractive hsc_env $
      do { (_, gbl_env) <- updGblEnv zap_rdr_env $
                           tcRnImports hsc_env $ map (,text "is directly imported") import_decls
         ; return (tcg_rdr_env gbl_env) }
    where
      zap_rdr_env gbl_env = gbl_env { tcg_rdr_env = emptyGlobalRdrEnv }
  
  
  tcRnTypeSkolemising :: HscEnv
                      -> LHsType GhcPs
                      -> IO (Messages TcRnMessage, Maybe (Type, Kind))
  -- tcRnTypeSkolemising skolemisese any free unification variables,
  -- and normalises the type
  tcRnTypeSkolemising env ty
    = do { skol_tv_ref <- liftIO (newIORef [])
         ; tcRnType env (SkolemiseFlexi skol_tv_ref) True ty }
  
  -- tcRnType just finds the kind of a type
  tcRnType :: HscEnv
           -> ZonkFlexi
           -> Bool        -- Normalise the returned type
           -> LHsType GhcPs
           -> IO (Messages TcRnMessage, Maybe (Type, Kind))
  tcRnType hsc_env flexi normalise rdr_type
    = runTcInteractive hsc_env $
      setXOptM LangExt.PolyKinds $   -- See Note [Kind-generalise in tcRnType]
      do { (HsWC { hswc_ext = wcs, hswc_body = rn_sig_type@(L _ (HsSig{sig_bndrs = outer_bndrs, sig_body = body })) }, _fvs)
                   -- we are using 'rnHsSigWcType' to bind the unbound type variables
                   -- and in combination with 'tcOuterTKBndrs' we are able to
                   -- implicitly quantify them as if the user wrote 'forall' by
                   -- hand (see #19217). This allows kind check to work in presence
                   -- of free type variables :
                   -- ghci> :k [a]
                   -- [a] :: *
                 <- rnHsSigWcType GHCiCtx (mkHsWildCardBndrs $ noLocA (mkHsImplicitSigType rdr_type))
                    -- The type can have wild cards, but no implicit
                    -- generalisation; e.g.   :kind (T _)
         ; failIfErrsM
  
          -- We follow Note [Recipe for checking a signature] in GHC.Tc.Gen.HsType here
  
          -- Now kind-check the type
          -- It can have any rank or kind
          -- First bring into scope any wildcards
         ; traceTc "tcRnType" (vcat [ppr wcs, ppr rn_sig_type])
         ; si <- mkSkolemInfo $ SigTypeSkol (GhciCtxt True)
         ; ((_, (ty, kind)), wanted)
                 <- captureTopConstraints $
                    pushTcLevelM_         $
                    bindNamedWildCardBinders wcs $ \ wcs' ->
                    do { mapM_ emitNamedTypeHole wcs'
                       ; tcOuterTKBndrs si outer_bndrs $ tcInferLHsTypeUnsaturated body }
         -- Since all the wanteds are equalities, the returned bindings will be empty
         ; empty_binds <- simplifyTop wanted
         ; massertPpr (isEmptyBag empty_binds) (ppr empty_binds)
  
         -- Do kind generalisation; see Note [Kind-generalise in tcRnType]
         ; kvs <- kindGeneralizeAll unkSkol kind
  
         ; ty  <- initZonkEnv flexi $ zonkTcTypeToTypeX ty
  
         -- Do validity checking on type
         ; checkValidType (GhciCtxt True) ty
  
         -- Optionally (:k vs :k!) normalise the type. Does two things:
         --   normaliseType: expand type-family applications
         --   expandTypeSynonyms: expand type synonyms (#18828)
         ; fam_envs <- tcGetFamInstEnvs
         ; let ty' | normalise = expandTypeSynonyms $ reductionReducedType $
                                 normaliseType fam_envs Nominal ty
                   | otherwise = ty
  
         ; traceTc "tcRnExpr" (debugPprType ty $$ debugPprType ty')
         ; return (ty', mkInfForAllTys kvs (typeKind ty')) }
  
  
  {- Note [TcRnExprMode]
  ~~~~~~~~~~~~~~~~~~~~~~
  How should we infer a type when a user asks for the type of an expression e
  at the GHCi prompt? We offer 2 different possibilities, described below. Each
  considers this example, with -fprint-explicit-foralls enabled.  See also
  https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0179-printing-foralls.rst
  
  :type / TM_Inst
  
    In this mode, we report the type obtained by instantiating only the
    /inferred/ quantifiers of e's type, solving constraints, and
    re-generalising, as discussed in #11376.
  
    > :type reverse
    reverse :: forall a. [a] -> [a]
  
    -- foo :: forall a f b. (Show a, Num b, Foldable f) => a -> f b -> String
    > :type foo @Int
    forall f b. (Show Int, Num b, Foldable f) => Int -> f b -> String
  
    Note that Show Int is still reported, because the solver never got a chance
    to see it.
  
  :type +d / TM_Default
  
    This mode is for the benefit of users who wish to see instantiations
    of generalized types, and in particular to instantiate Foldable and
    Traversable.  In this mode, all type variables (inferred or
    specified) are instantiated.  Because GHCi uses
    -XExtendedDefaultRules, this means that Foldable and Traversable are
    defaulted.
  
    > :type +d reverse
    reverse :: forall {a}. [a] -> [a]
  
    -- foo :: forall a f b. (Show a, Num b, Foldable f) => a -> f b -> String
    > :type +d foo @Int
    Int -> [Integer] -> String
  
    Note that this mode can sometimes lead to a type error, if a type variable is
    used with a defaultable class but cannot actually be defaulted:
  
    bar :: (Num a, Monoid a) => a -> a
    > :type +d bar
    ** error **
  
    The error arises because GHC tries to default a but cannot find a concrete
    type in the defaulting list that is both Num and Monoid. (If this list is
    modified to include an element that is both Num and Monoid, the defaulting
    would succeed, of course.)
  
    Note that the variables and constraints are reordered here, because this
    is possible during regeneralization. Also note that the variables are
    reported as Inferred instead of Specified.
  
  Note [Kind-generalise in tcRnType]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  We switch on PolyKinds when kind-checking a user type, so that we will
  kind-generalise the type, even when PolyKinds is not otherwise on.
  This gives the right default behaviour at the GHCi prompt, where if
  you say ":k T", and T has a polymorphic kind, you'd like to see that
  polymorphism. Of course.  If T isn't kind-polymorphic you won't get
  anything unexpected, but the apparent *loss* of polymorphism, for
  types that you know are polymorphic, is quite surprising.  See Trac
  #7688 for a discussion.
  
  Note that the goal is to generalise the *kind of the type*, not
  the type itself! Example:
    ghci> data SameKind :: k -> k -> Type
    ghci> :k SameKind _
  
  We want to get `k -> Type`, not `Any -> Type`, which is what we would
  get without kind-generalisation. Note that `:k SameKind` is OK, as
  GHC will not instantiate SameKind here, and so we see its full kind
  of `forall k. k -> k -> Type`.
  
  ************************************************************************
  *                                                                      *
                   tcRnDeclsi
  *                                                                      *
  ************************************************************************
  
  tcRnDeclsi exists to allow class, data, and other declarations in GHCi.
  -}
  
  tcRnDeclsi :: HscEnv
             -> [LHsDecl GhcPs]
             -> IO (Messages TcRnMessage, Maybe TcGblEnv)
  tcRnDeclsi hsc_env local_decls
    = runTcInteractive hsc_env $
      tcRnSrcDecls False Nothing local_decls
  
  externaliseAndTidyId :: Module -> Id -> TcM Id
  externaliseAndTidyId this_mod id
    = do { name' <- externaliseName this_mod (idName id)
         ; return $ globaliseId id
                       `setIdName` name'
                       `setIdType` tidyTopType (idType id) }
  
  
  {-
  ************************************************************************
  *                                                                      *
          More GHCi stuff, to do with browsing and getting info
  *                                                                      *
  ************************************************************************
  -}
  
  -- | ASSUMES that the module is either in the 'HomePackageTable' or is
  -- a package module with an interface on disk.  If neither of these is
  -- true, then the result will be an error indicating the interface
  -- could not be found.
  getModuleInterface :: HscEnv -> Module -> IO (Messages TcRnMessage, Maybe ModIface)
  getModuleInterface hsc_env mod
    = runTcInteractive hsc_env $
      loadModuleInterface (text "getModuleInterface") mod
  
  tcRnLookupRdrName :: HscEnv -> LocatedN RdrName
                    -> IO (Messages TcRnMessage, Maybe [Name])
  -- ^ Find all the Names that this RdrName could mean, in GHCi
  tcRnLookupRdrName hsc_env (L loc rdr_name)
    = runTcInteractive hsc_env $
      setSrcSpanA loc          $
      do {   -- If the identifier is a constructor (begins with an
             -- upper-case letter), then we need to consider both
             -- constructor and type class identifiers.
           let rdr_names = dataTcOccs rdr_name
         ; names_s <- mapM lookupInfoOccRn rdr_names
         ; let names = concat names_s
         ; when (null names) (addErrTc $ TcRnNotInScope NotInScope rdr_name)
         ; return names }
  
  tcRnLookupName :: HscEnv -> Name -> IO (Messages TcRnMessage, Maybe TyThing)
  tcRnLookupName hsc_env name
    = runTcInteractive hsc_env $
      tcRnLookupName' name
  
  -- To look up a name we have to look in the local environment (tcl_lcl)
  -- as well as the global environment, which is what tcLookup does.
  -- But we also want a TyThing, so we have to convert:
  
  tcRnLookupName' :: Name -> TcRn TyThing
  tcRnLookupName' name = do
     tcthing <- tcLookup name
     case tcthing of
       AGlobal thing    -> return thing
       ATcId{tct_id=id} -> return (AnId id)
       _ -> panic "tcRnLookupName'"
  
  tcRnGetInfo :: HscEnv
              -> Name
              -> IO ( Messages TcRnMessage
                    , Maybe (TyThing, Fixity, [ClsInst], [FamInst], SDoc))
  
  -- Used to implement :info in GHCi
  --
  -- Look up a RdrName and return all the TyThings it might be
  -- A capitalised RdrName is given to us in the DataName namespace,
  -- but we want to treat it as *both* a data constructor
  --  *and* as a type or class constructor;
  -- hence the call to dataTcOccs, and we return up to two results
  tcRnGetInfo hsc_env name
    = runTcInteractive hsc_env $
      do { loadUnqualIfaces hsc_env (hsc_IC hsc_env)
             -- Load the interface for all unqualified types and classes
             -- That way we will find all the instance declarations
             -- (Packages have not orphan modules, and we assume that
             --  in the home package all relevant modules are loaded.)
  
         ; thing  <- tcRnLookupName' name
         ; fixity <- lookupFixityRn name
         ; (cls_insts, fam_insts) <- lookupInsts thing
         ; let info = lookupKnownNameInfo name
         ; return (thing, fixity, cls_insts, fam_insts, info) }
  
  
  -- Lookup all class and family instances for a type constructor.
  --
  -- This function filters all instances in the type environment, so there
  -- is a lot of duplicated work if it is called many times in the same
  -- type environment. If this becomes a problem, the NameEnv computed
  -- in GHC.getNameToInstancesIndex could be cached in TcM and both functions
  -- could be changed to consult that index.
  lookupInsts :: TyThing -> TcM ([ClsInst],[FamInst])
  lookupInsts (ATyCon tc)
    = do  { InstEnvs { ie_global = pkg_ie, ie_local = home_ie, ie_visible = vis_mods } <- tcGetInstEnvs
          ; (pkg_fie, home_fie) <- tcGetFamInstEnvs
                  -- Load all instances for all classes that are
                  -- in the type environment (which are all the ones
                  -- we've seen in any interface file so far)
  
            -- Return only the instances relevant to the given thing, i.e.
            -- the instances whose head contains the thing's name.
          ; let cls_insts =
                   [ ispec        -- Search all
                   | ispec <- instEnvElts home_ie ++ instEnvElts pkg_ie
                   , instIsVisible vis_mods ispec
                   , tc_name `elemNameSet` orphNamesOfClsInst ispec ]
          ; let fam_insts =
                   [ fispec
                   | fispec <- famInstEnvElts home_fie ++ famInstEnvElts pkg_fie
                   , tc_name `elemNameSet` orphNamesOfFamInst fispec ]
          ; return (cls_insts, fam_insts) }
    where
      tc_name     = tyConName tc
  
  lookupInsts _ = return ([],[])
  
  loadUnqualIfaces :: HscEnv -> InteractiveContext -> TcM ()
  -- Load the interface for everything that is in scope unqualified
  -- This is so that we can accurately report the instances for
  -- something
  loadUnqualIfaces hsc_env ictxt
    = initIfaceTcRn $
      mapM_ (loadSysInterface doc) (moduleSetElts (mkModuleSet unqual_mods))
    where
      home_unit = hsc_home_unit hsc_env
  
      unqual_mods = [ nameModule name
                    | gre <- globalRdrEnvElts (icReaderEnv ictxt)
                    , let name = greName gre
                    , nameIsFromExternalPackage home_unit name
                    , isTcOcc (nameOccName name)   -- Types and classes only
                    , unQualOK gre ]               -- In scope unqualified
      doc = text "Need interface for module whose export(s) are in scope unqualified"
  
  
  
  {-
  ************************************************************************
  *                                                                      *
                  Debugging output
        This is what happens when you do -ddump-types
  *                                                                      *
  ************************************************************************
  -}
  
  -- | Dump, with a banner, if -ddump-rn
  rnDump :: (Outputable a, Data a) => a -> TcRn ()
  rnDump rn = dumpOptTcRn Opt_D_dump_rn "Renamer" FormatHaskell (ppr rn)
  
  tcDump :: TcGblEnv -> TcRn ()
  tcDump env
   = do { unit_state <- hsc_units <$> getTopEnv ;
          logger <- getLogger ;
  
          -- Dump short output if -ddump-types or -ddump-tc
          when (logHasDumpFlag logger Opt_D_dump_types || logHasDumpFlag logger Opt_D_dump_tc)
            (dumpTcRn True Opt_D_dump_types
              "" FormatText (pprWithUnitState unit_state short_dump)) ;
  
          -- Dump bindings if -ddump-tc
          dumpOptTcRn Opt_D_dump_tc "Typechecker" FormatHaskell full_dump;
  
          -- Dump bindings as an hsSyn AST if -ddump-tc-ast
          dumpOptTcRn Opt_D_dump_tc_ast "Typechecker AST" FormatHaskell ast_dump
     }
    where
      short_dump = pprTcGblEnv env
      full_dump  = pprLHsBinds (tcg_binds env)
          -- NB: foreign x-d's have undefined's in their types;
          --     hence can't show the tc_fords
      ast_dump = showAstData NoBlankSrcSpan NoBlankEpAnnotations (tcg_binds env)
  
  -- It's unpleasant having both pprModGuts and pprModDetails here
  pprTcGblEnv :: TcGblEnv -> SDoc
  pprTcGblEnv (TcGblEnv { tcg_type_env  = type_env,
                          tcg_insts     = insts,
                          tcg_fam_insts = fam_insts,
                          tcg_rules     = rules,
                          tcg_imports   = imports })
    = getPprDebug $ \debug ->
      vcat [ ppr_types debug type_env
           , ppr_tycons debug fam_insts type_env
           , ppr_datacons debug type_env
           , ppr_patsyns type_env
           , ppr_insts insts
           , ppr_fam_insts fam_insts
           , ppr_rules rules
           , text "Dependent modules:" <+>
                  (ppr . sort . installedModuleEnvElts $ imp_direct_dep_mods imports)
           , text "Dependent packages:" <+>
                  ppr (S.toList $ imp_dep_direct_pkgs imports)]
                  -- The use of sort is just to reduce unnecessary
                  -- wobbling in testsuite output
  
  ppr_rules :: [LRuleDecl GhcTc] -> SDoc
  ppr_rules rules
    = ppUnless (null rules) $
      hang (text "RULES")
         2 (vcat (map ppr rules))
  
  ppr_types :: Bool -> TypeEnv -> SDoc
  ppr_types debug type_env
    = ppr_things "TYPE SIGNATURES" ppr_sig
               (sortBy (comparing getOccName) ids)
    where
      ids = [id | id <- typeEnvIds type_env, want_sig id]
      want_sig id
        | debug     = True
        | otherwise = hasTopUserName id
                      && case idDetails id of
                           VanillaId              -> True
                           WorkerLikeId {}        -> True
                           RecSelId {}            -> True
                           ClassOpId {}           -> True
                           FCallId {}             -> True
                           _                      -> False
               -- Data cons (workers and wrappers), pattern synonyms,
               -- etc are suppressed (unless -dppr-debug),
               -- because they appear elsewhere
  
      ppr_sig id = hang (pprPrefixOcc id <+> dcolon) 2 (ppr (tidyTopType (idType id)))
  
  ppr_tycons :: Bool -> [FamInst] -> TypeEnv -> SDoc
  ppr_tycons debug fam_insts type_env
    = vcat [ ppr_things "TYPE CONSTRUCTORS" ppr_tc tycons
           , ppr_things "COERCION AXIOMS" ppr_ax
                        (typeEnvCoAxioms type_env) ]
    where
      fi_tycons = famInstsRepTyCons fam_insts
  
      tycons = sortBy (comparing getOccName) $
               [tycon | tycon <- typeEnvTyCons type_env
                      , want_tycon tycon]
               -- Sort by OccName to reduce unnecessary changes
      want_tycon tycon | debug      = True
                       | otherwise  = isExternalName (tyConName tycon) &&
                                      not (tycon `elem` fi_tycons)
      ppr_tc tc
         = vcat [ hang (ppr (tyConFlavour tc) <+> pprPrefixOcc (tyConName tc)
                        <> braces (ppr (tyConArity tc)) <+> dcolon)
                     2 (ppr (tidyTopType (tyConKind tc)))
                , nest 2 $
                  ppWhen show_roles $
                  text "roles" <+> (sep (map ppr roles)) ]
         where
           show_roles = debug || not (all (== boring_role) roles)
           roles = tyConRoles tc
           boring_role | isClassTyCon tc = Nominal
                       | otherwise       = Representational
              -- Matches the choice in GHC.Iface.Syntax, calls to pprRoles
  
      ppr_ax ax = ppr (coAxiomToIfaceDecl ax)
        -- We go via IfaceDecl rather than using pprCoAxiom
        -- This way we get the full axiom (both LHS and RHS) with
        -- wildcard binders tidied to _1, _2, etc.
  
  ppr_datacons :: Bool -> TypeEnv -> SDoc
  ppr_datacons debug type_env
    = ppr_things "DATA CONSTRUCTORS" ppr_dc wanted_dcs
        -- The filter gets rid of class data constructors
    where
      ppr_dc dc = ppr dc <+> dcolon <+> ppr (dataConWrapperType dc)
      all_dcs    = typeEnvDataCons type_env
      wanted_dcs | debug     = all_dcs
                 | otherwise = filterOut is_cls_dc all_dcs
      is_cls_dc dc = isClassTyCon (dataConTyCon dc)
  
  ppr_patsyns :: TypeEnv -> SDoc
  ppr_patsyns type_env
    = ppr_things "PATTERN SYNONYMS" ppr_ps
                 (typeEnvPatSyns type_env)
    where
      ppr_ps ps = pprPrefixOcc ps <+> dcolon <+> pprPatSynType ps
  
  ppr_insts :: [ClsInst] -> SDoc
  ppr_insts ispecs
    = ppr_things "CLASS INSTANCES" pprInstance ispecs
  
  ppr_fam_insts :: [FamInst] -> SDoc
  ppr_fam_insts fam_insts
    = ppr_things "FAMILY INSTANCES" pprFamInst fam_insts
  
  ppr_things :: String -> (a -> SDoc) -> [a] -> SDoc
  ppr_things herald ppr_one things
    | null things = empty
    | otherwise   = text herald $$ nest 2 (vcat (map ppr_one things))
  
  hasTopUserName :: NamedThing x => x -> Bool
  -- A top-level thing whose name is not "derived"
  -- Thus excluding things like $tcX, from Typeable boilerplate
  -- and C:Coll from class-dictionary data constructors
  hasTopUserName x
    = isExternalName name && not (isDerivedOccName (nameOccName name))
    where
      name = getName x
  
  {-
  ********************************************************************************
  
                           Running plugins
  
  ********************************************************************************
  -}
  
  runRenamerPlugin :: TcGblEnv
                   -> HsGroup GhcRn
                   -> TcM (TcGblEnv, HsGroup GhcRn)
  runRenamerPlugin gbl_env hs_group = do
      hsc_env <- getTopEnv
      withPlugins (hsc_plugins hsc_env)
        (\p opts (e, g) -> ( mark_plugin_unsafe (hsc_dflags hsc_env)
                              >> renamedResultAction p opts e g))
        (gbl_env, hs_group)
  
  
  -- XXX: should this really be a Maybe X?  Check under which circumstances this
  -- can become a Nothing and decide whether this should instead throw an
  -- exception/signal an error.
  type RenamedStuff =
          (Maybe (HsGroup GhcRn, [LImportDecl GhcRn], Maybe [(LIE GhcRn, Avails)],
                  Maybe (LHsDoc GhcRn), Maybe (XRec GhcRn ModuleName)))
  
  -- | Extract the renamed information from TcGblEnv.
  getRenamedStuff :: TcGblEnv -> RenamedStuff
  getRenamedStuff tc_result
    = fmap (\decls -> ( decls, tcg_rn_imports tc_result
                      , tcg_rn_exports tc_result, doc_hdr, name_hdr ))
           (tcg_rn_decls tc_result)
    where (doc_hdr, name_hdr) = tcg_hdr_info tc_result
  
  runTypecheckerPlugin :: ModSummary -> TcGblEnv -> TcM TcGblEnv
  runTypecheckerPlugin sum gbl_env = do
      hsc_env <- getTopEnv
      withPlugins (hsc_plugins hsc_env)
        (\p opts env -> mark_plugin_unsafe (hsc_dflags hsc_env)
                          >> typeCheckResultAction p opts sum env)
        gbl_env
  
  mark_plugin_unsafe :: DynFlags -> TcM ()
  mark_plugin_unsafe dflags = unless (gopt Opt_PluginTrustworthy dflags) $
    recordUnsafeInfer pluginUnsafe
    where
      !diag_opts = initDiagOpts dflags
      pluginUnsafe =
        singleMessage $
        mkPlainMsgEnvelope diag_opts noSrcSpan TcRnUnsafeDueToPlugin
  
  
  -- Note [Typechecking default declarations]
  -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  -- Typechecking default declarations requires careful placement:
  --
  -- 1. We must check them after types (tcTyAndClassDecls) because they can refer
  -- to them. E.g.
  --
  --    data T = MkT ...
  --    default(Int, T, Integer)
  --
  --    -- or even (tested by T11974b and T2245)
  --    default(Int, T, Integer)
  --    data T = MkT ...
  --
  -- 2. We must check them before typechecking deriving clauses (tcInstDeclsDeriv)
  -- otherwise we may lookup default default types (Integer, Double) while checking
  -- deriving clauses, ignoring the default declaration.
  --
  -- Before this careful placement (#24566), compiling the following example
  -- (T24566) with "-ddump-if-trace -ddump-tc-trace" showed a call to
  -- `applyDefaultingRules` with default types set to "(Integer,Double)":
  --
  --     module M where
  --
  --     import GHC.Classes
  --     default ()
  --
  --     data Foo a = Nothing | Just a
  --       deriving (Eq, Ord)
  --
  -- This was an issue while building modules like M in the ghc-internal package
  -- because they would spuriously fail to build if the module defining Integer
  -- (ghc-bignum:GHC.Num.Integer) wasn't compiled yet and its interface not to be
  -- found. The implicit dependency between M and GHC.Num.Integer isn't known to
  -- the build system.
  -- In addition, trying to explicitly avoid the implicit dependency with `default
  -- ()` didn't work, except if *standalone* deriving was used, which was an
  -- inconsistent behavior.
  