TTG: Move HsModule to L.H.S

Move the definition of HsModule defined in GHC.Hs to
Language.Haskell.Syntax with an added TTG parameter and corresponding
extension fields.

This is progress towards having the haskell-syntax package, as described
in #21592

22 files changed, 160 insertions, 112 deletions

diff --git a/compiler/GHC.hs b/compiler/GHC.hs
index 5d57c0d2fa..29a287efb4 100644
--- a/compiler/GHC.hs
+++ b/compiler/GHC.hs
@@ -175,7 +175,7 @@ module GHC (
 
         -- ** Modules
         Module, mkModule, pprModule, moduleName, moduleUnit,
-        ModuleName, mkModuleName, moduleNameString,
+        mkModuleName, moduleNameString,
 
         -- ** Names
         Name,
@@ -1120,7 +1120,7 @@ instance TypecheckedMod DesugaredModule where
 instance DesugaredMod DesugaredModule where
   coreModule m = dm_core_module m
 
-type ParsedSource      = Located HsModule
+type ParsedSource      = Located (HsModule GhcPs)
 type RenamedSource     = (HsGroup GhcRn, [LImportDecl GhcRn], Maybe [(LIE GhcRn, Avails)],
                           Maybe (LHsDoc GhcRn))
 type TypecheckedSource = LHsBinds GhcTc
@@ -1777,7 +1777,7 @@ lookupName name =
 parser :: String         -- ^ Haskell module source text (full Unicode is supported)
        -> DynFlags       -- ^ the flags
        -> FilePath       -- ^ the filename (for source locations)
-       -> (WarningMessages, Either ErrorMessages (Located HsModule))
+       -> (WarningMessages, Either ErrorMessages (Located (HsModule GhcPs)))
 
 parser str dflags filename =
    let
diff --git a/compiler/GHC/Driver/Backpack.hs b/compiler/GHC/Driver/Backpack.hs
index 06fdbb34e8..09a5678796 100644
--- a/compiler/GHC/Driver/Backpack.hs
+++ b/compiler/GHC/Driver/Backpack.hs
@@ -795,14 +795,16 @@ summariseRequirement pn mod_name = do
         ms_ghc_prim_import = False,
         ms_parsed_mod = Just (HsParsedModule {
                 hpm_module = L loc (HsModule {
-                        hsmodAnn = noAnn,
-                        hsmodLayout = NoLayoutInfo,
+                        hsmodExt = XModulePs {
+                            hsmodAnn = noAnn,
+                            hsmodLayout = NoLayoutInfo,
+                            hsmodDeprecMessage = Nothing,
+                            hsmodHaddockModHeader = Nothing
+                                             },
                         hsmodName = Just (L (noAnnSrcSpan loc) mod_name),
                         hsmodExports = Nothing,
                         hsmodImports = [],
-                        hsmodDecls = [],
-                        hsmodDeprecMessage = Nothing,
-                        hsmodHaddockModHeader = Nothing
+                        hsmodDecls = []
                     }),
                 hpm_src_files = []
             }),
@@ -816,7 +818,7 @@ summariseRequirement pn mod_name = do
 summariseDecl :: PackageName
               -> HscSource
               -> Located ModuleName
-              -> Located HsModule
+              -> Located (HsModule GhcPs)
               -> [NodeKey]
               -> BkpM ModuleGraphNode
 summariseDecl pn hsc_src (L _ modname) hsmod home_keys = hsModuleToModSummary home_keys pn hsc_src modname hsmod
@@ -830,7 +832,7 @@ hsModuleToModSummary :: [NodeKey]
                      -> PackageName
                      -> HscSource
                      -> ModuleName
-                     -> Located HsModule
+                     -> Located (HsModule GhcPs)
                      -> BkpM ModuleGraphNode
 hsModuleToModSummary home_keys pn hsc_src modname
                      hsmod = do
diff --git a/compiler/GHC/Driver/Backpack/Syntax.hs b/compiler/GHC/Driver/Backpack/Syntax.hs
index e67c62d6d8..572d650982 100644
--- a/compiler/GHC/Driver/Backpack/Syntax.hs
+++ b/compiler/GHC/Driver/Backpack/Syntax.hs
@@ -23,7 +23,6 @@ import GHC.Hs
 import GHC.Types.SrcLoc
 import GHC.Types.SourceFile
 
-import GHC.Unit.Module.Name
 import GHC.Unit.Types
 import GHC.Unit.Info
 
@@ -65,7 +64,7 @@ type LHsUnit n = Located (HsUnit n)
 -- | A declaration in a package, e.g. a module or signature definition,
 -- or an include.
 data HsUnitDecl n
-    = DeclD   HscSource (Located ModuleName) (Located HsModule)
+    = DeclD   HscSource (Located ModuleName) (Located (HsModule GhcPs))
     | IncludeD   (IncludeDecl n)
 type LHsUnitDecl n = Located (HsUnitDecl n)
 
diff --git a/compiler/GHC/Driver/Main.hs b/compiler/GHC/Driver/Main.hs
index 2936630db8..29ca1e42ae 100644
--- a/compiler/GHC/Driver/Main.hs
+++ b/compiler/GHC/Driver/Main.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE LambdaCase #-}
 
 {-# LANGUAGE NondecreasingIndentation #-}
 {-# LANGUAGE GADTs #-}
@@ -2051,7 +2052,7 @@ hscDecls :: HscEnv
          -> IO ([TyThing], InteractiveContext)
 hscDecls hsc_env str = hscDeclsWithLocation hsc_env str "<interactive>" 1
 
-hscParseModuleWithLocation :: HscEnv -> String -> Int -> String -> IO HsModule
+hscParseModuleWithLocation :: HscEnv -> String -> Int -> String -> IO (HsModule GhcPs)
 hscParseModuleWithLocation hsc_env source line_num str = do
     L _ mod <-
       runInteractiveHsc hsc_env $
@@ -2198,14 +2199,15 @@ hscAddSptEntries hsc_env entries = do
 
 hscImport :: HscEnv -> String -> IO (ImportDecl GhcPs)
 hscImport hsc_env str = runInteractiveHsc hsc_env $ do
-    (L _ (HsModule{hsmodImports=is})) <-
-       hscParseThing parseModule str
-    case is of
-        [L _ i] -> return i
-        _ -> liftIO $ throwOneError $
-                 mkPlainErrorMsgEnvelope noSrcSpan $
-                 GhcPsMessage $ PsUnknownMessage $ mkPlainError noHints $
-                     text "parse error in import declaration"
+    hscParseThing parseModule str >>= \case
+      (L _ (XModule x)) -> dataConCantHappen x
+      (L _ (HsModule{hsmodImports=is})) ->
+        case is of
+            [L _ i] -> return i
+            _ -> liftIO $ throwOneError $
+                     mkPlainErrorMsgEnvelope noSrcSpan $
+                     GhcPsMessage $ PsUnknownMessage $ mkPlainError noHints $
+                         text "parse error in import declaration"
 
 -- | Typecheck an expression (but don't run it)
 hscTcExpr :: HscEnv
diff --git a/compiler/GHC/Hs.hs b/compiler/GHC/Hs.hs
index 5a6f2cc2be..f06619d030 100644
--- a/compiler/GHC/Hs.hs
+++ b/compiler/GHC/Hs.hs
@@ -34,7 +34,7 @@ module GHC.Hs (
         Fixity,
 
         HsModule(..), AnnsModule(..),
-        HsParsedModule(..)
+        HsParsedModule(..), XModulePs(..)
 ) where
 
 -- friends:
@@ -58,53 +58,18 @@ import GHC.Hs.Instances () -- For Data instances
 import GHC.Utils.Outputable
 import GHC.Types.Fixity         ( Fixity )
 import GHC.Types.SrcLoc
-import GHC.Unit.Module          ( ModuleName )
 import GHC.Unit.Module.Warnings ( WarningTxt )
 
 -- libraries:
 import Data.Data hiding ( Fixity )
 
--- | Haskell Module
---
--- All we actually declare here is the top-level structure for a module.
-data HsModule
-  =  -- | 'GHC.Parser.Annotation.AnnKeywordId's
-     --
-     --  - 'GHC.Parser.Annotation.AnnModule','GHC.Parser.Annotation.AnnWhere'
-     --
-     --  - 'GHC.Parser.Annotation.AnnOpen','GHC.Parser.Annotation.AnnSemi',
-     --    'GHC.Parser.Annotation.AnnClose' for explicit braces and semi around
-     --    hsmodImports,hsmodDecls if this style is used.
-
-     -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
-    HsModule {
+-- | Haskell Module extension point: GHC specific 
+data XModulePs
+  = XModulePs {
       hsmodAnn :: EpAnn AnnsModule,
       hsmodLayout :: LayoutInfo,
         -- ^ Layout info for the module.
         -- For incomplete modules (e.g. the output of parseHeader), it is NoLayoutInfo.
-      hsmodName :: Maybe (LocatedA ModuleName),
-        -- ^ @Nothing@: \"module X where\" is omitted (in which case the next
-        --     field is Nothing too)
-      hsmodExports :: Maybe (LocatedL [LIE GhcPs]),
-        -- ^ Export list
-        --
-        --  - @Nothing@: export list omitted, so export everything
-        --
-        --  - @Just []@: export /nothing/
-        --
-        --  - @Just [...]@: as you would expect...
-        --
-        --
-        --  - 'GHC.Parser.Annotation.AnnKeywordId's : 'GHC.Parser.Annotation.AnnOpen'
-        --                                   ,'GHC.Parser.Annotation.AnnClose'
-
-        -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
-      hsmodImports :: [LImportDecl GhcPs],
-        -- ^ We snaffle interesting stuff out of the imported interfaces early
-        -- on, adding that info to TyDecls/etc; so this list is often empty,
-        -- downstream.
-      hsmodDecls :: [LHsDecl GhcPs],
-        -- ^ Type, class, value, and interface signature decls
       hsmodDeprecMessage :: Maybe (LocatedP (WarningTxt GhcPs)),
         -- ^ reason\/explanation for warning/deprecation of this module
         --
@@ -121,8 +86,14 @@ data HsModule
 
         -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
    }
+   deriving Data
+
+type instance XModule GhcPs = XModulePs
+type instance XModule GhcRn = DataConCantHappen
+type instance XModule GhcTc = DataConCantHappen
+type instance XXModule p = DataConCantHappen
 
-deriving instance Data HsModule
+deriving instance Data (HsModule GhcPs)
 
 data AnnsModule
   = AnnsModule {
@@ -130,13 +101,15 @@ data AnnsModule
     am_decls :: AnnList
     } deriving (Data, Eq)
 
-instance Outputable HsModule where
+instance Outputable (HsModule GhcPs) where
+    
+    ppr (XModule ext) = dataConCantHappen ext
 
-    ppr (HsModule _ _ Nothing _ imports decls _ mbDoc)
+    ppr (HsModule (XModulePs _ _ _ mbDoc) Nothing _ imports decls)
       = pprMaybeWithDoc mbDoc $ pp_nonnull imports
                              $$ pp_nonnull decls
 
-    ppr (HsModule _ _ (Just name) exports imports decls deprec mbDoc)
+    ppr (HsModule (XModulePs _ _ deprec mbDoc) (Just name) exports imports decls)
       = pprMaybeWithDoc mbDoc $
         vcat
           [ case exports of
@@ -161,7 +134,7 @@ pp_nonnull [] = empty
 pp_nonnull xs = vcat (map ppr xs)
 
 data HsParsedModule = HsParsedModule {
-    hpm_module    :: Located HsModule,
+    hpm_module    :: Located (HsModule GhcPs),
     hpm_src_files :: [FilePath]
        -- ^ extra source files (e.g. from #includes).  The lexer collects
        -- these from '# <file> <line>' pragmas, which the C preprocessor
diff --git a/compiler/GHC/Hs/Dump.hs b/compiler/GHC/Hs/Dump.hs
index de9848e139..77d2036425 100644
--- a/compiler/GHC/Hs/Dump.hs
+++ b/compiler/GHC/Hs/Dump.hs
@@ -30,7 +30,6 @@ import GHC.Types.Name
 import GHC.Types.SrcLoc
 import GHC.Types.Var
 import GHC.Types.SourceText
-import GHC.Unit.Module
 import GHC.Utils.Outputable
 
 import Data.Data hiding (Fixity)
diff --git a/compiler/GHC/Hs/Stats.hs b/compiler/GHC/Hs/Stats.hs
index bd3e2e6b6d..0c348e2c97 100644
--- a/compiler/GHC/Hs/Stats.hs
+++ b/compiler/GHC/Hs/Stats.hs
@@ -22,8 +22,9 @@ import GHC.Utils.Panic
 import Data.Char
 
 -- | Source Statistics
-ppSourceStats :: Bool -> Located HsModule -> SDoc
-ppSourceStats short (L _ (HsModule{ hsmodExports = exports, hsmodImports = imports, hsmodDecls = ldecls }))
+ppSourceStats :: Bool -> Located (HsModule GhcPs) -> SDoc
+ppSourceStats _ (L _ (XModule x)) = dataConCantHappen x
+ppSourceStats short (L _ (HsModule _ _ exports imports ldecls))
   = (if short then hcat else vcat)
         (map pp_val
             [("ExportAll        ", export_all), -- 1 if no export list
diff --git a/compiler/GHC/Iface/Ext/Ast.hs b/compiler/GHC/Iface/Ext/Ast.hs
index 9547296fe0..cbd46de9f5 100644
--- a/compiler/GHC/Iface/Ext/Ast.hs
+++ b/compiler/GHC/Iface/Ext/Ast.hs
@@ -61,7 +61,7 @@ import qualified GHC.Data.Strict as Strict
 import GHC.Iface.Ext.Types
 import GHC.Iface.Ext.Utils
 
-import GHC.Unit.Module            ( ModuleName, ml_hs_file )
+import GHC.Unit.Module            ( ml_hs_file )
 import GHC.Unit.Module.ModSummary
 
 import qualified Data.Array as A
diff --git a/compiler/GHC/Parser.y b/compiler/GHC/Parser.y
index 9d45b0c7c8..f819320d1f 100644
--- a/compiler/GHC/Parser.y
+++ b/compiler/GHC/Parser.y
@@ -853,12 +853,12 @@ unitdecl :: { LHsUnitDecl PackageName }
                    NotBoot -> HsSrcFile
                    IsBoot  -> HsBootFile)
                  (reLoc $3)
-                 (sL1 $1 (HsModule noAnn (thdOf3 $7) (Just $3) $5 (fst $ sndOf3 $7) (snd $ sndOf3 $7) $4 Nothing)) }
+                 (sL1 $1 (HsModule (XModulePs noAnn (thdOf3 $7) $4 Nothing) (Just $3) $5 (fst $ sndOf3 $7) (snd $ sndOf3 $7))) }
         | 'signature' modid maybemodwarning maybeexports 'where' body
              { sL1 $1 $ DeclD
                  HsigFile
                  (reLoc $2)
-                 (sL1 $1 (HsModule noAnn (thdOf3 $6) (Just $2) $4 (fst $ sndOf3 $6) (snd $ sndOf3 $6) $3 Nothing)) }
+                 (sL1 $1 (HsModule (XModulePs noAnn (thdOf3 $6) $3 Nothing) (Just $2) $4 (fst $ sndOf3 $6) (snd $ sndOf3 $6))) }
         | 'dependency' unitid mayberns
              { sL1 $1 $ IncludeD (IncludeDecl { idUnitId = $2
                                               , idModRenaming = $3
@@ -878,26 +878,32 @@ unitdecl :: { LHsUnitDecl PackageName }
 -- either, and DEPRECATED is only expected to be used by people who really
 -- know what they are doing. :-)
 
-signature :: { Located HsModule }
+signature :: { Located (HsModule GhcPs) }
        : 'signature' modid maybemodwarning maybeexports 'where' body
              {% fileSrcSpan >>= \ loc ->
-                acs (\cs-> (L loc (HsModule (EpAnn (spanAsAnchor loc) (AnnsModule [mj AnnSignature $1, mj AnnWhere $5] (fstOf3 $6)) cs)
-                              (thdOf3 $6) (Just $2) $4 (fst $ sndOf3 $6)
-                              (snd $ sndOf3 $6) $3 Nothing))
+                acs (\cs-> (L loc (HsModule (XModulePs
+                                               (EpAnn (spanAsAnchor loc) (AnnsModule [mj AnnSignature $1, mj AnnWhere $5] (fstOf3 $6)) cs)
+                                               (thdOf3 $6) $3 Nothing)
+                                            (Just $2) $4 (fst $ sndOf3 $6)
+                                            (snd $ sndOf3 $6)))
                     ) }
 
-module :: { Located HsModule }
+module :: { Located (HsModule GhcPs) }
        : 'module' modid maybemodwarning maybeexports 'where' body
              {% fileSrcSpan >>= \ loc ->
-                acsFinal (\cs -> (L loc (HsModule (EpAnn (spanAsAnchor loc) (AnnsModule [mj AnnModule $1, mj AnnWhere $5] (fstOf3 $6)) cs)
-                               (thdOf3 $6) (Just $2) $4 (fst $ sndOf3 $6)
-                              (snd $ sndOf3 $6) $3 Nothing)
+                acsFinal (\cs -> (L loc (HsModule (XModulePs
+                                                     (EpAnn (spanAsAnchor loc) (AnnsModule [mj AnnModule $1, mj AnnWhere $5] (fstOf3 $6)) cs)
+                                                     (thdOf3 $6) $3 Nothing)
+                                                  (Just $2) $4 (fst $ sndOf3 $6)
+                                                  (snd $ sndOf3 $6))
                     )) }
         | body2
                 {% fileSrcSpan >>= \ loc ->
-                   acsFinal (\cs -> (L loc (HsModule (EpAnn (spanAsAnchor loc) (AnnsModule [] (fstOf3 $1)) cs)
-                                (thdOf3 $1) Nothing Nothing
-                               (fst $ sndOf3 $1) (snd $ sndOf3 $1) Nothing Nothing))) }
+                   acsFinal (\cs -> (L loc (HsModule (XModulePs
+                                                        (EpAnn (spanAsAnchor loc) (AnnsModule [] (fstOf3 $1)) cs)
+                                                        (thdOf3 $1) Nothing Nothing)
+                                                     Nothing Nothing
+                                                     (fst $ sndOf3 $1) (snd $ sndOf3 $1)))) }
 
 missing_module_keyword :: { () }
         : {- empty -}                           {% pushModuleContext }
@@ -942,21 +948,24 @@ top1    :: { ([LImportDecl GhcPs], [LHsDecl GhcPs]) }
 -----------------------------------------------------------------------------
 -- Module declaration & imports only
 
-header  :: { Located HsModule }
+header  :: { Located (HsModule GhcPs) }
         : 'module' modid maybemodwarning maybeexports 'where' header_body
                 {% fileSrcSpan >>= \ loc ->
-                   acs (\cs -> (L loc (HsModule (EpAnn (spanAsAnchor loc) (AnnsModule [mj AnnModule $1,mj AnnWhere $5] (AnnList Nothing Nothing Nothing [] [])) cs)
-                              NoLayoutInfo (Just $2) $4 $6 [] $3 Nothing
+                   acs (\cs -> (L loc (HsModule (XModulePs
+                                                   (EpAnn (spanAsAnchor loc) (AnnsModule [mj AnnModule $1,mj AnnWhere $5] (AnnList Nothing Nothing Nothing [] [])) cs)
+                                                   NoLayoutInfo $3 Nothing)
+                                                (Just $2) $4 $6 []
                           ))) }
         | 'signature' modid maybemodwarning maybeexports 'where' header_body
                 {% fileSrcSpan >>= \ loc ->
-                   acs (\cs -> (L loc (HsModule (EpAnn (spanAsAnchor loc) (AnnsModule [mj AnnModule $1,mj AnnWhere $5] (AnnList Nothing Nothing Nothing [] [])) cs)
-                           NoLayoutInfo (Just $2) $4 $6 [] $3 Nothing
+                   acs (\cs -> (L loc (HsModule (XModulePs
+                                                   (EpAnn (spanAsAnchor loc) (AnnsModule [mj AnnModule $1,mj AnnWhere $5] (AnnList Nothing Nothing Nothing [] [])) cs)
+                                                   NoLayoutInfo $3 Nothing)
+                                                (Just $2) $4 $6 []
                           ))) }
         | header_body2
                 {% fileSrcSpan >>= \ loc ->
-                   return (L loc (HsModule noAnn NoLayoutInfo Nothing Nothing $1 [] Nothing
-                          Nothing)) }
+                   return (L loc (HsModule (XModulePs noAnn NoLayoutInfo Nothing Nothing) Nothing Nothing $1 [])) }
 
 header_body :: { [LImportDecl GhcPs] }
         :  '{'            header_top            { $2 }
@@ -4361,7 +4370,7 @@ pvL a = do { av <- a
 -- This is the only parser entry point that deals with Haddock comments.
 -- The other entry points ('parseDeclaration', 'parseExpression', etc) do
 -- not insert them into the AST.
-parseModule :: P (Located HsModule)
+parseModule :: P (Located (HsModule GhcPs))
 parseModule = parseModuleNoHaddock >>= addHaddockToModule
 
 commentsA :: (Monoid ann) => SrcSpan -> EpAnnComments -> SrcSpanAnn' (EpAnn ann)
diff --git a/compiler/GHC/Parser/Errors/Types.hs b/compiler/GHC/Parser/Errors/Types.hs
index b4ea2f42a0..1d3fcbc08e 100644
--- a/compiler/GHC/Parser/Errors/Types.hs
+++ b/compiler/GHC/Parser/Errors/Types.hs
@@ -15,7 +15,6 @@ import GHC.Types.Error
 import GHC.Types.Hint
 import GHC.Types.Name.Occurrence (OccName)
 import GHC.Types.Name.Reader
-import GHC.Unit.Module.Name
 import GHC.Utils.Outputable
 import Data.List.NonEmpty (NonEmpty)
 import GHC.Types.SrcLoc (PsLoc)
diff --git a/compiler/GHC/Parser/PostProcess.hs b/compiler/GHC/Parser/PostProcess.hs
index 94b689fe71..e67e6d734e 100644
--- a/compiler/GHC/Parser/PostProcess.hs
+++ b/compiler/GHC/Parser/PostProcess.hs
@@ -125,7 +125,6 @@ import GHC.Core.ConLike        ( ConLike(..) )
 import GHC.Core.Coercion.Axiom ( Role, fsFromRole )
 import GHC.Types.Name.Reader
 import GHC.Types.Name
-import GHC.Unit.Module (ModuleName)
 import GHC.Types.Basic
 import GHC.Types.Error
 import GHC.Types.Fixity
diff --git a/compiler/GHC/Parser/PostProcess/Haddock.hs b/compiler/GHC/Parser/PostProcess/Haddock.hs
index ea9118a525..95f02f8f21 100644
--- a/compiler/GHC/Parser/PostProcess/Haddock.hs
+++ b/compiler/GHC/Parser/PostProcess/Haddock.hs
@@ -178,7 +178,7 @@ we have to use 'flattenBindsAndSigs' to traverse it in the correct order.
 -- to a parsed HsModule.
 --
 -- Reports badly positioned comments when -Winvalid-haddock is enabled.
-addHaddockToModule :: Located HsModule -> P (Located HsModule)
+addHaddockToModule :: Located (HsModule GhcPs) -> P (Located (HsModule GhcPs))
 addHaddockToModule lmod = do
   pState <- getPState
   let all_comments = toList (hdk_comments pState)
@@ -239,7 +239,7 @@ instance HasHaddock a => HasHaddock [a] where
 --        item4
 --      ) where
 --
-instance HasHaddock (Located HsModule) where
+instance HasHaddock (Located (HsModule GhcPs)) where
   addHaddock (L l_mod mod) = do
     -- Step 1, get the module header documentation comment:
     --
@@ -287,13 +287,13 @@ instance HasHaddock (Located HsModule) where
     --      data C = MkC  -- ^ Comment on MkC
     --      -- ^ Comment on C
     --
-    let layout_info = hsmodLayout mod
+    let layout_info = hsmodLayout (hsmodExt mod)
     hsmodDecls' <- addHaddockInterleaveItems layout_info (mkDocHsDecl layout_info) (hsmodDecls mod)
 
     pure $ L l_mod $
       mod { hsmodExports = hsmodExports'
           , hsmodDecls = hsmodDecls'
-          , hsmodHaddockModHeader = join @Maybe headerDocs }
+          , hsmodExt = (hsmodExt mod) { hsmodHaddockModHeader = join @Maybe headerDocs } }
 
 lexHsDocString :: HsDocString -> HsDoc GhcPs
 lexHsDocString = lexHsDoc parseIdentifier
diff --git a/compiler/GHC/Tc/Errors/Types.hs b/compiler/GHC/Tc/Errors/Types.hs
index 62732ed8dd..1e52a526fe 100644
--- a/compiler/GHC/Tc/Errors/Types.hs
+++ b/compiler/GHC/Tc/Errors/Types.hs
@@ -104,7 +104,6 @@ import GHC.Core.TyCon (TyCon, TyConFlavour)
 import GHC.Core.Type (Kind, Type, ThetaType, PredType)
 import GHC.Driver.Backend (Backend)
 import GHC.Unit.State (UnitState)
-import GHC.Unit.Module.Name (ModuleName)
 import GHC.Types.Basic
 import GHC.Utils.Misc (capitalise, filterOut)
 import qualified GHC.LanguageExtensions as LangExt
diff --git a/compiler/GHC/Tc/Module.hs b/compiler/GHC/Tc/Module.hs
index 7345638d2d..d23fad536c 100644
--- a/compiler/GHC/Tc/Module.hs
+++ b/compiler/GHC/Tc/Module.hs
@@ -239,12 +239,14 @@ tcRnModuleTcRnM :: HscEnv
                 -> TcRn TcGblEnv
 -- Factored out separately from tcRnModule so that a Core plugin can
 -- call the type checker directly
+tcRnModuleTcRnM _ _
+                (HsParsedModule (L _ (XModule x)) _)
+                _ = dataConCantHappen x
 tcRnModuleTcRnM hsc_env mod_sum
                 (HsParsedModule {
                    hpm_module =
-                      (L loc (HsModule _ _ maybe_mod export_ies
-                                       import_decls local_decls mod_deprec
-                                       maybe_doc_hdr)),
+                      (L loc (HsModule (XModulePs _ _ mod_deprec maybe_doc_hdr)
+                                       maybe_mod export_ies import_decls local_decls)),
                    hpm_src_files = src_files
                 })
                 (this_mod, prel_imp_loc)
diff --git a/compiler/GHC/Tc/Utils/Backpack.hs b/compiler/GHC/Tc/Utils/Backpack.hs
index d553ec4fad..8758db5f47 100644
--- a/compiler/GHC/Tc/Utils/Backpack.hs
+++ b/compiler/GHC/Tc/Utils/Backpack.hs
@@ -521,6 +521,8 @@ merge_msg mod_name reqs =
 -- a final 'TcGblEnv' that matches the local signature and
 -- all required signatures.
 mergeSignatures :: HsParsedModule -> TcGblEnv -> ModIface -> TcRn TcGblEnv
+mergeSignatures (HsParsedModule { hpm_module = L _ (XModule ext) }) _ _
+  = dataConCantHappen ext
 mergeSignatures
   (HsParsedModule { hpm_module = L loc (HsModule { hsmodExports = mb_exports }),
                     hpm_src_files = src_files })
diff --git a/compiler/GHC/Unit/Module/Name.hs b/compiler/GHC/Unit/Module/Name.hs
index cc5e430bd6..9860914502 100644
--- a/compiler/GHC/Unit/Module/Name.hs
+++ b/compiler/GHC/Unit/Module/Name.hs
@@ -1,7 +1,7 @@
 
 -- | The ModuleName type
 module GHC.Unit.Module.Name
-    ( ModuleName
+    ( module Language.Haskell.Syntax
     , pprModuleName
     , moduleNameFS
     , moduleNameString
@@ -13,6 +13,8 @@ module GHC.Unit.Module.Name
     )
 where
 
+import {-# SOURCE #-} Language.Haskell.Syntax (ModuleName(..))
+
 import GHC.Prelude
 
 import GHC.Utils.Outputable
@@ -29,9 +31,6 @@ import qualified Text.ParserCombinators.ReadP as Parse
 import Text.ParserCombinators.ReadP (ReadP)
 import Data.Char (isAlphaNum)
 
--- | A ModuleName is essentially a simple string, e.g. @Data.List@.
-newtype ModuleName = ModuleName FastString deriving Show
-
 instance Uniquable ModuleName where
   getUnique (ModuleName nm) = getUnique nm
 
diff --git a/compiler/GHC/Unit/Module/Name.hs-boot b/compiler/GHC/Unit/Module/Name.hs-boot
index 7a48d807a7..deff51787e 100644
--- a/compiler/GHC/Unit/Module/Name.hs-boot
+++ b/compiler/GHC/Unit/Module/Name.hs-boot
@@ -1,6 +1,5 @@
-module GHC.Unit.Module.Name where
-
-import GHC.Prelude ()
-
-data ModuleName
+module GHC.Unit.Module.Name (
+    module Language.Haskell.Syntax
+                            ) where
 
+import {-# SOURCE #-} Language.Haskell.Syntax (ModuleName(..))
diff --git a/compiler/GHC/Unit/Types.hs-boot b/compiler/GHC/Unit/Types.hs-boot
index 0fe5302123..800b07db9a 100644
--- a/compiler/GHC/Unit/Types.hs-boot
+++ b/compiler/GHC/Unit/Types.hs-boot
@@ -3,7 +3,7 @@ module GHC.Unit.Types where
 
 import GHC.Prelude ()
 import {-# SOURCE #-} GHC.Utils.Outputable
-import {-# SOURCE #-} GHC.Unit.Module.Name ( ModuleName )
+import {-# SOURCE #-} Language.Haskell.Syntax ( ModuleName )
 import Data.Kind (Type)
 
 data UnitId
diff --git a/compiler/GHC/Utils/Outputable.hs b/compiler/GHC/Utils/Outputable.hs
index f711fd96aa..d759091850 100644
--- a/compiler/GHC/Utils/Outputable.hs
+++ b/compiler/GHC/Utils/Outputable.hs
@@ -107,7 +107,7 @@ module GHC.Utils.Outputable (
 import GHC.Prelude
 
 import {-# SOURCE #-}   GHC.Unit.Types ( Unit, Module, moduleName )
-import {-# SOURCE #-}   GHC.Unit.Module.Name( ModuleName )
+import {-# SOURCE #-}   Language.Haskell.Syntax( ModuleName )
 import {-# SOURCE #-}   GHC.Types.Name.Occurrence( OccName )
 
 import GHC.Utils.BufHandle (BufHandle)
diff --git a/compiler/Language/Haskell/Syntax.hs b/compiler/Language/Haskell/Syntax.hs
index 79012495ef..143b682405 100644
--- a/compiler/Language/Haskell/Syntax.hs
+++ b/compiler/Language/Haskell/Syntax.hs
@@ -24,6 +24,7 @@ module Language.Haskell.Syntax (
         module Language.Haskell.Syntax.Pat,
         module Language.Haskell.Syntax.Type,
         module Language.Haskell.Syntax.Extension,
+        ModuleName(..), HsModule(..)
 ) where
 
 import Language.Haskell.Syntax.Decls
@@ -34,6 +35,12 @@ import Language.Haskell.Syntax.Extension
 import Language.Haskell.Syntax.Pat
 import Language.Haskell.Syntax.Type
 
+import GHC.Data.FastString
+import GHC.Data.Maybe (Maybe)
+import GHC.Prelude (Show)
+import GHC.Parser.Annotation
+import GHC.Hs.ImpExp (LIE, LImportDecl)
+
 {-
 Note [Language.Haskell.Syntax.* Hierarchy]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -55,5 +62,47 @@ For more details, see
 https://gitlab.haskell.org/ghc/ghc/-/wikis/implementing-trees-that-grow
 -}
 
+-- | A ModuleName is essentially a simple string, e.g. @Data.List@.
+newtype ModuleName = ModuleName FastString deriving Show
+
+-- | Haskell Module
+--
+-- All we actually declare here is the top-level structure for a module.
+data HsModule p
+  =  -- | 'GHC.Parser.Annotation.AnnKeywordId's
+     --
+     --  - 'GHC.Parser.Annotation.AnnModule','GHC.Parser.Annotation.AnnWhere'
+     --
+     --  - 'GHC.Parser.Annotation.AnnOpen','GHC.Parser.Annotation.AnnSemi',
+     --    'GHC.Parser.Annotation.AnnClose' for explicit braces and semi around
+     --    hsmodImports,hsmodDecls if this style is used.
+
+     -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
+    HsModule {
+      hsmodExt :: XModule p,
+        -- ^ HsModule extension point
+      hsmodName :: Maybe (LocatedA ModuleName),
+        -- ^ @Nothing@: \"module X where\" is omitted (in which case the next
+        --     field is Nothing too)
+      hsmodExports :: Maybe (LocatedL [LIE p]),
+        -- ^ Export list
+        --
+        --  - @Nothing@: export list omitted, so export everything
+        --
+        --  - @Just []@: export /nothing/
+        --
+        --  - @Just [...]@: as you would expect...
+        --
+        --
+        --  - 'GHC.Parser.Annotation.AnnKeywordId's : 'GHC.Parser.Annotation.AnnOpen'
+        --                                   ,'GHC.Parser.Annotation.AnnClose'
 
--- TODO Add TTG parameter to 'HsModule' and move here.
+        -- For details on above see Note [exact print annotations] in GHC.Parser.Annotation
+      hsmodImports :: [LImportDecl p],
+        -- ^ We snaffle interesting stuff out of the imported interfaces early
+        -- on, adding that info to TyDecls/etc; so this list is often empty,
+        -- downstream.
+      hsmodDecls :: [LHsDecl p]
+        -- ^ Type, class, value, and interface signature decls
+   }
+  | XModule (XXModule p)
diff --git a/compiler/Language/Haskell/Syntax.hs-boot b/compiler/Language/Haskell/Syntax.hs-boot
new file mode 100644
index 0000000000..72ddcaa0e4
--- /dev/null
+++ b/compiler/Language/Haskell/Syntax.hs-boot
@@ -0,0 +1,9 @@
+{-# LANGUAGE StandaloneDeriving #-}
+module Language.Haskell.Syntax where
+
+import GHC.Prelude (Show)
+import GHC.Data.FastString
+
+newtype ModuleName = ModuleName FastString
+
+instance Show ModuleName
diff --git a/compiler/Language/Haskell/Syntax/Extension.hs b/compiler/Language/Haskell/Syntax/Extension.hs
index 47b693a9bd..f63ca09b30 100644
--- a/compiler/Language/Haskell/Syntax/Extension.hs
+++ b/compiler/Language/Haskell/Syntax/Extension.hs
@@ -397,6 +397,12 @@ type family XCInjectivityAnn  x
 type family XXInjectivityAnn  x
 
 -- =====================================================================
+-- Type families for the HsModule extension points
+
+type family XModule x
+type family XXModule x
+
+-- =====================================================================
 -- Type families for the HsExpr extension points
 
 type family XVar            x