    {-# LANGUAGE AllowAmbiguousTypes     #-} -- for unXRec, etc.
    {-# LANGUAGE ConstraintKinds         #-}
    {-# LANGUAGE DataKinds               #-}
    {-# LANGUAGE DeriveDataTypeable      #-}
    {-# LANGUAGE EmptyCase               #-}
    {-# LANGUAGE EmptyDataDeriving       #-}
    {-# LANGUAGE FlexibleContexts        #-}
    {-# LANGUAGE FlexibleInstances       #-}
    {-# LANGUAGE GADTs                   #-}
    {-# LANGUAGE MultiParamTypeClasses   #-}
    {-# LANGUAGE RankNTypes              #-}
    {-# LANGUAGE ScopedTypeVariables     #-}
    {-# LANGUAGE TypeFamilyDependencies  #-}
    {-# LANGUAGE UndecidableInstances    #-} -- Wrinkle in Note [Trees That Grow]
                                             -- in module Language.Haskell.Syntax.Extension

    -- See Note [Language.Haskell.Syntax.* Hierarchy] for why not GHC.Hs.*
    module Language.Haskell.Syntax.Extension where

    -- This module captures the type families to precisely identify the extension
    -- points for GHC.Hs syntax

    import GHC.Prelude

    import Data.Data hiding ( Fixity )
    import Data.Kind (Type)
    import GHC.Utils.Outputable

    {-
    Note [Trees that grow]
    ~~~~~~~~~~~~~~~~~~~~~~

    See https://gitlab.haskell.org/ghc/ghc/wikis/implementing-trees-that-grow

    The hsSyn AST is reused across multiple compiler passes. We also have the
    Template Haskell AST, and the haskell-src-exts one (outside of GHC)

    Supporting multiple passes means the AST has various warts on it to cope with
    the specifics for the phases, such as the 'ValBindsOut', 'ConPatOut',
    'SigPatOut' etc.

    The growable AST will allow each of these variants to be captured explicitly,
    such that they only exist in the given compiler pass AST, as selected by the
    type parameter to the AST.

    In addition it will allow tool writers to define their own extensions to capture
    additional information for the tool, in a natural way.

    A further goal is to provide a means to harmonise the Template Haskell and
    haskell-src-exts ASTs as well.

    Wrinkle: In order to print out the AST, we need to know it is Outputable.
    We also sometimes need to branch on the particular pass that we're in
    (e.g. to print out type information once we know it). In order to allow
    both of these actions, we define OutputableBndrId, which gathers the necessary
    OutputableBndr and IsPass constraints. The use of this constraint in instances
    generally requires UndecidableInstances.

    See also Note [IsPass] and Note [NoGhcTc] in GHC.Hs.Extension.

    -}

    -- | A placeholder type for TTG extension points that are not currently
    -- unused to represent any particular value.
    --
    -- This should not be confused with 'NoExtCon', which are found in unused
    -- extension /constructors/ and therefore should never be inhabited. In
    -- contrast, 'NoExtField' is used in extension /points/ (e.g., as the field of
    -- some constructor), so it must have an inhabitant to construct AST passes
    -- that manipulate fields with that extension point as their type.
    data NoExtField = NoExtField
      deriving (Typeable NoExtField
    NoExtField -> DataType
    NoExtField -> Constr
    (forall b. Data b => b -> b) -> NoExtField -> NoExtField
    forall a.
    Typeable a
    -> (forall (c :: * -> *).
        (forall d b. Data d => c (d -> b) -> d -> c b)
        -> (forall g. g -> c g) -> a -> c a)
    -> (forall (c :: * -> *).
        (forall b r. Data b => c (b -> r) -> c r)
        -> (forall r. r -> c r) -> Constr -> c a)
    -> (a -> Constr)
    -> (a -> DataType)
    -> (forall (t :: * -> *) (c :: * -> *).
        Typeable t =>
        (forall d. Data d => c (t d)) -> Maybe (c a))
    -> (forall (t :: * -> * -> *) (c :: * -> *).
        Typeable t =>
        (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c a))
    -> ((forall b. Data b => b -> b) -> a -> a)
    -> (forall r r'.
        (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
    -> (forall r r'.
        (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
    -> (forall u. (forall d. Data d => d -> u) -> a -> [u])
    -> (forall u. Int -> (forall d. Data d => d -> u) -> a -> u)
    -> (forall (m :: * -> *).
        Monad m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> Data a
    forall u. Int -> (forall d. Data d => d -> u) -> NoExtField -> u
    forall u. (forall d. Data d => d -> u) -> NoExtField -> [u]
    forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> NoExtField -> r
    forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> NoExtField -> r
    forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> NoExtField -> m NoExtField
    forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> NoExtField -> m NoExtField
    forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c NoExtField
    forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> NoExtField -> c NoExtField
    forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c NoExtField)
    forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c NoExtField)
    gmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> NoExtField -> m NoExtField
    $cgmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> NoExtField -> m NoExtField
    gmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> NoExtField -> m NoExtField
    $cgmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> NoExtField -> m NoExtField
    gmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> NoExtField -> m NoExtField
    $cgmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> NoExtField -> m NoExtField
    gmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> NoExtField -> u
    $cgmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> NoExtField -> u
    gmapQ :: forall u. (forall d. Data d => d -> u) -> NoExtField -> [u]
    $cgmapQ :: forall u. (forall d. Data d => d -> u) -> NoExtField -> [u]
    gmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> NoExtField -> r
    $cgmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> NoExtField -> r
    gmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> NoExtField -> r
    $cgmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> NoExtField -> r
    gmapT :: (forall b. Data b => b -> b) -> NoExtField -> NoExtField
    $cgmapT :: (forall b. Data b => b -> b) -> NoExtField -> NoExtField
    dataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c NoExtField)
    $cdataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c NoExtField)
    dataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c NoExtField)
    $cdataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c NoExtField)
    dataTypeOf :: NoExtField -> DataType
    $cdataTypeOf :: NoExtField -> DataType
    toConstr :: NoExtField -> Constr
    $ctoConstr :: NoExtField -> Constr
    gunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c NoExtField
    $cgunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c NoExtField
    gfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> NoExtField -> c NoExtField
    $cgfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> NoExtField -> c NoExtField
    Data,NoExtField -> NoExtField -> Bool
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    /= :: NoExtField -> NoExtField -> Bool
    $c/= :: NoExtField -> NoExtField -> Bool
    == :: NoExtField -> NoExtField -> Bool
    $c== :: NoExtField -> NoExtField -> Bool
    Eq,Eq NoExtField
    NoExtField -> NoExtField -> Bool
    NoExtField -> NoExtField -> Ordering
    NoExtField -> NoExtField -> NoExtField
    forall a.
    Eq a
    -> (a -> a -> Ordering)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> a)
    -> (a -> a -> a)
    -> Ord a
    min :: NoExtField -> NoExtField -> NoExtField
    $cmin :: NoExtField -> NoExtField -> NoExtField
    max :: NoExtField -> NoExtField -> NoExtField
    $cmax :: NoExtField -> NoExtField -> NoExtField
    >= :: NoExtField -> NoExtField -> Bool
    $c>= :: NoExtField -> NoExtField -> Bool
    > :: NoExtField -> NoExtField -> Bool
    $c> :: NoExtField -> NoExtField -> Bool
    <= :: NoExtField -> NoExtField -> Bool
    $c<= :: NoExtField -> NoExtField -> Bool
    < :: NoExtField -> NoExtField -> Bool
    $c< :: NoExtField -> NoExtField -> Bool
    compare :: NoExtField -> NoExtField -> Ordering
    $ccompare :: NoExtField -> NoExtField -> Ordering
    Ord)

    instance Outputable NoExtField where
      ppr :: NoExtField -> SDoc
    ppr NoExtField
    _ = String -> SDoc
    text String
    "NoExtField"

    -- | Used when constructing a term with an unused extension point.
    noExtField :: NoExtField
    noExtField :: NoExtField
    noExtField = NoExtField
    NoExtField

    -- | Used in TTG extension constructors that have yet to be extended with
    -- anything. If an extension constructor has 'NoExtCon' as its field, it is
    -- not intended to ever be constructed anywhere, and any function that consumes
    -- the extension constructor can eliminate it by way of 'noExtCon'.
    --
    -- This should not be confused with 'NoExtField', which are found in unused
    -- extension /points/ (not /constructors/) and therefore can be inhabited.

    -- See also [NoExtCon and strict fields].
    data NoExtCon
      deriving (Typeable NoExtCon
    NoExtCon -> DataType
    NoExtCon -> Constr
    (forall b. Data b => b -> b) -> NoExtCon -> NoExtCon
    forall a.
    Typeable a
    -> (forall (c :: * -> *).
        (forall d b. Data d => c (d -> b) -> d -> c b)
        -> (forall g. g -> c g) -> a -> c a)
    -> (forall (c :: * -> *).
        (forall b r. Data b => c (b -> r) -> c r)
        -> (forall r. r -> c r) -> Constr -> c a)
    -> (a -> Constr)
    -> (a -> DataType)
    -> (forall (t :: * -> *) (c :: * -> *).
        Typeable t =>
        (forall d. Data d => c (t d)) -> Maybe (c a))
    -> (forall (t :: * -> * -> *) (c :: * -> *).
        Typeable t =>
        (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c a))
    -> ((forall b. Data b => b -> b) -> a -> a)
    -> (forall r r'.
        (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
    -> (forall r r'.
        (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> a -> r)
    -> (forall u. (forall d. Data d => d -> u) -> a -> [u])
    -> (forall u. Int -> (forall d. Data d => d -> u) -> a -> u)
    -> (forall (m :: * -> *).
        Monad m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> (forall (m :: * -> *).
        MonadPlus m =>
        (forall d. Data d => d -> m d) -> a -> m a)
    -> Data a
    forall u. Int -> (forall d. Data d => d -> u) -> NoExtCon -> u
    forall u. (forall d. Data d => d -> u) -> NoExtCon -> [u]
    forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> NoExtCon -> r
    forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> NoExtCon -> r
    forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> NoExtCon -> m NoExtCon
    forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> NoExtCon -> m NoExtCon
    forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c NoExtCon
    forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> NoExtCon -> c NoExtCon
    forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c NoExtCon)
    forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c NoExtCon)
    gmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> NoExtCon -> m NoExtCon
    $cgmapMo :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> NoExtCon -> m NoExtCon
    gmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> NoExtCon -> m NoExtCon
    $cgmapMp :: forall (m :: * -> *).
    MonadPlus m =>
    (forall d. Data d => d -> m d) -> NoExtCon -> m NoExtCon
    gmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> NoExtCon -> m NoExtCon
    $cgmapM :: forall (m :: * -> *).
    Monad m =>
    (forall d. Data d => d -> m d) -> NoExtCon -> m NoExtCon
    gmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> NoExtCon -> u
    $cgmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> NoExtCon -> u
    gmapQ :: forall u. (forall d. Data d => d -> u) -> NoExtCon -> [u]
    $cgmapQ :: forall u. (forall d. Data d => d -> u) -> NoExtCon -> [u]
    gmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> NoExtCon -> r
    $cgmapQr :: forall r r'.
    (r' -> r -> r)
    -> r -> (forall d. Data d => d -> r') -> NoExtCon -> r
    gmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> NoExtCon -> r
    $cgmapQl :: forall r r'.
    (r -> r' -> r)
    -> r -> (forall d. Data d => d -> r') -> NoExtCon -> r
    gmapT :: (forall b. Data b => b -> b) -> NoExtCon -> NoExtCon
    $cgmapT :: (forall b. Data b => b -> b) -> NoExtCon -> NoExtCon
    dataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c NoExtCon)
    $cdataCast2 :: forall (t :: * -> * -> *) (c :: * -> *).
    Typeable t =>
    (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c NoExtCon)
    dataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c NoExtCon)
    $cdataCast1 :: forall (t :: * -> *) (c :: * -> *).
    Typeable t =>
    (forall d. Data d => c (t d)) -> Maybe (c NoExtCon)
    dataTypeOf :: NoExtCon -> DataType
    $cdataTypeOf :: NoExtCon -> DataType
    toConstr :: NoExtCon -> Constr
    $ctoConstr :: NoExtCon -> Constr
    gunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c NoExtCon
    $cgunfold :: forall (c :: * -> *).
    (forall b r. Data b => c (b -> r) -> c r)
    -> (forall r. r -> c r) -> Constr -> c NoExtCon
    gfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> NoExtCon -> c NoExtCon
    $cgfoldl :: forall (c :: * -> *).
    (forall d b. Data d => c (d -> b) -> d -> c b)
    -> (forall g. g -> c g) -> NoExtCon -> c NoExtCon
    Data,NoExtCon -> NoExtCon -> Bool
    forall a. (a -> a -> Bool) -> (a -> a -> Bool) -> Eq a
    /= :: NoExtCon -> NoExtCon -> Bool
    $c/= :: NoExtCon -> NoExtCon -> Bool
    == :: NoExtCon -> NoExtCon -> Bool
    $c== :: NoExtCon -> NoExtCon -> Bool
    Eq,Eq NoExtCon
    NoExtCon -> NoExtCon -> Bool
    NoExtCon -> NoExtCon -> Ordering
    NoExtCon -> NoExtCon -> NoExtCon
    forall a.
    Eq a
    -> (a -> a -> Ordering)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> Bool)
    -> (a -> a -> a)
    -> (a -> a -> a)
    -> Ord a
    min :: NoExtCon -> NoExtCon -> NoExtCon
    $cmin :: NoExtCon -> NoExtCon -> NoExtCon
    max :: NoExtCon -> NoExtCon -> NoExtCon
    $cmax :: NoExtCon -> NoExtCon -> NoExtCon
    >= :: NoExtCon -> NoExtCon -> Bool
    $c>= :: NoExtCon -> NoExtCon -> Bool
    > :: NoExtCon -> NoExtCon -> Bool
    $c> :: NoExtCon -> NoExtCon -> Bool
    <= :: NoExtCon -> NoExtCon -> Bool
    $c<= :: NoExtCon -> NoExtCon -> Bool
    < :: NoExtCon -> NoExtCon -> Bool
    $c< :: NoExtCon -> NoExtCon -> Bool
    compare :: NoExtCon -> NoExtCon -> Ordering
    $ccompare :: NoExtCon -> NoExtCon -> Ordering
    Ord)

    instance Outputable NoExtCon where
      ppr :: NoExtCon -> SDoc
    ppr = forall a. NoExtCon -> a
    noExtCon

    -- | Eliminate a 'NoExtCon'. Much like 'Data.Void.absurd'.
    noExtCon :: NoExtCon -> a
    noExtCon :: forall a. NoExtCon -> a
    noExtCon NoExtCon
    x = case NoExtCon
    x of {}

    -- | GHC's L prefixed variants wrap their vanilla variant in this type family,
    -- to add 'SrcLoc' info via 'Located'. Other passes than 'GhcPass' not
    -- interested in location information can define this as
    -- @type instance XRec NoLocated a = a@.
    -- See Note [XRec and SrcSpans in the AST]
    type family XRec p a = r | r -> a

    type family Anno a = b -- See Note [XRec and Anno in the AST] in GHC.Parser.Annotation

    {-
    Note [XRec and SrcSpans in the AST]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    XRec is meant to replace most of the uses of `Located` in the AST. It is another
    extension point meant to make it easier for non-GHC applications to reuse the
    AST for their own purposes, and not have to deal the hassle of (perhaps) useless
    SrcSpans everywhere.

    instead of `Located (HsExpr p)` or similar types, we will now have `XRec p
    (HsExpr p)`

    XRec allows annotating certain points in the AST with extra
    information. This maybe be source spans (for GHC), nothing (for TH),
    types (for HIE files), exact print annotations (for exactprint) or
    anything else.

    This should hopefully bring us one step closer to sharing the AST between GHC
    and TH.

    We use the `UnXRec`, `MapXRec` and `WrapXRec` type classes to aid us in writing
    pass-polymorphic code that deals with `XRec`s
    -}

    -- | We can strip off the XRec to access the underlying data.
    -- See Note [XRec and SrcSpans in the AST]
    class UnXRec p where
      unXRec :: XRec p a -> a

    -- | We can map over the underlying type contained in an @XRec@ while preserving
    -- the annotation as is.
    class MapXRec p where
      mapXRec :: (Anno a ~ Anno b) => (a -> b) -> XRec p a -> XRec p b
    -- See Note [XRec and SrcSpans in the AST]
    -- See Note [XRec and Anno in the AST] in GHC.Parser.Annotation
    -- AZ: Is there a way to not have Anno in this file, but still have MapXRec?
    --     Perhaps define XRec with an additional b parameter, only used in Hs as (Anno b)?

    -- | The trivial wrapper that carries no additional information
    -- See Note [XRec and SrcSpans in the AST]
    class WrapXRec p a where
      wrapXRec :: a -> XRec p a

    -- | Maps the "normal" id type for a given pass
    type family IdP p

    type LIdP p = XRec p (IdP p)

    -- =====================================================================
    -- Type families for the HsBinds extension points

    -- HsLocalBindsLR type families
    type family XHsValBinds      x x'
    type family XHsIPBinds       x x'
    type family XEmptyLocalBinds x x'
    type family XXHsLocalBindsLR x x'

    -- HsValBindsLR type families
    type family XValBinds    x x'
    type family XXValBindsLR x x'

    -- HsBindLR type families
    type family XFunBind    x x'
    type family XPatBind    x x'
    type family XVarBind    x x'
    type family XAbsBinds   x x'
    type family XPatSynBind x x'
    type family XXHsBindsLR x x'

    -- ABExport type families
    type family XABE x
    type family XXABExport x

    -- PatSynBind type families
    type family XPSB x x'
    type family XXPatSynBind x x'

    -- HsIPBinds type families
    type family XIPBinds    x
    type family XXHsIPBinds x

    -- IPBind type families
    type family XCIPBind x
    type family XXIPBind x

    -- Sig type families
    type family XTypeSig          x
    type family XPatSynSig        x
    type family XClassOpSig       x
    type family XIdSig            x
    type family XFixSig           x
    type family XInlineSig        x
    type family XSpecSig          x
    type family XSpecInstSig      x
    type family XMinimalSig       x
    type family XSCCFunSig        x
    type family XCompleteMatchSig x
    type family XXSig             x

    -- FixitySig type families
    type family XFixitySig          x
    type family XXFixitySig         x

    -- StandaloneKindSig type families
    type family XStandaloneKindSig  x
    type family XXStandaloneKindSig x

    -- =====================================================================
    -- Type families for the HsDecls extension points

    -- HsDecl type families
    type family XTyClD       x
    type family XInstD       x
    type family XDerivD      x
    type family XValD        x
    type family XSigD        x
    type family XKindSigD    x
    type family XDefD        x
    type family XForD        x
    type family XWarningD    x
    type family XAnnD        x
    type family XRuleD       x
    type family XSpliceD     x
    type family XDocD        x
    type family XRoleAnnotD  x
    type family XXHsDecl     x

    -- -------------------------------------
    -- HsGroup type families
    type family XCHsGroup      x
    type family XXHsGroup      x

    -- -------------------------------------
    -- SpliceDecl type families
    type family XSpliceDecl       x
    type family XXSpliceDecl      x

    -- -------------------------------------
    -- TyClDecl type families
    type family XFamDecl       x
    type family XSynDecl       x
    type family XDataDecl      x
    type family XClassDecl     x
    type family XXTyClDecl     x

    -- -------------------------------------
    -- FunDep type families
    type family XCFunDep      x
    type family XXFunDep      x

    -- -------------------------------------
    -- TyClGroup type families
    type family XCTyClGroup      x
    type family XXTyClGroup      x

    -- -------------------------------------
    -- FamilyResultSig type families
    type family XNoSig            x
    type family XCKindSig         x -- Clashes with XKindSig above
    type family XTyVarSig         x
    type family XXFamilyResultSig x

    -- -------------------------------------
    -- FamilyDecl type families
    type family XCFamilyDecl      x
    type family XXFamilyDecl      x

    -- -------------------------------------
    -- HsDataDefn type families
    type family XCHsDataDefn      x
    type family XXHsDataDefn      x

    -- -------------------------------------
    -- HsDerivingClause type families
    type family XCHsDerivingClause      x
    type family XXHsDerivingClause      x

    -- -------------------------------------
    -- DerivClauseTys type families
    type family XDctSingle       x
    type family XDctMulti        x
    type family XXDerivClauseTys x

    -- -------------------------------------
    -- ConDecl type families
    type family XConDeclGADT   x
    type family XConDeclH98    x
    type family XXConDecl      x

    -- -------------------------------------
    -- FamEqn type families
    type family XCFamEqn      x r
    type family XXFamEqn      x r

    -- -------------------------------------
    -- TyFamInstDecl type families
    type family XCTyFamInstDecl x
    type family XXTyFamInstDecl x

    -- -------------------------------------
    -- ClsInstDecl type families
    type family XCClsInstDecl      x
    type family XXClsInstDecl      x

    -- -------------------------------------
    -- InstDecl type families
    type family XClsInstD      x
    type family XDataFamInstD  x
    type family XTyFamInstD    x
    type family XXInstDecl     x

    -- -------------------------------------
    -- DerivDecl type families
    type family XCDerivDecl      x
    type family XXDerivDecl      x

    -- -------------------------------------
    -- DerivStrategy type family
    type family XStockStrategy    x
    type family XAnyClassStrategy x
    type family XNewtypeStrategy  x
    type family XViaStrategy      x

    -- -------------------------------------
    -- DefaultDecl type families
    type family XCDefaultDecl      x
    type family XXDefaultDecl      x

    -- -------------------------------------
    -- ForeignDecl type families
    type family XForeignImport     x
    type family XForeignExport     x
    type family XXForeignDecl      x

    -- -------------------------------------
    -- RuleDecls type families
    type family XCRuleDecls      x
    type family XXRuleDecls      x

    -- -------------------------------------
    -- RuleDecl type families
    type family XHsRule          x
    type family XXRuleDecl       x

    -- -------------------------------------
    -- RuleBndr type families
    type family XCRuleBndr      x
    type family XRuleBndrSig    x
    type family XXRuleBndr      x

    -- -------------------------------------
    -- WarnDecls type families
    type family XWarnings        x
    type family XXWarnDecls      x

    -- -------------------------------------
    -- WarnDecl type families
    type family XWarning        x
    type family XXWarnDecl      x

    -- -------------------------------------
    -- AnnDecl type families
    type family XHsAnnotation  x
    type family XXAnnDecl      x

    -- -------------------------------------
    -- RoleAnnotDecl type families
    type family XCRoleAnnotDecl  x
    type family XXRoleAnnotDecl  x

    -- -------------------------------------
    -- InjectivityAnn type families
    type family XCInjectivityAnn  x
    type family XXInjectivityAnn  x

    -- =====================================================================
    -- Type families for the HsExpr extension points

    type family XVar            x
    type family XUnboundVar     x
    type family XConLikeOut     x
    type family XRecFld         x
    type family XOverLabel      x
    type family XIPVar          x
    type family XOverLitE       x
    type family XLitE           x
    type family XLam            x
    type family XLamCase        x
    type family XApp            x
    type family XAppTypeE       x
    type family XOpApp          x
    type family XNegApp         x
    type family XPar            x
    type family XSectionL       x
    type family XSectionR       x
    type family XExplicitTuple  x
    type family XExplicitSum    x
    type family XCase           x
    type family XIf             x
    type family XMultiIf        x
    type family XLet            x
    type family XDo             x
    type family XExplicitList   x
    type family XRecordCon      x
    type family XRecordUpd      x
    type family XGetField       x
    type family XProjection     x
    type family XExprWithTySig  x
    type family XArithSeq       x
    type family XBracket        x
    type family XRnBracketOut   x
    type family XTcBracketOut   x
    type family XSpliceE        x
    type family XProc           x
    type family XStatic         x
    type family XTick           x
    type family XBinTick        x
    type family XPragE          x
    type family XXExpr          x

    -- -------------------------------------
    -- FieldLabel type families
    type family XCHsFieldLabel  x
    type family XXHsFieldLabel  x

    -- -------------------------------------
    -- HsPragE type families
    type family XSCC            x
    type family XXPragE         x

    -- -------------------------------------
    -- AmbiguousFieldOcc type families
    type family XUnambiguous        x
    type family XAmbiguous          x
    type family XXAmbiguousFieldOcc x

    -- -------------------------------------
    -- HsTupArg type families
    type family XPresent  x
    type family XMissing  x
    type family XXTupArg  x

    -- -------------------------------------
    -- HsSplice type families
    type family XTypedSplice   x
    type family XUntypedSplice x
    type family XQuasiQuote    x
    type family XSpliced       x
    type family XXSplice       x

    -- -------------------------------------
    -- HsBracket type families
    type family XExpBr      x
    type family XPatBr      x
    type family XDecBrL     x
    type family XDecBrG     x
    type family XTypBr      x
    type family XVarBr      x
    type family XTExpBr     x
    type family XXBracket   x

    -- -------------------------------------
    -- HsCmdTop type families
    type family XCmdTop  x
    type family XXCmdTop x

    -- -------------------------------------
    -- MatchGroup type families
    type family XMG           x b
    type family XXMatchGroup  x b

    -- -------------------------------------
    -- Match type families
    type family XCMatch  x b
    type family XXMatch  x b

    -- -------------------------------------
    -- GRHSs type families
    type family XCGRHSs  x b
    type family XXGRHSs  x b

    -- -------------------------------------
    -- GRHS type families
    type family XCGRHS  x b
    type family XXGRHS  x b

    -- -------------------------------------
    -- StmtLR type families
    type family XLastStmt        x x' b
    type family XBindStmt        x x' b
    type family XApplicativeStmt x x' b
    type family XBodyStmt        x x' b
    type family XLetStmt         x x' b
    type family XParStmt         x x' b
    type family XTransStmt       x x' b
    type family XRecStmt         x x' b
    type family XXStmtLR         x x' b

    -- -------------------------------------
    -- HsCmd type families
    type family XCmdArrApp  x
    type family XCmdArrForm x
    type family XCmdApp     x
    type family XCmdLam     x
    type family XCmdPar     x
    type family XCmdCase    x
    type family XCmdLamCase x
    type family XCmdIf      x
    type family XCmdLet     x
    type family XCmdDo      x
    type family XCmdWrap    x
    type family XXCmd       x

    -- -------------------------------------
    -- ParStmtBlock type families
    type family XParStmtBlock  x x'
    type family XXParStmtBlock x x'

    -- -------------------------------------
    -- ApplicativeArg type families
    type family XApplicativeArgOne   x
    type family XApplicativeArgMany  x
    type family XXApplicativeArg     x

    -- =====================================================================
    -- Type families for the HsImpExp extension points

    -- TODO

    -- =====================================================================
    -- Type families for the HsLit extension points

    -- We define a type family for each extension point. This is based on prepending
    -- 'X' to the constructor name, for ease of reference.
    type family XHsChar x
    type family XHsCharPrim x
    type family XHsString x
    type family XHsStringPrim x
    type family XHsInt x
    type family XHsIntPrim x
    type family XHsWordPrim x
    type family XHsInt64Prim x
    type family XHsWord64Prim x
    type family XHsInteger x
    type family XHsRat x
    type family XHsFloatPrim x
    type family XHsDoublePrim x
    type family XXLit x

    -- -------------------------------------
    -- HsOverLit type families
    type family XOverLit  x
    type family XXOverLit x

    -- =====================================================================
    -- Type families for the HsPat extension points

    type family XWildPat    x
    type family XVarPat     x
    type family XLazyPat    x
    type family XAsPat      x
    type family XParPat     x
    type family XBangPat    x
    type family XListPat    x
    type family XTuplePat   x
    type family XSumPat     x
    type family XConPat     x
    type family XViewPat    x
    type family XSplicePat  x
    type family XLitPat     x
    type family XNPat       x
    type family XNPlusKPat  x
    type family XSigPat     x
    type family XCoPat      x
    type family XXPat       x
    type family XHsRecField x

    -- =====================================================================
    -- Type families for the HsTypes type families

    -- -------------------------------------
    -- LHsQTyVars type families
    type family XHsQTvs       x
    type family XXLHsQTyVars  x

    -- -------------------------------------
    -- HsOuterTyVarBndrs type families
    type family XHsOuterImplicit    x
    type family XHsOuterExplicit    x flag
    type family XXHsOuterTyVarBndrs x

    -- -------------------------------------
    -- HsSigType type families
    type family XHsSig      x
    type family XXHsSigType x

    -- -------------------------------------
    -- HsWildCardBndrs type families
    type family XHsWC              x b
    type family XXHsWildCardBndrs  x b

    -- -------------------------------------
    -- HsPatSigType type families
    type family XHsPS x
    type family XXHsPatSigType x

    -- -------------------------------------
    -- HsType type families
    type family XForAllTy        x
    type family XQualTy          x
    type family XTyVar           x
    type family XAppTy           x
    type family XAppKindTy       x
    type family XFunTy           x
    type family XListTy          x
    type family XTupleTy         x
    type family XSumTy           x
    type family XOpTy            x
    type family XParTy           x
    type family XIParamTy        x
    type family XStarTy          x
    type family XKindSig         x
    type family XSpliceTy        x
    type family XDocTy           x
    type family XBangTy          x
    type family XRecTy           x
    type family XExplicitListTy  x
    type family XExplicitTupleTy x
    type family XTyLit           x
    type family XWildCardTy      x
    type family XXType           x

    -- ---------------------------------------------------------------------
    -- HsForAllTelescope type families
    type family XHsForAllVis        x
    type family XHsForAllInvis      x
    type family XXHsForAllTelescope x

    -- ---------------------------------------------------------------------
    -- HsTyVarBndr type families
    type family XUserTyVar   x
    type family XKindedTyVar x
    type family XXTyVarBndr  x

    -- ---------------------------------------------------------------------
    -- ConDeclField type families
    type family XConDeclField  x
    type family XXConDeclField x

    -- ---------------------------------------------------------------------
    -- FieldOcc type families
    type family XCFieldOcc x
    type family XXFieldOcc x

    -- =====================================================================
    -- Type families for the HsImpExp type families

    -- -------------------------------------
    -- ImportDecl type families
    type family XCImportDecl       x
    type family XXImportDecl       x

    -- -------------------------------------
    -- IE type families
    type family XIEVar             x
    type family XIEThingAbs        x
    type family XIEThingAll        x
    type family XIEThingWith       x
    type family XIEModuleContents  x
    type family XIEGroup           x
    type family XIEDoc             x
    type family XIEDocNamed        x
    type family XXIE               x

    -- -------------------------------------

    -- =====================================================================
    -- Misc

    -- | See Note [NoGhcTc] in GHC.Hs.Extension. It has to be in this
    -- module because it is used like an extension point (in the data definitions
    -- of types that should be parameter-agnostic.
    type family NoGhcTc (p :: Type)

    -- =====================================================================
    -- End of Type family definitions
    -- =====================================================================