GHC/Iface/Ext/Types.hs

    {-# LANGUAGE DeriveDataTypeable         #-}
    {-# LANGUAGE DeriveTraversable          #-}
    {-# LANGUAGE FlexibleInstances          #-}
    {-# LANGUAGE GeneralizedNewtypeDeriving #-}
    {-# LANGUAGE OverloadedStrings          #-}
    {-# LANGUAGE PatternSynonyms            #-}
    {-# LANGUAGE ScopedTypeVariables        #-}

    {-
    Types for the .hie file format are defined here.

    For more information see https://gitlab.haskell.org/ghc/ghc/wikis/hie-files
    -}

    module GHC.Iface.Ext.Types where

    import GHC.Prelude

    import GHC.Settings.Config
    import GHC.Utils.Binary
    import GHC.Data.FastString
    import GHC.Builtin.Utils
    import GHC.Iface.Type
    import GHC.Unit.Module            ( ModuleName, Module )
    import GHC.Types.Name
    import GHC.Utils.Outputable hiding ( (<>) )
    import GHC.Types.SrcLoc
    import GHC.Types.Avail
    import GHC.Types.Unique
    import qualified GHC.Utils.Outputable as O ( (<>) )
    import GHC.Utils.Misc
    import GHC.Utils.Panic

    import qualified Data.Array as A
    import qualified Data.Map as M
    import qualified Data.Set as S
    import Data.ByteString            ( ByteString )
    import Data.Data                  ( Typeable, Data )
    import Data.Semigroup             ( Semigroup(..) )
    import Data.Word                  ( Word8 )
    import Control.Applicative        ( (<|>) )
    import Data.Coerce                ( coerce  )
    import Data.Function              ( on )

    type Span = RealSrcSpan

    -- | Current version of @.hie@ files
    hieVersion :: Integer
    hieVersion = read (cProjectVersionInt ++ cProjectPatchLevel) :: Integer

    {- |
    GHC builds up a wealth of information about Haskell source as it compiles it.
    @.hie@ files are a way of persisting some of this information to disk so that
    external tools that need to work with haskell source don't need to parse,
    typecheck, and rename all over again. These files contain:

      * a simplified AST

           * nodes are annotated with source positions and types
           * identifiers are annotated with scope information

      * the raw bytes of the initial Haskell source

    Besides saving compilation cycles, @.hie@ files also offer a more stable
    interface than the GHC API.
    -}
    data HieFile = HieFile
        { hie_hs_file :: FilePath
        -- ^ Initial Haskell source file path

        , hie_module :: Module
        -- ^ The module this HIE file is for

        , hie_types :: A.Array TypeIndex HieTypeFlat
        -- ^ Types referenced in the 'hie_asts'.
        --
        -- See Note [Efficient serialization of redundant type info]

        , hie_asts :: HieASTs TypeIndex
        -- ^ Type-annotated abstract syntax trees

        , hie_exports :: [AvailInfo]
        -- ^ The names that this module exports

        , hie_hs_src :: ByteString
        -- ^ Raw bytes of the initial Haskell source
        }
    instance Binary HieFile where
      put_ bh hf = do
        put_ bh $ hie_hs_file hf
        put_ bh $ hie_module hf
        put_ bh $ hie_types hf
        put_ bh $ hie_asts hf
        put_ bh $ hie_exports hf
        put_ bh $ hie_hs_src hf

      get bh = HieFile
        <$> get bh
        <*> get bh
        <*> get bh
        <*> get bh
        <*> get bh
        <*> get bh

    {-
    Note [Efficient serialization of redundant type info]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    The type information in .hie files is highly repetitive and redundant. For
    example, consider the expression

        const True 'a'

    There is a lot of shared structure between the types of subterms:

      * const True 'a' ::                 Bool
      * const True     ::         Char -> Bool
      * const          :: Bool -> Char -> Bool

    Since all 3 of these types need to be stored in the .hie file, it is worth
    making an effort to deduplicate this shared structure. The trick is to define
    a new data type that is a flattened version of 'Type':

        data HieType a = HAppTy a a  -- data Type = AppTy Type Type
                       | HFunTy a a  --           | FunTy Type Type
                       | ...

        type TypeIndex = Int

    Types in the final AST are stored in an 'A.Array TypeIndex (HieType TypeIndex)',
    where the 'TypeIndex's in the 'HieType' are references to other elements of the
    array. Types recovered from GHC are deduplicated and stored in this compressed
    form with sharing of subtrees.
    -}

    type TypeIndex = Int

    -- | A flattened version of 'Type'.
    --
    -- See Note [Efficient serialization of redundant type info]
    data HieType a
      = HTyVarTy Name
      | HAppTy a (HieArgs a)
      | HTyConApp IfaceTyCon (HieArgs a)
      | HForAllTy ((Name, a),ArgFlag) a
      | HFunTy a a a
      | HQualTy a a           -- ^ type with constraint: @t1 => t2@ (see 'IfaceDFunTy')
      | HLitTy IfaceTyLit
      | HCastTy a
      | HCoercionTy
        deriving (Functor, Foldable, Traversable, Eq)

    type HieTypeFlat = HieType TypeIndex

    -- | Roughly isomorphic to the original core 'Type'.
    newtype HieTypeFix = Roll (HieType (HieTypeFix))

    instance Binary (HieType TypeIndex) where
      put_ bh (HTyVarTy n) = do
        putByte bh 0
        put_ bh n
      put_ bh (HAppTy a b) = do
        putByte bh 1
        put_ bh a
        put_ bh b
      put_ bh (HTyConApp n xs) = do
        putByte bh 2
        put_ bh n
        put_ bh xs
      put_ bh (HForAllTy bndr a) = do
        putByte bh 3
        put_ bh bndr
        put_ bh a
      put_ bh (HFunTy w a b) = do
        putByte bh 4
        put_ bh w
        put_ bh a
        put_ bh b
      put_ bh (HQualTy a b) = do
        putByte bh 5
        put_ bh a
        put_ bh b
      put_ bh (HLitTy l) = do
        putByte bh 6
        put_ bh l
      put_ bh (HCastTy a) = do
        putByte bh 7
        put_ bh a
      put_ bh (HCoercionTy) = putByte bh 8

      get bh = do
        (t :: Word8) <- get bh
        case t of
          0 -> HTyVarTy <$> get bh
          1 -> HAppTy <$> get bh <*> get bh
          2 -> HTyConApp <$> get bh <*> get bh
          3 -> HForAllTy <$> get bh <*> get bh
          4 -> HFunTy <$> get bh <*> get bh <*> get bh
          5 -> HQualTy <$> get bh <*> get bh
          6 -> HLitTy <$> get bh
          7 -> HCastTy <$> get bh
          8 -> return HCoercionTy
          _ -> panic "Binary (HieArgs Int): invalid tag"

    -- | A list of type arguments along with their respective visibilities (ie. is
    -- this an argument that would return 'True' for 'isVisibleArgFlag'?).
    newtype HieArgs a = HieArgs [(Bool,a)]
      deriving (Functor, Foldable, Traversable, Eq)

    instance Binary (HieArgs TypeIndex) where
      put_ bh (HieArgs xs) = put_ bh xs
      get bh = HieArgs <$> get bh

    -- A HiePath is just a lexical FastString. We use a lexical FastString to avoid
    -- non-determinism when printing or storing HieASTs which are sorted by their
    -- HiePath.
    type HiePath = LexicalFastString

    {-# COMPLETE HiePath #-}
    pattern HiePath :: FastString -> HiePath
    pattern HiePath fs = LexicalFastString fs

    -- | Mapping from filepaths to the corresponding AST
    newtype HieASTs a = HieASTs { getAsts :: M.Map HiePath (HieAST a) }
      deriving (Functor, Foldable, Traversable)

    instance Binary (HieASTs TypeIndex) where
      put_ bh asts = put_ bh $ M.toAscList $ getAsts asts
      get bh = HieASTs <$> fmap M.fromDistinctAscList (get bh)

    instance Outputable a => Outputable (HieASTs a) where
      ppr (HieASTs asts) = M.foldrWithKey go "" asts
        where
          go k a rest = vcat $
            [ "File: " O.<> ppr k
            , ppr a
            , rest
            ]

    data HieAST a =
      Node
        { sourcedNodeInfo :: SourcedNodeInfo a
        , nodeSpan :: Span
        , nodeChildren :: [HieAST a]
        } deriving (Functor, Foldable, Traversable)

    instance Binary (HieAST TypeIndex) where
      put_ bh ast = do
        put_ bh $ sourcedNodeInfo ast
        put_ bh $ nodeSpan ast
        put_ bh $ nodeChildren ast

      get bh = Node
        <$> get bh
        <*> get bh
        <*> get bh

    instance Outputable a => Outputable (HieAST a) where
      ppr (Node ni sp ch) = hang header 2 rest
        where
          header = text "Node@" O.<> ppr sp O.<> ":" <+> ppr ni
          rest = vcat (map ppr ch)

    -- | NodeInfos grouped by source
    newtype SourcedNodeInfo a = SourcedNodeInfo { getSourcedNodeInfo :: (M.Map NodeOrigin (NodeInfo a)) }
      deriving (Functor, Foldable, Traversable)

    instance Binary (SourcedNodeInfo TypeIndex) where
      put_ bh asts = put_ bh $ M.toAscList $ getSourcedNodeInfo asts
      get bh = SourcedNodeInfo <$> fmap M.fromDistinctAscList (get bh)

    instance Outputable a => Outputable (SourcedNodeInfo a) where
      ppr (SourcedNodeInfo asts) = M.foldrWithKey go "" asts
        where
          go k a rest = vcat $
            [ "Source: " O.<> ppr k
            , ppr a
            , rest
            ]

    -- | Source of node info
    data NodeOrigin
      = SourceInfo
      | GeneratedInfo
        deriving (Eq, Enum, Ord)

    instance Outputable NodeOrigin where
      ppr SourceInfo = text "From source"
      ppr GeneratedInfo = text "generated by ghc"

    instance Binary NodeOrigin where
      put_ bh b = putByte bh (fromIntegral (fromEnum b))
      get bh = do x <- getByte bh; pure $! (toEnum (fromIntegral x))

    -- | A node annotation
    data NodeAnnotation = NodeAnnotation
       { nodeAnnotConstr :: !FastString -- ^ name of the AST node constructor
       , nodeAnnotType   :: !FastString -- ^ name of the AST node Type
       }
       deriving (Eq)

    instance Ord NodeAnnotation where
       compare (NodeAnnotation c0 t0) (NodeAnnotation c1 t1)
          = mconcat [uniqCompareFS c0 c1, uniqCompareFS t0 t1]

    instance Outputable NodeAnnotation where
       ppr (NodeAnnotation c t) = ppr (c,t)

    instance Binary NodeAnnotation where
      put_ bh (NodeAnnotation c t) = do
        put_ bh c
        put_ bh t
      get bh = NodeAnnotation
        <$> get bh
        <*> get bh

    -- | The information stored in one AST node.
    --
    -- The type parameter exists to provide flexibility in representation of types
    -- (see Note [Efficient serialization of redundant type info]).
    data NodeInfo a = NodeInfo
        { nodeAnnotations :: S.Set NodeAnnotation
        -- ^ Annotations

        , nodeType :: [a]
        -- ^ The Haskell types of this node, if any.

        , nodeIdentifiers :: NodeIdentifiers a
        -- ^ All the identifiers and their details
        } deriving (Functor, Foldable, Traversable)

    instance Binary (NodeInfo TypeIndex) where
      put_ bh ni = do
        put_ bh $ S.toAscList $ nodeAnnotations ni
        put_ bh $ nodeType ni
        put_ bh $ M.toList $ nodeIdentifiers ni
      get bh = NodeInfo
        <$> fmap (S.fromDistinctAscList) (get bh)
        <*> get bh
        <*> fmap (M.fromList) (get bh)

    instance Outputable a => Outputable (NodeInfo a) where
      ppr (NodeInfo anns typs idents) = braces $ fsep $ punctuate ", "
        [ parens (text "annotations:" <+> ppr anns)
        , parens (text "types:" <+> ppr typs)
        , parens (text "identifier info:" <+> pprNodeIdents idents)
        ]

    pprNodeIdents :: Outputable a => NodeIdentifiers a -> SDoc
    pprNodeIdents ni = braces $ fsep $ punctuate ", " $ map go $ M.toList ni
      where
        go (i,id) = parens $ hsep $ punctuate ", " [pprIdentifier i, ppr id]

    pprIdentifier :: Identifier -> SDoc
    pprIdentifier (Left mod) = text "module" <+> ppr mod
    pprIdentifier (Right name) = text "name" <+> ppr name

    type Identifier = Either ModuleName Name

    type NodeIdentifiers a = M.Map Identifier (IdentifierDetails a)

    -- | Information associated with every identifier
    --
    -- We need to include types with identifiers because sometimes multiple
    -- identifiers occur in the same span(Overloaded Record Fields and so on)
    data IdentifierDetails a = IdentifierDetails
      { identType :: Maybe a
      , identInfo :: S.Set ContextInfo
      } deriving (Eq, Functor, Foldable, Traversable)

    instance Outputable a => Outputable (IdentifierDetails a) where
      ppr x = text "Details: " <+> ppr (identType x) <+> ppr (identInfo x)

    instance Semigroup (IdentifierDetails a) where
      d1 <> d2 = IdentifierDetails (identType d1 <|> identType d2)
                                   (S.union (identInfo d1) (identInfo d2))

    instance Monoid (IdentifierDetails a) where
      mempty = IdentifierDetails Nothing S.empty

    instance Binary (IdentifierDetails TypeIndex) where
      put_ bh dets = do
        put_ bh $ identType dets
        put_ bh $ S.toList $ identInfo dets
      get bh =  IdentifierDetails
        <$> get bh
        <*> fmap S.fromDistinctAscList (get bh)

    -- | Different contexts under which identifiers exist
    data ContextInfo
      = Use                -- ^ regular variable
      | MatchBind
      | IEThing IEType     -- ^ import/export
      | TyDecl

      -- | Value binding
      | ValBind
          BindType     -- ^ whether or not the binding is in an instance
          Scope        -- ^ scope over which the value is bound
          (Maybe Span) -- ^ span of entire binding

      -- | Pattern binding
      --
      -- This case is tricky because the bound identifier can be used in two
      -- distinct scopes. Consider the following example (with @-XViewPatterns@)
      --
      -- @
      -- do (b, a, (a -> True)) <- bar
      --    foo a
      -- @
      --
      -- The identifier @a@ has two scopes: in the view pattern @(a -> True)@ and
      -- in the rest of the @do@-block in @foo a@.
      | PatternBind
          Scope        -- ^ scope /in the pattern/ (the variable bound can be used
                       -- further in the pattern)
          Scope        -- ^ rest of the scope outside the pattern
          (Maybe Span) -- ^ span of entire binding

      | ClassTyDecl (Maybe Span)

      -- | Declaration
      | Decl
          DeclType     -- ^ type of declaration
          (Maybe Span) -- ^ span of entire binding

      -- | Type variable
      | TyVarBind Scope TyVarScope

      -- | Record field
      | RecField RecFieldContext (Maybe Span)
      -- | Constraint/Dictionary evidence variable binding
      | EvidenceVarBind
          EvVarSource  -- ^ how did this bind come into being
          Scope        -- ^ scope over which the value is bound
          (Maybe Span) -- ^ span of the binding site

      -- | Usage of evidence variable
      | EvidenceVarUse
        deriving (Eq, Ord)

    instance Outputable ContextInfo where
     ppr (Use) = text "usage"
     ppr (MatchBind) = text "LHS of a match group"
     ppr (IEThing x) = ppr x
     ppr (TyDecl) = text "bound in a type signature declaration"
     ppr (ValBind t sc sp) =
       ppr t <+> text "value bound with scope:" <+> ppr sc <+> pprBindSpan sp
     ppr (PatternBind sc1 sc2 sp) =
       text "bound in a pattern with scope:"
         <+> ppr sc1 <+> "," <+> ppr sc2
         <+> pprBindSpan sp
     ppr (ClassTyDecl sp) =
       text "bound in a class type declaration" <+> pprBindSpan sp
     ppr (Decl d sp) =
       text "declaration of" <+> ppr d <+> pprBindSpan sp
     ppr (TyVarBind sc1 sc2) =
       text "type variable binding with scope:"
         <+> ppr sc1 <+> "," <+> ppr sc2
     ppr (RecField ctx sp) =
       text "record field" <+> ppr ctx <+> pprBindSpan sp
     ppr (EvidenceVarBind ctx sc sp) =
       text "evidence variable" <+> ppr ctx
         $$ "with scope:" <+> ppr sc
         $$ pprBindSpan sp
     ppr (EvidenceVarUse) =
       text "usage of evidence variable"

    pprBindSpan :: Maybe Span -> SDoc
    pprBindSpan Nothing = text ""
    pprBindSpan (Just sp) = text "bound at:" <+> ppr sp

    instance Binary ContextInfo where
      put_ bh Use = putByte bh 0
      put_ bh (IEThing t) = do
        putByte bh 1
        put_ bh t
      put_ bh TyDecl = putByte bh 2
      put_ bh (ValBind bt sc msp) = do
        putByte bh 3
        put_ bh bt
        put_ bh sc
        put_ bh msp
      put_ bh (PatternBind a b c) = do
        putByte bh 4
        put_ bh a
        put_ bh b
        put_ bh c
      put_ bh (ClassTyDecl sp) = do
        putByte bh 5
        put_ bh sp
      put_ bh (Decl a b) = do
        putByte bh 6
        put_ bh a
        put_ bh b
      put_ bh (TyVarBind a b) = do
        putByte bh 7
        put_ bh a
        put_ bh b
      put_ bh (RecField a b) = do
        putByte bh 8
        put_ bh a
        put_ bh b
      put_ bh MatchBind = putByte bh 9
      put_ bh (EvidenceVarBind a b c) = do
        putByte bh 10
        put_ bh a
        put_ bh b
        put_ bh c
      put_ bh EvidenceVarUse = putByte bh 11

      get bh = do
        (t :: Word8) <- get bh
        case t of
          0 -> return Use
          1 -> IEThing <$> get bh
          2 -> return TyDecl
          3 -> ValBind <$> get bh <*> get bh <*> get bh
          4 -> PatternBind <$> get bh <*> get bh <*> get bh
          5 -> ClassTyDecl <$> get bh
          6 -> Decl <$> get bh <*> get bh
          7 -> TyVarBind <$> get bh <*> get bh
          8 -> RecField <$> get bh <*> get bh
          9 -> return MatchBind
          10 -> EvidenceVarBind <$> get bh <*> get bh <*> get bh
          11 -> return EvidenceVarUse
          _ -> panic "Binary ContextInfo: invalid tag"

    data EvVarSource
      = EvPatternBind -- ^ bound by a pattern match
      | EvSigBind -- ^ bound by a type signature
      | EvWrapperBind -- ^ bound by a hswrapper
      | EvImplicitBind -- ^ bound by an implicit variable
      | EvInstBind { isSuperInst :: Bool, cls :: Name } -- ^ Bound by some instance of given class
      | EvLetBind EvBindDeps -- ^ A direct let binding
      deriving (Eq,Ord)

    instance Binary EvVarSource where
      put_ bh EvPatternBind = putByte bh 0
      put_ bh EvSigBind = putByte bh 1
      put_ bh EvWrapperBind = putByte bh 2
      put_ bh EvImplicitBind = putByte bh 3
      put_ bh (EvInstBind b cls) = do
        putByte bh 4
        put_ bh b
        put_ bh cls
      put_ bh (EvLetBind deps) = do
        putByte bh 5
        put_ bh deps

      get bh = do
        (t :: Word8) <- get bh
        case t of
          0 -> pure EvPatternBind
          1 -> pure EvSigBind
          2 -> pure EvWrapperBind
          3 -> pure EvImplicitBind
          4 -> EvInstBind <$> get bh <*> get bh
          5 -> EvLetBind <$> get bh
          _ -> panic "Binary EvVarSource: invalid tag"

    instance Outputable EvVarSource where
      ppr EvPatternBind = text "bound by a pattern"
      ppr EvSigBind = text "bound by a type signature"
      ppr EvWrapperBind = text "bound by a HsWrapper"
      ppr EvImplicitBind = text "bound by an implicit variable binding"
      ppr (EvInstBind False cls) = text "bound by an instance of class" <+> ppr cls
      ppr (EvInstBind True cls) = text "bound due to a superclass of " <+> ppr cls
      ppr (EvLetBind deps) = text "bound by a let, depending on:" <+> ppr deps

    -- | Eq/Ord instances compare on the converted HieName,
    -- as non-exported names may have different uniques after
    -- a roundtrip
    newtype EvBindDeps = EvBindDeps { getEvBindDeps :: [Name] }
      deriving Outputable

    instance Eq EvBindDeps where
      (==) = coerce ((==) `on` map toHieName)

    instance Ord EvBindDeps where
      compare = coerce (compare `on` map toHieName)

    instance Binary EvBindDeps where
      put_ bh (EvBindDeps xs) = put_ bh xs
      get bh = EvBindDeps <$> get bh

    -- | Types of imports and exports
    data IEType
      = Import
      | ImportAs
      | ImportHiding
      | Export
        deriving (Eq, Enum, Ord)

    instance Outputable IEType where
      ppr Import = text "import"
      ppr ImportAs = text "import as"
      ppr ImportHiding = text "import hiding"
      ppr Export = text "export"

    instance Binary IEType where
      put_ bh b = putByte bh (fromIntegral (fromEnum b))
      get bh = do x <- getByte bh; pure $! (toEnum (fromIntegral x))

    data RecFieldContext
      = RecFieldDecl
      | RecFieldAssign
      | RecFieldMatch
      | RecFieldOcc
        deriving (Eq, Enum, Ord)

    instance Outputable RecFieldContext where
      ppr RecFieldDecl = text "declaration"
      ppr RecFieldAssign = text "assignment"
      ppr RecFieldMatch = text "pattern match"
      ppr RecFieldOcc = text "occurence"

    instance Binary RecFieldContext where
      put_ bh b = putByte bh (fromIntegral (fromEnum b))
      get bh = do x <- getByte bh; pure $! (toEnum (fromIntegral x))

    data BindType
      = RegularBind
      | InstanceBind
        deriving (Eq, Ord, Enum)

    instance Outputable BindType where
      ppr RegularBind = "regular"
      ppr InstanceBind = "instance"

    instance Binary BindType where
      put_ bh b = putByte bh (fromIntegral (fromEnum b))
      get bh = do x <- getByte bh; pure $! (toEnum (fromIntegral x))

    data DeclType
      = FamDec     -- ^ type or data family
      | SynDec     -- ^ type synonym
      | DataDec    -- ^ data declaration
      | ConDec     -- ^ constructor declaration
      | PatSynDec  -- ^ pattern synonym
      | ClassDec   -- ^ class declaration
      | InstDec    -- ^ instance declaration
        deriving (Eq, Ord, Enum)

    instance Outputable DeclType where
      ppr FamDec = text "type or data family"
      ppr SynDec = text "type synonym"
      ppr DataDec = text "data"
      ppr ConDec = text "constructor"
      ppr PatSynDec = text "pattern synonym"
      ppr ClassDec = text "class"
      ppr InstDec = text "instance"

    instance Binary DeclType where
      put_ bh b = putByte bh (fromIntegral (fromEnum b))
      get bh = do x <- getByte bh; pure $! (toEnum (fromIntegral x))

    data Scope
      = NoScope
      | LocalScope Span
      | ModuleScope
        deriving (Eq, Ord, Typeable, Data)

    instance Outputable Scope where
      ppr NoScope = text "NoScope"
      ppr (LocalScope sp) = text "LocalScope" <+> ppr sp
      ppr ModuleScope = text "ModuleScope"

    instance Binary Scope where
      put_ bh NoScope = putByte bh 0
      put_ bh (LocalScope span) = do
        putByte bh 1
        put_ bh span
      put_ bh ModuleScope = putByte bh 2

      get bh = do
        (t :: Word8) <- get bh
        case t of
          0 -> return NoScope
          1 -> LocalScope <$> get bh
          2 -> return ModuleScope
          _ -> panic "Binary Scope: invalid tag"

    -- | Scope of a type variable.
    --
    -- This warrants a data type apart from 'Scope' because of complexities
    -- introduced by features like @-XScopedTypeVariables@ and @-XInstanceSigs@. For
    -- example, consider:
    --
    -- @
    -- foo, bar, baz :: forall a. a -> a
    -- @
    --
    -- Here @a@ is in scope in all the definitions of @foo@, @bar@, and @baz@, so we
    -- need a list of scopes to keep track of this. Furthermore, this list cannot be
    -- computed until we resolve the binding sites of @foo@, @bar@, and @baz@.
    --
    -- Consequently, @a@ starts with an @'UnresolvedScope' [foo, bar, baz] Nothing@
    -- which later gets resolved into a 'ResolvedScopes'.
    data TyVarScope
      = ResolvedScopes [Scope]

      -- | Unresolved scopes should never show up in the final @.hie@ file
      | UnresolvedScope
            [Name]        -- ^ names of the definitions over which the scope spans
            (Maybe Span)  -- ^ the location of the instance/class declaration for
                          -- the case where the type variable is declared in a
                          -- method type signature
        deriving (Eq, Ord)

    instance Outputable TyVarScope where
      ppr (ResolvedScopes xs) =
        text "type variable scopes:" <+> hsep (punctuate ", " $ map ppr xs)
      ppr (UnresolvedScope ns sp) =
        text "unresolved type variable scope for name" O.<> plural ns
          <+> pprBindSpan sp

    instance Binary TyVarScope where
      put_ bh (ResolvedScopes xs) = do
        putByte bh 0
        put_ bh xs
      put_ bh (UnresolvedScope ns span) = do
        putByte bh 1
        put_ bh ns
        put_ bh span

      get bh = do
        (t :: Word8) <- get bh
        case t of
          0 -> ResolvedScopes <$> get bh
          1 -> UnresolvedScope <$> get bh <*> get bh
          _ -> panic "Binary TyVarScope: invalid tag"

    -- | `Name`'s get converted into `HieName`'s before being written into @.hie@
    -- files. See 'toHieName' and 'fromHieName' for logic on how to convert between
    -- these two types.
    data HieName
      = ExternalName !Module !OccName !SrcSpan
      | LocalName !OccName !SrcSpan
      | KnownKeyName !Unique
      deriving (Eq)

    instance Ord HieName where
      compare (ExternalName a b c) (ExternalName d e f) = compare (a,b) (d,e) `thenCmp` leftmost_smallest c f
        -- TODO (int-index): Perhaps use RealSrcSpan in HieName?
      compare (LocalName a b) (LocalName c d) = compare a c `thenCmp` leftmost_smallest b d
        -- TODO (int-index): Perhaps use RealSrcSpan in HieName?
      compare (KnownKeyName a) (KnownKeyName b) = nonDetCmpUnique a b
        -- Not actually non deterministic as it is a KnownKey
      compare ExternalName{} _ = LT
      compare LocalName{} ExternalName{} = GT
      compare LocalName{} _ = LT
      compare KnownKeyName{} _ = GT

    instance Outputable HieName where
      ppr (ExternalName m n sp) = text "ExternalName" <+> ppr m <+> ppr n <+> ppr sp
      ppr (LocalName n sp) = text "LocalName" <+> ppr n <+> ppr sp
      ppr (KnownKeyName u) = text "KnownKeyName" <+> ppr u

    hieNameOcc :: HieName -> OccName
    hieNameOcc (ExternalName _ occ _) = occ
    hieNameOcc (LocalName occ _) = occ
    hieNameOcc (KnownKeyName u) =
      case lookupKnownKeyName u of
        Just n -> nameOccName n
        Nothing -> pprPanic "hieNameOcc:unknown known-key unique"
                            (ppr (unpkUnique u))

    toHieName :: Name -> HieName
    toHieName name
      | isKnownKeyName name = KnownKeyName (nameUnique name)
      | isExternalName name = ExternalName (nameModule name)
                                           (nameOccName name)
                                           (nameSrcSpan name)
      | otherwise = LocalName (nameOccName name) (nameSrcSpan name)