basicTypes/Module.hs

    {-
    (c) The University of Glasgow, 2004-2006

    Module
    ~~~~~~~~~~
    Simply the name of a module, represented as a FastString.
    These are Uniquable, hence we can build Maps with Modules as
    the keys.
    -}

    {-# LANGUAGE RecordWildCards #-}
    {-# LANGUAGE MultiParamTypeClasses #-}

    module Module
        (
            -- * The ModuleName type
            ModuleName,
            pprModuleName,
            moduleNameFS,
            moduleNameString,
            moduleNameSlashes, moduleNameColons,
            moduleStableString,
            moduleFreeHoles,
            moduleIsDefinite,
            mkModuleName,
            mkModuleNameFS,
            stableModuleNameCmp,

            -- * The UnitId type
            ComponentId(..),
            UnitId(..),
            unitIdFS,
            unitIdKey,
            IndefUnitId(..),
            IndefModule(..),
            indefUnitIdToUnitId,
            indefModuleToModule,
            InstalledUnitId(..),
            toInstalledUnitId,
            ShHoleSubst,

            unitIdIsDefinite,
            unitIdString,
            unitIdFreeHoles,

            newUnitId,
            newIndefUnitId,
            newSimpleUnitId,
            hashUnitId,
            fsToUnitId,
            stringToUnitId,
            stableUnitIdCmp,

            -- * HOLE renaming
            renameHoleUnitId,
            renameHoleModule,
            renameHoleUnitId',
            renameHoleModule',

            -- * Generalization
            splitModuleInsts,
            splitUnitIdInsts,
            generalizeIndefUnitId,
            generalizeIndefModule,

            -- * Parsers
            parseModuleName,
            parseUnitId,
            parseComponentId,
            parseModuleId,
            parseModSubst,

            -- * Wired-in UnitIds
            -- $wired_in_packages
            primUnitId,
            integerUnitId,
            baseUnitId,
            rtsUnitId,
            thUnitId,
            dphSeqUnitId,
            dphParUnitId,
            mainUnitId,
            thisGhcUnitId,
            isHoleModule,
            interactiveUnitId, isInteractiveModule,
            wiredInUnitIds,

            -- * The Module type
            Module(Module),
            moduleUnitId, moduleName,
            pprModule,
            mkModule,
            mkHoleModule,
            stableModuleCmp,
            HasModule(..),
            ContainsModule(..),

            -- * Installed unit ids and modules
            InstalledModule(..),
            InstalledModuleEnv,
            installedModuleEq,
            installedUnitIdEq,
            installedUnitIdString,
            fsToInstalledUnitId,
            componentIdToInstalledUnitId,
            stringToInstalledUnitId,
            emptyInstalledModuleEnv,
            lookupInstalledModuleEnv,
            extendInstalledModuleEnv,
            filterInstalledModuleEnv,
            delInstalledModuleEnv,
            DefUnitId(..),

            -- * The ModuleLocation type
            ModLocation(..),
            addBootSuffix, addBootSuffix_maybe, addBootSuffixLocn,

            -- * Module mappings
            ModuleEnv,
            elemModuleEnv, extendModuleEnv, extendModuleEnvList,
            extendModuleEnvList_C, plusModuleEnv_C,
            delModuleEnvList, delModuleEnv, plusModuleEnv, lookupModuleEnv,
            lookupWithDefaultModuleEnv, mapModuleEnv, mkModuleEnv, emptyModuleEnv,
            moduleEnvKeys, moduleEnvElts, moduleEnvToList,
            unitModuleEnv, isEmptyModuleEnv,
            extendModuleEnvWith, filterModuleEnv,

            -- * ModuleName mappings
            ModuleNameEnv, DModuleNameEnv,

            -- * Sets of Modules
            ModuleSet,
            emptyModuleSet, mkModuleSet, moduleSetElts, extendModuleSet, elemModuleSet
        ) where

    import Config
    import Outputable
    import Unique
    import UniqFM
    import UniqDFM
    import UniqDSet
    import FastString
    import Binary
    import Util
    import Data.List
    import Data.Ord
    import GHC.PackageDb (BinaryStringRep(..), DbUnitIdModuleRep(..), DbModule(..), DbUnitId(..))

    import qualified Data.ByteString as BS
    import qualified Data.ByteString.Unsafe as BS
    import qualified Data.ByteString.Char8 as BS.Char8
    import System.IO.Unsafe
    import Foreign.Ptr (castPtr)
    import GHC.Fingerprint
    import Encoding

    import qualified Text.ParserCombinators.ReadP as Parse
    import Text.ParserCombinators.ReadP (ReadP, (<++))
    import Data.Char (isAlphaNum)
    import Control.DeepSeq
    import Data.Coerce
    import Data.Data
    import Data.Function
    import Data.Map (Map)
    import Data.Set (Set)
    import qualified Data.Map as Map
    import qualified Data.Set as Set
    import qualified FiniteMap as Map
    import System.FilePath

    import {-# SOURCE #-} DynFlags (DynFlags)
    import {-# SOURCE #-} Packages (componentIdString, improveUnitId, PackageConfigMap, getPackageConfigMap, displayInstalledUnitId)

    -- Note [The identifier lexicon]
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    -- Unit IDs, installed package IDs, ABI hashes, package names,
    -- versions, there are a *lot* of different identifiers for closely
    -- related things.  What do they all mean? Here's what.  (See also
    -- https://ghc.haskell.org/trac/ghc/wiki/Commentary/Packages/Concepts )
    --
    -- THE IMPORTANT ONES
    --
    -- ComponentId: An opaque identifier provided by Cabal, which should
    -- uniquely identify such things as the package name, the package
    -- version, the name of the component, the hash of the source code
    -- tarball, the selected Cabal flags, GHC flags, direct dependencies of
    -- the component.  These are very similar to InstalledPackageId, but
    -- an 'InstalledPackageId' implies that it identifies a package, while
    -- a package may install multiple components with different
    -- 'ComponentId's.
    --      - Same as Distribution.Package.ComponentId
    --
    -- UnitId/InstalledUnitId: A ComponentId + a mapping from hole names
    -- (ModuleName) to Modules.  This is how the compiler identifies instantiated
    -- components, and also is the main identifier by which GHC identifies things.
    --      - When Backpack is not being used, UnitId = ComponentId.
    --        this means a useful fiction for end-users is that there are
    --        only ever ComponentIds, and some ComponentIds happen to have
    --        more information (UnitIds).
    --      - Same as Language.Haskell.TH.Syntax:PkgName, see
    --          https://ghc.haskell.org/trac/ghc/ticket/10279
    --      - The same as PackageKey in GHC 7.10 (we renamed it because
    --        they don't necessarily identify packages anymore.)
    --      - Same as -this-package-key/-package-name flags
    --      - An InstalledUnitId corresponds to an actual package which
    --        we have installed on disk.  It could be definite or indefinite,
    --        but if it's indefinite, it has nothing instantiated (we
    --        never install partially instantiated units.)
    --
    -- Module/InstalledModule: A UnitId/InstalledUnitId + ModuleName. This is how
    -- the compiler identifies modules (e.g. a Name is a Module + OccName)
    --      - Same as Language.Haskell.TH.Syntax:Module
    --
    -- THE LESS IMPORTANT ONES
    --
    -- PackageName: The "name" field in a Cabal file, something like "lens".
    --      - Same as Distribution.Package.PackageName
    --      - DIFFERENT FROM Language.Haskell.TH.Syntax:PkgName, see
    --          https://ghc.haskell.org/trac/ghc/ticket/10279
    --      - DIFFERENT FROM -package-name flag
    --      - DIFFERENT FROM the 'name' field in an installed package
    --        information.  This field could more accurately be described
    --        as a munged package name: when it's for the main library
    --        it is the same as the package name, but if it's an internal
    --        library it's a munged combination of the package name and
    --        the component name.
    --
    -- LEGACY ONES
    --
    -- InstalledPackageId: This is what we used to call ComponentId.
    -- It's a still pretty useful concept for packages that have only
    -- one library; in that case the logical InstalledPackageId =
    -- ComponentId.  Also, the Cabal nix-local-build continues to
    -- compute an InstalledPackageId which is then forcibly used
    -- for all components in a package.  This means that if a dependency
    -- from one component in a package changes, the InstalledPackageId
    -- changes: you don't get as fine-grained dependency tracking,
    -- but it means your builds are hermetic.  Eventually, Cabal will
    -- deal completely in components and we can get rid of this.
    --
    -- PackageKey: This is what we used to call UnitId.  We ditched
    -- "Package" from the name when we realized that you might want to
    -- assign different "PackageKeys" to components from the same package.
    -- (For a brief, non-released period of time, we also called these
    -- UnitKeys).

    {-
    ************************************************************************
    *                                                                      *
    \subsection{Module locations}
    *                                                                      *
    ************************************************************************
    -}

    -- | Module Location
    --
    -- Where a module lives on the file system: the actual locations
    -- of the .hs, .hi and .o files, if we have them
    data ModLocation
       = ModLocation {
            ml_hs_file   :: Maybe FilePath,
                    -- The source file, if we have one.  Package modules
                    -- probably don't have source files.

            ml_hi_file   :: FilePath,
                    -- Where the .hi file is, whether or not it exists
                    -- yet.  Always of form foo.hi, even if there is an
                    -- hi-boot file (we add the -boot suffix later)

            ml_obj_file  :: FilePath
                    -- Where the .o file is, whether or not it exists yet.
                    -- (might not exist either because the module hasn't
                    -- been compiled yet, or because it is part of a
                    -- package with a .a file)
      } deriving Show

    instance Outputable ModLocation where
       ppr = text . show

    {-
    For a module in another package, the hs_file and obj_file
    components of ModLocation are undefined.

    The locations specified by a ModLocation may or may not
    correspond to actual files yet: for example, even if the object
    file doesn't exist, the ModLocation still contains the path to
    where the object file will reside if/when it is created.
    -}

    addBootSuffix :: FilePath -> FilePath
    -- ^ Add the @-boot@ suffix to .hs, .hi and .o files
    addBootSuffix path = path ++ "-boot"

    addBootSuffix_maybe :: Bool -> FilePath -> FilePath
    -- ^ Add the @-boot@ suffix if the @Bool@ argument is @True@
    addBootSuffix_maybe is_boot path
     | is_boot   = addBootSuffix path
     | otherwise = path

    addBootSuffixLocn :: ModLocation -> ModLocation
    -- ^ Add the @-boot@ suffix to all file paths associated with the module
    addBootSuffixLocn locn
      = locn { ml_hs_file  = fmap addBootSuffix (ml_hs_file locn)
             , ml_hi_file  = addBootSuffix (ml_hi_file locn)
             , ml_obj_file = addBootSuffix (ml_obj_file locn) }

    {-
    ************************************************************************
    *                                                                      *
    \subsection{The name of a module}
    *                                                                      *
    ************************************************************************
    -}

    -- | A ModuleName is essentially a simple string, e.g. @Data.List@.
    newtype ModuleName = ModuleName FastString

    instance Uniquable ModuleName where
      getUnique (ModuleName nm) = getUnique nm

    instance Eq ModuleName where
      nm1 == nm2 = getUnique nm1 == getUnique nm2

    instance Ord ModuleName where
      nm1 `compare` nm2 = stableModuleNameCmp nm1 nm2

    instance Outputable ModuleName where
      ppr = pprModuleName

    instance Binary ModuleName where
      put_ bh (ModuleName fs) = put_ bh fs
      get bh = do fs <- get bh; return (ModuleName fs)

    instance BinaryStringRep ModuleName where
      fromStringRep = mkModuleNameFS . mkFastStringByteString
      toStringRep   = fastStringToByteString . moduleNameFS

    instance Data ModuleName where
      -- don't traverse?
      toConstr _   = abstractConstr "ModuleName"
      gunfold _ _  = error "gunfold"
      dataTypeOf _ = mkNoRepType "ModuleName"

    instance NFData ModuleName where
      rnf x = x `seq` ()

    stableModuleNameCmp :: ModuleName -> ModuleName -> Ordering
    -- ^ Compares module names lexically, rather than by their 'Unique's
    stableModuleNameCmp n1 n2 = moduleNameFS n1 `compare` moduleNameFS n2

    pprModuleName :: ModuleName -> SDoc
    pprModuleName (ModuleName nm) =
        getPprStyle $ \ sty ->
        if codeStyle sty
            then ztext (zEncodeFS nm)
            else ftext nm

    moduleNameFS :: ModuleName -> FastString
    moduleNameFS (ModuleName mod) = mod

    moduleNameString :: ModuleName -> String
    moduleNameString (ModuleName mod) = unpackFS mod

    -- | Get a string representation of a 'Module' that's unique and stable
    -- across recompilations.
    -- eg. "$aeson_70dylHtv1FFGeai1IoxcQr$Data.Aeson.Types.Internal"
    moduleStableString :: Module -> String
    moduleStableString Module{..} =
      "$" ++ unitIdString moduleUnitId ++ "$" ++ moduleNameString moduleName

    mkModuleName :: String -> ModuleName
    mkModuleName s = ModuleName (mkFastString s)

    mkModuleNameFS :: FastString -> ModuleName
    mkModuleNameFS s = ModuleName s

    -- |Returns the string version of the module name, with dots replaced by slashes.
    --
    moduleNameSlashes :: ModuleName -> String
    moduleNameSlashes = dots_to_slashes . moduleNameString
      where dots_to_slashes = map (\c -> if c == '.' then pathSeparator else c)

    -- |Returns the string version of the module name, with dots replaced by colons.
    --
    moduleNameColons :: ModuleName -> String
    moduleNameColons = dots_to_colons . moduleNameString
      where dots_to_colons = map (\c -> if c == '.' then ':' else c)

    {-
    ************************************************************************
    *                                                                      *
    \subsection{A fully qualified module}
    *                                                                      *
    ************************************************************************
    -}

    -- | A Module is a pair of a 'UnitId' and a 'ModuleName'.
    --
    -- Module variables (i.e. @<H>@) which can be instantiated to a
    -- specific module at some later point in time are represented
    -- with 'moduleUnitId' set to 'holeUnitId' (this allows us to
    -- avoid having to make 'moduleUnitId' a partial operation.)
    --
    data Module = Module {
       moduleUnitId :: !UnitId,  -- pkg-1.0
       moduleName :: !ModuleName  -- A.B.C
      }
      deriving (Eq, Ord)

    -- | Calculate the free holes of a 'Module'.  If this set is non-empty,
    -- this module was defined in an indefinite library that had required
    -- signatures.
    --
    -- If a module has free holes, that means that substitutions can operate on it;
    -- if it has no free holes, substituting over a module has no effect.
    moduleFreeHoles :: Module -> UniqDSet ModuleName
    moduleFreeHoles m
        | isHoleModule m = unitUniqDSet (moduleName m)
        | otherwise = unitIdFreeHoles (moduleUnitId m)

    -- | A 'Module' is definite if it has no free holes.
    moduleIsDefinite :: Module -> Bool
    moduleIsDefinite = isEmptyUniqDSet . moduleFreeHoles

    -- | Create a module variable at some 'ModuleName'.
    -- See Note [Representation of module/name variables]
    mkHoleModule :: ModuleName -> Module
    mkHoleModule = mkModule holeUnitId

    instance Uniquable Module where
      getUnique (Module p n) = getUnique (unitIdFS p `appendFS` moduleNameFS n)

    instance Outputable Module where
      ppr = pprModule

    instance Binary Module where
      put_ bh (Module p n) = put_ bh p >> put_ bh n
      get bh = do p <- get bh; n <- get bh; return (Module p n)

    instance Data Module where
      -- don't traverse?
      toConstr _   = abstractConstr "Module"
      gunfold _ _  = error "gunfold"
      dataTypeOf _ = mkNoRepType "Module"

    instance NFData Module where
      rnf x = x `seq` ()

    -- | This gives a stable ordering, as opposed to the Ord instance which
    -- gives an ordering based on the 'Unique's of the components, which may
    -- not be stable from run to run of the compiler.
    stableModuleCmp :: Module -> Module -> Ordering
    stableModuleCmp (Module p1 n1) (Module p2 n2)
       = (p1 `stableUnitIdCmp`  p2) `thenCmp`
         (n1 `stableModuleNameCmp` n2)

    mkModule :: UnitId -> ModuleName -> Module
    mkModule = Module

    pprModule :: Module -> SDoc
    pprModule mod@(Module p n)  = getPprStyle doc
     where
      doc sty
        | codeStyle sty =
            (if p == mainUnitId
                    then empty -- never qualify the main package in code
                    else ztext (zEncodeFS (unitIdFS p)) <> char '_')
                <> pprModuleName n
        | qualModule sty mod =
            if isHoleModule mod
                then angleBrackets (pprModuleName n)
                else ppr (moduleUnitId mod) <> char ':' <> pprModuleName n
        | otherwise =
            pprModuleName n

    class ContainsModule t where
        extractModule :: t -> Module

    class HasModule m where
        getModule :: m Module

    instance DbUnitIdModuleRep InstalledUnitId ComponentId UnitId ModuleName Module where
      fromDbModule (DbModule uid mod_name)  = mkModule uid mod_name
      fromDbModule (DbModuleVar mod_name)   = mkHoleModule mod_name
      fromDbUnitId (DbUnitId cid insts)     = newUnitId cid insts
      fromDbUnitId (DbInstalledUnitId iuid) = DefiniteUnitId (DefUnitId iuid)
      -- GHC never writes to the database, so it's not needed
      toDbModule = error "toDbModule: not implemented"
      toDbUnitId = error "toDbUnitId: not implemented"

    {-
    ************************************************************************
    *                                                                      *
    \subsection{ComponentId}
    *                                                                      *
    ************************************************************************
    -}

    -- | A 'ComponentId' consists of the package name, package version, component
    -- ID, the transitive dependencies of the component, and other information to
    -- uniquely identify the source code and build configuration of a component.
    --
    -- This used to be known as an 'InstalledPackageId', but a package can contain
    -- multiple components and a 'ComponentId' uniquely identifies a component
    -- within a package.  When a package only has one component, the 'ComponentId'
    -- coincides with the 'InstalledPackageId'
    newtype ComponentId        = ComponentId        FastString deriving (Eq, Ord)

    instance BinaryStringRep ComponentId where
      fromStringRep = ComponentId . mkFastStringByteString
      toStringRep (ComponentId s) = fastStringToByteString s

    instance Uniquable ComponentId where
      getUnique (ComponentId n) = getUnique n

    instance Outputable ComponentId where
      ppr cid@(ComponentId fs) =
        getPprStyle $ \sty ->
        sdocWithDynFlags $ \dflags ->
          case componentIdString dflags cid of
            Just str | not (debugStyle sty) -> text str
            _ -> ftext fs

    {-
    ************************************************************************
    *                                                                      *
    \subsection{UnitId}
    *                                                                      *
    ************************************************************************
    -}

    -- | A unit identifier identifies a (possibly partially) instantiated
    -- library.  It is primarily used as part of 'Module', which in turn
    -- is used in 'Name', which is used to give names to entities when
    -- typechecking.
    --
    -- There are two possible forms for a 'UnitId'.  It can be a
    -- 'DefiniteUnitId', in which case we just have a string that uniquely
    -- identifies some fully compiled, installed library we have on disk.
    -- However, when we are typechecking a library with missing holes,
    -- we may need to instantiate a library on the fly (in which case
    -- we don't have any on-disk representation.)  In that case, you
    -- have an 'IndefiniteUnitId', which explicitly records the
    -- instantiation, so that we can substitute over it.
    data UnitId
        = IndefiniteUnitId {-# UNPACK #-} !IndefUnitId
        |   DefiniteUnitId {-# UNPACK #-} !DefUnitId
        deriving (Typeable)

    unitIdFS :: UnitId -> FastString
    unitIdFS (IndefiniteUnitId x) = indefUnitIdFS x
    unitIdFS (DefiniteUnitId (DefUnitId x)) = installedUnitIdFS x

    unitIdKey :: UnitId -> Unique
    unitIdKey (IndefiniteUnitId x) = indefUnitIdKey x
    unitIdKey (DefiniteUnitId (DefUnitId x)) = installedUnitIdKey x

    -- | A unit identifier which identifies an indefinite
    -- library (with holes) that has been *on-the-fly* instantiated
    -- with a substitution 'indefUnitIdInsts'.  In fact, an indefinite
    -- unit identifier could have no holes, but we haven't gotten
    -- around to compiling the actual library yet.
    --
    -- An indefinite unit identifier pretty-prints to something like
    -- @p[H=<H>,A=aimpl:A>]@ (@p@ is the 'ComponentId', and the
    -- brackets enclose the module substitution).
    data IndefUnitId
        = IndefUnitId {
            -- | A private, uniquely identifying representation of
            -- a UnitId.  This string is completely private to GHC
            -- and is just used to get a unique; in particular, we don't use it for
            -- symbols (indefinite libraries are not compiled).
            indefUnitIdFS :: FastString,
            -- | Cached unique of 'unitIdFS'.
            indefUnitIdKey :: Unique,
            -- | The component identity of the indefinite library that
            -- is being instantiated.
            indefUnitIdComponentId :: !ComponentId,
            -- | The sorted (by 'ModuleName') instantiations of this library.
            indefUnitIdInsts :: ![(ModuleName, Module)],
            -- | A cache of the free module variables of 'unitIdInsts'.
            -- This lets us efficiently tell if a 'UnitId' has been
            -- fully instantiated (free module variables are empty)
            -- and whether or not a substitution can have any effect.
            indefUnitIdFreeHoles :: UniqDSet ModuleName
        } deriving (Typeable)

    instance Eq IndefUnitId where
      u1 == u2 = indefUnitIdKey u1 == indefUnitIdKey u2

    instance Ord IndefUnitId where
      u1 `compare` u2 = indefUnitIdFS u1 `compare` indefUnitIdFS u2

    instance Binary IndefUnitId where
      put_ bh indef = do
        put_ bh (indefUnitIdComponentId indef)
        put_ bh (indefUnitIdInsts indef)
      get bh = do
        cid   <- get bh
        insts <- get bh
        let fs = hashUnitId cid insts
        return IndefUnitId {
                indefUnitIdComponentId = cid,
                indefUnitIdInsts = insts,
                indefUnitIdFreeHoles = unionManyUniqDSets (map (moduleFreeHoles.snd) insts),
                indefUnitIdFS = fs,
                indefUnitIdKey = getUnique fs
               }

    -- | Create a new 'IndefUnitId' given an explicit module substitution.
    newIndefUnitId :: ComponentId -> [(ModuleName, Module)] -> IndefUnitId
    newIndefUnitId cid insts =
        IndefUnitId {
            indefUnitIdComponentId = cid,
            indefUnitIdInsts = sorted_insts,
            indefUnitIdFreeHoles = unionManyUniqDSets (map (moduleFreeHoles.snd) insts),
            indefUnitIdFS = fs,
            indefUnitIdKey = getUnique fs
        }
      where
         fs = hashUnitId cid sorted_insts
         sorted_insts = sortBy (stableModuleNameCmp `on` fst) insts

    -- | Injects an 'IndefUnitId' (indefinite library which
    -- was on-the-fly instantiated) to a 'UnitId' (either
    -- an indefinite or definite library).
    indefUnitIdToUnitId :: DynFlags -> IndefUnitId -> UnitId
    indefUnitIdToUnitId dflags iuid =
        -- NB: suppose that we want to compare the indefinite
        -- unit id p[H=impl:H] against p+abcd (where p+abcd
        -- happens to be the existing, installed version of
        -- p[H=impl:H].  If we *only* wrap in p[H=impl:H]
        -- IndefiniteUnitId, they won't compare equal; only
        -- after improvement will the equality hold.
        improveUnitId (getPackageConfigMap dflags) $
            IndefiniteUnitId iuid

    data IndefModule = IndefModule {
            indefModuleUnitId :: IndefUnitId,
            indefModuleName   :: ModuleName
        } deriving (Typeable, Eq, Ord)

    instance Outputable IndefModule where
      ppr (IndefModule uid m) =
        ppr uid <> char ':' <> ppr m

    -- | Injects an 'IndefModule' to 'Module' (see also
    -- 'indefUnitIdToUnitId'.
    indefModuleToModule :: DynFlags -> IndefModule -> Module
    indefModuleToModule dflags (IndefModule iuid mod_name) =
        mkModule (indefUnitIdToUnitId dflags iuid) mod_name

    -- | An installed unit identifier identifies a library which has
    -- been installed to the package database.  These strings are
    -- provided to us via the @-this-unit-id@ flag.  The library
    -- in question may be definite or indefinite; if it is indefinite,
    -- none of the holes have been filled (we never install partially
    -- instantiated libraries.)  Put another way, an installed unit id
    -- is either fully instantiated, or not instantiated at all.
    --
    -- Installed unit identifiers look something like @p+af23SAj2dZ219@,
    -- or maybe just @p@ if they don't use Backpack.
    newtype InstalledUnitId =
        InstalledUnitId {
          -- | The full hashed unit identifier, including the component id
          -- and the hash.
          installedUnitIdFS :: FastString
        }
       deriving (Typeable)

    instance Binary InstalledUnitId where
      put_ bh (InstalledUnitId fs) = put_ bh fs
      get bh = do fs <- get bh; return (InstalledUnitId fs)

    instance BinaryStringRep InstalledUnitId where
      fromStringRep bs = InstalledUnitId (mkFastStringByteString bs)
      -- GHC doesn't write to database
      toStringRep   = error "BinaryStringRep InstalledUnitId: not implemented"

    instance Eq InstalledUnitId where
        uid1 == uid2 = installedUnitIdKey uid1 == installedUnitIdKey uid2

    instance Ord InstalledUnitId where
        u1 `compare` u2 = installedUnitIdFS u1 `compare` installedUnitIdFS u2

    instance Uniquable InstalledUnitId where
        getUnique = installedUnitIdKey

    instance Outputable InstalledUnitId where
        ppr uid@(InstalledUnitId fs) =
            getPprStyle $ \sty ->
            sdocWithDynFlags $ \dflags ->
              case displayInstalledUnitId dflags uid of
                Just str | not (debugStyle sty) -> text str
                _ -> ftext fs

    installedUnitIdKey :: InstalledUnitId -> Unique
    installedUnitIdKey = getUnique . installedUnitIdFS

    -- | Lossy conversion to the on-disk 'InstalledUnitId' for a component.
    toInstalledUnitId :: UnitId -> InstalledUnitId
    toInstalledUnitId (DefiniteUnitId (DefUnitId iuid)) = iuid
    toInstalledUnitId (IndefiniteUnitId indef) =
        componentIdToInstalledUnitId (indefUnitIdComponentId indef)

    installedUnitIdString :: InstalledUnitId -> String
    installedUnitIdString = unpackFS . installedUnitIdFS

    instance Outputable IndefUnitId where
        ppr uid =
          -- getPprStyle $ \sty ->
          ppr cid <>
            (if not (null insts) -- pprIf
              then
                brackets (hcat
                    (punctuate comma $
                        [ ppr modname <> text "=" <> ppr m
                        | (modname, m) <- insts]))
              else empty)
         where
          cid   = indefUnitIdComponentId uid
          insts = indefUnitIdInsts uid

    -- | A 'InstalledModule' is a 'Module' which contains a 'InstalledUnitId'.
    data InstalledModule = InstalledModule {
       installedModuleUnitId :: !InstalledUnitId,
       installedModuleName :: !ModuleName
      }
      deriving (Eq, Ord)

    instance Outputable InstalledModule where
      ppr (InstalledModule p n) =
        ppr p <> char ':' <> pprModuleName n

    fsToInstalledUnitId :: FastString -> InstalledUnitId
    fsToInstalledUnitId fs = InstalledUnitId fs

    componentIdToInstalledUnitId :: ComponentId -> InstalledUnitId
    componentIdToInstalledUnitId (ComponentId fs) = fsToInstalledUnitId fs

    stringToInstalledUnitId :: String -> InstalledUnitId
    stringToInstalledUnitId = fsToInstalledUnitId . mkFastString

    -- | Test if a 'Module' corresponds to a given 'InstalledModule',
    -- modulo instantiation.
    installedModuleEq :: InstalledModule -> Module -> Bool
    installedModuleEq imod mod =
        fst (splitModuleInsts mod) == imod

    -- | Test if a 'UnitId' corresponds to a given 'InstalledUnitId',
    -- modulo instantiation.
    installedUnitIdEq :: InstalledUnitId -> UnitId -> Bool
    installedUnitIdEq iuid uid =
        fst (splitUnitIdInsts uid) == iuid

    -- | A 'DefUnitId' is an 'InstalledUnitId' with the invariant that
    -- it only refers to a definite library; i.e., one we have generated
    -- code for.
    newtype DefUnitId = DefUnitId { unDefUnitId :: InstalledUnitId }
        deriving (Eq, Ord, Typeable)

    instance Outputable DefUnitId where
        ppr (DefUnitId uid) = ppr uid

    instance Binary DefUnitId where
        put_ bh (DefUnitId uid) = put_ bh uid
        get bh = do uid <- get bh; return (DefUnitId uid)

    -- | A map keyed off of 'InstalledModule'
    newtype InstalledModuleEnv elt = InstalledModuleEnv (Map InstalledModule elt)

    emptyInstalledModuleEnv :: InstalledModuleEnv a
    emptyInstalledModuleEnv = InstalledModuleEnv Map.empty

    lookupInstalledModuleEnv :: InstalledModuleEnv a -> InstalledModule -> Maybe a
    lookupInstalledModuleEnv (InstalledModuleEnv e) m = Map.lookup m e

    extendInstalledModuleEnv :: InstalledModuleEnv a -> InstalledModule -> a -> InstalledModuleEnv a
    extendInstalledModuleEnv (InstalledModuleEnv e) m x = InstalledModuleEnv (Map.insert m x e)

    filterInstalledModuleEnv :: (InstalledModule -> a -> Bool) -> InstalledModuleEnv a -> InstalledModuleEnv a
    filterInstalledModuleEnv f (InstalledModuleEnv e) =
      InstalledModuleEnv (Map.filterWithKey f e)

    delInstalledModuleEnv :: InstalledModuleEnv a -> InstalledModule -> InstalledModuleEnv a
    delInstalledModuleEnv (InstalledModuleEnv e) m = InstalledModuleEnv (Map.delete m e)

    -- Note [UnitId to InstalledUnitId improvement]
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    -- Just because a UnitId is definite (has no holes) doesn't
    -- mean it's necessarily a InstalledUnitId; it could just be
    -- that over the course of renaming UnitIds on the fly
    -- while typechecking an indefinite library, we
    -- ended up with a fully instantiated unit id with no hash,
    -- since we haven't built it yet.  This is fine.
    --
    -- However, if there is a hashed unit id for this instantiation
    -- in the package database, we *better use it*, because
    -- that hashed unit id may be lurking in another interface,
    -- and chaos will ensue if we attempt to compare the two
    -- (the unitIdFS for a UnitId never corresponds to a Cabal-provided
    -- hash of a compiled instantiated library).
    --
    -- There is one last niggle: improvement based on the package database means
    -- that we might end up developing on a package that is not transitively
    -- depended upon by the packages the user specified directly via command line
    -- flags.  This could lead to strange and difficult to understand bugs if those
    -- instantiations are out of date.  The solution is to only improve a
    -- unit id if the new unit id is part of the 'preloadClosure'; i.e., the
    -- closure of all the packages which were explicitly specified.

    -- | Retrieve the set of free holes of a 'UnitId'.
    unitIdFreeHoles :: UnitId -> UniqDSet ModuleName
    unitIdFreeHoles (IndefiniteUnitId x) = indefUnitIdFreeHoles x
    -- Hashed unit ids are always fully instantiated
    unitIdFreeHoles (DefiniteUnitId _) = emptyUniqDSet

    instance Show UnitId where
        show = unitIdString

    -- | A 'UnitId' is definite if it has no free holes.
    unitIdIsDefinite :: UnitId -> Bool
    unitIdIsDefinite = isEmptyUniqDSet . unitIdFreeHoles

    -- | Generate a uniquely identifying 'FastString' for a unit
    -- identifier.  This is a one-way function.  You can rely on one special
    -- property: if a unit identifier is in most general form, its 'FastString'
    -- coincides with its 'ComponentId'.  This hash is completely internal
    -- to GHC and is not used for symbol names or file paths.
    hashUnitId :: ComponentId -> [(ModuleName, Module)] -> FastString
    hashUnitId cid sorted_holes =
        mkFastStringByteString
      . fingerprintUnitId (toStringRep cid)
      $ rawHashUnitId sorted_holes

    -- | Generate a hash for a sorted module substitution.
    rawHashUnitId :: [(ModuleName, Module)] -> Fingerprint
    rawHashUnitId sorted_holes =
        fingerprintByteString
      . BS.concat $ do
            (m, b) <- sorted_holes
            [ toStringRep m,                BS.Char8.singleton ' ',
              fastStringToByteString (unitIdFS (moduleUnitId b)), BS.Char8.singleton ':',
              toStringRep (moduleName b),   BS.Char8.singleton '\n']

    fingerprintByteString :: BS.ByteString -> Fingerprint
    fingerprintByteString bs = unsafePerformIO
                             . BS.unsafeUseAsCStringLen bs
                             $ \(p,l) -> fingerprintData (castPtr p) l

    fingerprintUnitId :: BS.ByteString -> Fingerprint -> BS.ByteString
    fingerprintUnitId prefix (Fingerprint a b)
        = BS.concat
        $ [ prefix
          , BS.Char8.singleton '-'
          , BS.Char8.pack (toBase62Padded a)
          , BS.Char8.pack (toBase62Padded b) ]

    -- | Create a new, un-hashed unit identifier.
    newUnitId :: ComponentId -> [(ModuleName, Module)] -> UnitId
    newUnitId cid [] = newSimpleUnitId cid -- TODO: this indicates some latent bug...
    newUnitId cid insts = IndefiniteUnitId $ newIndefUnitId cid insts

    pprUnitId :: UnitId -> SDoc
    pprUnitId (DefiniteUnitId uid) = ppr uid
    pprUnitId (IndefiniteUnitId uid) = ppr uid

    instance Eq UnitId where
      uid1 == uid2 = unitIdKey uid1 == unitIdKey uid2

    instance Uniquable UnitId where
      getUnique = unitIdKey

    instance Ord UnitId where
      nm1 `compare` nm2 = stableUnitIdCmp nm1 nm2

    instance Data UnitId where
      -- don't traverse?
      toConstr _   = abstractConstr "UnitId"
      gunfold _ _  = error "gunfold"
      dataTypeOf _ = mkNoRepType "UnitId"

    instance NFData UnitId where
      rnf x = x `seq` ()

    stableUnitIdCmp :: UnitId -> UnitId -> Ordering
    -- ^ Compares package ids lexically, rather than by their 'Unique's
    stableUnitIdCmp p1 p2 = unitIdFS p1 `compare` unitIdFS p2

    instance Outputable UnitId where
       ppr pk = pprUnitId pk

    -- Performance: would prefer to have a NameCache like thing
    instance Binary UnitId where
      put_ bh (DefiniteUnitId def_uid) = do
        putByte bh 0
        put_ bh def_uid
      put_ bh (IndefiniteUnitId indef_uid) = do
        putByte bh 1
        put_ bh indef_uid
      get bh = do b <- getByte bh
                  case b of
                    0 -> fmap DefiniteUnitId   (get bh)
                    _ -> fmap IndefiniteUnitId (get bh)

    instance Binary ComponentId where
      put_ bh (ComponentId fs) = put_ bh fs
      get bh = do { fs <- get bh; return (ComponentId fs) }

    -- | Create a new simple unit identifier (no holes) from a 'ComponentId'.
    newSimpleUnitId :: ComponentId -> UnitId
    newSimpleUnitId (ComponentId fs) = fsToUnitId fs

    -- | Create a new simple unit identifier from a 'FastString'.  Internally,
    -- this is primarily used to specify wired-in unit identifiers.
    fsToUnitId :: FastString -> UnitId
    fsToUnitId = DefiniteUnitId . DefUnitId . InstalledUnitId

    stringToUnitId :: String -> UnitId
    stringToUnitId = fsToUnitId . mkFastString

    unitIdString :: UnitId -> String
    unitIdString = unpackFS . unitIdFS

    {-
    ************************************************************************
    *                                                                      *
                            Hole substitutions
    *                                                                      *
    ************************************************************************
    -}

    -- | Substitution on module variables, mapping module names to module
    -- identifiers.
    type ShHoleSubst = ModuleNameEnv Module

    -- | Substitutes holes in a 'Module'.  NOT suitable for being called
    -- directly on a 'nameModule', see Note [Representation of module/name variable].
    -- @p[A=<A>]:B@ maps to @p[A=q():A]:B@ with @A=q():A@;
    -- similarly, @<A>@ maps to @q():A@.
    renameHoleModule :: DynFlags -> ShHoleSubst -> Module -> Module
    renameHoleModule dflags = renameHoleModule' (getPackageConfigMap dflags)

    -- | Substitutes holes in a 'UnitId', suitable for renaming when
    -- an include occurs; see Note [Representation of module/name variable].
    --
    -- @p[A=<A>]@ maps to @p[A=<B>]@ with @A=<B>@.
    renameHoleUnitId :: DynFlags -> ShHoleSubst -> UnitId -> UnitId
    renameHoleUnitId dflags = renameHoleUnitId' (getPackageConfigMap dflags)

    -- | Like 'renameHoleModule', but requires only 'PackageConfigMap'
    -- so it can be used by "Packages".
    renameHoleModule' :: PackageConfigMap -> ShHoleSubst -> Module -> Module
    renameHoleModule' pkg_map env m
      | not (isHoleModule m) =
            let uid = renameHoleUnitId' pkg_map env (moduleUnitId m)
            in mkModule uid (moduleName m)
      | Just m' <- lookupUFM env (moduleName m) = m'
      -- NB m = <Blah>, that's what's in scope.
      | otherwise = m

    -- | Like 'renameHoleUnitId, but requires only 'PackageConfigMap'
    -- so it can be used by "Packages".
    renameHoleUnitId' :: PackageConfigMap -> ShHoleSubst -> UnitId -> UnitId
    renameHoleUnitId' pkg_map env uid =
        case uid of
          (IndefiniteUnitId
            IndefUnitId{ indefUnitIdComponentId = cid
                       , indefUnitIdInsts       = insts
                       , indefUnitIdFreeHoles   = fh })
              -> if isNullUFM (intersectUFM_C const (udfmToUfm fh) env)
                    then uid
                    -- Functorially apply the substitution to the instantiation,
                    -- then check the 'PackageConfigMap' to see if there is
                    -- a compiled version of this 'UnitId' we can improve to.
                    -- See Note [UnitId to InstalledUnitId] improvement
                    else improveUnitId pkg_map $
                            newUnitId cid
                                (map (\(k,v) -> (k, renameHoleModule' pkg_map env v)) insts)
          _ -> uid

    -- | Given a possibly on-the-fly instantiated module, split it into
    -- a 'Module' that we definitely can find on-disk, as well as an
    -- instantiation if we need to instantiate it on the fly.  If the
    -- instantiation is @Nothing@ no on-the-fly renaming is needed.
    splitModuleInsts :: Module -> (InstalledModule, Maybe IndefModule)
    splitModuleInsts m =
        let (uid, mb_iuid) = splitUnitIdInsts (moduleUnitId m)
        in (InstalledModule uid (moduleName m),
            fmap (\iuid -> IndefModule iuid (moduleName m)) mb_iuid)

    -- | See 'splitModuleInsts'.
    splitUnitIdInsts :: UnitId -> (InstalledUnitId, Maybe IndefUnitId)
    splitUnitIdInsts (IndefiniteUnitId iuid) =
        (componentIdToInstalledUnitId (indefUnitIdComponentId iuid), Just iuid)
    splitUnitIdInsts (DefiniteUnitId (DefUnitId uid)) = (uid, Nothing)

    generalizeIndefUnitId :: IndefUnitId -> IndefUnitId
    generalizeIndefUnitId IndefUnitId{ indefUnitIdComponentId = cid
                                     , indefUnitIdInsts = insts } =
        newIndefUnitId cid (map (\(m,_) -> (m, mkHoleModule m)) insts)

    generalizeIndefModule :: IndefModule -> IndefModule
    generalizeIndefModule (IndefModule uid n) = IndefModule (generalizeIndefUnitId uid) n

    parseModuleName :: ReadP ModuleName
    parseModuleName = fmap mkModuleName
                    $ Parse.munch1 (\c -> isAlphaNum c || c `elem` "_.")

    parseUnitId :: ReadP UnitId
    parseUnitId = parseFullUnitId <++ parseDefiniteUnitId <++ parseSimpleUnitId
      where
        parseFullUnitId = do
            cid <- parseComponentId
            insts <- parseModSubst
            return (newUnitId cid insts)
        parseDefiniteUnitId = do
            s <- Parse.munch1 (\c -> isAlphaNum c || c `elem` "-_.+")
            return (stringToUnitId s)
        parseSimpleUnitId = do
            cid <- parseComponentId
            return (newSimpleUnitId cid)

    parseComponentId :: ReadP ComponentId
    parseComponentId = (ComponentId . mkFastString)  `fmap` Parse.munch1 abi_char
       where abi_char c = isAlphaNum c || c `elem` "-_."

    parseModuleId :: ReadP Module
    parseModuleId = parseModuleVar <++ parseModule
        where
          parseModuleVar = do
            _ <- Parse.char '<'
            modname <- parseModuleName
            _ <- Parse.char '>'
            return (mkHoleModule modname)
          parseModule = do
            uid <- parseUnitId
            _ <- Parse.char ':'
            modname <- parseModuleName
            return (mkModule uid modname)

    parseModSubst :: ReadP [(ModuleName, Module)]
    parseModSubst = Parse.between (Parse.char '[') (Parse.char ']')
          . flip Parse.sepBy (Parse.char ',')
          $ do k <- parseModuleName
               _ <- Parse.char '='
               v <- parseModuleId
               return (k, v)

    -- -----------------------------------------------------------------------------
    -- $wired_in_packages
    -- Certain packages are known to the compiler, in that we know about certain
    -- entities that reside in these packages, and the compiler needs to
    -- declare static Modules and Names that refer to these packages.  Hence
    -- the wired-in packages can't include version numbers, since we don't want
    -- to bake the version numbers of these packages into GHC.
    --
    -- So here's the plan.  Wired-in packages are still versioned as
    -- normal in the packages database, and you can still have multiple
    -- versions of them installed.  However, for each invocation of GHC,
    -- only a single instance of each wired-in package will be recognised
    -- (the desired one is selected via @-package@\/@-hide-package@), and GHC
    -- will use the unversioned 'UnitId' below when referring to it,
    -- including in .hi files and object file symbols.  Unselected
    -- versions of wired-in packages will be ignored, as will any other
    -- package that depends directly or indirectly on it (much as if you
    -- had used @-ignore-package@).

    -- Make sure you change 'Packages.findWiredInPackages' if you add an entry here

    integerUnitId, primUnitId,
      baseUnitId, rtsUnitId,
      thUnitId, dphSeqUnitId, dphParUnitId,
      mainUnitId, thisGhcUnitId, interactiveUnitId  :: UnitId
    primUnitId        = fsToUnitId (fsLit "ghc-prim")
    integerUnitId     = fsToUnitId (fsLit n)
      where
        n = case cIntegerLibraryType of
            IntegerGMP    -> "integer-gmp"
            IntegerSimple -> "integer-simple"
    baseUnitId        = fsToUnitId (fsLit "base")
    rtsUnitId         = fsToUnitId (fsLit "rts")
    thUnitId          = fsToUnitId (fsLit "template-haskell")
    dphSeqUnitId      = fsToUnitId (fsLit "dph-seq")
    dphParUnitId      = fsToUnitId (fsLit "dph-par")
    thisGhcUnitId     = fsToUnitId (fsLit "ghc")
    interactiveUnitId = fsToUnitId (fsLit "interactive")

    -- | This is the package Id for the current program.  It is the default
    -- package Id if you don't specify a package name.  We don't add this prefix
    -- to symbol names, since there can be only one main package per program.
    mainUnitId      = fsToUnitId (fsLit "main")

    -- | This is a fake package id used to provide identities to any un-implemented
    -- signatures.  The set of hole identities is global over an entire compilation.
    -- Don't use this directly: use 'mkHoleModule' or 'isHoleModule' instead.
    -- See Note [Representation of module/name variables]
    holeUnitId :: UnitId
    holeUnitId      = fsToUnitId (fsLit "hole")

    isInteractiveModule :: Module -> Bool
    isInteractiveModule mod = moduleUnitId mod == interactiveUnitId

    -- Note [Representation of module/name variables]
    -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    -- In our ICFP'16, we use <A> to represent module holes, and {A.T} to represent
    -- name holes.  This could have been represented by adding some new cases
    -- to the core data types, but this would have made the existing 'nameModule'
    -- and 'moduleUnitId' partial, which would have required a lot of modifications
    -- to existing code.
    --
    -- Instead, we adopted the following encoding scheme:
    --
    --      <A>   ===> hole:A
    --      {A.T} ===> hole:A.T
    --
    -- This encoding is quite convenient, but it is also a bit dangerous too,
    -- because if you have a 'hole:A' you need to know if it's actually a
    -- 'Module' or just a module stored in a 'Name'; these two cases must be
    -- treated differently when doing substitutions.  'renameHoleModule'
    -- and 'renameHoleUnitId' assume they are NOT operating on a
    -- 'Name'; 'NameShape' handles name substitutions exclusively.

    isHoleModule :: Module -> Bool
    isHoleModule mod = moduleUnitId mod == holeUnitId

    wiredInUnitIds :: [UnitId]
    wiredInUnitIds = [ primUnitId,
                           integerUnitId,
                           baseUnitId,
                           rtsUnitId,
                           thUnitId,
                           thisGhcUnitId,
                           dphSeqUnitId,
                           dphParUnitId ]

    {-
    ************************************************************************
    *                                                                      *
    \subsection{@ModuleEnv@s}
    *                                                                      *
    ************************************************************************
    -}

    -- | A map keyed off of 'Module's
    newtype ModuleEnv elt = ModuleEnv (Map NDModule elt)

    {-
    Note [ModuleEnv performance and determinism]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    To prevent accidental reintroduction of nondeterminism the Ord instance
    for Module was changed to not depend on Unique ordering and to use the
    lexicographic order. This is potentially expensive, but when measured
    there was no difference in performance.

    To be on the safe side and not pessimize ModuleEnv uses nondeterministic
    ordering on Module and normalizes by doing the lexicographic sort when
    turning the env to a list.
    See Note [Unique Determinism] for more information about the source of
    nondeterminismand and Note [Deterministic UniqFM] for explanation of why
    it matters for maps.
    -}

    newtype NDModule = NDModule { unNDModule :: Module }
      deriving Eq
      -- A wrapper for Module with faster nondeterministic Ord.
      -- Don't export, See [ModuleEnv performance and determinism]

    instance Ord NDModule where
      compare (NDModule (Module p1 n1)) (NDModule (Module p2 n2)) =
        (getUnique p1 `nonDetCmpUnique` getUnique p2) `thenCmp`
        (getUnique n1 `nonDetCmpUnique` getUnique n2)

    filterModuleEnv :: (Module -> a -> Bool) -> ModuleEnv a -> ModuleEnv a
    filterModuleEnv f (ModuleEnv e) =
      ModuleEnv (Map.filterWithKey (f . unNDModule) e)

    elemModuleEnv :: Module -> ModuleEnv a -> Bool
    elemModuleEnv m (ModuleEnv e) = Map.member (NDModule m) e

    extendModuleEnv :: ModuleEnv a -> Module -> a -> ModuleEnv a
    extendModuleEnv (ModuleEnv e) m x = ModuleEnv (Map.insert (NDModule m) x e)

    extendModuleEnvWith :: (a -> a -> a) -> ModuleEnv a -> Module -> a
                        -> ModuleEnv a
    extendModuleEnvWith f (ModuleEnv e) m x =
      ModuleEnv (Map.insertWith f (NDModule m) x e)

    extendModuleEnvList :: ModuleEnv a -> [(Module, a)] -> ModuleEnv a
    extendModuleEnvList (ModuleEnv e) xs =
      ModuleEnv (Map.insertList [(NDModule k, v) | (k,v) <- xs] e)

    extendModuleEnvList_C :: (a -> a -> a) -> ModuleEnv a -> [(Module, a)]
                          -> ModuleEnv a
    extendModuleEnvList_C f (ModuleEnv e) xs =
      ModuleEnv (Map.insertListWith f [(NDModule k, v) | (k,v) <- xs] e)

    plusModuleEnv_C :: (a -> a -> a) -> ModuleEnv a -> ModuleEnv a -> ModuleEnv a
    plusModuleEnv_C f (ModuleEnv e1) (ModuleEnv e2) =
      ModuleEnv (Map.unionWith f e1 e2)

    delModuleEnvList :: ModuleEnv a -> [Module] -> ModuleEnv a
    delModuleEnvList (ModuleEnv e) ms =
      ModuleEnv (Map.deleteList (map NDModule ms) e)

    delModuleEnv :: ModuleEnv a -> Module -> ModuleEnv a
    delModuleEnv (ModuleEnv e) m = ModuleEnv (Map.delete (NDModule m) e)

    plusModuleEnv :: ModuleEnv a -> ModuleEnv a -> ModuleEnv a
    plusModuleEnv (ModuleEnv e1) (ModuleEnv e2) = ModuleEnv (Map.union e1 e2)

    lookupModuleEnv :: ModuleEnv a -> Module -> Maybe a
    lookupModuleEnv (ModuleEnv e) m = Map.lookup (NDModule m) e

    lookupWithDefaultModuleEnv :: ModuleEnv a -> a -> Module -> a
    lookupWithDefaultModuleEnv (ModuleEnv e) x m =
      Map.findWithDefault x (NDModule m) e

    mapModuleEnv :: (a -> b) -> ModuleEnv a -> ModuleEnv b
    mapModuleEnv f (ModuleEnv e) = ModuleEnv (Map.mapWithKey (\_ v -> f v) e)

    mkModuleEnv :: [(Module, a)] -> ModuleEnv a
    mkModuleEnv xs = ModuleEnv (Map.fromList [(NDModule k, v) | (k,v) <- xs])

    emptyModuleEnv :: ModuleEnv a
    emptyModuleEnv = ModuleEnv Map.empty

    moduleEnvKeys :: ModuleEnv a -> [Module]
    moduleEnvKeys (ModuleEnv e) = sort $ map unNDModule $ Map.keys e
      -- See Note [ModuleEnv performance and determinism]

    moduleEnvElts :: ModuleEnv a -> [a]
    moduleEnvElts e = map snd $ moduleEnvToList e
      -- See Note [ModuleEnv performance and determinism]

    moduleEnvToList :: ModuleEnv a -> [(Module, a)]
    moduleEnvToList (ModuleEnv e) =
      sortBy (comparing fst) [(m, v) | (NDModule m, v) <- Map.toList e]
      -- See Note [ModuleEnv performance and determinism]

    unitModuleEnv :: Module -> a -> ModuleEnv a
    unitModuleEnv m x = ModuleEnv (Map.singleton (NDModule m) x)

    isEmptyModuleEnv :: ModuleEnv a -> Bool
    isEmptyModuleEnv (ModuleEnv e) = Map.null e

    -- | A set of 'Module's
    type ModuleSet = Set NDModule

    mkModuleSet     :: [Module] -> ModuleSet
    extendModuleSet :: ModuleSet -> Module -> ModuleSet
    emptyModuleSet  :: ModuleSet
    moduleSetElts   :: ModuleSet -> [Module]
    elemModuleSet   :: Module -> ModuleSet -> Bool

    emptyModuleSet    = Set.empty
    mkModuleSet       = Set.fromList . coerce
    extendModuleSet s m = Set.insert (NDModule m) s
    moduleSetElts     = sort . coerce . Set.toList
    elemModuleSet     = Set.member . coerce

    {-
    A ModuleName has a Unique, so we can build mappings of these using
    UniqFM.
    -}

    -- | A map keyed off of 'ModuleName's (actually, their 'Unique's)
    type ModuleNameEnv elt = UniqFM elt

    -- | A map keyed off of 'ModuleName's (actually, their 'Unique's)
    -- Has deterministic folds and can be deterministically converted to a list
    type DModuleNameEnv elt = UniqDFM elt