Distribution/Backpack.hs

    {-# LANGUAGE FlexibleInstances #-}
    {-# LANGUAGE RankNTypes #-}
    {-# LANGUAGE PatternGuards #-}
    {-# LANGUAGE DeriveGeneric #-}
    {-# LANGUAGE DeriveDataTypeable #-}
    {-# LANGUAGE GeneralizedNewtypeDeriving #-}

    -- | This module defines the core data types for Backpack.  For more
    -- details, see:
    --
    --  <https://github.com/ezyang/ghc-proposals/blob/backpack/proposals/0000-backpack.rst>

    module Distribution.Backpack (
        -- * OpenUnitId
        OpenUnitId(..),
        openUnitIdFreeHoles,
        mkOpenUnitId,

        -- * DefUnitId
        DefUnitId,
        unDefUnitId,
        mkDefUnitId,

        -- * OpenModule
        OpenModule(..),
        openModuleFreeHoles,

        -- * OpenModuleSubst
        OpenModuleSubst,
        dispOpenModuleSubst,
        dispOpenModuleSubstEntry,
        parseOpenModuleSubst,
        parseOpenModuleSubstEntry,
        openModuleSubstFreeHoles,

        -- * Conversions to 'UnitId'
        abstractUnitId,
        hashModuleSubst,
    ) where

    import Prelude ()
    import Distribution.Compat.Prelude hiding (mod)
    import Distribution.Compat.ReadP
    import qualified Distribution.Compat.ReadP as Parse
    import qualified Text.PrettyPrint as Disp
    import Text.PrettyPrint (hcat)

    import Distribution.ModuleName
    import Distribution.Package
    import Distribution.Text
    import Distribution.Utils.Base62

    import qualified Data.Map as Map
    import Data.Set (Set)
    import qualified Data.Set as Set

    -----------------------------------------------------------------------
    -- OpenUnitId

    -- | An 'OpenUnitId' describes a (possibly partially) instantiated
    -- Backpack component, with a description of how the holes are filled
    -- in.  Unlike 'OpenUnitId', the 'ModuleSubst' is kept in a structured
    -- form that allows for substitution (which fills in holes.) This form
    -- of unit cannot be installed. It must first be converted to a
    -- 'UnitId'.
    --
    -- In the absence of Backpack, there are no holes to fill, so any such
    -- component always has an empty module substitution; thus we can lossly
    -- represent it as an 'OpenUnitId uid'.
    --
    -- For a source component using Backpack, however, there is more
    -- structure as components may be parametrized over some signatures, and
    -- these \"holes\" may be partially or wholly filled.
    --
    -- OpenUnitId plays an important role when we are mix-in linking,
    -- and is recorded to the installed packaged database for indefinite
    -- packages; however, for compiled packages that are fully instantiated,
    -- we instantiate 'OpenUnitId' into 'UnitId'.
    --
    -- For more details see the Backpack spec
    -- <https://github.com/ezyang/ghc-proposals/blob/backpack/proposals/0000-backpack.rst>
    --

    data OpenUnitId
        -- | Identifies a component which may have some unfilled holes;
        -- specifying its 'ComponentId' and its 'OpenModuleSubst'.
        -- TODO: Invariant that 'OpenModuleSubst' is non-empty?
        -- See also the Text instance.
        = IndefFullUnitId ComponentId OpenModuleSubst
        -- | Identifies a fully instantiated component, which has
        -- been compiled and abbreviated as a hash.  The embedded 'UnitId'
        -- MUST NOT be for an indefinite component; an 'OpenUnitId'
        -- is guaranteed not to have any holes.
        | DefiniteUnitId DefUnitId
      deriving (Generic, Read, Show, Eq, Ord, Typeable, Data)
    -- TODO: cache holes?

    instance Binary OpenUnitId

    instance NFData OpenUnitId where
        rnf (IndefFullUnitId cid subst) = rnf cid `seq` rnf subst
        rnf (DefiniteUnitId uid) = rnf uid

    instance Text OpenUnitId where
        disp (IndefFullUnitId cid insts)
            -- TODO: arguably a smart constructor to enforce invariant would be
            -- better
            | Map.null insts = disp cid
            | otherwise      = disp cid <<>> Disp.brackets (dispOpenModuleSubst insts)
        disp (DefiniteUnitId uid) = disp uid
        parse = parseOpenUnitId <++ fmap DefiniteUnitId parse
          where
            parseOpenUnitId = do
                cid <- parse
                insts <- Parse.between (Parse.char '[') (Parse.char ']')
                           parseOpenModuleSubst
                return (IndefFullUnitId cid insts)

    -- | Get the set of holes ('ModuleVar') embedded in a 'UnitId'.
    openUnitIdFreeHoles :: OpenUnitId -> Set ModuleName
    openUnitIdFreeHoles (IndefFullUnitId _ insts) = openModuleSubstFreeHoles insts
    openUnitIdFreeHoles _ = Set.empty

    -- | Safe constructor from a UnitId.  The only way to do this safely
    -- is if the instantiation is provided.
    mkOpenUnitId :: UnitId -> ComponentId -> OpenModuleSubst -> OpenUnitId
    mkOpenUnitId uid cid insts =
        if Set.null (openModuleSubstFreeHoles insts)
            then DefiniteUnitId (unsafeMkDefUnitId uid) -- invariant holds!
            else IndefFullUnitId cid insts

    -----------------------------------------------------------------------
    -- DefUnitId

    -- | Create a 'DefUnitId' from a 'ComponentId' and an instantiation
    -- with no holes.
    mkDefUnitId :: ComponentId -> Map ModuleName Module -> DefUnitId
    mkDefUnitId cid insts =
        unsafeMkDefUnitId (mkUnitId
            (unComponentId cid ++ maybe "" ("+"++) (hashModuleSubst insts)))
            -- impose invariant!

    -----------------------------------------------------------------------
    -- OpenModule

    -- | Unlike a 'Module', an 'OpenModule' is either an ordinary
    -- module from some unit, OR an 'OpenModuleVar', representing a
    -- hole that needs to be filled in.  Substitutions are over
    -- module variables.
    data OpenModule
        = OpenModule OpenUnitId ModuleName
        | OpenModuleVar ModuleName
      deriving (Generic, Read, Show, Eq, Ord, Typeable, Data)

    instance Binary OpenModule

    instance NFData OpenModule where
        rnf (OpenModule uid mod_name) = rnf uid `seq` rnf mod_name
        rnf (OpenModuleVar mod_name) = rnf mod_name

    instance Text OpenModule where
        disp (OpenModule uid mod_name) =
            hcat [disp uid, Disp.text ":", disp mod_name]
        disp (OpenModuleVar mod_name) =
            hcat [Disp.char '<', disp mod_name, Disp.char '>']
        parse = parseModuleVar <++ parseOpenModule
          where
            parseOpenModule = do
                uid <- parse
                _ <- Parse.char ':'
                mod_name <- parse
                return (OpenModule uid mod_name)
            parseModuleVar = do
                _ <- Parse.char '<'
                mod_name <- parse
                _ <- Parse.char '>'
                return (OpenModuleVar mod_name)

    -- | Get the set of holes ('ModuleVar') embedded in a 'Module'.
    openModuleFreeHoles :: OpenModule -> Set ModuleName
    openModuleFreeHoles (OpenModuleVar mod_name) = Set.singleton mod_name
    openModuleFreeHoles (OpenModule uid _n) = openUnitIdFreeHoles uid

    -----------------------------------------------------------------------
    -- OpenModuleSubst

    -- | An explicit substitution on modules.
    --
    -- NB: These substitutions are NOT idempotent, for example, a
    -- valid substitution is (A -> B, B -> A).
    type OpenModuleSubst = Map ModuleName OpenModule

    -- | Pretty-print the entries of a module substitution, suitable
    -- for embedding into a 'OpenUnitId' or passing to GHC via @--instantiate-with@.
    dispOpenModuleSubst :: OpenModuleSubst -> Disp.Doc
    dispOpenModuleSubst subst
        = Disp.hcat
        . Disp.punctuate Disp.comma
        $ map dispOpenModuleSubstEntry (Map.toAscList subst)

    -- | Pretty-print a single entry of a module substitution.
    dispOpenModuleSubstEntry :: (ModuleName, OpenModule) -> Disp.Doc
    dispOpenModuleSubstEntry (k, v) = disp k <<>> Disp.char '=' <<>> disp v

    -- | Inverse to 'dispModSubst'.
    parseOpenModuleSubst :: ReadP r OpenModuleSubst
    parseOpenModuleSubst = fmap Map.fromList
          . flip Parse.sepBy (Parse.char ',')
          $ parseOpenModuleSubstEntry

    -- | Inverse to 'dispModSubstEntry'.
    parseOpenModuleSubstEntry :: ReadP r (ModuleName, OpenModule)
    parseOpenModuleSubstEntry =
        do k <- parse
           _ <- Parse.char '='
           v <- parse
           return (k, v)

    -- | Get the set of holes ('ModuleVar') embedded in a 'OpenModuleSubst'.
    -- This is NOT the domain of the substitution.
    openModuleSubstFreeHoles :: OpenModuleSubst -> Set ModuleName
    openModuleSubstFreeHoles insts = Set.unions (map openModuleFreeHoles (Map.elems insts))

    -----------------------------------------------------------------------
    -- Conversions to UnitId

    -- | When typechecking, we don't demand that a freshly instantiated
    -- 'IndefFullUnitId' be compiled; instead, we just depend on the
    -- installed indefinite unit installed at the 'ComponentId'.
    abstractUnitId :: OpenUnitId -> UnitId
    abstractUnitId (DefiniteUnitId def_uid) = unDefUnitId def_uid
    abstractUnitId (IndefFullUnitId cid _) = newSimpleUnitId cid

    -- | Take a module substitution and hash it into a string suitable for
    -- 'UnitId'.  Note that since this takes 'Module', not 'OpenModule',
    -- you are responsible for recursively converting 'OpenModule'
    -- into 'Module'.  See also "Distribution.Backpack.ReadyComponent".
    hashModuleSubst :: Map ModuleName Module -> Maybe String
    hashModuleSubst subst
      | Map.null subst = Nothing
      | otherwise =
          Just . hashToBase62 $
            concat [ display mod_name ++ "=" ++ display m ++ "\n"
                   | (mod_name, m) <- Map.toList subst]