Udate hsSyn AST to use Trees that Grow

Summary:
See https://ghc.haskell.org/trac/ghc/wiki/ImplementingTreesThatGrow

This commit prepares the ground for a full extensible AST, by replacing the type
parameter for the hsSyn data types with a set of indices into type families,

    data GhcPs -- ^ Index for GHC parser output
    data GhcRn -- ^ Index for GHC renamer output
    data GhcTc -- ^ Index for GHC typechecker output

These are now used instead of `RdrName`, `Name` and `Id`/`TcId`/`Var`

Where the original name type is required in a polymorphic context, this is
accessible via the IdP type family, defined as

    type family IdP p
    type instance IdP GhcPs = RdrName
    type instance IdP GhcRn = Name
    type instance IdP GhcTc = Id

These types are declared in the new 'hsSyn/HsExtension.hs' module.

To gain a better understanding of the extension mechanism, it has been applied
to `HsLit` only, also replacing the `SourceText` fields in them with extension
types.

To preserve extension generality, a type class is introduced to capture the
`SourceText` interface, which must be honoured by all of the extension points
which originally had a `SourceText`.  The class is defined as

    class HasSourceText a where
      -- Provide setters to mimic existing constructors
      noSourceText  :: a
      sourceText    :: String -> a

      setSourceText :: SourceText -> a
      getSourceText :: a -> SourceText

And the constraint is captured in `SourceTextX`, which is a constraint type
listing all the extension points that make use of the class.

Updating Haddock submodule to match.

Test Plan: ./validate

Reviewers: simonpj, shayan-najd, goldfire, austin, bgamari

Subscribers: rwbarton, thomie, mpickering

Differential Revision: https://phabricator.haskell.org/D3609

1 files changed, 3 insertions, 3 deletions

diff --git a/ghc/GHCi/UI.hs b/ghc/GHCi/UI.hs
index 6954002645..5f81a2ce7c 100644
--- a/ghc/GHCi/UI.hs
+++ b/ghc/GHCi/UI.hs
@@ -59,7 +59,7 @@ import Packages ( trusted, getPackageDetails, getInstalledPackageDetails,
 import IfaceSyn ( showToHeader )
 import PprTyThing
 import PrelNames
-import RdrName ( RdrName, getGRE_NameQualifier_maybes, getRdrName )
+import RdrName ( getGRE_NameQualifier_maybes, getRdrName )
 import SrcLoc
 import qualified Lexer
 
@@ -1566,7 +1566,7 @@ cmdCmd str = handleSourceError GHC.printException $ do
 
 -- | Generate a typed ghciStepIO expression
 -- @ghciStepIO :: Ty String -> IO String@.
-getGhciStepIO :: GHCi (LHsExpr RdrName)
+getGhciStepIO :: GHCi (LHsExpr GhcPs)
 getGhciStepIO = do
   ghciTyConName <- GHC.getGHCiMonad
   let stringTy = nlHsTyVar stringTy_RDR
@@ -2385,7 +2385,7 @@ iiModuleName (IIDecl d)   = unLoc (ideclName d)
 preludeModuleName :: ModuleName
 preludeModuleName = GHC.mkModuleName "Prelude"
 
-sameImpModule :: ImportDecl RdrName -> InteractiveImport -> Bool
+sameImpModule :: ImportDecl GhcPs -> InteractiveImport -> Bool
 sameImpModule _ (IIModule _) = False -- we only care about imports here
 sameImpModule imp (IIDecl d) = unLoc (ideclName d) == unLoc (ideclName imp)