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

2 files changed, 3 insertions, 4 deletions

diff --git a/compiler/backpack/BkpSyn.hs b/compiler/backpack/BkpSyn.hs
index a7e4db30dd..842c0df49d 100644
--- a/compiler/backpack/BkpSyn.hs
+++ b/compiler/backpack/BkpSyn.hs
@@ -18,7 +18,6 @@ module BkpSyn (
     ) where
 
 import HsSyn
-import RdrName
 import SrcLoc
 import Outputable
 import Module
@@ -61,7 +60,7 @@ type LHsUnit n = Located (HsUnit n)
 -- or an include.
 data HsDeclType = ModuleD | SignatureD
 data HsUnitDecl n
-    = DeclD      HsDeclType (Located ModuleName) (Maybe (Located (HsModule RdrName)))
+    = DeclD   HsDeclType (Located ModuleName) (Maybe (Located (HsModule GhcPs)))
     | IncludeD   (IncludeDecl n)
 type LHsUnitDecl n = Located (HsUnitDecl n)
 
diff --git a/compiler/backpack/DriverBkp.hs b/compiler/backpack/DriverBkp.hs
index a82e66b7b0..6123bc8133 100644
--- a/compiler/backpack/DriverBkp.hs
+++ b/compiler/backpack/DriverBkp.hs
@@ -709,7 +709,7 @@ summariseRequirement pn mod_name = do
 summariseDecl :: PackageName
               -> HscSource
               -> Located ModuleName
-              -> Maybe (Located (HsModule RdrName))
+              -> Maybe (Located (HsModule GhcPs))
               -> BkpM ModSummary
 summariseDecl pn hsc_src (L _ modname) (Just hsmod) = hsModuleToModSummary pn hsc_src modname hsmod
 summariseDecl _pn hsc_src lmodname@(L loc modname) Nothing
@@ -736,7 +736,7 @@ summariseDecl _pn hsc_src lmodname@(L loc modname) Nothing
 hsModuleToModSummary :: PackageName
                      -> HscSource
                      -> ModuleName
-                     -> Located (HsModule RdrName)
+                     -> Located (HsModule GhcPs)
                      -> BkpM ModSummary
 hsModuleToModSummary pn hsc_src modname
                      hsmod = do