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/testsuite/tests/quasiquotation/T7918.hs b/testsuite/tests/quasiquotation/T7918.hs
index 0f32699415..42bb1b05c8 100644
--- a/testsuite/tests/quasiquotation/T7918.hs
+++ b/testsuite/tests/quasiquotation/T7918.hs
@@ -28,19 +28,19 @@ traverse a =
       showPatVar (cast a)
       gmapM traverse a
   where
-    showVar :: Maybe (HsExpr Id) -> Traverse ()
+    showVar :: Maybe (HsExpr GhcTc) -> Traverse ()
     showVar (Just (HsVar (L _ v))) =
       modify $ \(loc, ids) -> (loc, (varName v, loc) : ids)
     showVar _ =
       return ()
 
-    showTyVar :: Maybe (HsType Name) -> Traverse ()
+    showTyVar :: Maybe (HsType GhcRn) -> Traverse ()
     showTyVar (Just (HsTyVar _ (L _ v))) =
       modify $ \(loc, ids) -> (loc, (v, loc) : ids)
     showTyVar _ =
       return ()
 
-    showPatVar :: Maybe (Pat Id) -> Traverse ()
+    showPatVar :: Maybe (Pat GhcTc) -> Traverse ()
     showPatVar (Just (VarPat (L _ v))) =
       modify $ \(loc, ids) -> (loc, (varName v, loc) : ids)
     showPatVar _