WIP on combining Step 1 and 3 of Trees That Grow

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

Trees that grow extension points are added for
- ValBinds
- HsPat
- HsLit
- HsOverLit
- HsType
- HsTyVarBndr
- HsAppType
- FieldOcc
- AmbiguousFieldOcc

Updates haddock submodule

Test Plan: ./validate

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

Subscribers: goldfire, rwbarton, thomie, mpickering

Differential Revision: https://phabricator.haskell.org/D4147

1 files changed, 6 insertions, 3 deletions

diff --git a/compiler/hsSyn/PlaceHolder.hs b/compiler/hsSyn/PlaceHolder.hs
index 0b4711a364..55778d9adf 100644
--- a/compiler/hsSyn/PlaceHolder.hs
+++ b/compiler/hsSyn/PlaceHolder.hs
@@ -6,10 +6,10 @@
 
 module PlaceHolder where
 
-import GhcPrelude ()
+import GhcPrelude ( Eq(..), Ord(..) )
 
 import Type       ( Type )
-import Outputable
+import Outputable hiding ( (<>) )
 import Name
 import NameSet
 import RdrName
@@ -31,7 +31,10 @@ import Data.Data hiding ( Fixity )
 
 -- | used as place holder in PostTc and PostRn values
 data PlaceHolder = PlaceHolder
-  deriving (Data)
+  deriving (Data,Eq,Ord)
+
+instance Outputable PlaceHolder where
+  ppr _ = text "PlaceHolder"
 
 placeHolderKind :: PlaceHolder
 placeHolderKind = PlaceHolder