Introduce IsPass; refactor wrappers.

There are two main payloads of this patch:

1. This introduces IsPass, which allows e.g. printing
   code to ask what pass it is running in (Renamed vs
   Typechecked) and thus print extension fields. See
   Note [IsPass] in Hs.Extension

2. This moves the HsWrap constructor into an extension
   field, where it rightly belongs. This is done for
   HsExpr and HsCmd, but not for HsPat, which is left
   as an exercise for the reader.

There is also some refactoring around SyntaxExprs, but this
is really just incidental.

This patch subsumes !1721 (sorry @chreekat).

Along the way, there is a bit of refactoring in GHC.Hs.Extension,
including the removal of NameOrRdrName in favor of NoGhcTc.
This meant that we had no real need for GHC.Hs.PlaceHolder, so
I got rid of it.

Updates haddock submodule.

-------------------------
Metric Decrease:
    haddock.compiler
-------------------------

5 files changed, 48 insertions, 54 deletions

diff --git a/testsuite/tests/parser/should_compile/DumpParsedAst.stderr b/testsuite/tests/parser/should_compile/DumpParsedAst.stderr
index d7996df404..8ae907ee25 100644
--- a/testsuite/tests/parser/should_compile/DumpParsedAst.stderr
+++ b/testsuite/tests/parser/should_compile/DumpParsedAst.stderr
@@ -454,7 +454,6 @@
              (EmptyLocalBinds
               (NoExtField))))))])
        (FromSource))
-      (WpHole)
       [])))]
   (Nothing)
   (Nothing)))
diff --git a/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr b/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
index 53d4f37acf..57da7c2199 100644
--- a/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
+++ b/testsuite/tests/parser/should_compile/DumpRenamedAst.stderr
@@ -53,7 +53,6 @@
                   (EmptyLocalBinds
                    (NoExtField))))))])
             (FromSource))
-           (WpHole)
            []))]})]
      []))
    []
diff --git a/testsuite/tests/parser/should_compile/DumpTypecheckedAst.stderr b/testsuite/tests/parser/should_compile/DumpTypecheckedAst.stderr
index 5282c9f62a..3654edfa45 100644
--- a/testsuite/tests/parser/should_compile/DumpTypecheckedAst.stderr
+++ b/testsuite/tests/parser/should_compile/DumpTypecheckedAst.stderr
@@ -552,15 +552,15 @@
            (HsApp
             (NoExtField)
             ({ <no location info> }
-             (HsWrap
-              (NoExtField)
-              (WpTyApp
-               (TyConApp
-                ({abstract:TyCon})
-                []))
-              (HsConLikeOut
-               (NoExtField)
-               ({abstract:ConLike}))))
+             (XExpr
+              (HsWrap
+               (WpTyApp
+                (TyConApp
+                 ({abstract:TyCon})
+                 []))
+               (HsConLikeOut
+                (NoExtField)
+                ({abstract:ConLike})))))
             ({ <no location info> }
              (HsVar
               (NoExtField)
@@ -576,15 +576,15 @@
                (HsApp
                 (NoExtField)
                 ({ <no location info> }
-                 (HsWrap
-                  (NoExtField)
-                  (WpTyApp
-                   (TyConApp
-                    ({abstract:TyCon})
-                    []))
-                  (HsConLikeOut
-                   (NoExtField)
-                   ({abstract:ConLike}))))
+                 (XExpr
+                  (HsWrap
+                   (WpTyApp
+                    (TyConApp
+                     ({abstract:TyCon})
+                     []))
+                   (HsConLikeOut
+                    (NoExtField)
+                    ({abstract:ConLike})))))
                 ({ <no location info> }
                  (HsVar
                   (NoExtField)
@@ -600,30 +600,30 @@
                    (HsApp
                     (NoExtField)
                     ({ <no location info> }
-                     (HsWrap
-                      (NoExtField)
-                      (WpTyApp
-                       (TyConApp
-                        ({abstract:TyCon})
-                        []))
-                      (HsConLikeOut
-                       (NoExtField)
-                       ({abstract:ConLike}))))
+                     (XExpr
+                      (HsWrap
+                       (WpTyApp
+                        (TyConApp
+                         ({abstract:TyCon})
+                         []))
+                       (HsConLikeOut
+                        (NoExtField)
+                        ({abstract:ConLike})))))
                     ({ <no location info> }
                      (HsVar
                       (NoExtField)
                       ({ <no location info> }
                        {Var: $krep})))))
                   ({ <no location info> }
-                   (HsWrap
-                    (NoExtField)
-                    (WpTyApp
-                     (TyConApp
-                      ({abstract:TyCon})
-                      []))
-                    (HsConLikeOut
-                     (NoExtField)
-                     ({abstract:ConLike}))))))))))))))))))
+                   (XExpr
+                    (HsWrap
+                     (WpTyApp
+                      (TyConApp
+                       ({abstract:TyCon})
+                       []))
+                     (HsConLikeOut
+                      (NoExtField)
+                      ({abstract:ConLike})))))))))))))))))))
     (False)))
  ,({ <no location info> }
    (VarBind
@@ -645,15 +645,15 @@
           ({ <no location info> }
            {Var: DumpTypecheckedAst.$tcPeano})))))
       ({ <no location info> }
-       (HsWrap
-        (NoExtField)
-        (WpTyApp
-         (TyConApp
-          ({abstract:TyCon})
-          []))
-        (HsConLikeOut
-         (NoExtField)
-         ({abstract:ConLike}))))))
+       (XExpr
+        (HsWrap
+         (WpTyApp
+          (TyConApp
+           ({abstract:TyCon})
+           []))
+         (HsConLikeOut
+          (NoExtField)
+          ({abstract:ConLike})))))))
     (False)))
  ,({ <no location info> }
    (VarBind
@@ -718,8 +718,7 @@
     {Bag(Located (HsBind Var)):
      [({ DumpTypecheckedAst.hs:18:1-23 }
        (FunBind
-        {NameSet:
-         []}
+        (WpHole)
         ({ DumpTypecheckedAst.hs:18:1-4 }
          {Var: main})
         (MG
@@ -765,7 +764,6 @@
                (EmptyLocalBinds
                 (NoExtField))))))])
          (FromSource))
-        (WpHole)
         []))]}
     (False)))]}
 
diff --git a/testsuite/tests/parser/should_compile/KindSigs.stderr b/testsuite/tests/parser/should_compile/KindSigs.stderr
index 2873bfcfaa..06ed01539a 100644
--- a/testsuite/tests/parser/should_compile/KindSigs.stderr
+++ b/testsuite/tests/parser/should_compile/KindSigs.stderr
@@ -361,7 +361,6 @@
              (EmptyLocalBinds
               (NoExtField))))))])
        (FromSource))
-      (WpHole)
       [])))
   ,({ KindSigs.hs:26:1-29 }
     (TyClD
@@ -602,7 +601,6 @@
              (EmptyLocalBinds
               (NoExtField))))))])
        (FromSource))
-      (WpHole)
       [])))]
   (Nothing)
   (Nothing)))
diff --git a/testsuite/tests/plugins/simple-plugin/Simple/RemovePlugin.hs b/testsuite/tests/plugins/simple-plugin/Simple/RemovePlugin.hs
index 3867404d2c..4162fc24be 100644
--- a/testsuite/tests/plugins/simple-plugin/Simple/RemovePlugin.hs
+++ b/testsuite/tests/plugins/simple-plugin/Simple/RemovePlugin.hs
@@ -53,9 +53,9 @@ typecheckPlugin [name, "typecheck"] _ tc
 typecheckPlugin _ _ tc = return tc
 
 metaPlugin' :: [CommandLineOption] -> LHsExpr GhcTc -> TcM (LHsExpr GhcTc)
-metaPlugin' [name, "meta"] (L l (HsWrap ne w (HsPar x (L _ (HsApp noExt (L _ (HsVar _ (L _ id))) e)))))
+metaPlugin' [name, "meta"] (L l (XExpr (HsWrap w (HsPar x (L _ (HsApp noExt (L _ (HsVar _ (L _ id))) e))))))
   | occNameString (getOccName id) == name
-  = return (L l (HsWrap ne w (unLoc e)))
+  = return (L l (XExpr (HsWrap w (unLoc e))))
 -- The test should always match this first case. If the desugaring changes
 -- again in the future then the panic is more useful than the previous
 -- inscrutable failure.