Restore Trees That Grow reverted commits

The following commits were reverted prior to the release of GHC 8.4.1,
because the time to derive Data instances was too long [1].

 438dd1cbba13d35f3452b4dcef3f94ce9a216905 Phab:D4147
 e3ec2e7ae94524ebd111963faf34b84d942265b4 Phab:D4177
 47ad6578ea460999b53eb4293c3a3b3017a56d65 Phab:D4186

The work is continuing, as the minimum bootstrap compiler is now
GHC 8.2.1, and this allows Plan B[2] for instances to be used.  This
will land in a following commit.

Updates Haddock submodule

[1] https://ghc.haskell.org/trac/ghc/wiki/ImplementingTreesThatGrow/Instances
[2] https://ghc.haskell.org/trac/ghc/wiki/ImplementingTreesThatGrow/Instances#PLANB

1 files changed, 162 insertions, 159 deletions

diff --git a/compiler/rename/RnExpr.hs b/compiler/rename/RnExpr.hs
index ced46a367e..ec2b09f80d 100644
--- a/compiler/rename/RnExpr.hs
+++ b/compiler/rename/RnExpr.hs
@@ -95,7 +95,7 @@ finishHsVar (L l name)
  = do { this_mod <- getModule
       ; when (nameIsLocalOrFrom this_mod name) $
         checkThLocalName name
-      ; return (HsVar (L l name), unitFV name) }
+      ; return (HsVar noExt (L l name), unitFV name) }
 
 rnUnboundVar :: RdrName -> RnM (HsExpr GhcRn, FreeVars)
 rnUnboundVar v
@@ -107,13 +107,13 @@ rnUnboundVar v
                 ; uv <- if startsWithUnderscore occ
                         then return (TrueExprHole occ)
                         else OutOfScope occ <$> getGlobalRdrEnv
-                ; return (HsUnboundVar uv, emptyFVs) }
+                ; return (HsUnboundVar noExt uv, emptyFVs) }
 
         else -- Fail immediately (qualified name)
              do { n <- reportUnboundName v
-                ; return (HsVar (noLoc n), emptyFVs) } }
+                ; return (HsVar noExt (noLoc n), emptyFVs) } }
 
-rnExpr (HsVar (L l v))
+rnExpr (HsVar _ (L l v))
   = do { opt_DuplicateRecordFields <- xoptM LangExt.DuplicateRecordFields
        ; mb_name <- lookupOccRn_overloaded opt_DuplicateRecordFields v
        ; case mb_name of {
@@ -121,58 +121,57 @@ rnExpr (HsVar (L l v))
            Just (Left name)
               | name == nilDataConName -- Treat [] as an ExplicitList, so that
                                        -- OverloadedLists works correctly
-              -> rnExpr (ExplicitList placeHolderType Nothing [])
+              -> rnExpr (ExplicitList noExt Nothing [])
 
               | otherwise
               -> finishHsVar (L l name) ;
             Just (Right [s]) ->
-              return ( HsRecFld (ambiguousFieldOcc (FieldOcc (L l v) s))
-                     , unitFV s) ;
+              return ( HsRecFld noExt (Unambiguous s (L l v) ), unitFV s) ;
            Just (Right fs@(_:_:_)) ->
-              return ( HsRecFld (Ambiguous (L l v) PlaceHolder)
+              return ( HsRecFld noExt (Ambiguous noExt (L l v))
                      , mkFVs fs);
            Just (Right [])         -> panic "runExpr/HsVar" } }
 
-rnExpr (HsIPVar v)
-  = return (HsIPVar v, emptyFVs)
+rnExpr (HsIPVar x v)
+  = return (HsIPVar x v, emptyFVs)
 
-rnExpr (HsOverLabel _ v)
+rnExpr (HsOverLabel x _ v)
   = do { rebindable_on <- xoptM LangExt.RebindableSyntax
        ; if rebindable_on
          then do { fromLabel <- lookupOccRn (mkVarUnqual (fsLit "fromLabel"))
-                 ; return (HsOverLabel (Just fromLabel) v, unitFV fromLabel) }
-         else return (HsOverLabel Nothing v, emptyFVs) }
+                 ; return (HsOverLabel x (Just fromLabel) v, unitFV fromLabel) }
+         else return (HsOverLabel x Nothing v, emptyFVs) }
 
-rnExpr (HsLit lit@(HsString src s))
+rnExpr (HsLit x lit@(HsString src s))
   = do { opt_OverloadedStrings <- xoptM LangExt.OverloadedStrings
        ; if opt_OverloadedStrings then
-            rnExpr (HsOverLit (mkHsIsString src s placeHolderType))
+            rnExpr (HsOverLit x (mkHsIsString src s))
          else do {
             ; rnLit lit
-            ; return (HsLit (convertLit lit), emptyFVs) } }
+            ; return (HsLit x (convertLit lit), emptyFVs) } }
 
-rnExpr (HsLit lit)
+rnExpr (HsLit x lit)
   = do { rnLit lit
-       ; return (HsLit (convertLit lit), emptyFVs) }
+       ; return (HsLit x(convertLit lit), emptyFVs) }
 
-rnExpr (HsOverLit lit)
+rnExpr (HsOverLit x lit)
   = do { ((lit', mb_neg), fvs) <- rnOverLit lit -- See Note [Negative zero]
        ; case mb_neg of
-              Nothing -> return (HsOverLit lit', fvs)
-              Just neg -> return ( HsApp (noLoc neg) (noLoc (HsOverLit lit'))
+              Nothing -> return (HsOverLit x lit', fvs)
+              Just neg -> return (HsApp x (noLoc neg) (noLoc (HsOverLit x lit'))
                                  , fvs ) }
 
-rnExpr (HsApp fun arg)
+rnExpr (HsApp x fun arg)
   = do { (fun',fvFun) <- rnLExpr fun
        ; (arg',fvArg) <- rnLExpr arg
-       ; return (HsApp fun' arg', fvFun `plusFV` fvArg) }
+       ; return (HsApp x fun' arg', fvFun `plusFV` fvArg) }
 
-rnExpr (HsAppType fun arg)
+rnExpr (HsAppType arg fun)
   = do { (fun',fvFun) <- rnLExpr fun
        ; (arg',fvArg) <- rnHsWcType HsTypeCtx arg
-       ; return (HsAppType fun' arg', fvFun `plusFV` fvArg) }
+       ; return (HsAppType arg' fun', fvFun `plusFV` fvArg) }
 
-rnExpr (OpApp e1 op  _ e2)
+rnExpr (OpApp _ e1 op e2)
   = do  { (e1', fv_e1) <- rnLExpr e1
         ; (e2', fv_e2) <- rnLExpr e2
         ; (op', fv_op) <- rnLExpr op
@@ -183,15 +182,15 @@ rnExpr (OpApp e1 op  _ e2)
         -- more, so I've removed the test.  Adding HsPars in TcGenDeriv
         -- should prevent bad things happening.
         ; fixity <- case op' of
-              L _ (HsVar (L _ n)) -> lookupFixityRn n
-              L _ (HsRecFld f)    -> lookupFieldFixityRn f
+              L _ (HsVar _ (L _ n)) -> lookupFixityRn n
+              L _ (HsRecFld _ f)    -> lookupFieldFixityRn f
               _ -> return (Fixity NoSourceText minPrecedence InfixL)
                    -- c.f. lookupFixity for unbound
 
         ; final_e <- mkOpAppRn e1' op' fixity e2'
         ; return (final_e, fv_e1 `plusFV` fv_op `plusFV` fv_e2) }
 
-rnExpr (NegApp e _)
+rnExpr (NegApp _ e _)
   = do { (e', fv_e)         <- rnLExpr e
        ; (neg_name, fv_neg) <- lookupSyntaxName negateName
        ; final_e            <- mkNegAppRn e' neg_name
@@ -201,24 +200,24 @@ rnExpr (NegApp e _)
 -- Template Haskell extensions
 -- Don't ifdef-GHCI them because we want to fail gracefully
 -- (not with an rnExpr crash) in a stage-1 compiler.
-rnExpr e@(HsBracket br_body) = rnBracket e br_body
+rnExpr e@(HsBracket _ br_body) = rnBracket e br_body
 
-rnExpr (HsSpliceE splice) = rnSpliceExpr splice
+rnExpr (HsSpliceE _ splice) = rnSpliceExpr splice
 
 ---------------------------------------------
 --      Sections
 -- See Note [Parsing sections] in Parser.y
-rnExpr (HsPar (L loc (section@(SectionL {}))))
+rnExpr (HsPar x (L loc (section@(SectionL {}))))
   = do  { (section', fvs) <- rnSection section
-        ; return (HsPar (L loc section'), fvs) }
+        ; return (HsPar x (L loc section'), fvs) }
 
-rnExpr (HsPar (L loc (section@(SectionR {}))))
+rnExpr (HsPar x (L loc (section@(SectionR {}))))
   = do  { (section', fvs) <- rnSection section
-        ; return (HsPar (L loc section'), fvs) }
+        ; return (HsPar x (L loc section'), fvs) }
 
-rnExpr (HsPar e)
+rnExpr (HsPar x e)
   = do  { (e', fvs_e) <- rnLExpr e
-        ; return (HsPar e', fvs_e) }
+        ; return (HsPar x e', fvs_e) }
 
 rnExpr expr@(SectionL {})
   = do  { addErr (sectionErr expr); rnSection expr }
@@ -226,71 +225,72 @@ rnExpr expr@(SectionR {})
   = do  { addErr (sectionErr expr); rnSection expr }
 
 ---------------------------------------------
-rnExpr (HsCoreAnn src ann expr)
+rnExpr (HsCoreAnn x src ann expr)
   = do { (expr', fvs_expr) <- rnLExpr expr
-       ; return (HsCoreAnn src ann expr', fvs_expr) }
+       ; return (HsCoreAnn x src ann expr', fvs_expr) }
 
-rnExpr (HsSCC src lbl expr)
+rnExpr (HsSCC x src lbl expr)
   = do { (expr', fvs_expr) <- rnLExpr expr
-       ; return (HsSCC src lbl expr', fvs_expr) }
-rnExpr (HsTickPragma src info srcInfo expr)
+       ; return (HsSCC x src lbl expr', fvs_expr) }
+rnExpr (HsTickPragma x src info srcInfo expr)
   = do { (expr', fvs_expr) <- rnLExpr expr
-       ; return (HsTickPragma src info srcInfo expr', fvs_expr) }
+       ; return (HsTickPragma x src info srcInfo expr', fvs_expr) }
 
-rnExpr (HsLam matches)
+rnExpr (HsLam x matches)
   = do { (matches', fvMatch) <- rnMatchGroup LambdaExpr rnLExpr matches
-       ; return (HsLam matches', fvMatch) }
+       ; return (HsLam x matches', fvMatch) }
 
-rnExpr (HsLamCase matches)
+rnExpr (HsLamCase x matches)
   = do { (matches', fvs_ms) <- rnMatchGroup CaseAlt rnLExpr matches
-       ; return (HsLamCase matches', fvs_ms) }
+       ; return (HsLamCase x matches', fvs_ms) }
 
-rnExpr (HsCase expr matches)
+rnExpr (HsCase x expr matches)
   = do { (new_expr, e_fvs) <- rnLExpr expr
        ; (new_matches, ms_fvs) <- rnMatchGroup CaseAlt rnLExpr matches
-       ; return (HsCase new_expr new_matches, e_fvs `plusFV` ms_fvs) }
+       ; return (HsCase x new_expr new_matches, e_fvs `plusFV` ms_fvs) }
 
-rnExpr (HsLet (L l binds) expr)
+rnExpr (HsLet x (L l binds) expr)
   = rnLocalBindsAndThen binds $ \binds' _ -> do
       { (expr',fvExpr) <- rnLExpr expr
-      ; return (HsLet (L l binds') expr', fvExpr) }
+      ; return (HsLet x (L l binds') expr', fvExpr) }
 
-rnExpr (HsDo do_or_lc (L l stmts) _)
+rnExpr (HsDo x do_or_lc (L l stmts))
   = do  { ((stmts', _), fvs) <-
            rnStmtsWithPostProcessing do_or_lc rnLExpr
              postProcessStmtsForApplicativeDo stmts
              (\ _ -> return ((), emptyFVs))
-        ; return ( HsDo do_or_lc (L l stmts') placeHolderType, fvs ) }
+        ; return ( HsDo x do_or_lc (L l stmts'), fvs ) }
 
-rnExpr (ExplicitList _ _  exps)
+rnExpr (ExplicitList x _  exps)
   = do  { opt_OverloadedLists <- xoptM LangExt.OverloadedLists
         ; (exps', fvs) <- rnExprs exps
         ; if opt_OverloadedLists
            then do {
             ; (from_list_n_name, fvs') <- lookupSyntaxName fromListNName
-            ; return (ExplicitList placeHolderType (Just from_list_n_name) exps'
+            ; return (ExplicitList x (Just from_list_n_name) exps'
                      , fvs `plusFV` fvs') }
            else
-            return  (ExplicitList placeHolderType Nothing exps', fvs) }
+            return  (ExplicitList x Nothing exps', fvs) }
 
-rnExpr (ExplicitPArr _ exps)
+rnExpr (ExplicitPArr x exps)
   = do { (exps', fvs) <- rnExprs exps
-       ; return  (ExplicitPArr placeHolderType exps', fvs) }
+       ; return  (ExplicitPArr x exps', fvs) }
 
-rnExpr (ExplicitTuple tup_args boxity)
+rnExpr (ExplicitTuple x tup_args boxity)
   = do { checkTupleSection tup_args
        ; checkTupSize (length tup_args)
        ; (tup_args', fvs) <- mapAndUnzipM rnTupArg tup_args
-       ; return (ExplicitTuple tup_args' boxity, plusFVs fvs) }
+       ; return (ExplicitTuple x tup_args' boxity, plusFVs fvs) }
   where
-    rnTupArg (L l (Present e)) = do { (e',fvs) <- rnLExpr e
-                                    ; return (L l (Present e'), fvs) }
-    rnTupArg (L l (Missing _)) = return (L l (Missing placeHolderType)
+    rnTupArg (L l (Present x e)) = do { (e',fvs) <- rnLExpr e
+                                      ; return (L l (Present x e'), fvs) }
+    rnTupArg (L l (Missing _)) = return (L l (Missing noExt)
                                         , emptyFVs)
+    rnTupArg (L _ (XTupArg {})) = panic "rnExpr.XTupArg"
 
-rnExpr (ExplicitSum alt arity expr _)
+rnExpr (ExplicitSum x alt arity expr)
   = do { (expr', fvs) <- rnLExpr expr
-       ; return (ExplicitSum alt arity expr' PlaceHolder, fvs) }
+       ; return (ExplicitSum x alt arity expr', fvs) }
 
 rnExpr (RecordCon { rcon_con_name = con_id
                   , rcon_flds = rec_binds@(HsRecFields { rec_dotdot = dd }) })
@@ -298,53 +298,53 @@ rnExpr (RecordCon { rcon_con_name = con_id
        ; (flds, fvs)   <- rnHsRecFields (HsRecFieldCon con_name) mk_hs_var rec_binds
        ; (flds', fvss) <- mapAndUnzipM rn_field flds
        ; let rec_binds' = HsRecFields { rec_flds = flds', rec_dotdot = dd }
-       ; return (RecordCon { rcon_con_name = con_lname, rcon_flds = rec_binds'
-                           , rcon_con_expr = noPostTcExpr, rcon_con_like = PlaceHolder }
+       ; return (RecordCon { rcon_ext = noExt
+                           , rcon_con_name = con_lname, rcon_flds = rec_binds' }
                 , fvs `plusFV` plusFVs fvss `addOneFV` con_name) }
   where
-    mk_hs_var l n = HsVar (L l n)
+    mk_hs_var l n = HsVar noExt (L l n)
     rn_field (L l fld) = do { (arg', fvs) <- rnLExpr (hsRecFieldArg fld)
                             ; return (L l (fld { hsRecFieldArg = arg' }), fvs) }
 
 rnExpr (RecordUpd { rupd_expr = expr, rupd_flds = rbinds })
   = do  { (expr', fvExpr) <- rnLExpr expr
         ; (rbinds', fvRbinds) <- rnHsRecUpdFields rbinds
-        ; return (RecordUpd { rupd_expr = expr', rupd_flds = rbinds'
-                            , rupd_cons    = PlaceHolder, rupd_in_tys = PlaceHolder
-                            , rupd_out_tys = PlaceHolder, rupd_wrap   = PlaceHolder }
+        ; return (RecordUpd { rupd_ext = noExt, rupd_expr = expr'
+                            , rupd_flds = rbinds' }
                  , fvExpr `plusFV` fvRbinds) }
 
-rnExpr (ExprWithTySig expr pty)
+rnExpr (ExprWithTySig pty expr)
   = do  { (pty', fvTy)    <- rnHsSigWcType ExprWithTySigCtx pty
         ; (expr', fvExpr) <- bindSigTyVarsFV (hsWcScopedTvs pty') $
                              rnLExpr expr
-        ; return (ExprWithTySig expr' pty', fvExpr `plusFV` fvTy) }
+        ; return (ExprWithTySig pty' expr', fvExpr `plusFV` fvTy) }
 
-rnExpr (HsIf _ p b1 b2)
+rnExpr (HsIf x _ p b1 b2)
   = do { (p', fvP) <- rnLExpr p
        ; (b1', fvB1) <- rnLExpr b1
        ; (b2', fvB2) <- rnLExpr b2
        ; (mb_ite, fvITE) <- lookupIfThenElse
-       ; return (HsIf mb_ite p' b1' b2', plusFVs [fvITE, fvP, fvB1, fvB2]) }
+       ; return (HsIf x mb_ite p' b1' b2', plusFVs [fvITE, fvP, fvB1, fvB2]) }
 
-rnExpr (HsMultiIf _ty alts)
+rnExpr (HsMultiIf x alts)
   = do { (alts', fvs) <- mapFvRn (rnGRHS IfAlt rnLExpr) alts
        -- ; return (HsMultiIf ty alts', fvs) }
-       ; return (HsMultiIf placeHolderType alts', fvs) }
+       ; return (HsMultiIf x alts', fvs) }
 
-rnExpr (ArithSeq _ _ seq)
+rnExpr (ArithSeq x _ seq)
   = do { opt_OverloadedLists <- xoptM LangExt.OverloadedLists
        ; (new_seq, fvs) <- rnArithSeq seq
        ; if opt_OverloadedLists
            then do {
             ; (from_list_name, fvs') <- lookupSyntaxName fromListName
-            ; return (ArithSeq noPostTcExpr (Just from_list_name) new_seq, fvs `plusFV` fvs') }
+            ; return (ArithSeq x (Just from_list_name) new_seq
+                     , fvs `plusFV` fvs') }
            else
-            return (ArithSeq noPostTcExpr Nothing new_seq, fvs) }
+            return (ArithSeq x Nothing new_seq, fvs) }
 
-rnExpr (PArrSeq _ seq)
+rnExpr (PArrSeq x seq)
   = do { (new_seq, fvs) <- rnArithSeq seq
-       ; return (PArrSeq noPostTcExpr new_seq, fvs) }
+       ; return (PArrSeq x new_seq, fvs) }
 
 {-
 These three are pattern syntax appearing in expressions.
@@ -352,7 +352,7 @@ Since all the symbols are reservedops we can simply reject them.
 We return a (bogus) EWildPat in each case.
 -}
 
-rnExpr EWildPat        = return (hsHoleExpr, emptyFVs)   -- "_" is just a hole
+rnExpr (EWildPat _)  = return (hsHoleExpr, emptyFVs)   -- "_" is just a hole
 rnExpr e@(EAsPat {})
   = do { opt_TypeApplications <- xoptM LangExt.TypeApplications
        ; let msg | opt_TypeApplications
@@ -407,11 +407,11 @@ rnExpr e@(HsStatic _ expr) = do
 ************************************************************************
 -}
 
-rnExpr (HsProc pat body)
+rnExpr (HsProc x pat body)
   = newArrowScope $
     rnPat ProcExpr pat $ \ pat' -> do
       { (body',fvBody) <- rnCmdTop body
-      ; return (HsProc pat' body', fvBody) }
+      ; return (HsProc x pat' body', fvBody) }
 
 -- Ideally, these would be done in parsing, but to keep parsing simple, we do it here.
 rnExpr e@(HsArrApp {})  = arrowFail e
@@ -420,8 +420,8 @@ rnExpr e@(HsArrForm {}) = arrowFail e
 rnExpr other = pprPanic "rnExpr: unexpected expression" (ppr other)
         -- HsWrap
 
-hsHoleExpr :: HsExpr id
-hsHoleExpr = HsUnboundVar (TrueExprHole (mkVarOcc "_"))
+hsHoleExpr :: HsExpr (GhcPass id)
+hsHoleExpr = HsUnboundVar noExt (TrueExprHole (mkVarOcc "_"))
 
 arrowFail :: HsExpr GhcPs -> RnM (HsExpr GhcRn, FreeVars)
 arrowFail e
@@ -434,17 +434,17 @@ arrowFail e
 ----------------------
 -- See Note [Parsing sections] in Parser.y
 rnSection :: HsExpr GhcPs -> RnM (HsExpr GhcRn, FreeVars)
-rnSection section@(SectionR op expr)
+rnSection section@(SectionR x op expr)
   = do  { (op', fvs_op)     <- rnLExpr op
         ; (expr', fvs_expr) <- rnLExpr expr
         ; checkSectionPrec InfixR section op' expr'
-        ; return (SectionR op' expr', fvs_op `plusFV` fvs_expr) }
+        ; return (SectionR x op' expr', fvs_op `plusFV` fvs_expr) }
 
-rnSection section@(SectionL expr op)
+rnSection section@(SectionL x expr op)
   = do  { (expr', fvs_expr) <- rnLExpr expr
         ; (op', fvs_op)     <- rnLExpr op
         ; checkSectionPrec InfixL section op' expr'
-        ; return (SectionL expr' op', fvs_op `plusFV` fvs_expr) }
+        ; return (SectionL x expr' op', fvs_op `plusFV` fvs_expr) }
 
 rnSection other = pprPanic "rnSection" (ppr other)
 
@@ -466,26 +466,26 @@ rnCmdArgs (arg:args)
 rnCmdTop :: LHsCmdTop GhcPs -> RnM (LHsCmdTop GhcRn, FreeVars)
 rnCmdTop = wrapLocFstM rnCmdTop'
  where
-  rnCmdTop' (HsCmdTop cmd _ _ _)
+  rnCmdTop' (HsCmdTop _ cmd)
    = do { (cmd', fvCmd) <- rnLCmd cmd
         ; let cmd_names = [arrAName, composeAName, firstAName] ++
                           nameSetElemsStable (methodNamesCmd (unLoc cmd'))
         -- Generate the rebindable syntax for the monad
         ; (cmd_names', cmd_fvs) <- lookupSyntaxNames cmd_names
 
-        ; return (HsCmdTop cmd' placeHolderType placeHolderType
-                  (cmd_names `zip` cmd_names'),
+        ; return (HsCmdTop (cmd_names `zip` cmd_names') cmd',
                   fvCmd `plusFV` cmd_fvs) }
+  rnCmdTop' (XCmdTop{}) = panic "rnCmdTop"
 
 rnLCmd :: LHsCmd GhcPs -> RnM (LHsCmd GhcRn, FreeVars)
 rnLCmd = wrapLocFstM rnCmd
 
 rnCmd :: HsCmd GhcPs -> RnM (HsCmd GhcRn, FreeVars)
 
-rnCmd (HsCmdArrApp arrow arg _ ho rtl)
+rnCmd (HsCmdArrApp x arrow arg ho rtl)
   = do { (arrow',fvArrow) <- select_arrow_scope (rnLExpr arrow)
        ; (arg',fvArg) <- rnLExpr arg
-       ; return (HsCmdArrApp arrow' arg' placeHolderType ho rtl,
+       ; return (HsCmdArrApp x arrow' arg' ho rtl,
                  fvArrow `plusFV` fvArg) }
   where
     select_arrow_scope tc = case ho of
@@ -498,9 +498,9 @@ rnCmd (HsCmdArrApp arrow arg _ ho rtl)
         -- inside 'arrow'.  In the higher-order case (-<<), they are.
 
 -- infix form
-rnCmd (HsCmdArrForm op _ (Just _) [arg1, arg2])
+rnCmd (HsCmdArrForm _ op _ (Just _) [arg1, arg2])
   = do { (op',fv_op) <- escapeArrowScope (rnLExpr op)
-       ; let L _ (HsVar (L _ op_name)) = op'
+       ; let L _ (HsVar _ (L _ op_name)) = op'
        ; (arg1',fv_arg1) <- rnCmdTop arg1
        ; (arg2',fv_arg2) <- rnCmdTop arg2
         -- Deal with fixity
@@ -508,47 +508,48 @@ rnCmd (HsCmdArrForm op _ (Just _) [arg1, arg2])
        ; final_e <- mkOpFormRn arg1' op' fixity arg2'
        ; return (final_e, fv_arg1 `plusFV` fv_op `plusFV` fv_arg2) }
 
-rnCmd (HsCmdArrForm op f fixity cmds)
+rnCmd (HsCmdArrForm x op f fixity cmds)
   = do { (op',fvOp) <- escapeArrowScope (rnLExpr op)
        ; (cmds',fvCmds) <- rnCmdArgs cmds
-       ; return (HsCmdArrForm op' f fixity cmds', fvOp `plusFV` fvCmds) }
+       ; return (HsCmdArrForm x op' f fixity cmds', fvOp `plusFV` fvCmds) }
 
-rnCmd (HsCmdApp fun arg)
+rnCmd (HsCmdApp x fun arg)
   = do { (fun',fvFun) <- rnLCmd  fun
        ; (arg',fvArg) <- rnLExpr arg
-       ; return (HsCmdApp fun' arg', fvFun `plusFV` fvArg) }
+       ; return (HsCmdApp x fun' arg', fvFun `plusFV` fvArg) }
 
-rnCmd (HsCmdLam matches)
+rnCmd (HsCmdLam x matches)
   = do { (matches', fvMatch) <- rnMatchGroup LambdaExpr rnLCmd matches
-       ; return (HsCmdLam matches', fvMatch) }
+       ; return (HsCmdLam x matches', fvMatch) }
 
-rnCmd (HsCmdPar e)
+rnCmd (HsCmdPar x e)
   = do  { (e', fvs_e) <- rnLCmd e
-        ; return (HsCmdPar e', fvs_e) }
+        ; return (HsCmdPar x e', fvs_e) }
 
-rnCmd (HsCmdCase expr matches)
+rnCmd (HsCmdCase x expr matches)
   = do { (new_expr, e_fvs) <- rnLExpr expr
        ; (new_matches, ms_fvs) <- rnMatchGroup CaseAlt rnLCmd matches
-       ; return (HsCmdCase new_expr new_matches, e_fvs `plusFV` ms_fvs) }
+       ; return (HsCmdCase x new_expr new_matches, e_fvs `plusFV` ms_fvs) }
 
-rnCmd (HsCmdIf _ p b1 b2)
+rnCmd (HsCmdIf x _ p b1 b2)
   = do { (p', fvP) <- rnLExpr p
        ; (b1', fvB1) <- rnLCmd b1
        ; (b2', fvB2) <- rnLCmd b2
        ; (mb_ite, fvITE) <- lookupIfThenElse
-       ; return (HsCmdIf mb_ite p' b1' b2', plusFVs [fvITE, fvP, fvB1, fvB2]) }
+       ; return (HsCmdIf x mb_ite p' b1' b2', plusFVs [fvITE, fvP, fvB1, fvB2])}
 
-rnCmd (HsCmdLet (L l binds) cmd)
+rnCmd (HsCmdLet x (L l binds) cmd)
   = rnLocalBindsAndThen binds $ \ binds' _ -> do
       { (cmd',fvExpr) <- rnLCmd cmd
-      ; return (HsCmdLet (L l binds') cmd', fvExpr) }
+      ; return (HsCmdLet x (L l binds') cmd', fvExpr) }
 
-rnCmd (HsCmdDo (L l stmts) _)
+rnCmd (HsCmdDo x (L l stmts))
   = do  { ((stmts', _), fvs) <-
             rnStmts ArrowExpr rnLCmd stmts (\ _ -> return ((), emptyFVs))
-        ; return ( HsCmdDo (L l stmts') placeHolderType, fvs ) }
+        ; return ( HsCmdDo x (L l stmts'), fvs ) }
 
 rnCmd cmd@(HsCmdWrap {}) = pprPanic "rnCmd" (ppr cmd)
+rnCmd cmd@(XCmd {})      = pprPanic "rnCmd" (ppr cmd)
 
 ---------------------------------------------------
 type CmdNeeds = FreeVars        -- Only inhabitants are
@@ -560,26 +561,28 @@ methodNamesLCmd = methodNamesCmd . unLoc
 
 methodNamesCmd :: HsCmd GhcRn -> CmdNeeds
 
-methodNamesCmd (HsCmdArrApp _arrow _arg _ HsFirstOrderApp _rtl)
+methodNamesCmd (HsCmdArrApp _ _arrow _arg HsFirstOrderApp _rtl)
   = emptyFVs
-methodNamesCmd (HsCmdArrApp _arrow _arg _ HsHigherOrderApp _rtl)
+methodNamesCmd (HsCmdArrApp _ _arrow _arg HsHigherOrderApp _rtl)
   = unitFV appAName
 methodNamesCmd (HsCmdArrForm {}) = emptyFVs
-methodNamesCmd (HsCmdWrap _ cmd) = methodNamesCmd cmd
+methodNamesCmd (HsCmdWrap _ _ cmd) = methodNamesCmd cmd
 
-methodNamesCmd (HsCmdPar c) = methodNamesLCmd c
+methodNamesCmd (HsCmdPar _ c) = methodNamesLCmd c
 
-methodNamesCmd (HsCmdIf _ _ c1 c2)
+methodNamesCmd (HsCmdIf _ _ _ c1 c2)
   = methodNamesLCmd c1 `plusFV` methodNamesLCmd c2 `addOneFV` choiceAName
 
-methodNamesCmd (HsCmdLet _ c)          = methodNamesLCmd c
-methodNamesCmd (HsCmdDo (L _ stmts) _) = methodNamesStmts stmts
-methodNamesCmd (HsCmdApp c _)          = methodNamesLCmd c
-methodNamesCmd (HsCmdLam match)        = methodNamesMatch match
+methodNamesCmd (HsCmdLet _ _ c)          = methodNamesLCmd c
+methodNamesCmd (HsCmdDo _ (L _ stmts))   = methodNamesStmts stmts
+methodNamesCmd (HsCmdApp _ c _)          = methodNamesLCmd c
+methodNamesCmd (HsCmdLam _ match)        = methodNamesMatch match
 
-methodNamesCmd (HsCmdCase _ matches)
+methodNamesCmd (HsCmdCase _ _ matches)
   = methodNamesMatch matches `addOneFV` choiceAName
 
+methodNamesCmd (XCmd {}) = panic "methodNamesCmd"
+
 --methodNamesCmd _ = emptyFVs
    -- Other forms can't occur in commands, but it's not convenient
    -- to error here so we just do what's convenient.
@@ -863,7 +866,7 @@ rnStmt ctxt rnBody (L loc (BindStmt pat body _ _ _)) thing_inside
 
         ; rnPat (StmtCtxt ctxt) pat $ \ pat' -> do
         { (thing, fvs3) <- thing_inside (collectPatBinders pat')
-        ; return (( [( L loc (BindStmt pat' body' bind_op fail_op PlaceHolder)
+        ; return (( [( L loc (BindStmt pat' body' bind_op fail_op placeHolder)
                      , fv_expr )]
                   , thing),
                   fv_expr `plusFV` fvs1 `plusFV` fvs2 `plusFV` fvs3) }}
@@ -946,7 +949,7 @@ rnStmt ctxt _ (L loc (TransStmt { trS_stmts = stmts, trS_by = by, trS_form = for
        ; return (([(L loc (TransStmt { trS_stmts = stmts', trS_bndrs = bndr_map
                                     , trS_by = by', trS_using = using', trS_form = form
                                     , trS_ret = return_op, trS_bind = bind_op
-                                    , trS_bind_arg_ty = PlaceHolder
+                                    , trS_bind_arg_ty = placeHolder
                                     , trS_fmap = fmap_op }), fvs2)], thing), all_fvs) }
 
 rnStmt _ _ (L _ ApplicativeStmt{}) _ =
@@ -971,7 +974,7 @@ rnParallelStmts ctxt return_op segs thing_inside
            ; (thing, fvs) <- bindLocalNames bndrs' (thing_inside bndrs')
            ; return (([], thing), fvs) }
 
-    rn_segs env bndrs_so_far (ParStmtBlock stmts _ _ : segs)
+    rn_segs env bndrs_so_far (ParStmtBlock x stmts _ _ : segs)
       = do { ((stmts', (used_bndrs, segs', thing)), fvs)
                     <- rnStmts ctxt rnLExpr stmts $ \ bndrs ->
                        setLocalRdrEnv env       $ do
@@ -979,8 +982,9 @@ rnParallelStmts ctxt return_op segs thing_inside
                        ; let used_bndrs = filter (`elemNameSet` fvs) bndrs
                        ; return ((used_bndrs, segs', thing), fvs) }
 
-           ; let seg' = ParStmtBlock stmts' used_bndrs return_op
+           ; let seg' = ParStmtBlock x stmts' used_bndrs return_op
            ; return ((seg':segs', thing), fvs) }
+    rn_segs _ _ (XParStmtBlock{}:_) = panic "rnParallelStmts"
 
     cmpByOcc n1 n2 = nameOccName n1 `compare` nameOccName n2
     dupErr vs = addErr (text "Duplicate binding in parallel list comprehension for:"
@@ -1000,12 +1004,12 @@ lookupStmtNamePoly ctxt name
   = do { rebindable_on <- xoptM LangExt.RebindableSyntax
        ; if rebindable_on
          then do { fm <- lookupOccRn (nameRdrName name)
-                 ; return (HsVar (noLoc fm), unitFV fm) }
+                 ; return (HsVar noExt (noLoc fm), unitFV fm) }
          else not_rebindable }
   | otherwise
   = not_rebindable
   where
-    not_rebindable = return (HsVar (noLoc name), emptyFVs)
+    not_rebindable = return (HsVar noExt (noLoc name), emptyFVs)
 
 -- | Is this a context where we respect RebindableSyntax?
 -- but ListComp/PArrComp are never rebindable
@@ -1095,7 +1099,7 @@ rnRecStmtsAndThen rnBody s cont
 collectRecStmtsFixities :: [LStmtLR GhcPs GhcPs body] -> [LFixitySig GhcPs]
 collectRecStmtsFixities l =
     foldr (\ s -> \acc -> case s of
-            (L _ (LetStmt (L _ (HsValBinds (ValBindsIn _ sigs))))) ->
+            (L _ (LetStmt (L _ (HsValBinds (ValBinds _ _ sigs))))) ->
                 foldr (\ sig -> \ acc -> case sig of
                                            (L loc (FixSig s)) -> (L loc s) : acc
                                            _ -> acc) acc sigs
@@ -1196,7 +1200,7 @@ rn_rec_stmt rnBody _ (L loc (BindStmt pat' body _ _ _), fv_pat)
        ; let bndrs = mkNameSet (collectPatBinders pat')
              fvs   = fv_expr `plusFV` fv_pat `plusFV` fvs1 `plusFV` fvs2
        ; return [(bndrs, fvs, bndrs `intersectNameSet` fvs,
-                  L loc (BindStmt pat' body' bind_op fail_op PlaceHolder))] }
+                  L loc (BindStmt pat' body' bind_op fail_op placeHolder))] }
 
 rn_rec_stmt _ _ (L _ (LetStmt (L _ binds@(HsIPBinds _))), _)
   = failWith (badIpBinds (text "an mdo expression") binds)
@@ -1700,7 +1704,7 @@ stmtTreeToStmts monad_names ctxt (StmtTreeApplicative trees) tail tail_fvs = do
              return (unLoc tup, emptyNameSet)
            | otherwise -> do
              (ret,fvs) <- lookupStmtNamePoly ctxt returnMName
-             return (HsApp (noLoc ret) tup, fvs)
+             return (HsApp noExt (noLoc ret) tup, fvs)
      return ( ApplicativeArgMany stmts' mb_ret pat
             , fvs1 `plusFV` fvs2)
 
@@ -1786,25 +1790,24 @@ can do with the rest of the statements in the same "do" expression.
 isStrictPattern :: LPat id -> Bool
 isStrictPattern (L _ pat) =
   case pat of
-    WildPat{} -> False
-    VarPat{}  -> False
-    LazyPat{} -> False
-    AsPat _ p -> isStrictPattern p
-    ParPat p  -> isStrictPattern p
-    ViewPat _ p _ -> isStrictPattern p
-    SigPatIn p _ -> isStrictPattern p
-    SigPatOut p _ -> isStrictPattern p
-    BangPat{} -> True
-    ListPat{} -> True
-    TuplePat{} -> True
-    SumPat{} -> True
-    PArrPat{} -> True
-    ConPatIn{} -> True
-    ConPatOut{} -> True
-    LitPat{} -> True
-    NPat{} -> True
-    NPlusKPat{} -> True
-    SplicePat{} -> True
+    WildPat{}       -> False
+    VarPat{}        -> False
+    LazyPat{}       -> False
+    AsPat _ _ p     -> isStrictPattern p
+    ParPat _ p      -> isStrictPattern p
+    ViewPat _ _ p   -> isStrictPattern p
+    SigPat _ p      -> isStrictPattern p
+    BangPat{}       -> True
+    ListPat{}       -> True
+    TuplePat{}      -> True
+    SumPat{}        -> True
+    PArrPat{}       -> True
+    ConPatIn{}      -> True
+    ConPatOut{}     -> True
+    LitPat{}        -> True
+    NPat{}          -> True
+    NPlusKPat{}     -> True
+    SplicePat{}     -> True
     _otherwise -> panic "isStrictPattern"
 
 isLetStmt :: LStmt a b -> Bool
@@ -1912,15 +1915,15 @@ needJoin _monad_names stmts = (True, stmts)
 isReturnApp :: MonadNames
             -> LHsExpr GhcRn
             -> Maybe (LHsExpr GhcRn)
-isReturnApp monad_names (L _ (HsPar expr)) = isReturnApp monad_names expr
+isReturnApp monad_names (L _ (HsPar _ expr)) = isReturnApp monad_names expr
 isReturnApp monad_names (L _ e) = case e of
-  OpApp l op _ r | is_return l, is_dollar op -> Just r
-  HsApp f arg    | is_return f               -> Just arg
+  OpApp _ l op r | is_return l, is_dollar op -> Just r
+  HsApp _ f arg  | is_return f               -> Just arg
   _otherwise -> Nothing
  where
-  is_var f (L _ (HsPar e)) = is_var f e
-  is_var f (L _ (HsAppType e _)) = is_var f e
-  is_var f (L _ (HsVar (L _ r))) = f r
+  is_var f (L _ (HsPar _ e)) = is_var f e
+  is_var f (L _ (HsAppType _ e)) = is_var f e
+  is_var f (L _ (HsVar _ (L _ r))) = f r
        -- TODO: I don't know how to get this right for rebindable syntax
   is_var _ _ = False
 
@@ -2102,7 +2105,7 @@ patSynErr :: HsExpr GhcPs -> SDoc -> RnM (HsExpr GhcRn, FreeVars)
 patSynErr e explanation = do { addErr (sep [text "Pattern syntax in expression context:",
                                 nest 4 (ppr e)] $$
                                   explanation)
-                 ; return (EWildPat, emptyFVs) }
+                 ; return (EWildPat noExt, emptyFVs) }
 
 badIpBinds :: Outputable a => SDoc -> a -> SDoc
 badIpBinds what binds