Desugar RecordUpd in `tcExpr`wip/T18802

This patch typechecks record updates by desugaring them inside
the typechecker using the HsExpansion mechanism, and then typechecking
this desugared result.

Example:

    data T p q = T1 { x :: Int, y :: Bool, z :: Char }
               | T2 { v :: Char }
               | T3 { x :: Int }
               | T4 { p :: Float, y :: Bool, x :: Int }
               | T5

The record update `e { x=e1, y=e2 }` desugars as follows

  e { x=e1, y=e2 }
    ===>
  let { x' = e1; y' = e2 } in
  case e of
     T1 _ _ z -> T1 x' y' z
     T4 p _ _ -> T4 p y' x'

The desugared expression is put into an HsExpansion, and we typecheck
that.

The full details are given in Note [Record Updates] in GHC.Tc.Gen.Expr.

Fixes #2595 #3632 #10808 #10856 #16501 #18311 #18802 #21158 #21289

Updates haddock submodule

1 files changed, 0 insertions, 36 deletions

diff --git a/compiler/GHC/Tc/Utils/Zonk.hs b/compiler/GHC/Tc/Utils/Zonk.hs
index eee43e8ed1..6fa47f8b64 100644
--- a/compiler/GHC/Tc/Utils/Zonk.hs
+++ b/compiler/GHC/Tc/Utils/Zonk.hs
@@ -857,32 +857,6 @@ zonkExpr env expr@(RecordCon { rcon_ext = con_expr, rcon_flds = rbinds })
         ; return (expr { rcon_ext  = new_con_expr
                        , rcon_flds = new_rbinds }) }
 
--- Record updates via dot syntax are replaced by desugared expressions
--- in the renamer. See Note [Rebindable syntax and HsExpansion]. This
--- is why we match on 'rupd_flds = Left rbinds' here and panic otherwise.
-zonkExpr env (RecordUpd { rupd_flds = Left rbinds
-                        , rupd_expr = expr
-                        , rupd_ext = RecordUpdTc {
-                                       rupd_cons = cons
-                                     , rupd_in_tys = in_tys
-                                     , rupd_out_tys = out_tys
-                                     , rupd_wrap = req_wrap }})
-  = do  { new_expr    <- zonkLExpr env expr
-        ; new_in_tys  <- mapM (zonkTcTypeToTypeX env) in_tys
-        ; new_out_tys <- mapM (zonkTcTypeToTypeX env) out_tys
-        ; new_rbinds  <- zonkRecUpdFields env rbinds
-        ; (_, new_recwrap) <- zonkCoFn env req_wrap
-        ; return (
-            RecordUpd {
-                  rupd_expr = new_expr
-                , rupd_flds = Left new_rbinds
-                , rupd_ext = RecordUpdTc {
-                               rupd_cons = cons
-                             , rupd_in_tys = new_in_tys
-                             , rupd_out_tys = new_out_tys
-                             , rupd_wrap = new_recwrap }}) }
-zonkExpr _ (RecordUpd {}) = panic "GHC.Tc.Utils.Zonk: zonkExpr: The impossible happened!"
-
 zonkExpr env (ExprWithTySig _ e ty)
   = do { e' <- zonkLExpr env e
        ; return (ExprWithTySig noExtField e' ty) }
@@ -1309,16 +1283,6 @@ zonkRecFields env (HsRecFields flds dd)
            ; return (L l (fld { hfbLHS = new_id
                               , hfbRHS = new_expr })) }
 
-zonkRecUpdFields :: ZonkEnv -> [LHsRecUpdField GhcTc]
-                 -> TcM [LHsRecUpdField GhcTc]
-zonkRecUpdFields env = mapM zonk_rbind
-  where
-    zonk_rbind (L l fld)
-      = do { new_id   <- wrapLocMA (zonkFieldOcc env) (hsRecUpdFieldOcc fld)
-           ; new_expr <- zonkLExpr env (hfbRHS fld)
-           ; return (L l (fld { hfbLHS = fmap ambiguousFieldOcc new_id
-                              , hfbRHS = new_expr })) }
-
 {-
 ************************************************************************
 *                                                                      *