Remove ConDeclGADTPrefixPs

This removes the `ConDeclGADTPrefixPs` per the discussion in #18517.
Most of this patch simply removes code, although the code in the
`rnConDecl` case for `ConDeclGADTPrefixPs` had to be moved around a
bit:

* The nested `forall`s check now lives in the `rnConDecl` case for
  `ConDeclGADT`.
* The `LinearTypes`-specific code that used to live in the
  `rnConDecl` case for `ConDeclGADTPrefixPs` now lives in
  `GHC.Parser.PostProcess.mkGadtDecl`, which is now monadic so that
  it can check if `-XLinearTypes` is enabled.

Fixes #18157.

1 files changed, 6 insertions, 42 deletions

diff --git a/compiler/GHC/Rename/Module.hs b/compiler/GHC/Rename/Module.hs
index 2bcee1f15f..5e82ebdb7f 100644
--- a/compiler/GHC/Rename/Module.hs
+++ b/compiler/GHC/Rename/Module.hs
@@ -1856,7 +1856,6 @@ rnDataDefn doc (HsDataDefn { dd_ND = new_or_data, dd_cType = cType
   where
     h98_style = case condecls of  -- Note [Stupid theta]
                      (L _ (ConDeclGADT {}))                    : _ -> False
-                     (L _ (XConDecl (ConDeclGADTPrefixPs {}))) : _ -> False
                      _                                             -> True
 
     rn_derivs (L loc ds)
@@ -2246,6 +2245,12 @@ rnConDecl decl@(ConDeclGADT { con_names   = names
         ; (new_args, fvs2)   <- rnConDeclDetails (unLoc (head new_names)) ctxt args
         ; (new_res_ty, fvs3) <- rnLHsType ctxt res_ty
 
+         -- Ensure that there are no nested `forall`s or contexts, per
+         -- Note [GADT abstract syntax] (Wrinkle: No nested foralls or contexts)
+         -- in GHC.Hs.Type.
+       ; addNoNestedForallsContextsErr ctxt
+           (text "GADT constructor type signature") new_res_ty
+
         ; let all_fvs = fvs1 `plusFV` fvs2 `plusFV` fvs3
 
         ; traceRn "rnConDecl (ConDeclGADT)"
@@ -2257,47 +2262,6 @@ rnConDecl decl@(ConDeclGADT { con_names   = names
                        , con_forall = forall }, -- Remove when #18311 is fixed
                   all_fvs) } }
 
--- This case is only used for prefix GADT constructors generated by GHC's
--- parser, where we do not know the argument types until type operator
--- precedence has been resolved. See Note [GADT abstract syntax] in
--- GHC.Hs.Decls for the full story.
-rnConDecl (XConDecl (ConDeclGADTPrefixPs { con_gp_names = names, con_gp_ty = ty
-                                         , con_gp_doc = mb_doc }))
-  = do { mapM_ (addLocM checkConName) names
-       ; new_names <- mapM lookupLocatedTopBndrRn names
-       ; mb_doc'   <- rnMbLHsDoc mb_doc
-
-       ; let ctxt = ConDeclCtx new_names
-       ; (ty', fvs) <- rnHsSigType ctxt TypeLevel ty
-       ; linearTypes <- xopt LangExt.LinearTypes <$> getDynFlags
-
-         -- Now that operator precedence has been resolved, we can split the
-         -- GADT type into its individual components below.
-       ; let HsIB { hsib_ext = implicit_tkvs, hsib_body = body } = ty'
-             (mb_explicit_tkvs, mb_cxt, tau) = splitLHsGADTPrefixTy body
-             lhas_forall       = L (getLoc body) $ isJust mb_explicit_tkvs
-             explicit_tkvs     = fromMaybe [] mb_explicit_tkvs
-             (arg_tys, res_ty) = splitHsFunType tau
-             arg_details | linearTypes = PrefixCon arg_tys
-                         | otherwise   = PrefixCon $ map (hsLinear . hsScaledThing) arg_tys
-
-               -- NB: The only possibility here is PrefixCon. RecCon is handled
-               -- separately, through ConDeclGADT, from the parser onwards.
-
-         -- Ensure that there are no nested `forall`s or contexts, per
-         -- Note [GADT abstract syntax] (Wrinkle: No nested foralls or contexts)
-         -- in GHC.Hs.Type.
-       ; addNoNestedForallsContextsErr ctxt
-           (text "GADT constructor type signature") res_ty
-
-       ; traceRn "rnConDecl (ConDeclGADTPrefixPs)"
-           (ppr names $$ ppr implicit_tkvs $$ ppr explicit_tkvs)
-       ; pure (ConDeclGADT { con_g_ext = implicit_tkvs, con_names = new_names
-                           , con_forall = lhas_forall, con_qvars = explicit_tkvs
-                           , con_mb_cxt = mb_cxt, con_args = arg_details
-                           , con_res_ty = res_ty, con_doc = mb_doc' },
-               fvs) }
-
 rnMbContext :: HsDocContext -> Maybe (LHsContext GhcPs)
             -> RnM (Maybe (LHsContext GhcRn), FreeVars)
 rnMbContext _    Nothing    = return (Nothing, emptyFVs)