Introduce and use ConGadtSigBody (preparatory refactor for #18389)wip/T18389-task-zero

This patch removes the `con_g_args :: HsConDeclGADTDetails pass` and
`con_res_ty :: LHsType pass` fields of `ConDeclGADT` in favor of a unified
`con_body :: ConGadtSigBody pass` field. There are two major differences
between `HsConDeclGADTDetails` and `ConGadtSigBody`:

1. `HsConDeclGADTDetails` only contains the argument type, while
   `ConGadtSigBody` contains both the argument and result types.
2. The `PrefixConGADT` constructor of `ConGadtSigBody` now uses a new
   `PrefixConGadtSigBody` data type. `PrefixConGadtSigBody` closely mirrors the
   structure of `HsType`, but with minor, data constructor–specific tweaks.
   This will become vital in a future patch which implements nested `forall`s
   and contexts in prefix GADT constructor types (see #18389).

Besides the refactoring in the GHC API (and some minor changes in
GHC AST–related test cases) this does not introduce any user-visible
changes in behavior.

2 files changed, 13 insertions, 6 deletions

diff --git a/utils/check-exact/ExactPrint.hs b/utils/check-exact/ExactPrint.hs
index 3d493cfd22..0e81894017 100644
--- a/utils/check-exact/ExactPrint.hs
+++ b/utils/check-exact/ExactPrint.hs
@@ -3224,8 +3224,8 @@ instance ExactPrint (ConDecl GhcPs) where
   exact (ConDeclGADT { con_g_ext = an
                      , con_names = cons
                      , con_bndrs = bndrs
-                     , con_mb_cxt = mcxt, con_g_args = args
-                     , con_res_ty = res_ty, con_doc = doc }) = do
+                     , con_mb_cxt = mcxt
+                     , con_body = body, con_doc = doc }) = do
     mapM_ markAnnotated doc
     mapM_ markAnnotated cons
     markEpAnn an AnnDcolon
@@ -3237,13 +3237,14 @@ instance ExactPrint (ConDecl GhcPs) where
     mapM_ markAnnotated mcxt
     when (isJust mcxt) $ markEpAnn an AnnDarrow
     -- mapM_ markAnnotated args
-    case args of
-        PrefixConGADT args' -> mapM_ markAnnotated args'
-        RecConGADT fields arr -> do
+    case body of
+        PrefixConGADT body' ->
+          exact_prefix_con_gadt_sig_body body'
+        RecConGADT fields arr res_ty -> do
           markAnnotated fields
           markUniToken arr
+          markAnnotated res_ty
           -- mapM_ markAnnotated (unLoc fields)
-    markAnnotated res_ty
   -- markAST _ (GHC.ConDeclGADT _ lns (GHC.L l forall) qvars mbCxt args typ _) = do
   --   setContext (Set.singleton PrefixOp) $ markListIntercalate lns
   --   mark GHC.AnnDcolon
@@ -3254,6 +3255,12 @@ instance ExactPrint (ConDecl GhcPs) where
   --   markLocated typ
   --   markManyOptional GHC.AnnCloseP
   --   markTrailingSemi
+      where
+        exact_prefix_con_gadt_sig_body (PCGSRes res_ty) =
+          markAnnotated res_ty
+        exact_prefix_con_gadt_sig_body (PCGSAnonArg arg_ty body') = do
+          markAnnotated arg_ty
+          exact_prefix_con_gadt_sig_body body'
 
 -- pprConDecl (ConDeclGADT { con_names = cons, con_qvars = qvars
 --                         , con_mb_cxt = mcxt, con_args = args
diff --git a/utils/haddock b/utils/haddock
-Subproject 58237d76c96325f25627bfd7cdad5b93364d29a
+Subproject d1aa841631b018c00b65e7a129c7e103cc8df6a