rewrite case jane_syntax to use extension nodes

ocaml/parsing/jane_syntax_parsing.ml

@@ -569,18 +569,15 @@ module Make_with_extension_node
     (AST_syntactic_category : sig
        include AST_syntactic_category
 
-       (** How to construct an extension node for this AST (something of the
-          shape [[%name]]). Should just be [Ast_helper.CAT.extension] for the
-          appropriate syntactic category [CAT]. (This means that [?loc] should
-          default to [!Ast_helper.default_loc.].) *)
-      val make_extension_node :
-        ?loc:Location.t -> ?attrs:attributes -> extension -> ast
-
-      (** Given an extension node (as created by [make_extension_node]) with an
-          appropriately-formed name and a body, combine them into the special
-          syntactic form we use for novel syntactic features in this syntactic
-          category. Partial inverse of [match_extension_use]. *)
-      val make_extension_use  : extension_node:ast -> ast -> ast
+      (** Combine information about a construct into the special syntactic form
+          we use for novel syntactic features in this syntactic category. The
+          form should contain an extension_node of the shape [[%name]],
+          constructed by [Ast_helper.CAT.extension] for the appropriate
+          syntactic category [CAT], so that [?loc] defaults to
+          [!Ast_helper.default_loc].
+          Partial inverse of [match_extension_use]. *)
+      val make_extension_use :
+        ?loc:Location.t -> ?attrs:attributes -> extension -> ast -> ast
 
       (** Given an AST node, check if it's of the special syntactic form
           indicating that this is one of our novel syntactic features (as
@@ -597,12 +594,10 @@ module Make_with_extension_node
 
     let make_jane_syntax name ast =
       make_extension_use
+        ( { txt = Embedded_name.to_string name
+          ; loc = !Ast_helper.default_loc }
+        , PStr [])
         ast
-        ~extension_node:
-          (make_extension_node
-             ({ txt = Embedded_name.to_string name
-              ; loc = !Ast_helper.default_loc },
-              PStr []))
 
     let match_jane_syntax ast =
       match match_extension_use ast with
@@ -659,8 +654,8 @@ module Expression0 = Make_with_attribute (struct
   let with_attributes expr pexp_attributes = { expr with pexp_attributes }
 end)
 
-(** Cases; embedded using an attribute on the rhs. *)
-module Case0 = Make_with_attribute (struct
+(** Cases; embedded using an extension node. *)
+module Case0 = Make_with_extension_node (struct
   type ast = case
 
   let plural = "cases"
@@ -669,10 +664,15 @@ module Case0 = Make_with_attribute (struct
     let pc_rhs = { case.pc_rhs with pexp_loc = l } in
     { case with pc_rhs  }
 
-  let attributes case = case.pc_rhs.pexp_attributes
-  let with_attributes case pexp_attributes =
-    let pc_rhs = { case.pc_rhs with pexp_attributes = pexp_attributes } in
-    { case with pc_rhs }
+  let make_extension_use ?loc ?attrs extension ast =
+    let ext = Ast_helper.Exp.extension ?loc ?attrs extension in
+    { ast with pc_rhs = Ast_helper.Exp.apply ext [ Nolabel, ast.pc_rhs ] }
+
+  let match_extension_use case =
+    match case.pc_rhs.pexp_desc with
+    | Pexp_apply ({ pexp_desc = Pexp_extension ext }, [ Nolabel, pc_rhs ]) ->
+        Some (ext, { case with pc_rhs })
+    | _ -> None
 end)
 
 (** Patterns; embedded using an attribute on the pattern. *)
@@ -723,9 +723,8 @@ module Signature_item0 = Make_with_extension_node (struct
     let location sigi = sigi.psig_loc
     let with_location sigi l = { sigi with psig_loc = l }
 
-    let make_extension_node = Ast_helper.Sig.extension
-
-    let make_extension_use ~extension_node sigi =
+    let make_extension_use ?loc ?attrs extension sigi =
+      let extension_node = Ast_helper.Sig.extension ?loc ?attrs extension in
       Ast_helper.Sig.include_
         { pincl_mod = Ast_helper.Mty.signature [extension_node; sigi]
         ; pincl_loc = !Ast_helper.default_loc
@@ -758,9 +757,8 @@ module Structure_item0 = Make_with_extension_node (struct
     let location stri = stri.pstr_loc
     let with_location stri l = { stri with pstr_loc = l }
 
-    let make_extension_node = Ast_helper.Str.extension
-
-    let make_extension_use ~extension_node stri =
+    let make_extension_use ?loc ?attrs extension stri =
+      let extension_node = Ast_helper.Str.extension ?loc ?attrs extension in
       Ast_helper.Str.include_
         { pincl_mod = Ast_helper.Mod.structure [extension_node; stri]
         ; pincl_loc = !Ast_helper.default_loc