Add support for 5.4 bivariant params in Psig_typesubst

Signed-off-by: Nathan Rebours <nathan.rebours@ocamlpro.com>

Author: Nathan Rebours

astlib/encoding_504.ml

@@ -406,15 +406,23 @@ module To_503 = struct
     in
     Psig_extension (ext, [])
 
+  let encode_bivariant_psig_typesubst ~loc tds =
+    let loc = { loc with Location.loc_ghost = true } in
+    let ext =
+      ( { txt = Ext_name.bivariant_psig; loc },
+        PSig [ { psig_loc = loc; psig_desc = Psig_typesubst tds } ] )
+    in
+    Psig_extension (ext, [])
+
   let decode_bivariant_pstr ~loc payload =
     match payload with
     | PStr [ { pstr_desc = Pstr_type _ as x; _ } ] -> x
     | _ -> invalid_encoding ~loc "bivariant structure_item"
 
   let decode_bivariant_psig ~loc payload =
     match payload with
-    | PSig [ { psig_desc = Psig_type _ as x; _ } ] -> x
-    | _ -> invalid_encoding ~loc "bivariant structure_item"
+    | PSig [ { psig_desc = (Psig_type _ | Psig_typesubst _) as x; _ } ] -> x
+    | _ -> invalid_encoding ~loc "bivariant signature_item"
 end
 
 module To_502 = struct

astlib/encoding_504.mli

@@ -43,6 +43,9 @@ module To_503 : sig
   val encode_bivariant_psig_type :
     loc:Location.t -> rec_flag -> type_declaration list -> signature_item_desc
 
+  val encode_bivariant_psig_typesubst :
+    loc:Location.t -> type_declaration list -> signature_item_desc
+
   val decode_bivariant_pstr : loc:Location.t -> payload -> structure_item_desc
   val decode_bivariant_psig : loc:Location.t -> payload -> signature_item_desc
 end

astlib/migrate_504_503.ml

@@ -838,8 +838,11 @@ and copy_signature_item_desc_with_loc ~loc :
       | tds -> Ast_503.Parsetree.Psig_type (rec_flag, tds)
       | exception Bivariant_param.Type_decl_list tds ->
           Encoding_504.To_503.encode_bivariant_psig_type ~loc rec_flag tds)
-  | Ast_504.Parsetree.Psig_typesubst x0 ->
-      Ast_503.Parsetree.Psig_typesubst (List.map copy_type_declaration x0)
+  | Ast_504.Parsetree.Psig_typesubst x0 -> (
+      match copy_type_declaration_list x0 with
+      | tds -> Ast_503.Parsetree.Psig_typesubst tds
+      | exception Bivariant_param.Type_decl_list tds ->
+          Encoding_504.To_503.encode_bivariant_psig_typesubst ~loc tds)
   | Ast_504.Parsetree.Psig_typext x0 ->
       Ast_503.Parsetree.Psig_typext (copy_type_extension x0)
   | Ast_504.Parsetree.Psig_exception x0 ->

test/encoding/504/migrations/run.t

@@ -60,10 +60,13 @@ Bivariant are also correctly handled in a signature context:
 
   $ cat > bivariant.mli << EOF
   > type +-'a t
+  > type +-'a u := 'a v
   > EOF
 
   $ ./id_driver.exe bivariant.mli
   [%%ppxlib.migration.bivariant_sig_item_5_4 : type 'a t]
+  [%%ppxlib.migration.bivariant_sig_item_5_4 : type 'a u := 'a v]
 
   $ ./id_driver.exe bivariant.mli --use-compiler-pp
   type +-'a t
+  type +-'a u := 'a v