experiment with allowing empty inline records

Author: zth

jscomp/ml/typecore.ml

@@ -1273,7 +1273,7 @@ and type_pat_aux ~constrs ~labels ~no_existentials ~mode ~explode ~env
         | _            -> k None
       end
   | Ppat_record(lid_sp_list, closed) ->
-      assert (lid_sp_list <> []);
+      (*assert (lid_sp_list <> []);*)
       let opath, record_ty =
         try
           let (p0, p, _, _) = extract_concrete_record !env expected_ty in

jscomp/syntax/src/res_core.ml

@@ -4544,7 +4544,6 @@ and parseConstrDeclArgs p =
       (* TODO: this could use some cleanup/stratification *)
       match p.Parser.token with
       | Lbrace -> (
-        let lbrace = p.startPos in
         Parser.next p;
         let startPos = p.Parser.startPos in
         match p.Parser.token with
@@ -4683,14 +4682,6 @@ and parseConstrDeclArgs p =
                 :: parseCommaDelimitedRegion ~grammar:Grammar.FieldDeclarations
                      ~closing:Rbrace ~f:parseFieldDeclarationRegion p
             in
-            let () =
-              match fields with
-              | [] ->
-                Parser.err ~startPos:lbrace p
-                  (Diagnostics.message
-                     "An inline record declaration needs at least one field")
-              | _ -> ()
-            in
             Parser.expect Rbrace p;
             Parser.optional p Comma |> ignore;
             Parser.expect Rparen p;

jscomp/test/inline_record_test.js

@@ -117,3 +117,12 @@ let ff1 = (x: t1): t1 =>
   }
 
 let () = Mt.from_pair_suites(__MODULE__, suites.contents)
+
+type emptyRecord = A | B({})
+
+let b = B({})
+
+let () = switch b {
+| A => Js.log("A!")
+| B(_) => Js.log("B")
+}