fix loc of duplicate label error to be the loc of the type definition with the spreads, not one of the duplicate labels

Author: zth

jscomp/build_tests/super_errors/expected/record_type_spreads.res.expected

@@ -1,11 +1,10 @@
 
   We've found a bug for you!
-  /.../fixtures/record_type_spreads.res:3:12-20
+  /.../fixtures/record_type_spreads.res:5:1-23
 
-  1 │ type t = {x: int, y: string}
-  2 │ 
-  3 │ type t2 = {x: string, y: float}
+  3 │ type t2 = {x: string, y: float}
   4 │ 
-  5 │ type t3 = {...t, ...t2}
+  5 │ type t3 = {...t, ...t2}
+  6 │ 
 
   Two labels are named x

jscomp/ml/typedecl.ml

@@ -470,15 +470,15 @@ let transl_declaration ~typeRecordAsObject env sdecl id =
               in
               process_lbls ([], []) lbls lbls'
             | _ -> Some (lbls, lbls') in
-          let rec check_duplicates (lbls : Typedtree.label_declaration list) seen = match lbls with
+          let rec check_duplicates loc (lbls : Typedtree.label_declaration list) seen = match lbls with
           | [] -> ()
           | lbl::rest ->
             let name = lbl.ld_id.name in
-            if StringSet.mem name seen then raise(Error(lbl.ld_loc, Duplicate_label name));
-            check_duplicates rest (StringSet.add name seen) in
+            if StringSet.mem name seen then raise(Error(loc, Duplicate_label name));
+            check_duplicates loc rest (StringSet.add name seen) in
           (match lbls_opt with
           | Some (lbls, lbls') ->
-            check_duplicates lbls StringSet.empty;
+            check_duplicates sdecl.ptype_loc lbls StringSet.empty;
             Ttype_record lbls, Type_record(lbls', rep), sdecl
           | None ->
              (* Could not find record type decl for ...t: assume t is an object type and this is syntax ambiguity *)