Fix record type spread loc (rescript-lang#6157)

Author: zth

CHANGELOG.md

@@ -16,6 +16,7 @@
 
 - Fix broken formatting in uncurried mode for functions with _ placeholder args. https://github.com/rescript-lang/rescript-compiler/pull/6148
 - Fix issue where spreading record types with optional labels would not have their labels preserved as optional. https://github.com/rescript-lang/rescript-compiler/pull/6154
+- Fix error location to be the type with the spreads when spreading record types with duplicate labels. https://github.com/rescript-lang/rescript-compiler/pull/6157
 
 # 11.0.0-alpha.3
 

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

@@ -0,0 +1,10 @@
+
+  We've found a bug for you!
+  /.../fixtures/record_type_spreads.res:5:1-23
+
+  3 │ type t2 = {x: string, y: float}
+  4 │ 
+  5 │ type t3 = {...t, ...t2}
+  6 │ 
+
+  Two labels are named x

jscomp/build_tests/super_errors/fixtures/record_type_spreads.res

@@ -0,0 +1,5 @@
+type t = {x: int, y: string}
+
+type t2 = {x: string, y: float}
+
+type t3 = {...t, ...t2}

jscomp/ml/typedecl.ml

@@ -463,15 +463,15 @@ 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;
             let optionalLabels =
               Ext_list.filter_map lbls (fun lbl ->
                   if has_optional lbl.ld_attributes then Some lbl.ld_name.txt else None)