3 files changed, 9 insertions, 1 deletions
diff --git a/typing/typecore.ml b/typing/typecore.ml
index f81b58f53..44a0738e2 100644
--- a/typing/typecore.ml
+++ b/typing/typecore.ml
@@ -1049,7 +1049,9 @@ let rec type_exp env sexp =
         in
         let missing = missing_labels 0 label_names in
         raise(Error(sexp.pexp_loc, Label_missing missing))
-      end;
+      end
+      else if opt_sexp <> None && List.length lid_sexp_list = !num_fields then
+        Location.prerr_warning sexp.pexp_loc Warnings.Useless_record_with;
       re {
         exp_desc = Texp_record(lbl_exp_list, opt_exp);
         exp_loc = sexp.pexp_loc;
diff --git a/utils/warnings.ml b/utils/warnings.ml
index f45d68b97..3adda4666 100644
--- a/utils/warnings.ml
+++ b/utils/warnings.ml
@@ -37,6 +37,7 @@ type t =                             (* A is all *)
   | Nonreturning_statement
   | Camlp4 of string
   | All_clauses_guarded
+  | Useless_record_with
   | Unused_var of string             (* Y *)
   | Unused_var_strict of string      (* Z *)
 ;;
@@ -63,6 +64,7 @@ let letter = function        (* 'a' is all *)
   | Unused_argument
   | Nonreturning_statement
   | Camlp4 _
+  | Useless_record_with
   | All_clauses_guarded ->      'x'
   | Unused_var _ ->             'y'
   | Unused_var_strict _ ->      'z'
@@ -149,6 +151,9 @@ let message = function
   | Camlp4 s -> s
   | All_clauses_guarded ->
       "bad style, all clauses in this pattern-matching are guarded."
+  | Useless_record_with ->
+      "this record is defined by a `with' expression,\n\
+       but no fields are borrowed from the original."
 ;;
 
 let nerrors = ref 0;;
diff --git a/utils/warnings.mli b/utils/warnings.mli
index a623bb2c7..5f22c91be 100644
--- a/utils/warnings.mli
+++ b/utils/warnings.mli
@@ -37,6 +37,7 @@ type t =                             (* A is all *)
   | Nonreturning_statement
   | Camlp4 of string
   | All_clauses_guarded
+  | Useless_record_with
   | Unused_var of string             (* Y *)
   | Unused_var_strict of string      (* Z *)
 ;;