warning when [@@deprecated] is present on exceptions

parsing/builtin_attributes.ml

@@ -62,11 +62,22 @@ let rec error_of_extension ext =
 let cat s1 s2 =
   if s2 = "" then s1 else s1 ^ "\n" ^ s2
 
-let rec deprecated_of_attrs = function
+let deprecated_attr x =
+  match x with
+  | ({txt = "ocaml.deprecated"|"deprecated"; _},_) -> Some x
+  | _ -> None
+
+let rec deprecated_attrs = function
   | [] -> None
-  | ({txt = "ocaml.deprecated"|"deprecated"; _}, p) :: _ ->
-      Some (string_of_opt_payload p)
-  | _ :: tl -> deprecated_of_attrs tl
+  | hd :: tl ->
+    match deprecated_attr hd with
+    | Some x -> Some x
+    | None -> deprecated_attrs tl
+
+let deprecated_of_attrs l =
+  match deprecated_attrs l with
+  | None -> None
+  | Some (_,p) -> Some (string_of_opt_payload p)
 
 let check_deprecated loc attrs s =
   match deprecated_of_attrs attrs with
@@ -117,6 +128,12 @@ let rec deprecated_of_str = function
   | _ -> None
 
 
+let check_no_deprecated attrs =
+  match deprecated_attrs attrs with
+  | None -> ()
+  | Some ({txt;loc},_) ->
+    Location.prerr_warning loc (Warnings.Misplaced_attribute txt)
+
 let warning_attribute ?(ppwarning = true) =
   let process loc txt errflag payload =
     match string_of_payload payload with

parsing/builtin_attributes.mli

@@ -42,6 +42,8 @@ val check_deprecated_mutable_inclusion:
   def:Location.t -> use:Location.t -> Location.t -> Parsetree.attributes ->
   Parsetree.attributes -> string -> unit
 
+val check_no_deprecated : Parsetree.attributes -> unit
+
 val error_of_extension: Parsetree.extension -> Location.error
 
 val warning_attribute: ?ppwarning:bool -> Parsetree.attribute -> unit

testsuite/tests/warnings/ocamltests

@@ -2,6 +2,7 @@ deprecated_module_assigment.ml
 deprecated_module.ml
 deprecated_module_use.ml
 w01.ml
+w03.ml
 w04_failure.ml
 w04.ml
 w06.ml

testsuite/tests/warnings/w03.compilers.reference

@@ -0,0 +1,4 @@
+File "w03.ml", line 14, characters 8-9:
+Warning 3: deprecated: A
+File "w03.ml", line 17, characters 15-25:
+Warning 53: the "deprecated" attribute cannot appear in this context

testsuite/tests/warnings/w03.ml

@@ -0,0 +1,24 @@
+(* TEST
+
+flags = "-w A"
+
+* setup-ocamlc.byte-build-env
+** ocamlc.byte
+compile_only = "true"
+*** check-ocamlc.byte-output
+
+*)
+
+exception A [@deprecated]
+
+let _ = A
+
+
+exception B [@@deprecated]
+
+let _ = B
+
+
+exception C [@deprecated]
+
+let _ = B [@warning "-53"]

typing/typedecl.ml

@@ -1649,6 +1649,7 @@ let transl_exception env sext =
   ext, newenv
 
 let transl_type_exception env t =
+  Builtin_attributes.check_no_deprecated t.ptyexn_attributes;
   let contructor, newenv =
     Builtin_attributes.warning_scope t.ptyexn_attributes
       (fun () ->