flambda-backend: Zero alloc misplaced attr warning (ocaml-flambda#2153)

* Fix missing warning for misplaced attribute

* Add a test

lambda/translattribute.ml

@@ -54,9 +54,9 @@ let is_opaque_attribute =
   [ ["opaque"; "ocaml.opaque"], true ]
 
 
-let find_attribute p attributes =
+let find_attribute ?mark_used p attributes =
   let inline_attribute =
-    Builtin_attributes.filter_attributes
+    Builtin_attributes.filter_attributes ?mark:mark_used
       (Builtin_attributes.Attributes_filter.create p)
       attributes
   in
@@ -461,9 +461,9 @@ let add_local_attribute expr loc attributes =
     end
   | _ -> expr
 
-let assume_zero_alloc attributes =
+let assume_zero_alloc ?mark_used attributes =
   let p = Zero_alloc in
-  let attr = find_attribute (is_property_attribute p) attributes in
+  let attr = find_attribute ?mark_used (is_property_attribute p) attributes in
   match parse_property_attribute attr p with
   | Default_check -> false
   | Ignore_assert_all _ -> false
@@ -478,7 +478,7 @@ let get_assume_zero_alloc ~with_warnings attributes =
      that affect [Scoped_location] settings before translation
      of expressions in that scope.
      Warnings will be produced by [add_check_attribute]. *)
-    Warnings.without_warnings (fun () -> assume_zero_alloc attributes)
+    Warnings.without_warnings (fun () -> assume_zero_alloc ~mark_used:false attributes)
 
 let add_check_attribute expr loc attributes =
   let to_string = function

parsing/builtin_attributes.ml

@@ -435,11 +435,11 @@ module Attributes_filter = struct
   let create (t : t) = t
 end
 
-let filter_attributes (nms_and_conds : Attributes_filter.t) attrs =
+let filter_attributes ?(mark=true) (nms_and_conds : Attributes_filter.t) attrs =
   List.filter (fun a ->
     List.exists (fun (nms, cond) ->
       if List.mem a.attr_name.txt nms
-      then (mark_used a.attr_name; cond)
+      then (if mark then mark_used a.attr_name; cond)
       else false)
       nms_and_conds
   ) attrs

parsing/builtin_attributes.mli

@@ -159,6 +159,7 @@ end
     count as misplaced if the compiler could use it in some configuration.
 *)
 val filter_attributes :
+  ?mark:bool ->
   Attributes_filter.t -> Parsetree.attributes -> Parsetree.attributes
 
 val warn_on_literal_pattern: Parsetree.attributes -> bool