1 files changed, 39 insertions, 30 deletions

diff --git a/lib/configuration/read_conf.ml b/lib/configuration/read_conf.ml
index 69240c1..11f6726 100644
--- a/lib/configuration/read_conf.ml
+++ b/lib/configuration/read_conf.ml
@@ -126,44 +126,51 @@ end = struct
   let column = Expression_parser.Incremental.column_expr
 end
 
+exception Divergent
 (** Ensure the group criteria in window functions match the global group by
-    criteria.
+    criteria. *)
 
-    Traverse the configuration tree until finding a group window. *)
+exception NestedGroup
+(** Raised when a group contains another one *)
+
+(** Traverse the configuration tree until finding a group window. *)
 let matchWindowGroup :
     eq:('a -> 'a -> bool) ->
     subset:'a ImportExpression.T.t list ->
     'a ImportExpression.T.t ->
-    bool =
+    unit =
  fun ~eq ~subset expression ->
-  let exception Divergent in
   let open ImportExpression.T in
-  let rec f = function
+  let rec f isIngroup = function
     | Empty | Literal _ | Integer _ | Path _ -> ()
-    | Expr e -> f e
+    | Expr e -> f isIngroup e
     | Concat pp | Function' (_, pp) | Function (_, pp) | Nvl pp | Join (_, pp)
-      -> List.iter ~f pp
-    | Window (_, pp1, _) ->
-        if List.equal ~eq:(ImportExpression.T.equal eq) subset pp1 then ()
-        else raise_notrace Divergent
+      -> List.iter ~f:(f isIngroup) pp
+    | Window (expr, pp1, pp2) ->
+        let () =
+          if List.equal ~eq:(ImportExpression.T.equal eq) subset pp1 then ()
+          else
+            match subset with
+            | [] -> ()
+            | _ -> raise_notrace Divergent
+        in
+        let () =
+          match isIngroup with
+          | true -> raise NestedGroup
+          | false -> ()
+        in
+
+        ignore @@ ImportExpression.T.map_window ~f:(f true) expr;
+        List.iter ~f:(f true) pp1;
+        List.iter ~f:(f true) pp2
     | BOperator (_, arg1, arg2) ->
-        f arg1;
-        f arg2
+        f isIngroup arg1;
+        f isIngroup arg2
     | GEquality (_, arg1, args) ->
-        f arg1;
-        List.iter ~f args
+        f isIngroup arg1;
+        List.iter ~f:(f isIngroup) args
   in
-  match subset with
-  | [] ->
-      (* Do not bother traversing the tree if there is no group by, just
-         return Ok *)
-      true
-  | _ -> (
-      try
-        f expression;
-        true
-      with
-      | Divergent -> false)
+  f false expression
 
 module Make (S : Decoders.Decode.S) = struct
   let ( let* ) = S.( let* )
@@ -185,13 +192,15 @@ module Make (S : Decoders.Decode.S) = struct
           | Error e -> S.fail_with Decoders.Error.(make e)
           | Ok expr -> (
               (* Now check that every window function include at least the uniq list *)
-              let valid_subset = matchWindowGroup ~eq ~subset:groups expr in
-              match valid_subset with
-              | true -> S.succeed expr
-              | false ->
+              match matchWindowGroup ~eq ~subset:groups expr with
+              | () -> S.succeed expr
+              | exception Divergent ->
                   S.fail
                     "The group function shall match the same arguments as the \
-                     \"uniq\" parameter")
+                     \"uniq\" parameter"
+              | exception NestedGroup ->
+                  S.fail
+                    "A group function cannot contains another group function")
 
       method source =
         let* file = S.field "file" S.string