fix: overshoot, concat_map is only TRMC after 5.1

Author: c-cube

src/core/CCList.ml

@@ -404,6 +404,8 @@ let rec equal f l1 l2 =
   | [], _ | _, [] -> false
   | x1 :: l1', x2 :: l2' -> f x1 x2 && equal f l1' l2'
 
+[@@@iflt 5.1]
+
 let rec flat_map_kont f l kont =
   match l with
   | [] -> kont []
@@ -415,8 +417,6 @@ let rec flat_map_kont f l kont =
     let kont' tail = kont (append x tail) in
     flat_map_kont f l' kont'
 
-[@@@iflt 4.14]
-
 let[@inline] flat_map f l =
   match l with
   | [] -> []

tests/core/t_list.ml

@@ -216,8 +216,12 @@ t @@ fun () ->
 flat_map (fun x -> [ x + 1; x * 2 ]) [ 10; 100 ] = [ 11; 20; 101; 200 ]
 ;;
 
+
 t @@ fun () -> List.length (flat_map (fun x -> [ x ]) (1 -- 300_000)) = 300_000
 ;;
+t @@ fun () ->
+List.length (flat_map (fun _ -> 1 -- 300_000) (1 -- 2)) = 600_000
+;;
 
 eq [ 1; 2; 2; 3; 3; 3 ]
   (flat_map_i (fun i x -> replicate (i + 1) x) [ 1; 2; 3 ])