Fix List.drop

Reviewed By: ngorogiannis

Differential Revision: D8162217

fbshipit-source-id: 69a6557

infer/src/absint/ProcCfg.ml

@@ -309,11 +309,9 @@ struct
 
   let exceptional_succs _ _ = (* not used *) assert false
 
-  let list_mem_nth list index = List.drop list index |> List.is_empty |> not
-
   let succs cfg (node, index) =
     let succ_index = index + 1 in
-    if list_mem_nth (Base.instrs node) succ_index then [(node, succ_index)]
+    if IList.mem_nth (Base.instrs node) succ_index then [(node, succ_index)]
     else List.map ~f:first_of_node (Base.succs cfg node)
 
 

infer/src/biabduction/BuiltinDefn.ml

@@ -672,7 +672,7 @@ let execute_scan_function skip_n_arguments ({Builtin.args; ret_id_typ} as call_a
   match args with
   | _ when List.length args >= skip_n_arguments ->
       let varargs = ref args in
-      varargs := List.drop !varargs skip_n_arguments ;
+      varargs := IList.drop !varargs skip_n_arguments ;
       SymExec.unknown_or_scan_call ~is_scan:true ~reason:"execute scan function" (snd ret_id_typ)
         Annot.Item.empty {call_args with args= !varargs}
   | _ ->

infer/src/clang/ComponentKit.ml

@@ -311,7 +311,7 @@ let component_with_multiple_factory_methods_advice context an =
                    document which are optional."
             ; doc_url= None
             ; loc= CFrontend_checkers.location_from_decl context meth_decl } )
-          (List.drop factory_methods 1)
+          (IList.drop factory_methods 1)
     | _ ->
         assert false
   in

infer/src/eradicate/typeCheck.ml

@@ -401,7 +401,7 @@ let typecheck_instr tenv ext calls_this checks (node: Procdesc.Node.t) idenv get
                 0
           in
           let n = drop_n_args proc_attributes.ProcAttributes.formals in
-          let visible_params = List.drop params n in
+          let visible_params = IList.drop params n in
           (* Drop the trailing hidden parameter if the constructor is synthetic. *)
           if proc_attributes.ProcAttributes.is_synthetic_method then
             List.take visible_params (List.length visible_params - 1)

infer/src/istd/IList.ml

@@ -137,3 +137,11 @@ let merge_dedup l1 l2 ~compare =
         else loop (h2 :: acc) l1 t2
   in
   loop [] l1 l2
+
+
+(* Remove when Base.List.drop perf is fixed *)
+let rec drop list index =
+  match list with _ :: tl when index > 0 -> drop tl (index - 1) | _ -> list
+
+
+let mem_nth list index = drop list index |> List.is_empty |> not

infer/src/istd/IList.mli

@@ -35,3 +35,9 @@ val append_no_duplicates : cmp:('a -> 'a -> int) -> ('a list -> 'a list -> 'a li
     duplicates. *)
 
 val merge_dedup : 'a list -> 'a list -> compare:('a -> 'a -> int) -> 'a list
+
+val drop : 'a list -> int -> 'a list
+(** [drop l n] returns [l] without the first [n] elements, or the empty list if [n > length l]. *)
+
+val mem_nth : 'a list -> int -> bool
+(** [mem_nth l n] returns whether the list [l] contains a [n]th element. *)