only use a single commit in rename

src/git_kv.ml

@@ -648,13 +648,6 @@ module Make (Pclock : Mirage_clock.PCLOCK) = struct
     let open Lwt.Infix in
     remove ?and_commit:t.committed t key >|= Result.map_error to_write_error
 
-  let rename t ~source ~dest =
-    (* TODO(dinosaure): optimize it! It was done on the naive way. *)
-    let open Lwt_result.Infix in
-    get t source >>= fun contents ->
-    remove t source >>= fun () ->
-    set t dest contents
-
   let allocate t key ?last_modified:_ size =
     let open Lwt.Infix in
     exists t key >>= function
@@ -714,4 +707,18 @@ module Make (Pclock : Mirage_clock.PCLOCK) = struct
       Lwt.wakeup_later wk () ;
       t.committed <- None ;
       Lwt.return res
+
+  let rename t ~source ~dest =
+    let open Lwt_result.Infix in
+    let op t =
+      get t source >>= fun contents ->
+      remove t source >>= fun () ->
+      set t dest contents
+    in
+    match t.committed with
+    | Some _ -> op t
+    | None ->
+      change_and_push t op >>! function
+      | Ok a -> Lwt.return a
+      | Error _ as e -> Lwt.return e
 end