default root to C:\opamroot and ask for path

src/client/opamClient.ml

@@ -1147,15 +1147,17 @@ let init
     let root = OpamStateConfig.(!r.root_dir) in
     if Sys.win32 &&
        OpamStd.String.contains_char (OpamFilename.Dir.to_string root) ' ' then
-      (let new_root_f =
-         (* TODO: don't keep! *)
-         Filename.concat
-           (Filename.get_temp_dir_name ())
-           (Printf.sprintf "opam-root-%06x" (Random.int 0xffffff))
+      (let default = Filename.concat "C:" "opamroot" in
+       let new_root_f =
+         if OpamConsole.confirm ~default:false
+             "Your opam root path '%s' contains a space, we'll redirect to \
+              '%s'.\nDo you want to choose and enter another spaceless folder"
+             (OpamFilename.Dir.to_string root) default then
+           match OpamConsole.read "Opam root: " with
+           | Some r -> r
+           | None -> default
+         else default
        in
-       OpamConsole.note
-         "Your opam root path '%s' contains a space, we'll redirect to '%s'"
-         (OpamFilename.Dir.to_string root) new_root_f;
        let new_root = OpamFilename.Dir.of_string new_root_f in
        OpamFilename.write (OpamPath.redirected root) new_root_f;
        OpamStateConfig.update ~root_dir:new_root ();