drush_backend_invoke() assumes single word command names

drush_backend_invoke assumes

1) $command is a string
2) $args is an array, with OPTIONS as string indexed items and ARGUMENTS as numerically indexed items.

so in the command

drush.php mycommand here arg1 arg2 --option1=option1 --option2=option2

you would have

drush_backend_invoke('mycommand here', array( 'arg1', 'arg2', 'option1'=> 'option1', 'option2' => 'option2'));

hence :

drush.php $command $numeric_indexed_items $string_indexed_items

also, see drush_backend_invoke_args()

There is this function:

function drush_backend_invoke($command, $data = array(), $method = 'GET', $integrate = TRUE, $drush_path = NULL, $hostname = NULL, $username = NULL) {
  $args = explode(" ", $command);
  $command = array_shift($args);
  return drush_backend_invoke_args($command, $args, $data, $method, $integrate, $drush_path, $hostname, $username);
}

The $command = array_shift($args); assumes that the first word is the command, and the second and subsequent words are args. _drush_backend_generate_command puts everything back together correctly again, so it's not a huge problem, but please also see the discussion in #658420: helper functions for drush_backend_invoke().

Perhaps the best solution would be to have drush_backend_invoke_args($command, $args, ...) call through to drush_backend_invoke_args($args, ...) after first exploding $command and merging it with $args. In this case, then _drush_backend_generate_command also would take only $args.

If you were calling backend invoke from code, you'd do it as you suggest in #1, but if you were re-dispatching using the $args list that were passed in on the command line you could instead do something like this:

/*
* Spawn a subshell which runs the same command we are currently running.
*/
function drush_migrate_backend_invoke() {
  $args = drush_get_arguments();
  $options = drush_migrate_get_options();
  drush_backend_invoke_args($args, $options);
}

(n.b. the two polymorphic drush_backend_invoke_args probably need different names due to the default arguments; I apologize for any confusion caused by giving them the same name here.)

In this case, it is neither assumed nor specified how many elements of $args are the command and how many are the other arguments.