Getting index of subcommand within passed arguments

[hotsphink]

I'm doing matches.try_get_matches_from(&string_args) with allow_external_subcommands, where I will process the subcommand name by checking it against a table of aliases and update string_args to resolve the alias to a different subcommand name plus some additional options. In order to do this correctly, I need the index of the subcommand within string_args so I can truncate string_args to just before it, then extend it with the new command name plus additional args plus any arguments pushed on. Example:

  ["myapp", "--initial-arg", "myalias", "--a"];
  // my config file defines the alias myalias = ["basecommand", "--b"]
  // so string_args becomes
  ["myapp", "--initial-arg", "basecommand", "--b", "--a"];

This is actually doable by counting the arguments passed to the subcommand (here, --a), dropping those off the end, dropping one more for the alias, and then adding things onto that stem. But I can't use that when my subcommands can have subcommands. I would like to do:

  string_args.truncate(matches.subcommand_index());

I can find the subcommand index by searching through string_args, but I may run into something like ["myapp", "--title", "myalias", "myalias"]. So I thought I'd use matches.indices_of(id) for all of the ids and remove all such indices from consideration. But as far as I can tell, indices_of does not refer to elements of string_args at all, but in some virtual list.

Honestly, I don't understand what they refer to. The argv vs clap indices thing makes sense, but when I actually use it, it seems like it's returning indices well outside of my vector. My actual scenario:

  string_args are ["target/debug/jj", "--no-pager", "shove", "--two"]
  matches.ids() are ["no_pager", "EarlyArgs", "ignore_working_copy", "ignore_immutable", "debug", "quiet"]
  for id in matches.ids() { display "{id}: {matches.indices_of(id)}" } gives
    no_pager: Some([1])
    EarlyArgs: Some([])
    ignore_working_copy: Some([2])
    ignore_immutable: Some([3])
    debug: Some([4])
    quiet: Some([5])

Sorry, that's a lot of detail, but I was worried a simple question would end up being an X/Y problem. Those indices seem to be for... maybe the list of arguments in my Command? I don't even know what they are. Is it confused because "--two" isn't even a real option? (But it can't know what "myalias" should resolve to, so it can't know what is or isn't valid yet.) What is it doing?

[epage]

Currently, we don't track argv indices, only relative order of arguments.

Cargo has a similar need but solves the problem in a different way. If you are curious, the code is at https://github.com/rust-lang/cargo/blob/340d1239a89d0030fd547beae74d87a1dccb8bd6/src/bin/cargo/cli.rs#L51