Support multiple values in native completions

[shannmu]

Related issue #3921

Work in this PR

• Support multi-values for both short flag and long flag
  What we can complete now?

  dynamic --flag bar1 [TAB]
  

  It will completebar1 bar2 bar3.
  Also,

  dynamic -F bar1 [TAB]
  

  will completebar1 bar2 bar3.
• Support multi-values for positional argument with num_args(N) which N is fixed.

  dynamic pos_a [TAB]
  

  will complete pos_a pos_b pos_c

  dynamic -- pos_a [TAB]
  

  will complete pos_a pos_b pos_c

What may be is left

• Support multi-values for both short flag and long flag with format as follows

  dynamic --flag=bar1 [TAB]
  dynamic -F=bar1 [TAB]
  

• Support multi-values for positional argument with last or trailing_var_arg

[shannmu]

I can pass the clap_complete/tests/testsuite/bash.rs::complete test on my PC. I'm not sure if the CI failed because of my code changes.

[shannmu]

Thank you for your review! Sorry for the late response. I have made the changes to the code. During the modification process, I discovered a small error. For ParseState::Pos(usize), using only a single usize to record the takes_num_args of that positional argument is insufficient. There is a command line like this:

dynamic --flag bar -- pos_1 pos_2 pos_2 pos_2

The original incorrect logic would treat pos_1 as the first value of the positional argument with index=2, leading to a count error for index=2. Therefore, I changed ParseState::Pos(usize) to ParseState::Pos((usize, usize)). The first usize represents the pos_index of the current argument, and the second usize represents the count of the positional argument the current parameter is. This way, we can avoid the original error.

[epage]

. There is a command line like this:

If we've identified a bug like this during development, it means we should probably add a test case for it.