feat(complete): Add ValueCompleter::complete_at for indexed multi-value completion#6353
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Snapshot existing behavior for a custom `ValueCompleter` on a multi-value option. Without an index-aware API, the completer cannot differentiate by argument position, so both the first and second values surface the same merged candidate set. This pins down the baseline so a follow-up commit can show the behavior change in the test diff.
Add `ValueCompleter::complete_at(arg_index, current)` and a matching `ArgValueCompleter::complete_at` shim. The default trait impl delegates to `complete`, so existing implementors are unaffected. The dynamic engine now threads each value's position within an argument's `num_args` range into the completer, so a multi-value argument can return different candidates per slot (for example, a remote name first and a branch name second for `--set-upstream <REMOTE> <BRANCH>`). `arg_index` counts shell arguments and is unaffected by `value_delimiter`. Closes clap-rs#6284
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I'll merge when I have a chance to release
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Closes #6284.
Adds
ValueCompleter::complete_at(arg_index, current)so a custom completercan return different candidates for each value of a multi-value argument.
The motivating case from the issue:
--set-upstream <REMOTE> <BRANCH>shouldcomplete remotes at index 0 and branches at index 1.
The new method has a default implementation that delegates to
complete, soexisting implementations of
ValueCompleter(including all closure-basedcompleters) keep working unchanged.
arg_indexis the zero-based positionwithin the argument's
num_argsrange and is unaffected byvalue_delimiter.Engine plumbing computes the index from the existing
ParseState:ParseState::Opt((opt, count)):arg_index = count - 1ParseState::Pos((_, num_arg)):arg_index = num_arg - 10(single-value paths).The new test
suggest_custom_arg_completer_at_indexcovers both indices fora
num_args(2)flag, including prefix-filtered completions, and confirmsthe default
complete_atstill defers tocompletefor the unindexed case.