Apply show_only_unused to arguments (fixes #125)

[Sanjays2402]

Fixes #125

ClickCompleter(show_only_unused=True) only hid options that were already present on the line; click.Argument was never checked, so an argument kept being completed after a value had been supplied. _get_completion_for_cmd_args now skips an argument whose value is already bound in the completion context, mirroring the existing option handling; variadic arguments (nargs=-1) accept further values and are never hidden.

Regression tests were added to tests/test_completion/test_common_tests/test_arg_completion.py for both the plain and the variadic case; they fail on master and pass with the fix. Full suite: 69 passed, 5 skipped.

This change was prepared with AI assistance; the regression test was run locally and fails without the fix.

[Copilot]

🟡 Changes recommended

The new argument “already used” detection relies on ctx.params, which can reflect defaults/envvars (not just command-line input) and may incorrectly hide argument completions under show_only_unused=True.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR fixes ClickCompleter(show_only_unused=True) so it also suppresses completions for click.Argument values that have already been provided, matching the existing behavior for click.Option, while keeping variadic arguments (nargs=-1) completable.

Changes:

• Update _get_completion_for_cmd_args to skip completing an argument when it is already “used” (except variadic args).
• Add regression tests covering both single-value and variadic arguments with show_only_unused.
• Document the behavior change in Changelog.rst.

File summaries

File	Description
click_repl/_completer.py	Extends show_only_unused behavior to arguments during completion generation.
tests/test_completion/test_common_tests/test_arg_completion.py	Adds regression tests for unused-argument hiding and the variadic exception.
Changelog.rst	Notes the new show_only_unused behavior for arguments.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Lite

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[Copilot]

🟡 Changes recommended

The fallback argument detection can incorrectly hide completions for default or environment-derived values.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

Suppressed comments (1)

click_repl/_completer.py:284

• Fixed-arity multi-value arguments are hidden before all their values have been entered. With nargs=2, parsing cmd foo records the source as COMMANDLINE, but resilient parsing leaves the argument value unbound because the second token is missing; this continue then suppresses the choices needed for that second value. Hide the argument only after its processed value is actually bound.

                if self.show_only_unused and already_present and param.nargs != -1:
                    continue

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Balanced

[Copilot]

🟢 Approval recommended

The change is narrowly scoped, aligns argument behavior with existing option handling, and includes targeted regression tests plus a changelog entry.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 0 new
• Review effort level: Lite