🐛 Ensure that the default option name is not changed by setting a metavar

[svlandeg]

Pull Request

Discussion: #1900

Description

Metavar annotations aren't supposed to influence the display/usage of the option name, as demonstrated by the test test_parameter_metavar which ensures that name: Annotated[str, typer.Option(metavar="CUSTOM") is called with --name.

A recent PR #1863 (released with 0.27.0) introduced a small regression on this behaviour, where a metavar corresponding to the option name (if both were lower-cased) could actually overwrite the casing. In retrospect, and after studying the reports & arguments in #1900, I think this was a bug/mistake on my end.

This PR fixes things to make the rule consistent: metavars are only for display (as already documented) and should never influence how an option is used.

⚠️ Note that this is breaking behaviour compared to 0.27.0 ⚠️
(while being less breaking with the original 0.26.8 behaviour)

AI Disclaimer

Used Cursor as a sparring partner to check my understanding & reasoning, we agreed on all edits in this PR 🙂

Checklist

• This PR links to a GitHub Discussion for the proposed code change.
• I added tests for the change.
• The new or updated tests fail on the main branch and pass on this PR.
• Coverage stays at 100%.
• The documentation explains the change if needed.

[svlandeg]

I actually think this was the originally intended behaviour of the test, as the print-out on L399 has arg9, not ARG9 (while ARG4 upper-cased does make sense)