🐛 Fix highlighting of optional variadic argument metavars

[BenjyWiener]

Due to a mistake in one of the metavar_sep regexes, a closing bracket followed by '...' does not get the correct highlighting in the arguments help panel.

Minimum reproducible example:

from typing import Annotated

import typer


def main(args: Annotated[list[str] | None, typer.Argument()] = None): ...

typer.run(main)

Current --help output (note the closing bracket of [ARGS]... in the Arguments panel):

With this PR:

[svlandeg]

Thanks for the report, I'll have a look!

[BenjyWiener]

I was taking another look, and I'm wondering if there's a specific reason the opening and closing brackets are only matched at the beginning/end of the string. If not, it might make more sense to just remove the ^ and $, instead of specifically allowing a trailing ....

[BenjyWiener]

The dots indicate that multiple arguments are accepted (hence the list annotation).

[svlandeg]

This test succeeds on master with the normal [ARGS] but fails with [ARGS].... Succeeds with this PR.

[svlandeg]

Confirmed the bug though it was hardly noticeable on my console 🥲

To write a regression test for this, I decided to move MetavarHighlighter to the module level, I think it's nicer anyway to define it together with the other highlighters. Then we can test for the highlighting directly, which works fine without the 3 dots but indeed fails as the regex doesn't consider the possibility of seeing 3 dots before the end of the string.

As @BenjyWiener mentioned, another option would be to remove the $. It just feels that these start and end markers are put in the regex on purpose, so I think the current solution is fine.

[svlandeg]

Tiangolo: notice how this code was moved, but also changed to add the optional 3 dots at the end of the regex.