default completions should be used only when user did not provide any

[adamsitnik]

My proposal for fixing #1884: use the default completions only when user has not provided their own.

Cons: we lose the possibility to extend the default completions with custom ones.

fixes #1884

cc @KalleOlaviNiemitalo

[KalleOlaviNiemitalo]

Huh, so if I read this property, then the getter assigns an empty collection to _completions, and after that, GetCompletions will no longer use the default completions. It seems wrong that the getter would have a side effect like that.

[jonsequitur]

The behavior seems unintuitive. If I know for example that Option<DayOfWeek> returns seven well-known values, I would not expect calling Completions.Add to replace them.

[KalleOlaviNiemitalo]

For the DayOfWeek case, although adding more completions to the seven original seems a bit odd, I can imagine adding "today", "tomorrow", "yesterday" with a custom parser.

[jozkee]

If I know for example that Option returns seven well-known values, I would not expect calling Completions.Add to replace them.

That's what @KalleOlaviNiemitalo describes as expected in the linked issue. I was first thinking that a possibility could be to only use defaults as long as users don't Add their own completions.

If that's not good, we could also just expose a method to Clear() the completions, or AddReplace()?

[KalleOlaviNiemitalo]

If you add public ICollection<Func<CompletionContext, IEnumerable<CompletionItem>>> Completions => Argument.Completions; to Option so that I can call ICollection<T>.Clear(), that will suffice.

[adamsitnik]

I've opened #1972 to discuss better solution. Thank you all for your feedback!