proposal: flag: add All, AllSet iterators

[earthboundkid]

Proposal Details

The flag package currently has Visit and VisitAll iterators, but unfortunately, the iterators don't return bool, so they aren't compatible with the range func experiment. I propose to add All() iter.Seq[*Flag], AllSet() iter.Seq[*Flag], and methods on FlagSet. The name "AllSet" isn't ideal, and I'm open to suggestions for better names.

[earthboundkid]

Seems like this has only gotten thumbs up. Any objections?

[earthboundkid]

Maybe instead just have FlagSet.All() iter.Seq2[*Flag, bool] where the bool represents whether the Flag was set or not. It's simpler to just have one method, and it's good for my usecase of looping through to find unset flags and see if I can set them with an environmental variable.

[mvdan]

Worth noting that today, "all flags" and "set flags" are kept as two separate maps, so an iterator like iter.Seq2[*Flag, bool] would need to look up both maps to work properly. So if we really wanted to go that route, it seems to me like we should try joining the two maps. Otherwise, it seems best to add two separate iterator APIs as originally proposed.

[earthboundkid]

It doesn't strike me as being that computationally expensive to loop over f.formal and return _, ok := f.actual[name] whereas the other way around, if we have two iterators, you need to loop over both and keep a set to figure out if it's formal or actual. That's how I do it in flagx.listVistedFlagNames currently, for example.

[earthboundkid]

@aclements Can this be evaluated for Go 1.26?

[earthboundkid]

Go 1.27?

This is functionality that can be done outside the stdlib, but much less efficiently because you have to walk everything twice to see what's formal and actual before you can return anything. Not that it matters much for flag parsing, but it bugs me knowing this could be better. 😆