Conflicting options

[tertsdiepraam]

It doesn't occur often in coreutils, but sometimes options conflict. They might even conflict with themselves. This is tricky to support while also maintaining good error messages.

One design could be to define conflict groups (leaving out some boilerplate in the example):

enum Arg {
    #[arg("--foo", conflict_group="foobar")]
    Foo,
    #[arg("--bar", conflict_group="foobar")]
    Bar,
}

"foobar" is a key into some hashset of options that have been set.

An example of conflicting options are cut's --fields, --bytes and --characters.

[tertsdiepraam]

Interestingly, those options in cut are also required.

[tertsdiepraam]

There's another possible design:

#[arguments(
    conflicts = [
        (Foo, Bar)
    ]
)]
enum Arg {
    #[arg("--foo", conflict_group="foobar")]
    Foo,
    #[arg("--bar", conflict_group="foobar")]
    Bar,
}

[tertsdiepraam]

But there are some difficulties:

• Should arguments conflict with themselves?
• How do we customize the errors? (GNU checks most manually probably so they have different errors for each util)
• How do we do conflict groups and more pairwise conflicts nicely?

I wonder if there's some convenience function we can make for the Settings struct that makes this easier?