feat: make ColorGenerator const friendly

[Swiftb0y]

This allows precomputing a set of colors ahead of time (for people that are into that). To avoid generating the same colors for each instance, users can leverage the const_random crate to properly seed their generator.

I don't actually know how useful this is. I just saw a "constexpr all the things" opportunity and wanted to see if there was anything obvious preventing this.

One usecase I could think about is users wanting to generate a couple colors ahead of time, give each one semantic meaning and then use their meaning consistently. Something like this:

struct ColorPalette {
    types: Color,
    identifiers: Color,
    other: Color,
}
const COLORS: ColorPalette = {
    let mut gen = ColorGenerator::new();
    ColorPalette {
        types: gen.next(),
        identifiers: gen.next(),
        others: gen.next(),
    }
}

[zesterer]

This is neat, great idea! It never occurred to me that this even could be made const.

[zesterer]

You mentioned const-random: was this PR intended to provide integration with that?

Also, it looks like CI might need some fixing.

[Swiftb0y]

You mentioned const-random: was this PR intended to provide integration with that?

I didn't want to pull in extra dependencies unprompted, especially proc macros like const-random that affect the build time. If you think it makes sense to build in support natively (maybe behind a feature flag?) I can do that.

Also, it looks like CI might need some fixing.

I'll take a look. I only ran cargo test locally.

[zesterer]

Ah, still some non-const stuff. Just min/max though, so shouldn't be too difficult to fix with a custom impl.

[Swiftb0y]

either that or bump the rust version enough again (I overlooked that previously) if thats okay for you (idk if you have a MSRV policy). I'm not sure about the &mut T in const fn, the feature is stabilized but I couldn't find the corresponding compiler version. Maybe the one I just pushed is enough, but I can't tell without trying on CI again (or testing a bunch of versions locally, which I don't have the disk space for). I'd appreciate if you could just keep on approving the workflow runs until CI finally passes.

[Swiftb0y]

@zesterer I believe this is ready, I just need another CI run again.

[zesterer]

Thanks so much!

[Swiftb0y]

Thank you for your review patience.