> it's one of those features that outside of Rust you only really find in ML-family languages

Or in Scala, technically not an ML, but is as close as you'll get in a nominally typed language.

    enum RGB:
      case Red, Green, Blue

    def log(x: RGB) = x match
      case Red => print("red")
      case Green => print("green")
      // error, not exhaustive

Obviously Scala can do a lot more, including GADTs, which Rust will never have until HKTs are supported.

Ton of powerful languages to choose from these days, good times...