I don't think there is really a "better" option than this. Personally I find it distasteful because (if I understand this feature correctly) it means I have to

I don't think there is really a "better" option than this. Personally I find it distasteful because (if I understand this feature correctly) it means I have to know whether somebody turned on the async flag in another file to fully understand the possible control flow of a function I'm reading. This is different from Erlang because we just assume that every line can be preempted, and different from async-await because seeing async-await means you don't know if the code is actually going to run asynchronously. It's not the choice I would have made, but I am a stickler for theoretical cohesiveness and local readability, and Zig is kind of an anti-theory language. I would have chosen function colors, in all likelihood.